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Molecular Genetics of Ulcerative Colitis-associated Colon Cancer in the Interleukin 2- and ß₂-Microglobulin-deficient Mouse¹

Departments of Medicine [K-J. S., J. C., Y-I. K.] and Nutritional Sciences [S. R., M. C., Y-I. K.], University of Toronto, Toronto, Ontario, M5S 1A8 Canada; Division of Gastroenterology, St. Michael’s Hospital, University of Toronto, Toronto, Ontario, M5B 1W8 Canada [Y-I. K.]; Division of Gastroenterology, Brown University, Providence, Rhode Island 02904 [S. A. S.]; and Division of Immunology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215 [M. C., C. T.]

	ABSTRACT

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Mice deficient in ß₂-microglobulin and interleukin 2 (ß₂m^null x IL-2^null) spontaneously develop colon cancer in the setting of chronic ulcerative colitis (UC). We investigated mutations of the Apc and p53 genes and microsatellite instability in colonic adenocarcinomas arising in this model. Mutations of the Apc and p53 genes in the regions corresponding to mutation hot spots in human colorectal cancer were determined by sequencing in 11 colonic adenocarcinomas. Microsatellite instability was determined in matched normal and neoplastic DNA at five loci. All 11 adenocarcinomas harbored Apc mutations. Of these 11 tumors, 5 harbored truncating mutations. A total of 67 Apc mutations were found in these 11 tumors; 59 were missense mutations, whereas 8 were frameshift or nonsense mutations. Six of the 11 adenocarcinomas harbored p53 mutations. A total of seven p53 mutations were found in these 11 tumors; all mutations were transitions, 4 of which were C:GT:A transitions occurring in codon 229 at cytosine-guanine dinucleotides. Nine adenocarcinomas exhibited microsatellite instability in at least one of the five loci examined; 1 tumor had microsatellite instability in two loci. Molecular genetics, as well as clinical features, of colon cancer in the ß₂m^null x IL-2^null mice are similar to those of human UC-associated colorectal cancer. As such, this model appears to be an excellent animal model to study UC-associated colorectal carcinogenesis.

	INTRODUCTION

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Chronic UC³ is associated with a 10- to 40-fold increased risk of developing CRC compared with the general population (1) . Recently, population-based, large, prospective studies have confirmed this association, although the actual magnitude of risk has been shown to be less than that observed from retrospective analyses (2) . Molecular alterations accompanying the histological progression of the normal colonic mucosa to dysplasia and to cancer in chronic UC have just begun to be elucidated; UC-associated CRC appears to develop through a molecular pathway slightly different from that involved in sporadic colorectal carcinogenesis (3 , 4) . Point mutations and allelic loss of the APC gene have been reported in UC-related dysplasia and cancer (5 , 6) , although a recent study suggests that APC mutations occur much less commonly in UC-related neoplasia (6%) than in sporadic colorectal neoplasia (74%; Ref. 7 ). Point mutations and/or allelic loss of the p53 gene have been reported in the majority of UC-related dysplasia and cancers that have been investigated (5 , 8, 9, 10, 11, 12, 13, 14) . In contrast to its involvement in late stages of sporadic colorectal carcinogenesis (3 , 4) , alterations in p53 appear to be an earlier event in UC-associated colorectal carcinogenesis (5 , 8, 9, 10, 11, 12, 13, 14) . p53 mutations have also been observed in noncancerous colon tissue from patients with chronic UC (15 , 16) . In UC-associated dysplasia and cancer, K-ras mutations are either common or unusual, depending on the study referenced (6 , 9 , 10 , 17, 18, 19, 20) . Point mutations in one of the mismatch repair genes, MSH2 (21) , and microsatellite instability, the hallmark of DNA replication error defects, have been found in UC-associated dysplasia and cancer (22, 23, 24) and even in nonneoplastic mucosa (24 , 25) .

Currently available animal models to study UC-associated CRC include chemical carcinogen, transgenic, and genetic knockout models (26) . Mice deficient in IL-2 (IL-2^null) have been found to develop wasting syndrome with colonic inflammation resembling UC (27) . Approximately 50% of the IL-2^null mice die within the first 9 weeks because of severe anemia (27) . The remainder develop diarrhea, colitis, and anemia accompanied by a systemic wasting disease, resulting in death usually within 6 months (27) . None of these mice surviving beyond 6 months have been observed to develop CRC (27) . Previously, mice deficient in CD8⁺ T cells and MHC class I expression as a result of a targeted mutation in the ß₂m gene (ß₂m^null) were bred with IL-2^null mice to generate double knockout mice (ß₂m^null x IL-2^null; Ref. 28 ). The ß₂m^null x IL-2^null develop pancolitis as severe as seen in the IL-2^null mice (28) . However, in contrast to the IL-2^null mice, the ß₂m^null x IL-2^null mice appear less systemically ill (less wasting and anemic) and survive beyond 6 months, suggesting a milder overall disease (28) . Most of these mice show signs of diarrhea and several develop rectal prolapse (28) . At times, some of these mice appear ill with signs of diarrhea and wasting, especially between 8 and 12 weeks, and then recover with normal stools, weight gain, and normal appearance, suggesting disease flare followed by remission from colitis (28) . Histologically, 75% of these mice have mild to moderate colonic inflammation restricted to the mucosa, and 25% have no inflammation at the time of necropsy (28) . Recently, it has been shown that 32% of the ß₂m^null x IL-2^null mice develop adenocarcinoma in the proximal half of the colon between 6 and 12 months (29) . No tumors have been observed in mice <6 months of age, suggesting that adenocarcinomas arose only after a prolonged period of colonic inflammation (29) . All of the tumors are well to moderately differentiated adenocarcinomas invading into or through the muscularis propria (29) . More recently, the ß₂m^null x IL-2^null mice have been observed to develop low- and high-grade dysplasia (30) . Therefore, it appears that the ß₂m^null x IL-2^null mice are an excellent animal model to study UC-associated colorectal carcinogenesis.

The present study investigated molecular genetics of UC-associated colon cancer arising in this murine model. In particular, we studied mutations of the Apc and p53 genes and microsatellite instability, three commonly observed molecular alterations in human UC-associated and sporadic CRCs.

	MATERIALS AND METHODS

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Tissue Samples
Eleven histologically confirmed colonic adenocarcinomas from 11 ß₂m^null x IL-2^null mice were analyzed in the present study. The detailed protocol of the study where 11 of 34 (32%) ß₂m^null x IL-2^null mice developed moderately differentiated adenocarcinomas invading into or through the muscularis propria in the proximal half of the colon between 6 and 12 months of age has been published previously (29) . The ß₂m^null x IL-2^null mice were generated on a C57BL/6 x 129/OLA or 129/Sv mixed background (29) . All macroscopically identifiable tumors were harvested at the time of necropsy, fixed in 10% buffered formalin, and embedded in paraffin in a standard fashion. Five-µm-thick sections were cut and mounted on microscope slides for staining with H&E using standard techniques.

DNA Extraction
Areas corresponding to histologically confirmed adenocarcinomas on H&E staining were marked on matched unstained slides. DNA from each adenocarcinoma was extracted as crude preparations using proteinase K lysis mix [10 mM Tris-HCl (pH 8.0), 100 mM KCl, 2.5 mM MgCl₂, 0.45% Tween 20, and 1 mg/ml proteinase K] as described previously (31) . Care was taken to avoid contamination from adjacent nonneoplastic tissues. The sections were homogenized in the lysis mix and digested for 1 h at 65°C, followed by 10 min at 95°C. Extracted DNA was stored at -20°C until subsequent analyses. DNA from the adjacent nonneoplastic colonic mucosa was extracted from areas corresponding to normal histology on H&E section from matched unstained slides in a similar fashion (31) . DNA from the liver (negative control), snap-frozen at the time of sacrifice and stored at -70°C, was extracted by a standard technique using a lysis buffer containing proteinase K, followed by phenol, chloroform, and isoamyl alcohol organic extraction (32) .

Mutation Analyses
Apc Gene.
A 2738-bp region, between nucleotides 2020 and 4758 in exon 15 of the Apc gene, including a region designated as the MCR in human CRC (nucleotides 3906–4589), was amplified by PCR using three pairs of exon primers to generate three overlapping segments (segment A, nucleotides 2020–2996; segment B, nucleotides 2863–3925; segment C, nucleotides 3829–4758) as described previously (31) . About 60% of the somatic mutations of the APC gene in human CRC are clustered in a 500-bp region in the MCR (33) . The primer sequences, which contain flanking sequences of EcoRI and XhoI restriction sites to facilitate subcloning into a vector, were constructed based on the published murine Apc cDNA sequence (Ref. 34 ; GenBank accession no. M88127) and synthesized by the ACGT Corp. (Toronto, Ontario, Canada). The sequences of the primers were as follows: segment A, 5'-ACACTCGAATTCAATCCTAAAGACCAGGAAGC-3' (sense) and 5'-ACACTCATCGATTGGCCTCTTTTACCATATCC-3' (antisense); segment B, 5'-TCTAGGTCTAGAAAACCCTCAGTTGAATCC-3' (sense) and 5'-ACACTCCTCGAGTGTTGTCTGATCACATCC-3' (antisense); and segment C, 5'-TCTAGGGAATTCAACACAGGAAGCAGATTC-3' (sense) and 5'-ACACTCCTCGAGTCTACCTCTTTATCCTGG-3' (antisense).

Each 5.0 µl of DNA sample was amplified by PCR in a 50-µl volume containing 350 ng of each primer, 0.25 mM each dNTP, PCR buffer (Qiagen, Mississauga, Ontario, Canada), 1.5 mM MgCl₂, and 2 units of HotStart Taq DNA polymerase (Qiagen). After hot start PCR at 95°C for 5 min, 35 cycles of denaturation (95°C) for 1 min, annealing (54°C) for 1 min, and extension (72°C) for 1 min were performed in a thermal cycler (PTC-200 DNA Engine; MJ Research, Watertown, MA). All PCR amplifications included a 10-min extension at 72°C after cycle 35.

p53 Gene.
Exons 5–6 (366 bp) and 7–8 (576 bp) of the p53 gene were amplified by PCR using two pairs of intron primers. The majority of p53 mutations in human CRC occur within a highly conserved area spanning from codon 110 to 307 (exons 5–8; Ref. 35 ). The primer sequences, which contain flanking sequences of EcoRI and XhoI restriction sites to facilitate subcloning into a vector, were constructed based on the published murine p53 cDNA sequence (Ref. 36 ; GenBank accession nos. X01237 and K01700) and synthesized by the ACGT Corp. The sequences of the primers were as follows: exons 5–6, 5'-ACACTCGAATTCCTTCCAGTACTCTCCTCCCC-3' (sense) and 5'-TCTGTGCTCGAGAAGGTACCACCACGCTGTGG-3' (antisense); and exons 7–8, 5'-GTGTCTGAATTCCCGGCTCTGAGTATACCACC-3' (sense) and 5'-GTGTCTCTCGAGGCCTGCGTACCTCTCTTTGC-3' (antisense).

Each 2.5 µl of DNA sample was amplified by PCR in a 50-µl volume containing 350 ng of each primer, 0.25 mM each dNTP, PCR buffer (Qiagen), 1.5 mM MgCl₂, and 2 units of HotStart Taq DNA polymerase (Qiagen). After hot start PCR at 95°C for 5 min, 35 cycles of denaturation (95°C) for 30 s, annealing (54°C) for 30 s, and extension (72°C) for 45 s were performed in a thermal cycler (PTC-200 DNA Engine; MJ Research). All PCR amplifications included a 10-min extension at 72°C after cycle 35.

Subcloning and Sequencing.
The PCR products for the Apc (segments A–C) and p53 (exons 5–8) genes were gel purified using the Qiaex II Agarose Gel Extraction kit (Qiagen) according to the manufacturer’s protocol, re-extracted, and dissolved in 50 µl of double-distilled H₂O. The PCR products were then subcloned into pBluescript II KS(+) vector (Stratagene, Cambridge, United Kingdom) at EcoRI and XhoI sites. Sequencing was performed on a total of 2 clones from each PCR product using the Dideoxy Terminator Label Cycle Sequencing kit (Applied Biosystems, Foster City, CA) and an Applied Biosystems 373 Sequencer (Applied Biosystems) as described previously (31) . The Apc and p53 sequences thus generated were analyzed against the GenBank sequences [Apc, accession no. M88127 (34) ; p53, accession nos. X01237 and K01700 (36) ] using the DNASIS software program (Hitachi, San Diego, CA). Mutations were confirmed by sequencing the opposite strand as well as sequencing 1 independent clone from each of three to five independently performed PCR reactions. In total, therefore, 2 clones from the initial PCR reaction and 3–5 independent clones from three to five separate PCR reactions were sequenced per tumor. Only those mutations consistently present in all of the sequencing analyses were considered to be real mutations. Liver and nonneoplastic colonic mucosal DNA from each mouse harboring colonic adenocarcinoma were PCR amplified under the same conditions for tumor DNA, and a total of 2 clones from each PCR reaction were sequenced initially, followed by sequencing 1 independent clone from a separately performed PCR reaction as described above.

Microsatellite Instability Assay
Microsatellite instability was detected by comparison of electrophoretic mobility of amplified nonneoplastic and neoplastic colonic DNA from each mouse harboring colonic adenocarcinoma using primers from five loci on mouse chromosomes 6 (D6 Mit8), 7 (D7 Mit91), 10 (D10 Mit2), 18 (D18 Mit14), and 19 (D19 Mit36) as described previously (Research Genetics, Huntsville, AL; Refs. 32 , 37 ). Each 3.0 µl of DNA sample was amplified by PCR in a 15-µl volume containing 0.4 µM of each primer, 0.20 mM each dNTP, 0.033 µM [-³³P]dATP (New England Nuclear, Boston, MA), PCR buffer (Life Technologies, Inc., Gaithersburg, MD), 1.5 mM MgCl₂, and 1 unit of Taq DNA polymerase (Life Technologies, Inc.). All reactions were overlaid with 10 µl of mineral oil. After hot start PCR at 95°C for 5 min, 40 cycles of denaturation (95°C) for 15 s, annealing (58°C) for 20 s, and extension (72°C) for 20 s were performed in a thermal cycler (PTC-200 DNA Engine; MJ Research). All PCR amplifications included a 10-min extension at 72°C after cycle 40. A 4-µl aliquot of the PCR products was mixed with formaldehyde dye mix (2 µl), denatured at 95°C for 3 min and electrophoresed on 6% polyacrylamide gels under denaturing conditions for 2 h. Gels were dried and exposed to X-ray film for 16 h. A positive case was confirmed in two independently performed PCR reactions.

	RESULTS

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Apc Mutations.
A total of 67 mutations were found in the 2738-bp region in exon 15 of the Apc gene from all of the 11 adenocarcinomas analyzed (mutation frequency of 100%; Table 1 ). On average, each adenocarcinoma harbored 6.1 mutations (Table 1) . In contrast, no mutations were observed in the same region in the adjacent nonneoplastic colonic mucosal and liver DNA from all of the 11 animals harboring colonic adenocarcinomas. Fifty-nine of the 67 mutations (88%) were single base substitutions resulting in missense mutations, whereas the remaining 8 mutations (12%) were frameshift or nonsense mutations resulting in truncation of the Apc protein (Table 1) . Five of the 11 tumors (45%) harbored frameshift or nonsense mutations (Table 1) . Six of the 8 truncating mutations were frameshifts (3 deletions and 3 insertions), and 2 were point mutations creating a nonsense codon. Of the 59 missense mutations, 5 (8%) were transversions and 54 (92%) were transitions (Table 1) . Of the 54 transitions, 27 (50%) were A:TG:C, 14 (26%) T:AC:G, 8 (15%) G:CA:T, and 5 (9%) C:GT:A (Table 1) . No C:GT:A transitional mutations at cytosine-guanine dinucleotides (CpG) were observed. Seventeen of the 67 mutations (25%) were located within the MCR (Table 1) . In contrast, 54% of the observed mutations (36 of 67) were located in a 791-bp region between nucleotides 3020 and 3811 in segment B upstream of the MCR (Table 1) .

p53 Mutations.
A total of 7 mutations in exons 5–8 were found in 6 of the 11 adenocarcinomas analyzed (mutation frequency of 54%; Table 2 ). No p53 mutations in exons 5–8 were observed in the adjacent nonneoplastic colonic mucosal and liver DNA from all of the 11 animals harboring colonic adenocarcinomas. Five of the 7 mutations (71%) were in exon 5, whereas each of exon 6 and 8 contained 1 mutation. No mutation was detected in exon 7. All mutations were single base substitutions resulting in missense mutations (Table 2) . All mutations were transitions; 4 C:GT:A; 2 A:TG:C; and 1 G:CA:T (Table 2) . Four of the 7 mutations (57%) were C:GT:A transitions occurring at nucleotides 688 (codon 229) within CpG sites (Table 2) .

View larger version (63K): [in this window] [in a new window] [Download PPT slide]   Fig. 1. Representative autoradiograms of microsatellite instability assay in colonic adenocarcinomas arising from the ß2mnull x IL-2null mice. A, D7 Mit91 locus. Colonic adenocarcinomas (T) from samples 874 and 1822A demonstrate a contraction of microsatellite sequences compared with normal colonic mucosa (N), thereby demonstrating microsatellite instability. In contrast, no difference in electrophoretic mobility was observed between normal and tumor tissue in sample 775 (i.e., microsatellite stable). B, D19 Mit36 locus. In contrast to microsatellite stable sample 874, colonic adenocarcinoma from sample 380 demonstrates an expansion of microsatellite sequences compared with normal colonic mucosa (i.e., microsatellite unstable).

	DISCUSSION

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In the present study, 100% of the adenocarcinomas analyzed harbored Apc mutations in the 2738-bp region in exon 15 flanking the human MCR. Forty-five % of the adenocarcinomas analyzed had frameshift or nonsense mutations resulting in truncation of the Apc protein. This observation is consistent with a previous study, which reported a truncating mutation frequency of 50% in human UC-associated dysplasia and CRC (6) but contrasts with a much lower frequency of 6% in another human study (7) . APC mutations are considered to be among the earliest events in colorectal carcinogenesis in humans; >60% of sporadic adenoma and CRCs in humans possess a mutation within the APC gene (3 , 4) . The majority (88%) of the observed mutations in the present analysis were missense mutations resulting in an amino acid substitution. Previous human studies of UC-associated CRC only analyzed for truncating APC mutations (6 , 7) , and hence the frequency and nature of missense mutations in human UC-associated CRC are unknown at present. In some chemical rodent models of sporadic CRC, however, missense Apc mutations are not uncommon. For instance, we have observed previously that all Apc mutations in the same region of exon 15 were missense mutations in the dimethylhydrazine rat model of sporadic CRC (31) . The majority (>50%) of the missense mutations in the present study were A:TG:C transitions. The frequency of the A:TG:C transitions ranges from 3.5 to 10.9% in published APC mutation databases for human CRCs (33) . However, more than two-thirds of the missense Apc mutations observed in the dimethylhydrazine rat model of sporadic CRC were A:TG:C transitions (31) . Taken together, the predominant missense Apc point mutations, the majority of which are A:TG:C transitions, may be unique to UC-associated and sporadic rodent models of CRC.

In contrast to observations made in human sporadic and UC-associated CRCs, where 60–100% of the somatic APC mutations are clustered in the MCR in exon 15 (6 , 7 , 33) , only 25% of the observed Apc mutations in the present study were found in the MCR. Over 50% of the observed Apc mutations were located in a 791-bp region between nucleotides 3020 and 3811 in exon 15 upstream of the MCR. Interestingly, previous studies in chemical rodent models of sporadic CRC have suggested that a 757-bp region between nucleotides 3078 and 3835 in exon 15 upstream of the MCR may be a mutational hot spot for CRC (31 , 38) . It is possible that an analysis of the entire coding region of the Apc gene might have detected a higher frequency of mutations as well as other mutational hot spots for UC-associated CRCs in the ß₂m^null x IL-2^null mice. Therefore, the frequency, nature, and location of Apc mutations in CRCs in the ß₂m^null x IL-2^null mice are different from those observed in human sporadic and UC-associated CRCs.

The functional ramifications of predominant missense Apc mutations, >50% of which were located in a unique region upstream of the human MCR, observed in this murine model of UC-associated CRC were not studied in the present study. Because this region of the murine Apc gene contains ß-catenin binding and down-regulation domains and Ser-Ala-Met-Pro motifs necessary for Apc to bind to conductin and axin (39 , 40) , the observed missense mutations in the present analysis may impair ß-catenin down-regulation by Apc and binding of Apc to conductin and axin. The functional significance of missense Apc mutations needs to be determined in future studies.

One surprising finding of the present study is the multiple number of Apc mutations per tumor analyzed (6.1 mutations/tumor). Some tumors exhibited multiple missense mutations even in the presence of truncating mutations. We believe that the observed Apc mutations are real mutations for the following reasons: (a) all potential Apc mutations detected on initial sequencing were confirmed by sequencing three to five independent clones from three to five separately performed PCR reactions, and only those mutations consistently present in all of the confirmatory sequencing were reported; (b) no Apc mutations were detected in liver and adjacent nonneoplastic colonic DNA from each animal harboring tumors with Apc mutations; (c) the analysis of p53 mutations from the same neoplastic tissues demonstrated a "normal" degree of mutations. Recently, Msh2 deficiency has been observed to be associated with a hypermutable state within the same region of the Apc gene in the normal intestinal mucosa from Apc+/-Msh2-/- mice, which carry a heterozygous germ-line mutation at codon 850 of the Apc gene and a homozygous mutation of the Msh2 mismatch repair gene (41) . Furthermore, intestinal adenomas from these mice contained multiple somatic Apc mutations (an average of 10 mutations/tumor) within the same region of the Apc gene, the majority of which were missense mutations (41) . Although the exact frequency and nature of microsatellite instability, and hence mismatch repair defects, were not comprehensively analyzed in the present study, a significant portion of CRCs from this murine model demonstrated microsatellite instability at several loci. Future studies are warranted to determine whether mismatch repair defects inherent in UC-associated CRCs in the ß₂m^null x IL-2^null mice are responsible for the hypermutability of the Apc gene observed in the present study. The allelic location of the observed Apc mutations was not determined in the present study. The unusual large number of Apc mutations would have likely come either from multiple mutations on all alleles or from the presence of cells having more than two sets of chromosomes (i.e., polyploidy), or would have resulted from multiclonality. The occurrence of polyploidy has been observed in several human cancers as well as in murine tumors (42, 43, 44) . The issues of polyploidy and multiclonality in CRCs from this murine model need further clarification in future studies.

In the present study, 54% of the adenocarcinomas analyzed demonstrated p53 mutations in exons 5, 7, and 8. This mutation frequency is comparable with those (33–100%) observed in human UC-associated CRCs (9, 10, 11 , 13 , 14) . All mutations were transitional missense mutations resulting in an amino acid substitution. Of particular interest is the finding of C:GT:A transitions occurring at nucleotide 688 (codon 229) within CpG sites in 4 (57%) of the 7 p53 mutations. It appears that this site, which corresponds to codon 264 in humans, is a mutation hot spot for UC-associated CRCs in the ß₂m^null x IL-2^null mice. One point mutation at nucleotide 631 (codon 211) corresponds to one of the p53 mutational hot spots in human sporadic CRCs (i.e., codon 245). Two human studies have also showed that transitional missense mutations are a predominant type of p53 mutation in UC-associated CRCs in humans (10 , 13) . Although p53 mutations were scattered in exons 5–8 in these studies, codons 248 and 282 appear to be mutational hot spots for UC-associated CRCs in humans (10 , 13) . Deletions in p53 and mutations in exons 5–8 in the remaining allele are observed in up to 75% of sporadic CRCs in humans (3 , 4 , 35) . Up to 50% of mutations in human sporadic CRCs are C:GT:A transitions occurring at CpG sites within these exons (35) , despite the fact that CpG sequences represent only a very small proportion of the total genomic sequence. The CpG sequence is also the major site for cytosine methylation, suggesting a possible association between methylation and the genesis of p53 mutations.

Among the informative samples analyzed for microsatellite instability, 9 adenocarcinomas exhibited microsatellite instability in at least one of the five loci examined. One tumor (no. 380) had microsatellite instability in two loci. This suggests that microsatellite instability, and hence mismatch repair defects, may be a significant molecular event in UC-associated CRCs in this murine model. In humans, microsatellite instability has been found in UC-associated dysplasia (8–21%) and cancer (13–21%; Refs. 22, 23, 24) and even in nonneoplastic mucosa (16–50%; Refs. 24 , 25) . Widespread microsatellite instability is observed in the majority of hereditary nonpolyposis CRCs and 15–20% of sporadic CRCs in humans (45) . Because not all samples could be amplified in the present analysis and only five loci were examined, the exact frequency and nature of microsatellite instability cannot be ascertained in this study. One interesting observation is that the tumor (no. 380) with microsatellite instability at two loci had 16 Apc mutations (13 missense, 1 nonsense, and 2 frameshift) compared with other tumors with microsatellite instability at 1 loci (2–9 Apc mutations/tumor). This suggests that mismatch repair defects might have caused hypermutability in the region of the Apc gene analyzed in this tumor. This is further supported by prior observations of hypermutability within the same region of the Apc gene in intestinal adenomas from Apc+/-Msh2-/- mice as described previously (41) .

Several animal models of UC-associated CRC are currently available (26) . The most commonly used animal model of UC-associated CRC is the chemical carcinogen model. In this model, UC is induced in rodents by chemicals (e.g., trinitrobenzenesulfonic acid, dextran sulfate sodium, or 1-hydroxyanthraquinone), and CRC is induced by coadministration of chemical carcinogens (46, 47, 48) . These models mimic some aspects of the histopathology of the human UC-associated CRCs. However, the use of different strains and species (that may differ appreciably in their relative susceptibility to various agents), different dosing schedules, and different routes of carcinogen administration influence the outcome of such studies. Furthermore, the relatively high dosages of genotoxic chemical carcinogens differ from the natural etiological causes involved in most cases of human sporadic and UC-associated CRCs. Also, the development of CRC arising from relatively acute and severe colitis associated with these chemical carcinogen animal models does not truly reflect that of CRC arising from chronic quiescent UC in humans. Probably, the most serious limitation of the chemical rodent model of UC-associated CRC is the lack of molecular alterations of the Apc, K-ras, and p53 genes that are commonly implicated in sporadic and UC-associated CRC in humans (49 , 50) .

To date, several genetically altered animal models of inflammatory bowel disease have been reported to develop adenomas or CRC spontaneously. Sixty % of the IL-10-deficient mice develop adenocarcinoma in the setting of chronic transmural and segmental inflammation of the colon (51 , 52) . This model, therefore, may be useful for studying tumorigenesis in Crohn’s disease (51 , 52) . Interestingly, colonic adenocarcinomas from the IL-10-deficient mice are not associated with mutations in the p53, Apc, Msh2, and K-ras genes and with microsatellite instability (53) . The chimeric-transgenic mouse model which expresses a dominant N-cadherin (which is essential for maintaining cell adhesion and for epithelial polarity, migration and normal development) has been found to develop a Crohn’s disease-like inflammatory bowel disease with skip lesions with the development of adenomas in the duodenum and ileum without progression to adenocarcinoma (54) . The G_i2-knockout mice develop inflammation limited to the colon, and 31% develop colonic neoplasia in all parts of the colon between 15 and 36 weeks of age (55) . However, 75% of the mice die by 28 weeks, which makes long-term studies investigating the effects of environmental factors on tumorigenesis difficult (55) . Transgenic rats, expressing the human MHC molecule HLA-B27 alone or in combination with the ß₂m gene, develop a spontaneous multisystem disease manifested by colitis, arthritis, and skin changes (56) . In HLA-B27 transgenic rats on an inbred F344 background, hyperplastic lesions have been observed to evolve in the setting of chronic colitis, with a high frequency of colorectal polyp formation and frequent histological progression from adenoma to adenocarcinoma (57) . However, molecular genetics of CRC arising in these genetic models are largely unknown at present.

In summary, the ß₂m^null x IL-2^null mouse appears to be an excellent animal model of UC-associated CRC because the clinical features and molecular genetics, except for the mutational spectrum of the Apc gene, of this genetically predisposed murine model are similar to those of UC-associated CRC in humans. This model provides an excellent opportunity to investigate the effects of environmental and genetic factors on colorectal carcinogenesis associated with chronic UC. Furthermore, this model may be used for chemoprevention with agents such as folate (58 , 59) , short-chain fatty acids (60) , and 5-aminosalicylic acid (61 , 62) that appear to be promising in the prevention of the development of UC-associated CRC.

	FOOTNOTES

 
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This project has been supported in part by grants from the Medical Research Council of Canada (to Y-I. K.), the Crohn’s and Colitis Foundation of America (to C. T. and Y-I. K.), and NIH Diabetes and Digestive and Kidney Diseases and PPG (to C. T.). S. A. S. was a Howard Hughes Medical Institute Physician Postdoctoral fellow. Y-I. K. is a recipient of a scholarship from the Medical Research Council of Canada. Presented in part at the 2001 American Gastroenterological Association meeting, May 20–23, 2001, Atlanta, GA, and published in abstract form in Gastroenterology, 120 (Suppl. 1): A2278, 2001.

² To whom requests for reprints should be addressed, at Medical Sciences Building, Room 7258, University of Toronto, 1 King’s College Circle, Toronto, Ontario, M5S 1A8 Canada. Phone: (416) 978-1183; Fax: (416) 978-8765; E-mail: youngin.kim{at}utoronto.ca

³ The abbreviations used are: UC, ulcerative colitis; CRC, colorectal cancer; APC, adenomatous polyposis coli; IL, interleukin; ß2m, ß2 microglobulin; dNTP, deoxynucleotide triphosphate; MCR, mutation cluster region.

Received 1/ 8/01. Accepted 7/18/01.

	REFERENCES

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. Itzkowitz S. H. Inflammatory bowel disease and cancer. Gastroenterol. Clin. North Am., 26: 129-139, 1997.[Medline]
2. Ekbom A., Helmick C., Zack M., Adami H. O. Ulcerative colitis and colorectal cancer. A population-based study. N. Engl. J. Med., 323: 1228-1233, 1990.[Abstract]
3. Fearon E. R. Molecular genetics of colorectal cancer. Ann. NY Acad. Sci., 768: 101-110, 1995.[Medline]
4. Kinzler K. W., Vogelstein B. Lessons from hereditary colorectal cancer. Cell, 87: 159-170, 1996.[Medline]
5. Greenwald B. D., Harpaz N., Yin J., Huang Y., Tong Y., Brown V. L., McDaniel T., Newkirk C., Resau J. H., Meltzer S. J. Loss of heterozygosity affecting the p53, Rb, and mcc/apc tumor suppressor gene loci in dysplastic and cancerous ulcerative colitis. Cancer Res., 52: 741-745, 1992.[Abstract/Free Full Text]
6. Redston M. S., Papadopoulos N., Caldas C., Kinzler K. W., Kern S. E. Common occurrence of APC and K-ras gene mutations in the spectrum of colitis-associated neoplasias. Gastroenterology, 108: 383-392, 1995.[Medline]
7. Tarmin L., Yin J., Harpaz N., Kozam M., Noordzij J., Antonio L. B., Jiang H. Y., Chan O., Cymes K., Meltzer S. J. Adenomatous polyposis coli gene mutations in ulcerative colitis-associated dysplasias and cancers versus sporadic colon neoplasms. Cancer Res., 55: 2035-2038, 1995.[Abstract/Free Full Text]
8. Burmer G. C., Crispin D. A., Kolli V. R., Haggitt R. C., Kulander B. G., Rubin C. E., Rabinovitch P. S. Frequent loss of a p53 allele in carcinomas and their precursors in ulcerative colitis. Cancer Commun., 3: 167-172, 1991.[Medline]
9. Chaubert P., Benhattar J., Saraga E., Costa J. K-ras mutations and p53 alterations in neoplastic and nonneoplastic lesions associated with longstanding ulcerative colitis. Am. J. Pathol., 144: 767-775, 1994.[Abstract]
10. Kern S. E., Redston M., Seymour A. B., Caldas C., Powell S. M., Kornacki S., Kinzler K. W. Molecular genetic profiles of colitis-associated neoplasms. Gastroenterology, 107: 420-428, 1994.[Medline]
11. Brentnall T. A., Crispin D. A., Rabinovitch P. S., Haggitt R. C., Rubin C. E., Stevens A. C., Burmer G. C. Mutations in the p53 gene: an early marker of neoplastic progression in ulcerative colitis. Gastroenterology, 107: 369-378, 1994.[Medline]
12. Burmer G. C., Rabinovitch P. S., Haggitt R. C., Crispin D. A., Brentnall T. A., Kolli V. R., Stevens A. C., Rubin C. E. Neoplastic progression in ulcerative colitis: histology, DNA content, and loss of a p53 allele. Gastroenterology, 103: 1602-1610, 1992.[Medline]
13. Yin J., Harpaz N., Tong Y., Huang Y., Laurin J., Greenwald B. D., Hontanosas M., Newkirk C., Meltzer S. J. p53 point mutations in dysplastic and cancerous ulcerative colitis lesions. Gastroenterology, 104: 1633-1639, 1993.[Medline]
14. Harpaz N., Peck A. L., Yin J., Fiel I., Hontanosas M., Tong T. R., Laurin J. N., Abraham J. M., Greenwald B. D., Meltzer S. J. p53 protein expression in ulcerative colitis-associated colorectal dysplasia and carcinoma. Hum. Pathol., 25: 1069-1074, 1994.[Medline]
15. Holzmann K., Klump B., Borchard F., Hsieh C. J., Kuhn A., Gaco V., Gregor M., Porschen R. Comparative analysis of histology, DNA content, p53 and Ki-ras mutations in colectomy specimens with long-standing ulcerative colitis. Int. J. Cancer, 76: 1-6, 1998.[Medline]
16. Hussain S. P., Amstad P., Raja K., Ambs S., Nagashima M., Bennett W. P., Shields P. G., Ham A. J., Swenberg J. A., Marrogi A. J., Harris C. C. Increased p53 mutation load in noncancerous colon tissue from ulcerative colitis: a cancer-prone chronic inflammatory disease. Cancer Res., 60: 3333-3337, 2000.[Abstract/Free Full Text]
17. Burmer G. C., Levine D. S., Kulander B. G., Haggitt R. C., Rubin C. E., Rabinovitch P. S. c-Ki-ras mutations in chronic ulcerative colitis and sporadic colon carcinoma. Gastroenterology, 99: 416-420, 1990.[Medline]
18. Bell S. M., Kelly S. A., Hoyle J. A., Lewis F. A., Taylor G. R., Thompson H., Dixon M. F., Quirke P. c-Ki-ras gene mutations in dysplasia and carcinomas complicating ulcerative colitis. Br. J. Cancer, 64: 174-178, 1991.[Medline]
19. Chen J., Compton C., Cheng E., Fromowitz F., Viola M. V. c-Ki-ras mutations in dysplastic fields and cancers in ulcerative colitis. Gastroenterology, 102: 1983-1987, 1992.[Medline]
20. Meltzer S. J., Mane S. M., Wood P. K., Resau J. H., Newkirk C., Terzakis J. A., Korelitz B. I., Weinstein W. M., Needleman S. W. Activation of c-Ki-ras in human gastrointestinal dysplasias determined by direct sequencing of polymerase chain reaction products. Cancer Res., 50: 3627-3630, 1990.[Abstract/Free Full Text]
21. Brentnall T. A., Rubin C. E., Crispin D. A., Stevens A., Batchelor R. H., Haggitt R. C., Bronner M. P., Evans J. P., McCahill L. E., Bilir N., et al A germline substitution in the human MSH2 gene is associated with high-grade dysplasia and cancer in ulcerative colitis. Gastroenterology, 109: 151-155, 1995.[Medline]
22. Suzuki H., Harpaz N., Tarmin L., Yin J., Jiang H. Y., Bell J. D., Hontanosas M., Groisman G. M., Abraham J. M., Meltzer S. J. Microsatellite instability in ulcerative colitis-associated colorectal dysplasias and cancers. Cancer Res., 54: 4841-4844, 1994.[Abstract/Free Full Text]
23. Willenbucher R. F., Aust D. E., Chang C. G., Zelman S. J., Ferrell L. D., Moore D. H., II, Waldman F. M. Genomic instability is an early event during the progression pathway of ulcerative-colitis-related neoplasia. Am. J. Pathol., 154: 1825-1830, 1999.[Abstract/Free Full Text]
24. Lyda M. H., Noffsinger A., Belli J., Fenoglio-Preiser C. M. Microsatellite instability and K-ras mutations in patients with ulcerative colitis. Hum. Pathol., 31: 665-671, 2000.[Medline]
25. Brentnall T. A., Crispin D. A., Bronner M. P., Cherian S. P., Hueffed M., Rabinovitch P. S., Rubin C. E., Haggitt R. C., Boland C. R. Microsatellite instability in nonneoplastic mucosa from patients with chronic ulcerative colitis. Cancer Res., 56: 1237-1240, 1996.[Abstract/Free Full Text]
26. Elson C. O., Sartor R. B., Tennyson G. S., Riddell R. H. Experimental models of inflammatory bowel disease. Gastroenterology, 109: 1344-1367, 1995.[Medline]
27. Sadlack B., Merz H., Schorle H., Schimpl A., Feller A. C., Horak I. Ulcerative colitis-like disease in mice with a disrupted interleukin-2 gene. Cell, 75: 253-261, 1993.[Medline]
28. Simpson S. J., Mizoguchi E., Allen D., Bhan A. K., Terhorst C. Evidence that CD4+, but not CD8+ T cells are responsible for murine interleukin-2-deficient colitis. Eur. J. Immunol., 25: 2618-2625, 1995.[Medline]
29. Shah S. A., Simpson S. J., Brown L. F., Comiskey M., de Jong Y. P., Allen D., Terhorst C. Development of colonic adenocarcinomas in a mouse model of ulcerative colitis. Inflamm. Bowel Dis., 4: 196-202, 1998.[Medline]
30. Carrier J., Medline A., Sohn K-J., Hwang S., Kim Y. I. Effects of dietary folate on colorectal carcinogenesis in a genetically-predisposed murine model of ulcerative colitis-associated colon cancer. Gastroenterology, 120 (Suppl. 1): A447 2001.
31. Sohn K-J., Puchyr M., Salomon R. N., Graeme-Cook F., Fung L., Choi S. W., Mason J. B., Medline A., Kim Y. I. The effect of dietary folate on Apc and p53 mutations in the dimethylhydrazine rat model of colorectal cancer. Carcinogenesis (Lond.), 20: 2345-2350, 1999.[Abstract/Free Full Text]
32. Song J., Sohn K-J., Medline A., Ash C., Gallinger S., Kim Y. I. Chemopreventive effects of dietary folate on intestinal polyps in Apc+/-Msh2-/- mice. Cancer Res., 60: 3191-3199, 2000.[Abstract/Free Full Text]
33. Beroud C., Soussi T. APC gene: database of germline and somatic mutations in human tumors and cell lines. Nucleic Acids Res., 24: 121-124, 1996.[Abstract/Free Full Text]
34. Su L. K., Kinzler K. W., Vogelstein B., Preisinger A. C., Moser A. R., Luongo C., Gould K. A., Dove W. F. Multiple intestinal neoplasia caused by a mutation in the murine homolog of the APC gene [published erratum appears in Science (Wash. DC). 256:1114, 1992]. Science (Wash. DC), 256: 668-670, 1992.[Abstract/Free Full Text]
35. Hollstein M., Sidransky D., Vogelstein B., Harris C. C. p53 mutations in human cancers. Science (Wash. DC), 253: 49-53, 1991.[Abstract/Free Full Text]
36. Bienz B., Zakut-Houri R., Givol D., Oren M. Analysis of the gene coding for the murine cellular tumour antigen p53. EMBO J., 3: 2179-2183, 1984.[Medline]
37. Baker S. M., Bronner C. E., Zhang L., Plug A. W., Robatzek M., Warren G., Elliott E. A., Yu J., Ashley T., Arnheim N., et al Male mice defective in the DNA mismatch repair gene PMS2 exhibit abnormal chromosome synapsis in meiosis. Cell, 82: 309-319, 1995.[Medline]
38. De Filippo C., Caderni G., Bazzicalupo M., Briani C., Giannini A., Fazi M., Dolara P. Mutations of the Apc gene in experimental colorectal carcinogenesis induced by azoxymethane in F344 rats. Br. J. Cancer, 77: 2148-2151, 1998.[Medline]
39. Smits R., Hofland N., Edelmann W., Geugien M., Jagmohan-Changur S., Albuquerque C., Breukel C., Kucherlapati R., Kielman M. F., Fodde R. Somatic Apc mutations are selected upon their capacity to inactivate the ß-catenin downregulating activity. Genes Chromosomes Cancer, 29: 229-239, 2000.[Medline]
40. Kuraguchi M., Edelmann W., Yang K., Lipkin M., Kucherlapati R., Brown A. M. Tumor-associated Apc mutations in Mlh1-/- Apc1638N mice reveal a mutational signature of Mlh1 deficiency. Oncogene, 19: 5755-5763, 2000.[Medline]
41. Sohn K-J., Song J., Chan S., Medline A., Gallinger S., Kim Y. I. Effects of dietary folate on somatic APC mutations in APC+/-MSH2-/- mice. Proc. Am. Assoc. Cancer Res., 41: 84 2000.
42. Andley U. P., Song Z., Wawrousek E. F., Brady J. P., Bassnett S., Fleming T. P. Lens epithelial cells derived from B-crystallin knockout mice demonstrate hyperproliferation and genomic instability. FASEB J., 15: 221-229, 2001.[Abstract/Free Full Text]
43. Kusuzaki K., Takeshita H., Murata H., Gebhardt M. C., Springfield D. S., Mankin H. J., Ashihara T., Hirasawa Y. Polyploidization induced by acridine orange in mouse osteosarcoma cells. Anticancer Res., 20: 965-970, 2000.[Medline]
44. Reinke V., Bortner D. M., Amelse L. L., Lundgren K., Rosenberg M. P., Finlay C. A., Lozano G. Overproduction of MDM2 in vivo disrupts S phase independent of E2F1. Cell Growth Differ., 10: 147-154, 1999.[Abstract/Free Full Text]
45. Chung D. C., Rustgi A. K. DNA mismatch repair and cancer. Gastroenterology, 109: 1685-1699, 1995.[Medline]
46. Okayasu I., Hatakeyama S., Yamada M., Ohkusa T., Inagaki Y., Nakaya R. A novel method in the induction of reliable experimental acute and chronic ulcerative colitis in mice. Gastroenterology, 98: 694-702, 1990.[Medline]
47. Okayasu I., Ohkusa T., Kajiura K., Kanno J., Sakamoto S. Promotion of colorectal neoplasia in experimental murine ulcerative colitis. Gut, 39: 87-92, 1996.[Abstract/Free Full Text]
48. Tamaru T., Kobayashi H., Kishimoto S., Kajiyama G., Shimamoto F., Brown W. R. Histochemical study of colonic cancer in experimental colitis of rats. Dig. Dis. Sci., 38: 529-537, 1993.[Medline]
49. Suzui M., Yoshimi N., Ushijima T., Hirose Y., Makita H., Wang A., Kawamori T., Tanaka T., Mori H., Nagao M. No involvement of Ki-ras or p53 gene mutations in colitis-associated rat colon tumors induced by 1-hydroxyanthraquinone and methylazoxymethanol acetate. Mol. Carcinog., 12: 193-197, 1995.[Medline]
50. Suzui M., Ushijima T., Yoshimi N., Nakagama H., Hara A., Sugimura T., Nagao M., Mori H. No involvement of APC gene mutations in ulcerative colitis-associated rat colon carcinogenesis induced by 1-hydroxyanthraquinone and methylazoxymethanol acetate. Mol. Carcinog., 20: 389-393, 1997.[Medline]
51. Kuhn R., Lohler J., Rennick D., Rajewsky K., Muller W. Interleukin-10-deficient mice develop chronic enterocolitis. Cell, 75: 263-274, 1993.[Medline]
52. Berg D. J., Davidson N., Kuhn R., Muller W., Menon S., Holland G., Thompson-Snipes L., Leach M. W., Rennick D. Enterocolitis and colon cancer in interleukin-10-deficient mice are associated with aberrant cytokine production and CD4(+) TH1-like responses. J. Clin. Investig., 98: 1010-1020, 1996.[Medline]
53. Sturlan S., Oberhuber G., Beinhauer B. G., Tichy B., Kappel S., Wang J., Rogy M. A. Interleukin-10-deficient mice and inflammatory bowel disease associated cancer development. Carcinogenesis (Lond.), 22: 665-671, 2001.[Abstract/Free Full Text]
54. Hermiston M. L., Gordon J. I. Inflammatory bowel disease and adenomas in mice expressing a dominant negative N-cadherin. Science (Wash. DC), 270: 1203-1207, 1995.[Abstract/Free Full Text]
55. Rudolph U., Finegold M. J., Rich S. S., Harriman G. R., Srinivasan Y., Brabet P., Boulay G., Bradley A., Birnbaumer L. Ulcerative colitis and adenocarcinoma of the colon in Gi2-deficient mice. Nat. Genet., 10: 143-150, 1995.[Medline]
56. Hammer R. E., Maika S. D., Richardson J. A., Tang J. P., Taurog J. D. Spontaneous inflammatory disease in transgenic rats expressing HLA-B27 and human ß2m: an animal model of HLA-B27-associated human disorders. Cell, 63: 1099-1112, 1990.[Medline]
57. Hammer R. E., Richardson J. A., Simmons W. A., White A. L., Breban M., Taurog J. D. High prevalence of colorectal cancer in HLA-B27 transgenic F344 rats with chronic inflammatory bowel disease. J. Investig. Med., 43: 262-268, 1995.[Medline]
58. Lashner B. A., Provencher K. S., Seidner D. L., Knesebeck A., Brzezinski A. The effect of folic acid supplementation on the risk for cancer or dysplasia in ulcerative colitis. Gastroenterology, 112: 29-32, 1997.[Medline]
59. Kim Y. I. Folate and carcinogenesis: evidence, mechanisms and implications. J. Nutr. Biochem., 10: 66-88, 1999.[Medline]
60. D’Argenio G., Cosenza V., Delle Cave M., Iovino P., Delle Valle N., Lombardi G., Mazzacca G. Butyrate enemas in experimental colitis and protection against large bowel cancer in a rat model. Gastroenterology, 110: 1727-1734, 1996.[Medline]
61. Pinczowski D., Ekbom A., Baron J., Yuen J., Adami H. O. Risk factors for colorectal cancer in patients with ulcerative colitis: a case-control study. Gastroenterology, 107: 117-120, 1994.[Medline]
62. Eaden J., Abrams K., Ekbom A., Jackson E., Mayberry J. Colorectal cancer prevention in ulcerative colitis: a case-control study. Aliment. Pharmacol. Ther., 14: 145-153, 2000.[Medline]

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