| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Advances in Brief |
Johns Hopkins Oncology Center, Baltimore, Maryland 21231 [M. T., M.O-T., J-P. J. I.], and The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 [L. S., S. R. H., F. A. S., J-P. J. I.]
 |
ABSTRACT |
|---|
 Top ABSTRACT IntroductionMaterials and MethodsResultsDiscussionREFERENCES |
|---|
|
Introduction |
|---|
|
TopABSTRACTIntroductionMaterials and MethodsResultsDiscussionREFERENCES |
|---|
COX2 overexpression is frequent but not universal in colorectal cancer. Initial studies indicated that about 85% of cancers had detectable expression of COX2 (5) . More recently, it was reported that COX2 expression is reduced in a subset of sporadic colorectal cancers with MSI resulting from defective DNA mismatch repair and in colorectal cancer associated with hereditary nonpolyposis colorectal cancer (13 , 14) . Similar reduced expression of COX2 was reported in gastric cancers with MSI (15) . In contrast, rectal cancers appear to express significantly higher levels of COX2 than cancers in other sites (16) . These results indicate that expression of COX2 is not necessary for the development of a subset of colorectal tumors, which must then arise from a pathway independent of COX2. The molecular mechanism of COX2 activation, or lack thereof, in colorectal cancers remains unclear. It has been reported that COX2 expression is repressed by wild-type p53 (17) , suggesting interactions between classical genetic changes and COX2 expression in these tumors. The lack of COX2 expression in subsets of cancers also raised the possibility of a specific silencing mechanism for the gene.
Cytosine methylation of CpG islands is an epigenetic mechanism of gene silencing through modulation of the chromatin structure (18) . Aberrant hypermethylation of 5' CpG islands has been implicated in the transcriptional silencing of various genes in aging and cancer (19 , 20) . Because subsets of sporadic colorectal cancers are often associated with hypermethylation of multiple loci (21 , 22) , and these subsets often include tumors with MSI because of the methylation and silencing of the hMLH1 mismatch repair gene promoter, we hypothesized that COX2 could be silenced by hypermethylation of its 5' CpG island in some cases. In this study, we have examined the methylation status of COX2 in a series of cell lines and colorectal tumors. Our results indicate that COX2 is inactivated in association with aberrant methylation in a subset of colorectal tumors that are CIMP positive.
|
Materials and Methods |
|---|
|
TopABSTRACTIntroductionMaterials and MethodsResultsDiscussionREFERENCES |
|---|
COBRA and Bisulfite Sequencing.
Bisulfite treatment of DNA and COBRA were performed as described
previously (22, 23, 24, 25)
. After treatment, 2 µl of aliquot
were amplified in 50 µl of solution containing 1x buffer, 1.25
mM deoxynucleotide triphosphate mixtures, 2.5 pmol of each
primer, and 1 unit of Taq DNA polymerase (Life Technologies,
Inc.). Touchdown PCR was carried out as follows. After a
hot start, the cycling parameters were: (a) 94°C
for 30 s, 53°C for 30 s, and 72°C for 30 s for 3
cycles; (b) 94°C for 30 s, 51°C for 30 s, and
72°C for 30 s for 4 cycles; (c) 94°C for 30 s,
49°C for 30 s, and 72°C for 30 s for 5 cycles; and
(d) 94°C for 30 s, 47°C for 30 s, and 72°C
for 30 s for 26 cycles. Primers were designed based on the
nucleotide sequences submitted to GenBank (AF044206, HSU44805, and
D28235). Primers used for COBRA were as follows: (a)
COX2-AF, 5'-GATTTGTAGTGAGYGTTAGGAGT-3'; (b) COX2-AR,
5'-RCCAAATACTCACCTATATAACTAAA-3'; (c) COX2-BF,
5'-GTTYGYGTTTTGTTGTTGTG-3'; and (d) COX2-BR,
5'-AATACTAAAATAAACCCAAAAAATCAA-3'. After amplification, 50–80% of PCR
products were digested with the restriction enzyme RsaI (New
England Biolabs) or TaiI (MBI Fermentas), both of
which recognize sequences unique to the methylated and
bisulfite-converted alleles. DNA was then precipitated and
electrophoresed in 6% polyacrylamide gels. The gels were stained with
ethidium bromide, and the intensity of methylated alleles was
calculated by densitometry using ImageQuant software (Molecular
Dynamics). Using this approach, the sensitivity of COBRA is
about 5% (in our hands) because methylation of <5% is poorly
reproducible and likely represents the background of this assay. For
this reason, we adopted a threshold of 5% to call a sample methylation
positive.
For bisulfite sequencing analysis, the region +13 to +270 from the transcriptional start site was amplified using COX2-AF primer and SEQR primer (5'-TGGGATAAACCCAAAAAATCAA-3') and cloned into the PCRII-TOPO vector using the TOPO-TA Cloning KIT (Invitrogen). Multiple clones from each PCR product were sequenced at the Johns Hopkins University Sequencing Facility using automated DNA sequencers (Applied Biosystems).
RT-PCR.
Five µg of total RNA were transcribed using Thermoscript Reverse
Transciptase (Life Technologies, Inc.) at 50°C for cDNA synthesis.
The COX2 RT-PCR reaction was carried out in a solution
containing 1 µl of cDNA (200 ng of RNA), 1x PCR buffer (Life
Technologies, Inc.), 200 µM of each
deoxynucleotide triphosphate, 2.5 pmol of each primer, 1 unit of Taq
DNA polymerase, and 5% (v/v) DMSO.
Primers used were COX2RT-F (5'-CAAAAGCTGGGAAGCCTTCTCTAACC-3') and COX2RT-R (5'-GCCCAGCCCGTTGGTGAAAG-3'). To check the integrity of mRNA, GAPDH was also amplified as described previously (26) . Each sample included reverse transcription-negative controls in which the reverse transcriptase was omitted from the initial reverse transcription step.
|
Results |
|---|
|
TopABSTRACTIntroductionMaterials and MethodsResultsDiscussionREFERENCES |
|---|
). The CpG:GpC ratio is 0.8, and the GC content is 64%,
satisfying the criteria for a CpG island (27)
. This CpG
island is somewhat atypical in that it appears to start just after the
transcription start site. First, we examined the methylation status of
selected CpG sites within this CpG island in several normal tissues
including colon mucosa, placenta, and fibroblasts. Methylation was not
detected (<5%) in the RsaI and TaiI sites in
region 1 by the semiquantitative methylation assay, COBRA (Fig. 1 and C
). In contrast, all normal tissues showed
a slight amount of methylation in the TaiI site in region 2,
which is 40 bp downstream from the exon/intron boundary of exon 1. To
investigate whether aberrant methylation is detected in this CpG
island, a total of 33 cell lines from various tissue types were
investigated for the methylation status of region 1 (Fig. 1C
). Five of the 33 cell lines [RKO (colon), DUPRO
(prostate), HL60 (acute myelogenous leukemia), MB-474 (breast),
and CAMA1 (breast)] showed a methylation level of more than 70%, and
10 cell lines (D283, CEM, Raji, DU145, LNCAP, MB-435, MB-453, BT20,
MB-468, and HepG2) showed partial methylation, ranging from 13–64%.
Eighteen cell lines had no detectable methylation (<5%). Concordant
results were obtained for the RsaI and TaiI sites
in region 1. Of note, the hypermethylated colon cancer cell line RKO is
mismatch repair deficient due to promoter methylation of the
hMLH1 gene. The other hypermethylated cell lines are not
known to be mismatch repair deficient.
|
and the examples in
Fig. 1D
]. In normal colon mucosa from an 18-year-old
patient without tumor, a slight amount of methylation was detected (in
10 alleles sequenced, methylation averaged 2.3 of 24 CpG sites
or 10%). This methylation was predominantly in the 3' region of the
island in intron 1, which is consistent with our earlier COBRA data. No
methylation was detected in the five CpG sites closest to the
transcription start site. In a colorectal cancer cell line,
LOVO, which was unmethylated by COBRA, very little methylation in the
entire region was observed (2 of 312 CpG sites in 14 total alleles
sequenced). In contrast, the colorectal cancer cell line RKO, which
appeared highly methylated by COBRA, showed methylation of nearly all
CpG sites examined in the region (232 of 240 CpGs in 10 alleles
sequenced). The LNCAP cell line, which was partially methylated by
COBRA, also showed a high degree of methylation by sequencing, but 1 of
10 alleles sequenced was completely unmethylated.
Dense Methylation of COX2 Is Associated with
Transcriptional Silencing.
To examine whether methylation of the 5' region of COX2 is
associated with loss of expression, we performed RT-PCR using cDNA from
normal colon as well as six unmethylated cell lines, two heavily
methylated cell lines, and one partially methylated cell line. COX2 was
expressed at varying levels in normal colon, consistent with previous
reports (Fig. 2A
). RKO and DUPRO, which showed dense methylation, did not
express COX2 (Fig. 2A
). LNCAP, which showed
heterogeneous methylation, expressed a slight amount of
COX2. All of the unmethylated cell lines expressed
COX2, albeit at various levels. These results suggest that
dense methylation of the upstream region of COX2 is
associated with transcriptional silencing of the gene.
|
). In both cell lines,
expression of COX2 was restored after treatment, together
with a significant amount of demethylation in the 5' region of
COX2, as determined by bisulfite sequencing (Fig. 2B
; data not shown). These results indicated that
methylation of the 5' region of COX2 plays a role in the
loss of expression of this gene in neoplastic cells.
Aberrant Methylation of COX2 in Primary Colorectal
Tumors.
To determine whether aberrant methylation of COX2 is also
present in primary colorectal tumors, we investigated a series of
colorectal adenomas and cancers by COBRA (see the examples in Fig. 3A
). Aberrant methylation of COX2 (>5%) was
detected in 12 of 92 (13%) colorectal cancers and 7 of 50 (14%)
colorectal adenomas. The similar frequency of COX2
methylation in preneoplastic adenomas and carcinomas indicates that it
is an early event in colorectal tumorigenesis. The results obtained
using digestion with RsaI were identical to those obtained
using digestion with TaiI. In both adenomas and carcinomas,
methylated alleles coexisted with unmethylated alleles. Because we used
tumor samples without microdissection, these results could be due to
infiltration of the tumor samples with nonneoplastic cells.
Alternatively, they could be due to intratumor heterogeneity (some
alleles are methylated, whereas others are not) or to partial
heterogeneous methylation (all alleles are lightly methylated).
|
). The cases that showed
aberrant methylation by COBRA had dense methylation of multiple alleles
throughout the region examined. In each case, the densely methylated
alleles coexisted with completely unmethylated alleles, which likely
originated from nonneoplastic cells. In contrast, the three
unmethylated tumors (by COBRA) had very little methylation throughout
the CpG island. In one case (C13), 1 of 10 alleles appeared to have
dense methylation, suggesting intratumor heterogeneity in methylation. We next examined clinicopathological and molecular features of colorectal cancers with or without COX2 methylation. There was no association between COX2 methylation and the location of tumors, age, gender, or stage of the patients. The presence of CIMP was determined previously for 92 of these cases. There was a significant concordance between COX2 methylation and the presence of CIMP: methylation was present in 11 of 46 (24%) CIMP-positive tumors versus 2 of 46 (4%) CIMP-negative tumors (two-sided P = 0.01, Fisher’s exact test). Methylation of COX2 was inversely related to mutations of p53. Overall, 1 of 13 (8%) cases with COX2 methylation has p53 mutations, whereas 40 of 79 (51%) cases without COX2 methylation had p53 mutations (two-sided P = 0.005, Fisher’s exact test). MSI had been determined previously for 46 cancers, and 19 cases were MSI positive. Of these, 3 of 19 (16%) MSI-positive cases showed COX2 methylation, compared with 7 of 27 (26%) MSI-negative cases (P = 0.61).
Finally, we examined whether hypermethylation of COX2 is
associated with transcriptional silencing of the gene in primary
tumors. We examined 18 cancers that had been studied previously for
COX2 protein expression by IHC (14)
. Of
the 18 tumors, 10 cases had no detectable methylation, and 8 of these
expressed COX2 protein. Six cases had low levels of
methylation (5–20%), and three of these cases were COX2
negative, whereas the other three expressed the protein (examples are
shown in Fig. 3A
). Two cases had high methylation levels
(>20%), and both were negative for COX2 expression by IHC.
|
Discussion |
|---|
|
TopABSTRACTIntroductionMaterials and MethodsResultsDiscussionREFERENCES |
|---|
The mechanism of aberrant methylation of COX2 remains to be
determined. We have shown previously that genes slightly methylated in
normal colon mucosa tend to be methylated very frequently in colorectal
cancers. These genes include ER (29)
,
N33 (30)
, MYOD (30)
,
and VERSICAN (26)
. On the other hand,
methylation of some genes appears to be exclusive to a subset of
cancers that are characterized by CIMP (22
, 31)
. From the
data presented here, methylation of the upstream part of the
COX2 CpG island seems to be tumor specific because
methylation was detected only in a subset of cancers and adenomas.
Indeed, there was a significant correlation between COX2
methylation and the presence of the CIMP. However, the frequency of
COX2 methylation is lower than that of p16
(22)
, THBS1 (21
, 22)
, and
CACNA1G (31)
, which is consistent with the fact
that in some tumors, loss of COX2 might result in growth
disadvantage. Thus, one can envision that the expression of
COX2 in CIMP-positive colorectal tumors results from a
balance between the pressure to silence the gene via methylation and
the pressure to keep the gene active because of its positive effect on
growth (through inhibited apoptosis). Those cases in which a separate
pathway replaces COX2 activation can then become methylated
as a result of CIMP. This model may then explain the relatively high
degree of heterogeneity observed for COX2 methylation in
primary tumors. This heterogeneity is well exemplified by case C13
(Fig. 3B
), which is CIMP positive and has less than 5%
COX2 methylation by COBRA but still has a densely methylated
allele (among unmethylated alleles) detected by sequencing. It also
could explain our finding that some cases with low levels of
COX2 methylation (5–20%) have detectable COX2
protein by IHC.
One alternative explanation for COX2 methylation is that it follows loss of expression (or failure to activate the gene in some cases). Such a hypothesis has been proposed to explain methylation of E-cadherin in breast cancer (32) . Interestingly, we found an inverse correlation between COX2 methylation and p53 mutations in primary tumors. Recently, COX2 expression was shown to be repressed by wild-type p53 (17) . Thus, it is possible that tumors without p53 mutations fail to activate the gene efficiently and become predisposed to methylation that way. This possibility deserves further exploration, but the fact that the gene can be readily reactivated by demethylation in RKO (a cell line with wild-type p53) does not support this hypothesis. In addition, the HCT116 and MCF7 cell lines are also p53 wild type, but they do not hypermethylate COX2, indicating that factors other than p53 mutations must be important for this process to occur.
What are the functional consequences of aberrant methylation of COX2 in colorectal tumorigenesis? It has recently been reported that COX2 is not expressed in some colorectal cancers with MSI (13 , 14) . In these tumors, overproduction of arachidonic acids may not be necessary for tumor progression. Alternatively, colorectal cancers without COX2 expression might have altered regulation of the prostaglandin synthesis pathway through other enzymes such as COX1. Although we found a strong association between COX2 methylation and CIMP, we did not find such an association with MSI. One possible explanation for this is posttranscriptional extinction of COX2 expression in some cases (14) . In fact, the MSI-positive colorectal cancer cell line HCT116, which was reported to express COX2 mRNA (33) but not COX2 protein (14) , is completely unmethylated at this CpG island. Furthermore, low levels of COX2 expression in MSI-positive cancers could also be related to the fact that most of these tumors lack p53 mutations. Regardless of the mechanism of COX2 down-regulation, the existence of tumors with little COX2 expression raises the possibility that these tumors may be relatively resistant to treatment with specific COX2 inhibitors (3) .
|
FOOTNOTES |
|---|
1 Supported by NIH Colon Cancer Spore Grant
CA62924 and American Cancer Society Grant RPG9909801 MGO. M. T.
is a postdoctoral fellow from Japan Society for Promotion of Science. 
2 To whom requests for reprints should be
addressed, at Leukemia Department, The University of Texas M. D.
Anderson Cancer Center, Box 61, 1515 Holcombe Boulevard, Houston, TX
77030. Phone: (713) 745-2260; Fax: (713) 745-2261; E-mail: jpissa{at}mdanderson.org
3 The abbreviations used are: COX, cyclooxygenase;
MSI, microsatellite instability; CIMP, CpG island methylator phenotype;
COBRA, combined bisulfite restriction analysis; RT-PCR, reverse
transcription-PCR; IHC, immunohistochemistry.
Received 2/10/00. Accepted 6/15/00.
|
REFERENCES |
|---|
|
TopABSTRACTIntroductionMaterials and MethodsResultsDiscussionREFERENCES |
|---|
716 knockout mice by inhibition of cyclooxygenase 2 (COX2). Cell, 87: 803-809, 1996.[Medline]
This article has been cited by other articles:
|
|
 |
|
  C. Lofton-Day, F. Model, T. DeVos, R. Tetzner, J. Distler, M. Schuster, X. Song, R. Lesche, V. Liebenberg, M. Ebert, et al. DNA Methylation Biomarkers for Blood-Based Colorectal Cancer Screening Clin. Chem., February 1, 2008; 54(2): 414 - 423. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. Shen, Y. Kondo, S. Ahmed, Y. Boumber, K. Konishi, Y. Guo, X. Chen, J. N. Vilaythong, and J.-P. J. Issa Drug Sensitivity Prediction by CpG Island Methylation Profile in the NCI-60 Cancer Cell Line Panel Cancer Res., December 1, 2007; 67(23): 11335 - 11343. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Nishida, T. Nishimura, T. Nagasaka, I. Ikai, G. Ajay, and C. R. Boland Extensive Methylation Is Associated with {beta}-Catenin Mutations in Hepatocellular Carcinoma: Evidence for Two Distinct Pathways of Human Hepatocarcinogenesis Cancer Res., May 15, 2007; 67(10): 4586 - 4594. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J.-P. J. Issa DNA Methylation as a Therapeutic Target in Cancer Clin. Cancer Res., March 15, 2007; 13(6): 1634 - 1637. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T Ishii, J Murakami, K Notohara, H M Cullings, H Sasamoto, T Kambara, Y Shirakawa, Y Naomoto, M Ouchida, K Shimizu, et al. Oesophageal squamous cell carcinoma may develop within a background of accumulating DNA methylation in normal and dysplastic mucosa Gut, January 1, 2007; 56(1): 13 - 19. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Shu, J. Jelinek, H. Chang, L. Shen, T. Qin, W. Chung, Y. Oki, and J.-P. J. Issa Silencing of bidirectional promoters by DNA methylation in tumorigenesis. Cancer Res., May 15, 2006; 66(10): 5077 - 5084. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Castells, A. Paya, C. Alenda, F. Rodriguez-Moranta, R. Agrelo, M. Andreu, V. Pinol, S. Castellvi-Bel, R. Jover, X. Llor, et al. Cyclooxygenase 2 expression in colorectal cancer with DNA mismatch repair deficiency. Clin. Cancer Res., March 15, 2006; 12(6): 1686 - 1692. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. D. Mitchell Unique Suppression of Prostaglandin H Synthase-2 Expression by Inhibition of Histone Deacetylation, Specifically in Human Amnion but Not Adjacent Choriodecidua Mol. Biol. Cell, January 1, 2006; 17(1): 549 - 553. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. V. Brock, C. M. Hooker, R. Yung, M. Guo, Y. Han, S. E. Ames, D. Chang, S. C. Yang, D. Mason, M. Sussman, et al. Can We Improve the Cytologic Examination of Malignant Pleural Effusions Using Molecular Analysis? Ann. Thorac. Surg., October 1, 2005; 80(4): 1241 - 1247. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Woodson, D. J. Weisenberger, M. Campan, P. W. Laird, J. Tangrea, L. L. Johnson, A. Schatzkin, and E. Lanza Gene-Specific Methylation and Subsequent Risk of Colorectal Adenomas among Participants of the Polyp Prevention Trial Cancer Epidemiol. Biomarkers Prev., May 1, 2005; 14(5): 1219 - 1223. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Soo, T. Putti, Q. Tao, B.-C. Goh, K.-H. Lee, L. Kwok-Seng, L. Tan, and W.-S. Hsieh Overexpression of Cyclooxygenase-2 in Nasopharyngeal Carcinoma and Association With Epidermal Growth Factor Receptor Expression Arch Otolaryngol Head Neck Surg, February 1, 2005; 131(2): 147 - 152. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Nagasaka, H. Sasamoto, K. Notohara, H. M. Cullings, M. Takeda, K. Kimura, T. Kambara, D. G. MacPhee, J. Young, B. A. Leggett, et al. Colorectal Cancer With Mutation in BRAF, KRAS, and Wild-Type With Respect to Both Oncogenes Showing Different Patterns of DNA Methylation J. Clin. Oncol., November 15, 2004; 22(22): 4584 - 4594. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Sato, N. Maehara, and M. Goggins Gene Expression Profiling of Tumor-Stromal Interactions between Pancreatic Cancer Cells and Stromal Fibroblasts Cancer Res., October 1, 2004; 64(19): 6950 - 6956. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y Shoji, M Takahashi, T Kitamura, K Watanabe, T Kawamori, T Maruyama, Y Sugimoto, M Negishi, S Narumiya, T Sugimura, et al. Downregulation of prostaglandin E receptor subtype EP3 during colon cancer development Gut, August 1, 2004; 53(8): 1151 - 1158. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Guo, M. G. House, C. Hooker, Y. Han, E. Heath, E. Gabrielson, S. C. Yang, S. B. Baylin, J. G. Herman, and M. V. Brock Promoter Hypermethylation of Resected Bronchial Margins: A Field Defect of Changes? Clin. Cancer Res., August 1, 2004; 10(15): 5131 - 5136. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. S. Tsao, E. S. Kim, and W. K. Hong Chemoprevention of Cancer CA Cancer J Clin, May 1, 2004; 54(3): 150 - 180. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Yegnasubramanian, J. Kowalski, M. L. Gonzalgo, M. Zahurak, S. Piantadosi, P. C. Walsh, G. S. Bova, A. M. De Marzo, W. B. Isaacs, and W. G. Nelson Hypermethylation of CpG Islands in Primary and Metastatic Human Prostate Cancer Cancer Res., March 15, 2004; 64(6): 1975 - 1986. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Obata, M. Toyota, A. Satoh, Y. Sasaki, K. Ogi, K. Akino, H. Suzuki, M. Murai, T. Kikuchi, H. Mita, et al. Identification of HRK as a Target of Epigenetic Inactivation in Colorectal and Gastric Cancer Clin. Cancer Res., December 15, 2003; 9(17): 6410 - 6418. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. Kopelovich, J. A. Crowell, and J. R. Fay The Epigenome as a Target for Cancer Chemoprevention J Natl Cancer Inst, December 3, 2003; 95(23): 1747 - 1757. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. M. JUBB, P. QUIRKE, and A. J. OATES DNA Methylation, a Biomarker for Colorectal Cancer: Implications for Screening and Pathological Utility Ann. N.Y. Acad. Sci., March 1, 2003; 983(1): 251 - 267. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. M. Thomas, K. Haleem, A. B. Siddique, W. J. Simmons, N. Sen, D.-J. Zhang, and V. K. Tsiagbe Regulation of Mouse Mammary Tumor Virus env Transcriptional Activator Initiated Mammary Tumor Virus Superantigen Transcripts in Lymphomas of SJL/J Mice: Role of Ikaros, Demethylation, and Chromatin Structural Change in the Transcriptional Activation of Mammary Tumor Virus Superantigen J. Immunol., January 1, 2003; 170(1): 218 - 227. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M van Rijnsoever, F Grieu, H Elsaleh, D Joseph, and B Iacopetta Characterisation of colorectal cancers showing hypermethylation at multiple CpG islands Gut, December 1, 2002; 51(6): 797 - 802. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J.-P. Issa Epigenetic Variation and Human Disease J. Nutr., August 1, 2002; 132(8): 2388S - 2392. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. Shen, N. Ahuja, Y. Shen, N. A. Habib, M. Toyota, A. Rashid, and J.-P. J. Issa DNA Methylation and Environmental Exposures in Human Hepatocellular Carcinoma J Natl Cancer Inst, May 15, 2002; 94(10): 755 - 761. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. C. Sombroek, A. G. M. Stam, A. J. Masterson, S. M. Lougheed, M. J. A. G. Schakel, C. J. L. M. Meijer, H. M. Pinedo, A. J. M. van den Eertwegh, R. J. Scheper, and T. D. de Gruijl Prostanoids Play a Major Role in the Primary Tumor-Induced Inhibition of Dendritic Cell Differentiation J. Immunol., May 1, 2002; 168(9): 4333 - 4343. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. Fosslien Molecular Pathology of Cyclooxygenase-2 in Cancer-induced Angiogenesis Ann. Clin. Lab. Sci., October 1, 2001; 31(4): 325 - 348. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. Zhang, P. M. Laborde, K. R. Coombes, D. A. Berry, and S. R. Hamilton Cancer Genomics: Promises and Complexities Clin. Cancer Res., August 1, 2001; 7(8): 2159 - 2167. [Abstract] [Full Text] [PDF]
|
|
|
|
], whereas methylated CpG
sites are indicated by •. Note the variable but low degree of
methylation in normal colon, the almost complete lack of methylation in
the LOVO cell line, and the high degree of methylation in RKO and
LNCAP.
