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[Cancer Research 63, 2364-2368, May 15, 2003]
© 2003 American Association for Cancer Research

Advances in Brief

BALB/c Alleles for Prkdc and Cdkn2a Interact to Modify Tumor Susceptibility in Trp53+/- Mice1

Anneke C. Blackburn2, Jennifer S. Brown, Stephen P. Naber3, Christopher N. Otis, Jeff T. Wood and D. Joseph Jerry4

Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, Massachusetts 01003 [A. C. B., J. S. B., D. J. J.]; Department of Pathology, Baystate Medical Center, Springfield, Massachusetts 01199 [S. P. N., C. N. O.]; and Statistical Consulting Unit, Australian National University, Canberra ACT 2601, Australia [J. T. W.]


   ABSTRACT
Top
 ABSTRACT
Introduction
 Materials and Methods
 Results
 Discussion
 REFERENCES
 
In mice heterozygous for p53 (Trp53+/-), the incidence of mammary tumors varies among strains, with C57BL/6 being resistant and BALB/c being susceptible. Mammary tumor phenotypes were examined in female Trp53+/- F1 mice (C57BL/6 x BALB/c;n = 19) and N2 backcross mice [(C57BL/6 x BALB/c) x BALB/c] (n = 224). Susceptibility to mammary tumors segregated as a dominant phenotype in F1 females, but a higher frequency and shorter latency in N2 mice indicated a contribution from recessive-acting modifiers. Segregation of the hypomorphic BALB/c alleles for DNA-dependent protein kinase catalytic subunit (Prkdc) and p16INK4A (Cdkn2a) was analyzed in the N2 mice. The time to first tumor (considering all tumor types) was significantly different among the four genotype combinations (P = 0.01). Cdkn2a had a strong effect (P = 0.008) but was restricted to PrkdcB/B mice (P = 0.001), indicating a strong interaction between the loci. Differences in mammary tumor occurrence among genotypes for Prkdc and Cdkn2a in N2 mice were not statistically significant. This study indicates that BALB/c Prkdc and Cdkn2a alleles do modify tumor incidence in Trp53+/- mice and highlights the complexity of gene interaction effects in determining cancer phenotypes but discounts these alleles as major recessive loci contributing to spontaneous mammary tumor susceptibility.


   Introduction
Top
 ABSTRACT
 Introduction
Materials and Methods
 Results
 Discussion
 REFERENCES
 
Breast cancer is a complex disease with many environmental and genetic factors contributing to an individual’s risk of developing the disease. In the presence of rare, highly penetrant alleles, such as BRCA1 and BRCA2, genetics can play a major role in determining an individual’s risk. More common alleles may modify the risk associated with these high penetrance alleles, as is suggested by the relatively low penetrance of BRCA1 mutations present in Ashkenazi Jewish population (1 , 2) . In the absence of high penetrance alleles, a study of twins has suggested that as much as 27% of breast cancer risk may still be attributed to genetic factors (3) . Low penetrance alleles, which are common in the population, are likely to contribute to risk in this setting (1) and overlap with the modifiers of high penetrance alleles (4) . Thus, the study of modifier genes in the setting of a high penetrance allele may point to alleles contributing to cancer risk in the general population.

Germ-line mutations in the tumor suppressor gene TP53, which have been found in approximately half of Li-Fraumeni Syndrome families, also confer a high risk of breast cancer (5) . Variation in the age of onset of disease between siblings carrying the same mutation also suggests the existence of modifier genes altering breast cancer risk. Li-Fraumeni Syndrome is characterized by the occurrence of various cancers at an early age, including breast cancer, soft tissue sarcomas, osteosarcomas, and adrenocortical carcinoma (6) . Similarly, Trp53+/- mice succumb to a range of tumor types; however, only on a BALB/c genetic background do they have a significant incidence of mammary adenocarcinomas, indicating that BALB/c mice possess alleles of modifier genes which increase their susceptibility to mammary tumors (7) . The BALB/c strain also displays increased susceptibility to radiation- and carcinogen-induced mammary tumors compared with C57BL/6 mice (8 , 9) . The susceptibility to radiation-induced tumors has been demonstrated to be a recessive trait of the mammary epithelium, as C57BL/6 x BALB/c F1 epithelium showed the same low rate of mammary tumor formation as C57BL/6 epithelium (8) . Thus, we undertook to identify recessive alleles present in BALB/c which would confer increased risk of spontaneous mammary tumors in the Trp53+/- breast cancer model.

Two candidate genes have been described for which mutant alleles in the BALB/c strain may confer increased risk to mammary tumors. The Prkdc locus, encoding the catalytic subunit of the DNA double-strand break repair protein DNA-PK,5 contains two point mutations in BALB/c which result in increased radiation-induced genomic instability in mammary epithelial cells and thus may be involved in increased susceptibility to radiation-induced mammary tumors (10) . The BALB/c allele of the Cdkn2a locus, encoding p16INK4A and p19ARF, also contains two point mutations which result in decreased ability of p16INK4A to inhibit Rb phosphorylation and induce growth arrest but do not appear to alter p19ARF function (11 , 12) . Therefore, these candidate genes were examined for their contribution to the formation of mammary and other tumor types in a [C57BL/6 x BALB/c] x BALB/c backcross population of female Trp53+/- mice.


   Materials and Methods
Top
 ABSTRACT
 Introduction
 Materials and Methods
Results
 Discussion
 REFERENCES
 
Mice and Breeding Strategy.
BALB/c-Trp53+/- mice were generated previously (13) by backcrossing C57BL/6 x 129/Sv Trp53-/- mice onto the BALB/cMed strain for 11 generations. F1 intercross mice were Trp53+/- offspring of inbred C57BL/6J-Trp53+/+ female and BALB/cMed-Trp53-/- male mice. N2 backcross mice were the offspring of [C57BL/6J x BALB/cMed]-Trp53+/+ F1 females x BALB/cMed-Trp53-/- males. Nineteen virgin female (C57BL/6 x BALB/c)-Trp53+/- F1-study mice and 224 virgin female [(C57BL/6 x BALB/c) x BALB/c]-Trp53+/- N2-study mice were monitored weekly for tumor development or morbidity and palpated for mammary tumors. Tissues for DNA extraction were collected from 218 N2 mice. Four N2 mice survived to 18 months of age tumor free. Mice were sacrificed before tumors reached 1 cm in size or when signs of morbidity were observed. Tumor tissues were fixed overnight in neutral-buffered formalin, processed, and stained with H&E for histological assessment. Mammary glands without tumors were whole mounted for examination of ductal tree structure. Ninety-seven virgin female BALB/c-Trp53+/- were monitored similarly, but healthy mice were removed at set time points for <=1 year for a study of precancerous changes, such that 56 mice were sacrificed for time points and 41 mice for tumors. No BALB/c-Trp53+/- mice survived tumor free; the last tumor was found at 54 weeks of age.

Analysis of the Genotypes at the Prkdc and Cdkn2a Loci.
Normal tail tissues from each mouse were snap frozen in liquid nitrogen at the time of necropsy. The tissue was digested overnight with 100 µg/ml proteinase K in 100 mM Tris, 5 mM EDTA, 0.2% sodium dodecyl sulfate, and 200 mM NaCl, and genomic DNA was isolated by phenol:chloroform:isoamyl alcohol extraction. PCR followed by restriction digestion was performed using published primers and cycling temperatures to distinguish between the C57BL/6 and BALB/c alleles at the Prkdc (10) and Cdkn2a (11) loci. PCR was performed with 10–50 ng of genomic DNA with 300 pmol/ml each primer in a 20-µl reaction volume containing 1 x PCR buffer (Sigma), 2 mM MgCl (Sigma), 250 µM deoxynucleotide triphosphates (Sigma), and 0.5 unit of Taq polymerase (Sigma). The allelic variants in exon 1 of Cdkn2a were examined after digestion with NlaIII (New England Biolabs, Beverly, MA) at 37°C, and fragments were separated by PAGE using 10% acrylamide in 1 x Tris-borate EDTA and stained with ethidium bromide. The allelic variants at position 2140 of Prkdc were examined after digestion with BsmBI (New England Biolabs) at 55°C, and fragments were separated on 1.5% agarose gels with 1 x Tris-borate EDTA and stained with ethidium bromide.

Statistical Analysis.
Mice were categorized according to tumor types observed and alleles present at the Prkdc and Cdkn2a loci. Kaplan-Meier estimates of the tumor-free survival curves were calculated and plotted (This analysis takes into account the removal of healthy BALB/c mice at various times). The median time to tumor with 95% confidence limits was used for comparison of latencies where possible, avoiding biases caused by rare events at early and late ages that can influence mean results. The significance of differences in latency (tumor-free survival times) was analyzed by the Log-rank test. To test the effect of a single locus, the test was stratified by homozygosity or heterozygosity at the other locus. Latency of mammary tumors was defined as the age when a palpable lump was first detected in the mammary gland. Latency for lymphomas was defined as the age at which enlarged nodes or spleen were first detected or the age when first signs of illness were observed, which progressed to morbidity and sacrifice of the mouse and consequent diagnosis of lymphoma. The majority of osteosarcomas occurred on peripheral limbs; thus, the latency for osteosarcomas was simply defined as the age at which the tumor was first observed. When analyzing mammary tumors, mice bearing carcinosarcomas of the mammary gland were excluded to focus on tumors of definite epithelial origin.


   Results
Top
 ABSTRACT
 Introduction
 Materials and Methods
 Results
Discussion
 REFERENCES
 
Survival and Tumor Spectrum.
The tumor-free survival of female Trp53+/- mice was altered considerably by genetic background of the three populations studied. BALB/c mice succumbed to tumors at the earliest age, whereas N2 and F1 study mice survived significantly longer (P < 0.001 for BALB/c versus either N2 or F1). The median time to tumor was 47.4, 57.6, and 61 weeks (95% confidence limits 45.6–52.9, 56.3–59.7, and 53–74) for BALB/c-, N2-, and F1-Trp53+/- mice, respectively (Fig. 1A)Citation . The F1 mice survived slightly longer than N2 mice; however, this was not significantly different (P = 0.1) because of the small number of F1 mice studied. All F1-Trp53+/- mice succumbed to tumors or morbidity by 18 months of age, whereas 4 N2-Trp53+/- mice remained healthy at 18 months.



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  		Fig. 1. Kaplan-Meier tumor-free survival curves for Trp53+/- mice. Probability of tumor-free survival (all tumor types; A) and mammary tumor-free survival (B) for BALB/c (C57BL/6 x BALB/c)-F1 and [(C57BL/6 x BALB/c) x BALB/c]-N2 Trp53+/- mouse populations.

 
The most frequent tumor type observed in all three populations was mammary tumors. This has been reported previously for BALB/c-Trp53+/- mice but is a characteristic that was not observed in other genetic backgrounds (7 , 14) . The BALB/c data from the present study cannot be directly compared with the published data of Kuperwasser et al. because of the inclusion of males and breeder females in the previous study. However, when just the virgin female mice of the previous study were analyzed, 65% of mice developed mammary tumors at a median age of 54 weeks (n = 17), consistent with the current study. BALB/c mice were significantly more susceptible to mammary tumors than N2 and F1 mice (P < 0.001 and 0.005, respectively; Fig. 1BCitation ), with median times to first mammary tumor of 52.9, 66.4, and 74.7 weeks (95% confidence limits 50.4–NA, 64.6–68.3, and 74–NA, with NA indicating not available because of a lack of sufficient tumors occurring after the median age) for BALB/c-, N2-, and F1-Trp53+/- mice, respectively. Mammary tumors occurred in 98 of 218 (45%) N2 mice, displaying both a lower incidence and increased latency compared with the BALB/c study mice, indicating the presence of recessive BALB/c alleles contributing to mammary tumor susceptibility. N2 and F1 mice were not statistically significant because of the small number of F1 mice (P = 0.1). Mammary adenocarcinoma was found in 6 of 19 (32%) F1 study mice (Fig. 1B)Citation . The occurrence of mammary tumors in the F1-Trp53+/- mice compared with the lack of reports of occurrences in C57BL/6 mice indicates the presence of dominant BALB/c alleles contributing to BALB/c-Trp53+/- mammary tumor susceptibility. Thus, both dominant and recessive BALB/c alleles contribute to spontaneous mammary tumor susceptibility in Trp53+/- mice.

The mammary tumors arising in the three populations had similar histological characteristics, although the extent of squamous differentiation appeared to vary with genetic background. In the present study, 16 of 17 (94%) mammary tumors arising in BALB/c-Trp53+/- mice were adenocarcinomas, with one case of mammary intraepithelial neoplasia and no adenosquamous carcinomas. In the F1 mice, of the 6 mammary tumors, 4 (66%) were acinar or alveolar adenocarcinomas, and 2 (33%) were adenosquamous in character. An additional 2 mice displayed significant mammary epithelial lesions in the form of sclerosing adenosis, a benign lesion, and adenosquamous hyperplasias, a likely precursor to adenosquamous carcinoma. The N2 mammary tumors consisted mainly of adenocarcinomas (76 of 98, 78%), with 9 (9%) cases of carcinosarcomas, 10 (10%) adenosquamous carcinomas, and 3 (3%) mammary intraepithelial neoplasias. Thus, in addition to increased latency and decreased frequency of mammary tumors, the introduction of C57BL/6 alleles into Trp53+/- mice increased the extent of adenosquamous differentiation occurring within mammary tumors from none to 10 and 33% in the BALB/c, N2, and F1 mice, respectively.

The remainder of the tumor spectrum observed in F1- and N2-Trp53+/- study mice included the tumor types most commonly reported in Trp53+/- mice on other genetic backgrounds (14) . Lymphoma was the second most frequent tumor type in both F1- and N2-populations, occurring in 4 of 19 (21%) F1 mice and 44 of 218 (20%) N2 mice. Osteosarcomas were observed in 28 of 218 (13%) N2 mice and in only 1 (5%) F1 mouse. However, in addition to these commonly observed tumors, two tumor types not reported previously in Trp53+/- mice occurred in the F1 and N2 mice. Adrenal gland tumors were observed in two F1 mice (11%) at 73 and 78 weeks of age and were the third most abundant tumor type in the N2 mice (31 mice, 14%), also occurring with a latency of >70 weeks (Table 1)Citation . Four mice with adrenal tumors displayed bilateral adrenal gland tumors. Histologically, the tumors were poorly differentiated carcinomas. The adrenal gland tumors varied in size at time of detection depending on whether they were found by palpation or on necropsy. Because of this inconsistent determination of latency, adrenal gland tumors were not subject to statistical analysis. Pituitary adenomas were observed in 2 F1 mice (11%) and 4 (2%) N2 mice occurring at 51–75 weeks of age (mean 62 weeks). Secretion of prolactin by these tumors was inferred from the abundant milky secretions in the mammary glands. No other tumor type affected >5% of the N2-Trp53+/- mice.


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  		Table 1 Analysis of tumor-free survival in N2-Trp53+/- mice according to Prkdc and Cdkn2a genotypes

 
Modifier Effects of Cdkn2a and Prkdc in N2 Mice.
Polymorphisms at the Prkdc and Cdkn2a loci, which alter gene function, have been identified in the BALB/c strain. To determine whether the BALB/c alleles contributed to tumor occurrence, the genotypes of the N2 mice were determined at these two loci by PCR-RFLP analysis. The tumor-free survival curves for the four different genotype combinations differed significantly (Fig. 2ACitation ; P = 0.01). Analysis of the occurrence of all tumors within the N2 population according to single loci suggested that Prkdc had no significant effect (P = 0.94; Table 1Citation ) but that the differences were attributable entirely to the Cdkn2a locus (P = 0.008; Table 1Citation ). However, examination of the two loci in combination indicates that Prkdc genotype was not without effect. Analysis of the interaction of Prkdc and Cdkn2a revealed an 8-week delay in tumor appearance in PrkdcB/B, Cdkn2a+/B mice compared with PrkdcB/B, Cdkn2aB/B mice (P = 0.001; Table 1Citation ). In contrast, Cdkn2a genotype makes no significant difference to survival in Prkdc+/B mice (P = 0.60; Fig. 2ACitation ). Thus, when considering all tumor types, a strong modifying effect of the Cdkn2a locus is detected among mice homozygous for the BALB/c Prkdc allele.



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  		Fig. 2. Kaplan-Meier tumor-free survival curves for Trp53+/- mice. Probability of tumor-free survival (all tumor types; A), osteosarcoma-free survival (B), lymphoma-free survival (C), and mammary tumor-free survival (D) of N2-Trp53+/- mice segregated according to genotypes at both the Prkdc (P) and Cdkn2a (C) loci. *, comparisons highlighted in Table 1Citation .

 
Interactions between these two loci were also observed when examining individual tumor types (Table 1)Citation . Osteosarcoma-free survival was modified by Cdkn2a (P = 0.01) but not Prkdc (P = 0.24). Considering interactions between Cdkn2a and Prkdc, Cdkn2a heterozygosity significantly increased osteosarcoma-free survival in Prkdc+/B mice (P = 0.01), with Prkdc+/B, Cdkn2a+/B mice having a particularly low incidence of osteosarcomas. The other genotypes all displayed similar latencies and probabilities for developing osteosarcoma (Fig. 2B)Citation . Analysis of mice bearing lymphoma was suggestive of Cdkn2a being a modifier of lymphoma-free survival (P = 0.09). Considering interactions, this effect was most prominent in PrkdcB/B mice (P = 0.1), with Cdkn2a+/B genotype being associated with an increased average latency of 5 weeks and a higher probability of developing lymphoma at an older age (Fig. 2C)Citation .

Analysis of mice bearing mammary tumors, considering either Prkdc or Cdkn2a alone, did not produce statistically significant results. However, when considering interactions between the loci, a suggestion of Cdkn2a being a modifier was observed in PrkdcB/B mice, with the PrkdcB/B, Cdkn2aB/B genotype reducing the median latency of mammary tumor development by 2.5 weeks compared with PrkdcB/B, Cdkn2a+/B mice (P = 0.11; Table 1Citation ). Interestingly, this effect was limited to mice developing mammary tumors at >55 weeks of age, where the latency difference was generally 5–7 weeks (Fig. 2D)Citation .


   Discussion
Top
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
REFERENCES
 
We undertook to identify recessive alleles present in BALB/c which increase risk of breast cancer in Trp53+/- mice. The multiple tumor phenotype in Trp53+/- mice allowed analysis of the effects of modifiers on other tumor types also. The BALB/c alleles of Cdkn2a and Prkdc were shown to interact and alter tumor latency in the experiments reported, but their effects differed among tissues, such that strong effects were seen on osteosarcomas, whereas no significant effects were seen on mammary tumors. Cdkn2a and Prkdc are both logical candidates for genes that would modify a tumor phenotype resulting from p53 deficiency (10 , 11 , 12) . Prkdc encodes the catalytic subunit of DNA-PK. This kinase, which senses double-strand DNA breaks, is one of the kinases which stabilizes and activates p53 protein by phosphorylation (15) . Thus, in cells already haploinsufficient for p53 function (16) , decreased DNA-PK activity may further attenuate the p53 tumor suppression response. The p53 response can include induction of cell cycle arrest at both G1 and G2 checkpoints. p16INK4A, one of the products of the Cdkn2a gene, also inhibits cell cycle progression through the G1-S restriction point by preventing the phosphorylation of Rb by Cdk4, thereby preventing the release from Rb of the transcription factor E2F, which is necessary for transcription of genes involved in progression to S phase of the cell cycle (17) . Thus, a less functional Cdkn2a allele will further diminish the fidelity of the G1-S-phase checkpoint in Trp53+/- cells.

The effect on all tumor types of these two hypomorphic alleles in combination was that mice homozygous for BALB/c alleles at both loci displayed the shortest time to first tumor, as might be expected, because the combination of decreased DNA repair and reduced cell cycle control would be complementary in allowing the survival of mutation-bearing cells, which can progress on to become cancer. However, the strength of the modifying effects and particular genotype combination of greatest difference varied between tumor types, with Prkdc+/B, Cdkn2a+/B mice standing out for low incidence of osteosarcomas (Fig. 2B)Citation and PrkdcB/B, Cdkn2a+/B mice standing out for high incidence of lymphomas, whereas PrkdcB/B Cdkn2aB/B mice had a noticeably shorter latency for lymphomas (Fig. 2C)Citation . The intricacies of these interactions depend on the level of expression of DNA-PK and p16INK4A in a particular tissue and on the integration of the signals and activities of many different mechanisms involved in determining the outcome of p53 activation. A p53 response can result in cell cycle arrest, stimulation of DNA repair, and apoptosis, and it is the balance between cell survival and maintenance of genomic integrity that is critical in protection against cancer. The p53 response of a cell can also vary with the proliferative status of a tissue, as is the case in the mammary gland (18) ; thus, the complex web of p53 regulation and cell fate decisions means that the effect of modifier alleles could be highly cell type, cell cycle, and carcinogen specific. The integration of these factors is complex and subtle in the controlled experimental setting of the Trp53+/- model, indicating that the discovery of low penetrance alleles contributing to cancer phenotypes within the highly variable human population will be a very difficult task. However, the study of cancer susceptibility in animal models provides the opportunity to identify novel loci for investigation in the human disease setting.

The occurrence of mammary tumors in the F1 population of Trp53+/- mice and increased latency of mammary tumors in the N2 population compared with the BALB/c mice indicate that both dominant and recessive alleles contribute to BALB/c susceptibility to mammary tumor formation. Both Cdkn2a and Prkdc have been suggested as mammary tumor susceptibility loci; however, neither locus made a major contribution as recessive alleles to the occurrence of mammary tumors in this model. The BALB/c allele of Prkdc was discovered as a gene contributing to the radiation sensitivity of mammary epithelial cells in BALB/c mice (10) and suggested to be involved in mammary tumorigenesis of this strain. Although Prkdc is not a recessive contributor to spontaneous Trp53+/- mammary tumors, the possibility that it could be a dominant contributor cannot be ruled out. DNA-PK is a particularly attractive candidate for breast cancer susceptibility because of its already low expression level in the mammary epithelium (19) , its involvement in DNA double-strand break repair, and the mounting evidence of the involvement of these repair pathways in breast cancer (20 , 21) .

Several human studies of melanoma families with mutations in CDKN2A have suggested that these families may also be at greater risk of developing breast cancer (22 , 23) . The Cdkn2aB/B genotype, when present with PrkdcB/B, decreased mammary tumor latency in this study by 5–7 weeks in the older mammary tumor-bearing mice. Although not statistically significant, this is of interest because the absence of a modifying effect on the younger onset mammary tumors suggests differences in the mechanism of tumorigenesis between early and late onset mammary tumors in the N2 population. This may point to an unknown allele which accelerates mammary tumor development and renders any contribution from Cdkn2aB/B genotype insignificant. It will be of interest to examine any locus identified in future studies to be involved in mammary tumor susceptibility for interactions with Cdkn2a.

Two tumor types novel for Trp53+/- mice, pituitary adenomas and adrenal gland tumors, were observed in the F1- and N2-Trp53+/- mice of this study. Pituitary adenomas have been described in Trp53+/- mice only when also deficient in Rb, where Rb+/- mice characteristically develop pituitary adenomas (24) . Perhaps the hypomorphic BALB/c Cdkn2a allele resulting in reduced Rb activity, combined with the decreased susceptibility to mammary tumors allowing longer survival times, contribute to the occurrence of this tumor type in the F1- and N2-Trp53+/- mice. The occurrence of adrenal gland tumors in the F1- and N2-Trp53+/- mice is of particular interest because adrenocortical carcinomas are strongly associated with Li-Fraumeni Syndrome while rare in the general population (6) . Although these tumors were not observed in the BALB/c-Trp53+/- mice of this study, they were observed at 59–73 weeks and often bilateral in retired breeders kept for monitoring,6 suggesting that more time is required to develop these long latency tumors. The occurrence of adrenal tumors further supports the idea that BALB/c alleles contribute toward making BALB/c-Trp53+/- mice a unique model for Li-Fraumeni Syndrome.

The current study demonstrates clearly that although Cdkn2a may be a weak modifier of Trp53+/- mammary tumor susceptibility, homozygosity at either Cdkn2a or Prkdc cannot account for the susceptibility of BALB/c mice to spontaneous mammary tumors in this model. Genome scans on the N2-Trp53+/- mice are currently underway in the search for other alleles responsible for BALB/c mammary tumor susceptibility.


   ACKNOWLEDGMENTS
 
We thank Ellen Dickinson for her assistance with histology and Christine Donnelly for her assistance in preparation of the figures.


   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 Supported by NIH Grants CA66670 and CA87531 (to D. J. J.), the Massachusetts Department of Public Health (43088PP1017), and Department of Defense Breast Cancer Program award DAMD17-00-1-0632, administered by United States Army Medical Research Acquisition Activity. A. C. Blackburn was supported by Department of Defense Breast Cancer Program award DAMD17-01-1-0315, administered by United States Army Medical Research Acquisition Activity. Back

2 Present address: John Curtin School of Medical Research, Australian National University, Canberra ACT 2601, Australia. Back

3 Present address: Tufts-New England Medical Center, Boston, MA 01199. Back

4 To whom requests for reprints should be addressed, at Department of Veterinary and Animal Sciences, Paige Laboratory, 161 Holdsworth Way, University of Massachusetts, Amherst, MA 01003-6410. Phone: (413) 545-5335; Fax: (413) 545-6326; E-mail: jjerry{at}vasci.umass.edu Back

5 The abbreviations used are: DNA-PK, DNA-dependent protein kinase; Rb, retinoblastoma. Back

6 A. C. Blackburn, personal observation. Back

Received 12/17/02. Accepted 3/26/03.


   REFERENCES
Top
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
 REFERENCES
 

  1. Nathanson K. L., Weber B. L. "Other" breast cancer susceptibility genes: searching for more holy grail. Hum. Mol. Genet., 10: 715-720, 2001.[Abstract/Free Full Text]
  2. Fodor F. H., Weston A., Bleiweiss I. J., McCurdy L. D., Walsh M. M., Tartter P. I., Brower S. T., Eng C. M. Frequency and carrier risk associated with common BRCA1 and BRCA2 mutations in Ashkenazi Jewish breast cancer patients. Am. J. Hum. Genet., 63: 45-51, 1998.[Medline]
  3. Lichtenstein P., Holm N. V., Verkasalo P. K., Iliadou A., Kaprio J., Koskenvuo M., Pukkala E., Skytthe A., Hemminki K. Environmental and heritable factors in the causation of cancer–analyses of cohorts of twins from Sweden. Denmark, and Finland. N. Engl. J. Med., 343: 78-85, 2000.[Abstract/Free Full Text]
  4. Ponder B. A. Cancer genetics. Nature (Lond.), 411: 336-341, 2001.[Medline]
  5. Kleihues P., Schauble B., zur Hausen A., Esteve J., Ohgaki H. Tumors associated with p53 germline mutations: a synopsis of 91 families. Am. J. Pathol., 150: 1-13, 1997.[Abstract]
  6. Birch J. M., Alston R. D., McNally R. J., Evans D. G., Kelsey A. M., Harris M., Eden O. B., Varley J. M. Relative frequency and morphology of cancers in carriers of germline TP53 mutations. Oncogene, 20: 4621-4628, 2001.[Medline]
  7. Kuperwasser C., Hurlbut G. D., Kittrell F. S., Medina D., Naber S. P., Jerry D. J. Development of mammary tumors in BALB/c p53 heterozygous mice: a model for Li-Fraumeni Syndrome. Am. J. Pathol., 157: 2151-2159, 2000.[Abstract/Free Full Text]
  8. Ullrich R. L., Bowles N. D., Satterfield L. C., Davis C. M. Strain-dependent susceptibility to radiation-induced mammary cancer is a result of differences in epithelial cell sensitivity to transformation. Radiat. Res., 146: 353-355, 1996.[Medline]
  9. Medina D. Mammary tumorigenesis in chemical carcinogen-treated mice. I. Incidence in BALB/c and C57BL mice. J. Natl. Cancer Inst. (Bethesda), 53: 213-221, 1974.
  10. Yu Y., Okayasu R., Weil M. M., Silver A., McCarthy M., Zabriskie R., Long S., Cox R., Ullrich R. L. Elevated breast cancer risk in irradiated BALB/c mice associates with unique functional polymorphism of the Prkdc (DNA-dependent protein kinase catalytic subunit) gene. Cancer Res., 61: 1820-1824, 2001.[Abstract/Free Full Text]
  11. Zhang S., Ramsay E., Mock B. Cdkn2a, the cyclin-dependent kinase inhibitor encoding p16INK4{alpha} and p19ARF, is a candidate for the plasmacytoma susceptibility locus. Pctr1. Proc. Natl. Acad. Sci. USA, 95: 2429-2434, 1998.[Abstract/Free Full Text]
  12. Zhang S. L., DuBois W., Ramsay E. S., Bliskovski V., Morse H. C., Taddesse-Heath L., Vass W. C., DePinho R. A., Mock B. A. Efficiency alleles of the Pctr1 modifier locus for plasmacytoma susceptibility. Mol. Cell. Biol., 21: 310-318, 2001.[Abstract/Free Full Text]
  13. Jerry D. J., Kuperwasser C., Downing S. R., Pinkas J., He C., Dickinson E., Marconi S., Naber S. P. Delayed involution in the mammary epithelium in BALB/c-p53null mice. Oncogene, 17: 2305-2312, 1998.[Medline]
  14. Donehower L. A., Harvey M., Vogel H., McArthur M. J., Montgomery C. A., Jr., Park S. H., Thompson T., Ford R. J., Bradley A. Effects of genetic background on tumorigenesis in p53-deficient mice. Mol. Carcinog., 14: 16-22, 1995.[Medline]
  15. Lakin N. D., Jackson S. P. Regulation of p53 in response to DNA damage. Oncogene, 18: 7644-7655, 1999.[Medline]
  16. Venkatachalam S., Tyner S. D., Pickering C. R., Boley S., Recio L., French J. E., Donehower L. A. Is p53 haploinsufficient for tumor suppression? Implications for the p53+/- mouse model in carcinogenicity testing. Toxicol. Pathol., 29(Suppl.): 147-154, 2001.
  17. Sherr C. J. The INK4a/ARF network in tumour suppression. Nat. Rev. Mol. Cell. Biol., 2: 731-737, 2001.[Medline]
  18. Minter L. M., Dickinson E. S., Naber S. P., Jerry D. J. Epithelial cell cycling predicts p53 responsiveness to {gamma}-irradiation during post-natal mammary gland development. Development, 129: 2997-3008, 2002.
  19. Moll U., Lau R., Sypes M. A., Gupta M. M., Anderson C. W. DNA-PK, the DNA-activated protein kinase, is differentially expressed in normal and malignant human tissues. Oncogene, 18: 3114-3126, 1999.[Medline]
  20. Khanna K. K., Jackson S. P. DNA double-strand breaks: signaling, repair and the cancer connection. Nat. Genet., 27: 247-254, 2001.[Medline]
  21. Venkitaraman A. R. Cancer susceptibility and the functions of BRCA1 and BRCA2. Cell, 108: 171-182, 2002.[Medline]
  22. Borg A., Sandberg T., Nilsson K., Johannsson O., Klinker M., Masback A., Westerdahl J., Olsson H., Ingvar C. High frequency of multiple melanomas and breast and pancreas carcinomas in CDKN2A mutation-positive melanoma families. J. Natl. Cancer Inst. (Bethesda), 92: 1260-1266, 2000.[Abstract/Free Full Text]
  23. Plna K., Hemminki K. High frequency of multiple melanomas and breast and pancreas carcinomas in CDKN2A mutation-positive melanoma families. J. Natl. Cancer Inst. (Bethesda), 93: 323-325, 2001.[Free Full Text]
  24. Harvey M., Vogel H., Lee E. Y., Bradley A., Donehower L. Mice deficient in both p53 and Rb develop tumors primarily of endocrine origin. Cancer Res., 55: 1146-1151, 1995.[Abstract/Free Full Text]



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