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Luminal breast tumors with little or no estrogen receptor α expression confer poor prognosis. Using the Met1 murine model of luminal breast cancer, we characterized the IGF1-dependency of diet-induced obesity (DIO) and calorie restriction (CR) effects on tumor growth, growth factor signaling, epithelial-to-mesenchymal transition (EMT), and chemokine expression. Liver-specific IGF1-deficient (LID) and littermate control (LC) mice were administered control, DIO, or 30% CR diets for 3 months before orthotopic injection of Met1 cells. Tumors grew for 1 month and then were assessed for Akt pathway activation and mRNA expression of chemokine and EMT constituents. LID mice, regardless of diet, displayed reduced Met1 tumor growth and downregulated Akt, EMT, and chemokine pathways. CR, relative to control, reduced serum IGF1 and Met1 tumor growth in LC (but not LID) mice. DIO, relative to control, increased Met1 tumor growth and chemokine expression in LID mice, and had no effect on serum IGF1 or pAkt or cyclin D1 expression in either genotype. Thus, circulating IGF1 (in association with Akt, EMT, and chemokines) regulated Met1 tumor growth. While the anticancer effects of CR were largely IGF1-dependent, the procancer effects of DIO manifested only when circulating IGF1 levels were low. Thus, in a murine model of luminal breast cancer, IGF1 and its downstream signaling pathway, EMT, and chemokines present possible mechanistic regulatory targets. Transplanted MMTV1 Wnt1 mammary tumor growth was also reduced in LID mice, relative to LC mice, suggesting that the IGF1 effects on mammary tumor growth are not limited to Met1 tumors.

Background: Evidence shows that obesity increases the risk and mortality of many cancers, specifically breast cancer in post-menopausal women. Epidemiological studies demonstrate that males are at an increased risk for developing obesity, diabetes, and cancer compared to females, and after menopause, females mimic the males in their susceptibility to the above diseases. Furthermore, it has been established that obesity increases systemic and adipose tissue inflammation and oxidative stress, which is known to augment cancer progression. However, the role of estrogen in regulating these metabolic processes in adipose tissue is unclear; therefore, our objective is to determine the role of estrogen in adipose tissue morphology, inflammation and oxidative stress. Methods: To determine the role of estrogen in gender differences in the susceptibility to obesity we used C57BL/6J mice (15/group): 1) males 2) nonovariectomized females 3) ovariectomized females and 4) ovariectomized females supplemented with estrogen, which were randomized to the following diets: 30% calorie-restricted, low-fat or high-fat diet. We measured weight gain, percent body fat, abdominal adipose tissue, and adipocyte size. Additionally, we assessed markers of adipose tissue inflammation, DNA damage, and oxidative stress. Results: Male mice were more susceptible to obesity than female mice. Removal of the ovaries eliminated the protection to obesity and estrogen supplementation restored this protection in females. In the low-fat and high-fat diet groups, male and ovariectomized female mice gained more abdominal adipose tissue due to increased adipocyte size compared to nonovariectomized female mice and ovariectomized female mice supplemented with estrogen. In the mice consuming the high fat diet, the enlarged adipocytes observed in the male and ovariectomized female mice were accompanied with crownlike structures surrounding necrotic adipocytes and F480 positive macrophages, suggesting macrophage infiltration. To determine if there were sex differences in oxidative stress, we stained adipose tissue with γH2AX. Results suggest that nonovariectomized female mice and ovariectomized female mice supplemented with estrogen have less oxidative stress compared to males and ovariectomized females. Additionally, our results show that nonovariectomized female and ovariectomized female mice supplemented with estrogen had significantly lower CD68, TNFα and iNOS mRNA expression levels, but higher catalase mRNA expression levels. Conclusion: Male mice are more susceptible to the obesogenic effects of high fat diets compared to nonovariectomized female mice. In ovariectomized females, estrogen supplementation has a protective effect against obesity, adipose tissue inflammation and oxidative stress. Our future studies will determine the mechanisms by which estrogen protects female mice from adipose tissue inflammation and oxidative stress, whether it is a direct or indirect effect. Determining the role of estrogen on the above key metabolic processes related to obesity is necessary to develop effective strategies for cancer prevention specifically in post-menopausal females. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-09-05.

Obesity increases the risk of diabetes. The dysregulation of estrogen metabolism has been associated with the susceptibility to obesity and diabetes. Here, we explore the role estrogen plays in sex differences in obesity and glucose metabolism, specifically adipocyte biology. We randomized C57BL/6 J male, non-ovariectomized female, ovariectomized female, and ovariectomized female mice supplemented with 17β estradiol to receive a calorie-restricted, low- or a high-fat diet (15 mice per group). We measured weight gained, calories consumed, percent body fat, abdominal adipose tissue, adipocyte size, lipogenic and adipogenic gene expression, and glucose tolerance. Male mice had a higher susceptibility to obesity than intact female mice. However, removal of the ovaries in female mice eliminated the protection to obesity and estrogen supplementation restored this protection. Male and ovariectomized female mice gained weight predominately in the form of abdominal adipose tissue possibly due to an increase in adipocyte size. Moreover, for mice consuming the high-fat diet, male and ovariectomized female mice had significantly higher levels of leptin mRNA and lower hormone-sensitive lipase mRNA relative to intact female mice and ovariectomized female mice supplemented with estrogen. Additionally, estrogen had a strong inhibitory effect on key adipogenic genes in non-ovariectomized female and ovx-female mice supplemented with estrogen. Finally, we show that male and ovariectomized female mice consuming the high-fat diet had a higher incidence of glucose intolerance. Estrogen protects female mice from obesity and impaired glucose tolerance possibly by modulating the expression of genes regulating adipogenesis, lipogenesis, and lipolysis.

Background: Alcohol consumption is an established risk factor for breast cancer. Yet, the mechanism by which alcohol affects breast cancer development remains unresolved. The transition from the premenopausal to the postmenopausal phase is associated with a drastic reduction in systemic estrogen levels. It is not clear whether the risk of breast cancer attributable to alcohol consumption is modified by the different levels of estrogen found in pre- and postmenopausal women. The objective of this study is to determine whether the effects of alcohol on mammary tumor development are dependent on the presence of ovarian estrogen. Methods: As a model of breast cancer, we used mouse mammary tumor virus (MMTV)-neu transgenic mice that overexpress the human epidermal growth factor receptor 2 (HER2/neu) in the mammary epithelium, resulting in the development of estrogen receptor alpha (ERα)-negative mammary tumors. The mammary tumorigenesis process in these mice is similar to that of patients with HER2 breast cancer. Nonovariectomized (NOVX) and ovariectomized (OVX) MMTV-neu mice were exposed to 0, 5, and 20% ethanol in the drinking water. Breast cancer development and progression were determined alongside the effects of alcohol on estrogen availability and signaling. Results: Our data show that 20% alcohol consumption promoted tumor development in MMTV-neu mice only in the presence of ovarian hormones. Tumor promotion was associated with increased systemic estrogen levels, increased expression of aromatase (the rate-limiting enzyme in estrogen synthesis), and increased expression of ERα in the tumors of 20% alcohol-consuming MMTV-neu mice. Additionally, we show that ovariectomy (removal of the ovaries and ovarian hormone production) blocked the effects of 20% alcohol on tumor development. Conclusions: Our results support the notion that alcohol consumption promotes HER2 breast cancer development via the estrogen signaling pathway. Additionally, they suggest that the effects of alcohol on breast cancer may be prevented by blocking estrogen signaling.

Ku80 facilitates DNA repair and therefore should suppress cancer. However, ku80−/− mice exhibit reduced cancer, although they age prematurely and have a shortened life span. We tested the hypothesis that Ku80 deletion suppresses cancer by enhancing cellular tumor-suppressive responses to inefficiently repaired DNA damage. In support of this hypothesis, Ku80 deletion ameliorated tumor burden in APCMIN mice and increased a p53-mediated DNA damage response, DNA lesions, and chromosomal rearrangements. Thus, contrary to its assumed role as a caretaker tumor suppressor, Ku80 facilitates tumor growth most likely by dampening baseline cellular DNA damage responses. [Cancer Res 2008;68(22):9497–502]

Animal models of premature aging are often defective for DNA repair. Ku80-mutant mice are disabled for nonhomologous end joining; a pathway that repairs both spontaneous DNA double-strand breaks (DSBs) and induced DNA DSBs generated by the action of a complex composed of Rag-1 and Rag-2 (Rag). Rag is essential for inducing DSBs important for assembling V(D)J segments of antigen receptor genes that are required for lymphocyte development. Thus, deletion of either Rag-1 or Ku80 causes severe combined immunodeficiency (scid) leading to chronic inflammation. In addition, Rag-1 induces breaks at non-B DNA structures. Previously we reported Ku80-mutant mice undergo premature aging, yet we do not know the root cause of this phenotype. Early aging may be caused by either defective repair of spontaneous DNA damage, defective repair of Rag-1-induced breaks or chronic inflammation caused by scid. To address this issue, we analyzed aging in control and Ku80-mutant mice deleted for Rag-1 such that both cohorts are scid and suffer from chronic inflammation. We make two observations: (1) chronic inflammation does not cause premature aging in these mice and (2) Ku80-mutant mice exhibit early aging independent of Rag-1. Therefore, this study supports defective repair of spontaneous DNA damage as the root cause of early aging in Ku80-mutant mice.

Objective Breast cancer is the second leading cause of cancer death among American women. Risk factors for breast cancer include obesity, alcohol consumption, and estrogen therapy. In the present studies, we determine the simultaneous effects of these three risk factors on wingless int (Wnt)-1 mammary tumor growth. Methods Ovariectomized female mice were fed diets to induce different body weights (calorie restricted, low fat, high fat), provided water or 20% alcohol, implanted with placebo or estrogen pellets and injected with Wnt-1 mouse mammary cancer cells. Results Our results show that obesity promoted the growth of Wnt-1 tumors and induced fatty liver. Tumors tended to be larger in alcohol-consuming mice and alcohol exacerbated fatty liver in obese mice. Estrogen treatment promoted weight loss in obese mice, which was associated with the suppression of tumor growth and fatty liver. Conclusions In summary, we show that estrogen protects against obesity, which is associated with the inhibition of fatty liver and tumor growth.

The risk of developing breast cancer and fatty liver is increased by alcohol consumption. The objective of the present study was to determine if obesity and exogenous estrogen supplementation alter the effects of alcohol on mammary tumorigenesis and fatty liver. Ovariectomized female mice were (1) fed diets to induce overweight and obese phenotypes, (2) provided water or 20% alcohol, (3) implanted with placebo, low- or high-dose estrogen pellets and (4) injected with Met-1 mouse mammary cancer cells. Alcohol-consuming mice were more insulin sensitive and developed larger tumors than water consuming mice. Obese mice developed slightly larger tumors than control mice. Alcohol consumption and obesity increased growth factors, hepatic steatosis, activation of Akt, and inhibited the caspase-3 cascade. Estrogen treatment triggered the loss of body fat, induced insulin sensitivity, suppressed tumor growth, reduced growth factors and improved hepatic steatosis. Results show that the effects of alcohol on mammary tumor and fatty liver are modified by obesity and estrogen supplementation.

Aims: Obesity is associated with insulin resistance, liver steatosis and low-grade inflammation. The role of oestrogen in sex differences in the above co-morbidities is not fully understood. Our aim was to assess the role oestrogen has in modulating adipocyte size, adipose tissue oxidative stress, inflammation, insulin resistance and liver steatosis. Methods: To determine the role oestrogen has in the above co-morbidities related to obesity, we randomized C57BL/6J mice into four groups (15 mice per group): (i) male, (ii) non-ovariectomized female (novx), (iii) ovariectomized female (ovx) and (iv) ovariectomized female mice supplemented with 17β estradiol (ovx-E). Mice received either a low-fat (LF) or a high-fat (HF) diet for 10 weeks. Outcomes measured were bodyweight, body fat, adipocyte diameter, adipose tissue lipolysis markers, adipose tissue oxidative stress, inflammation, insulin resistance and liver steatosis. Results: Male and ovx-female mice consuming the HF diet had a higher propensity of gaining weight, specifically in the form of body fat. Oestrogen protected female mice from adipocyte hypertrophy and from developing adipose tissue oxidative stress and inflammation. Moreover, novx-female and ovx-female+E mice had higher phosphorylated levels of protein kinase A and hormone sensitive lipase, markers associated with lipolysis. Additionally, male and ovx female mice had a higher propensity of developing liver steatosis and insulin resistance. In contrast, oestrogen protected female mice from developing liver steatosis and from becoming insulin resistant. Conclusion: We show that oestrogen protects female mice from adipocyte hypertrophy and adipose tissue oxidative stress and inflammation. Furthermore, oestrogen prevented female mice from developing liver steatosis and from becoming insulin resistant.

Epidemiological data show that in women, alcohol has a beneficial effect by increasing insulin sensitivity but also a deleterious effect by increasing breast cancer risk. These effects have not been shown concurrently in an animal model of breast cancer. Our objective is to identify a mouse model of breast cancer whereby alcohol increases insulin sensitivity and promotes mammary tumorigenesis. Our results from the glucose tolerance test and the homeostasis model assessment show that alcohol consumption improved insulin sensitivity. However, alcohol-consuming mice developed larger mammary tumors and developed them earlier than water-consuming mice. In vitro results showed that alcohol exposure increased the invasiveness of breast cancer cells in a dose-dependent manner. Thus, this animal model, an in vitro model of breast cancer, may be used to elucidate the mechanism(s) by which alcohol affects breast cancer.

Alcohol consumption increases breast cancer risk in postmenopausal women in a dose-dependent manner. The objective of the present study was to determine if the effect of alcohol on mammary cancer is modified by body weight and exogenous estrogen. Ovariectomized mice of various body weights, receiving estrogen or placebo supplementation, and consuming water or alcohol were injected with mammary cancer cells. Alcohol intake resulted in insulin sensitivity and increased tumor growth in obese mice. Exogenous estrogen alone inhibited tumor growth. The combination of estrogen and alcohol overcame the inhibitory effects of estrogen on tumor growth in obese mice. Alcohol consumption increased the circulating estrogen and leptin levels. In conclusion, alcohol and estrogen treatment can modify mammary tumor growth, possibly through the regulation of estrogen and leptin, especially in obese mice.

Background Obesity is a risk factor for the development of insulin resistance, which can eventually lead to type-2 diabetes. Alcohol consumption is a protective factor against insulin resistance, and thus protects against the development of type-2 diabetes. The mechanism by which alcohol protects against the development of type-2 diabetes is not well known. To determine the mechanism by which alcohol improves insulin sensitivity, we fed water or alcohol to lean, control, and obese mice. The aim of this study was to determine whether alcohol consumption and body weights affect overlapping metabolic pathways and to identify specific target genes that are regulated in these pathways. Method Adipose tissue dysfunction has been associated with the development of type-2 diabetes. We assessed possible gene expression alterations in epididymal white adipose tissue (WAT). We obtained WAT from mice fed a calorie restricted (CR), low fat (LF Control) or high fat (HF) diets and either water or 20% ethanol in the drinking water. We screened the expression of genes related to the regulation of energy homeostasis and insulin regulation using a gene array composed of 384 genes. Results Obesity induced insulin resistance and calorie restriction and alcohol improved insulin sensitivity. The insulin resistance in obese mice was associated with the increased expression of inflammatory markers Cd68, Il-6 and Il-1α; in contrast, most of these genes were down-regulated in CR mice. Anti-inflammatory factors such as Il-10 and adrenergic beta receptor kinase 1 (Adrbk1) were decreased in obese mice and increased by CR and alcohol. Also, we report a direct correlation between body weight and the expression of the following genes: Kcnj11 (potassium inwardly-rectifying channel, subfamily J, member 11), Lpin2 (lipin2), and Dusp9 (dual-specificity MAP kinase phosphatase 9). Conclusion We show that alcohol consumption increased insulin sensitivity. Additionally, alterations in insulin sensitivity related with obesity were coupled with alterations in inflammatory genes. We provide evidence that alcohol may improve insulin sensitivity by up-regulating anti-inflammatory genes. Moreover, we have indentified potential gene targets in energy metabolic pathways and signal transducers that may contribute to obesity-related insulin resistance as well as calorie restriction and alcohol-induced insulin sensitivity.

Ku70 forms a heterodimer with Ku80, called Ku, that is critical for repairing DNA double-stand breaks by nonhomologous end joining and for maintaining telomeres. Mice with either gene mutated exhibit similar phenotypes that include increased sensitivity to ionizing radiation and severe combined immunodeficiency. However, there are also differences in the reported phenotypes. For example, only Ku70 mutants are reported to exhibit a high incidence of thymic lymphomas while only Ku80 mutants are reported to exhibit early aging with very low cancer levels. There are two explanations for these differences. First, either Ku70 or Ku80 functions outside the Ku heterodimer such that deletion of one is not identical to deletion of the other. Second, divergent genetic backgrounds or environments influence the phenotype. To distinguish between these possibilities, the Ku70 and Ku80 mutations were crossed together to generate Ku70, Ku80, and double-mutant mice in the same genetic background raised in the same environment. We show that these three cohorts have similar phenotypes that most resemble the previous report for Ku80 mutant mice, i.e., early aging without substantially increased cancer levels. Thus, our observations suggest that the Ku heterodimer is important for longevity assurance in mice since divergent genetic backgrounds and/or environments likely account for these previously reported differences.

Semantic distinctions between "normal" aging, "pathological" aging (or age-related disease) and "premature" aging (otherwise known as segmental progeria) potentially confound important insights into the nature of each of the complex processes. Here we review a recent, unexpected discovery: the presence of longevity-associated characteristics typical of long-lived endocrine-mutant and dietary-restricted animals in short-lived progeroid mice. These data suggest that a subset of symptoms observed in premature aging, and possibly normal aging as well, may be indirect manifestations of a beneficial adaptive stress response to endogenous oxidative damage, rather than a detrimental result of the damage itself.

Ku80 maintains the genome by repairing DNA double-strand breaks (DSBs) through nonhomologous end joining (NHEJ), a pathway that repairs nonspecific DSBs and Rag-1 Rag-2 (Rag)-specific DSBs. As a result, Ku80 deletion results in phenotypes characteristic of defective repair for both nonspecific DSBs (gamma-radiation hypersensitivity and genomic instability) and Rag-specific DSBs (immunodeficiency). ku80(-/-) mice also exhibit neuronal apoptosis, but we do not know the type of DSBs responsible for this response. In spite of genomic instability and immunodeficiency, cancer incidence is not increased in ku80(-/-) mice. However, deletion of the tumor suppressor, p53 greatly increases pro-B-cell lymphoma in ku80(-/-) mice due to IgH/c-Myc translocations suggesting that responses to Rag-specific DNA DSBs suppress cancer. Like suppression of pro-B-cell lymphoma, neuronal apoptosis requires p53 presenting the intriguing possibility that Rag-specific DSBs mediate neuronal development as they do lymphocyte development. Here we delete Rag-1 from ku80(-/-)p53(-/-) mice to differentiate the impact nonspecific vs Rag-specific DSBs have on ku80(-/-) mice. We find that deleting Rag-1 prevents pro-B cell lymphoma confirming Rag-induced DSBs induce this form of cancer. Both the triple mutant mice and the p53(-/-)rag-1(-/-) mice exhibit T-cell lymphoma and medulloblastoma; incidence of T-cell lymphoma is the same for both cohorts whereas incidence of medulloblastoma is higher for the triple-mutant cohort. Thus, p53-mediated neuronal apoptosis likely suppresses medulloblastoma in Ku80-deleted mice and Ku80 likely suppresses medulloblastoma by repairing nonspecific DNA DSBs instead of Rag-specific DSBs. Our observations are the first to show that Ku80 suppresses cancer caused by nonspecific DNA damage and we present a novel mouse model for medulloblastoma.

Alcohol, obesity and estrogen modulate mammary tumor growth through adiposity and angiogenensis Jina Hong, Valerie B. Holcomb, and Nomelí P Núñez Background: Alcohol consumption increases breast cancer risk in women. Postmenopausal women who consume alcohol come in all shapes and sizes, including overweight and obese; some of these women may also take estrogen to prevent the side effects of menopause. It is unclear whether the effects of alcohol on breast cancer development are modified by body weight or exogenous estrogen. In this study, we will determine if the effects alcohol on breast cancer are modified by body weight and exogenous estrogen. Methods: To determine whether the effects of alcohol on mammary cancer are modified by body weight, we injected subcutaneously Met-1 mouse mammary cancer cells to lean, overweight, and obese female mice consuming water or alcohol. Likewise, to determine if the effects of alcohol on mammary tumorigenesis are modified by exogenous estrogen, we implanted estrogen pellets (0.18mg/day or 0.72mg/day) into ovariectomized female mice; subsequently, we injected Met-1 cancer cells into these mice and then measured tumor growth. Results: Results show that alcohol-consuming mice were more insulin sensitive than water-consuming mice; also, alcohol-consuming mice developed earlier and larger tumors than water-consuming mice (p Conclusion: Results suggest that alcohol consumption, obesity, and estrogen treatment modulate mammary tumorigenesis through adipose tissue and angiogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3268.

How congenital defects causing genome instability can result in the pleiotropic symptoms reminiscent of aging but in a segmental and accelerated fashion remains largely unknown. Most segmental progerias are associated with accelerated fibroblast senescence, suggesting that cellular senescence is a likely contributing mechanism. Contrary to expectations, neither accelerated senescence nor acute oxidative stress hypersensitivity was detected in primary fibroblast or erythroblast cultures from multiple progeroid mouse models for defects in the nucleotide excision DNA repair pathway, which share premature aging features including postnatal growth retardation, cerebellar ataxia, and death before weaning. Instead, we report a prominent phenotypic overlap with long-lived dwarfism and calorie restriction during postnatal development (2 wk of age), including reduced size, reduced body temperature, hypoglycemia, and perturbation of the growth hormone/insulin-like growth factor 1 neuroendocrine axis. These symptoms were also present at 2 wk of age in a novel progeroid nucleotide excision repair-deficient mouse model (XPDG602D/R722W/XPA−/−) that survived weaning with high penetrance. However, despite persistent cachectic dwarfism, blood glucose and serum insulin-like growth factor 1 levels returned to normal by 10 wk, with hypoglycemia reappearing near premature death at 5 mo of age. These data strongly suggest changes in energy metabolism as part of an adaptive response during the stressful period of postnatal growth. Interestingly, a similar perturbation of the postnatal growth axis was not detected in another progeroid mouse model, the double-strand DNA break repair deficient Ku80 −/− mouse. Specific (but not all) types of genome instability may thus engage a conserved response to stress that evolved to cope with environmental pressures such as food shortage., Synopsis Oxidative damage to cellular components, including fats, proteins, and DNA, is an inevitable consequence of cellular energy use and may underlie both normal and pathological aging. Calorie restriction delays the aging process and extends lifespan in a number of lower organisms including rodents. Inborn defects in the postnatal growth axis resulting in dwarfism can also extend lifespan. Both may function via overlapping pathways impacting on energy metabolism. Here, we report a novel DNA repair-deficient mouse model with symptoms of the related premature aging disorders Cockayne syndrome and trichothiodystrophy, namely reduced fat deposits, neurological dysfunction, failure to thrive, and reduced lifespan. Surprisingly, we also observed traits usually associated with extended longevity as found in calorie restriction and dwarfism, including reduced blood sugar and reduced insulin-like growth factor-1. These characteristics were present at 2 wk of age, that is, during the period of rapid postnatal development, but returned to normal by sexual maturation at 10 wk. Furthermore, they were absent altogether in another premature aging mouse model with a distinct DNA repair defect. Specific types of unrepaired DNA damage may thus elicit a preservative organismal response affecting energy metabolism that is similar to the one that evolved to cope with the stress of food shortage.

Ku80 is often referred to as a tumor suppressor since it maintains the genome by repairing DNA double-strand breaks (DSBs) via the nonhomologous end joining (NHEJ) pathway. Even though Ku80 deletion causes hypersensitivity to gamma-radiation, DNA damage and chromosomal rearrangements, Ku80-mutant mice exhibit very low cancer levels. We previously hypothesized these low cancer levels were caused by enhanced cell cycle checkpoints that responded to inefficiently repaired DNA damage because Ku80-mutant fibroblasts exhibit premature cellular senescence that was dependent on a p53-mediated DNA damage response. In addition, Ku80 and p53 show a genetic interaction to suppress pro-B cell lymphoma and medulloblastoma. Here we tested for a similar anti-tumor genetic interaction between Ku80 and the cyclin kinase inhibitor, p27(Kip1) (p27) since p27 mutant mice showed elevated levels of pituitary adenoma that were exacerbated by gamma-radiation-induced DNA damage (damage repaired by Ku80). We found that deleting both Ku80 and p27 did not exacerbate cancer as compared to either single mutant. In addition, fibroblasts deleted for both exhibited premature cellular senescence similar to Ku80-mutant fibroblasts. Thus, p27 did not exhibit an obvious genetic interaction with Ku80 to suppress tumors. This observation suggests that DNA damage (or DNA damage responses) induced by either gamma-radiation or Ku80 deletion are not equivalent since gamma-radiation exacerbates oncogenesis in mice deleted for either p53 or p27 while Ku80 deletion exacerbates oncogenesis for only the former genotype.