Effects of Different Calorie Restriction Protocols on Oxidative Stress Parameters in a Transgenic Mouse Model of Breast Cancer.

Aging and diseases related to aging, such as cancer, have been linked to oxidative stress. On the other hand, calorie restriction (CR) is one of the most effective interventions to slow down aging and prevent a variety of diseases such as cancer in preclinical models. CR has also been reported to modify oxidative stress. The aim of this study was to investigate the effects of different CR protocols and aging on oxidative stress parameters in the MMTV-TGF-α breast cancer mouse model in a cross-sectional study. Female mice were randomly enrolled in three groups: ad libitum (AL), chronic calorie restriction (CCR, 15% CR) or intermittent calorie restriction (ICR, three weeks AL followed by one week 60% CR in cyclic periods) starting at the age of 10 weeks until 81/82 weeks of age. Liver samples were analyzed for malondialdehyde (MDA), catalase (CAT), superoxide dismutase (SOD), glutathione (GSH), and glutathione peroxidase (GSH-Px) levels. At week 49/50, the GSH level increased significantly in the CCR group compared to the AL and ICR-R groups which had higher mammary tumor (MT) incidence rates. Additionally, liver MDA levels in ICR groups were significantly increased, while aging led to decreased CAT and SOD activities in all CR groups. The application of different CR protocols did not have any significant effect on MDA, CAT, and SOD parameters in the liver at week 81/82. These results suggest that although GSH may interfere with MT development at the systemic level, many of the oxidative stress parameters may have more local effects on tumor development than the systemic effects.

Inhibition of triple­negative breast cancer proliferation and motility by reactivating p53 and inhibiting overactivated Akt.

Mutations of p53 tumor suppressors occur more frequently in cancers at advanced stages or in more malignant cancer subtypes such as triple­negative breast cancer. Thus, restoration of p53 tumor suppressor function constitutes a valuable cancer therapeutic strategy. In the present study, it was revealed that a specific inhibitor of histone deacetylase 6, ACY­1215, caused increased acetylation of p53 in breast cancer cells with mutated p53, which was accompanied by increased expression of p21. These results suggested that ACY­1215 may lead to enhanced transcriptional activity of p53. It was also determined that ACY­1215 treatment resulted in G1 cell cycle arrest and apoptosis in these cancer cells. Furthermore, ACY­1215 displayed a synergistic effect with specific inhibitors of ATM, an activator of Akt, in inducing cancer cell apoptosis and inhibiting their motility. More importantly, it was observed that combination of ACY­1215 and ATM inhibitors exhibited markedly more potent antitumor activity than the individual compound in xenograft mouse models of breast cancer with mutant p53. Collectively, our results demonstrated that ACY­1215 is a novel chemotherapeutic agent that could restore mutant p53 function in cancer cells with strong antitumor activity, either alone or in combination with inhibitors of the ATM protein kinase.

ATM inhibitor KU-55933 induces apoptosis and inhibits motility by blocking GLUT1-mediated glucose uptake in aggressive cancer cells with sustained activation of Akt.

Enhanced glucose uptake is coupled with elevated aerobic glycolysis (the Warburg effect) in cancer cells and is closely correlated with increased tumor aggressiveness and poor prognosis. We previously discovered that ATM, a protein kinase deficient in Ataxia-telangiectasia (A-T) disease, is an insulin-responsive protein that participates in insulin-mediated glucose uptake in muscle cells by stimulating glucose transporter 4 (GLUT4) translocation. However, the role of ATM in glucose uptake and tumorigenesis of cancer cells is unclear. In the present study, we found that aggressive breast and prostate cancer cell lines with overactivated Akt activity exhibit enhanced glucose uptake and GLUT1 translocation upon insulin treatment, and KU-55933, a specific inhibitor of ATM, inhibits insulin-mediated glucose uptake by blocking translocation of GLUT1 to the cell surface. KU-55933 also inhibits aerobic glycolysis and ATP production in these cells. Moreover, KU-55933 induces apoptosis and inhibits motility of cancer cells by inhibiting glucose uptake. Our results showed that while high concentration of glucose and insulin promote the expression of a mesenchymal biomarker (vimentin) in these cancer cells, KU-55933 strongly inhibits its expression as well as epithelial to mesenchymal transition. The roles of ATM in stimulating glucose uptake, glycolysis, motility, and proliferation of cancer cells were demonstrated by knocking-down ATM in these cells. KU-55933 treatment also inhibits tumor growth and metastasis in vivo in mouse mammary tumors through inhibition of GLUT1 translocation and vimentin expression. These results suggest that ATM acts as a promoter of tumorigenesis in cancer cells with overactivated Akt, and KU-55933 induces apoptosis and inhibits motility by blocking GLUT1-mediated glucose uptake and glycolysis in these cancer cells, which may lead to the use of KU-55933 and its analogs as new preventive or therapeutic agents against cancer.

Roles of adiponectin and leptin signaling-related microRNAs in the preventive effects of calorie restriction in mammary tumor development.

Calorie restriction (CR) is suggested to prevent the development of mammary tumors (MTs); however, the mechanism remains to be clarified. We aimed to determine the microRNA (miRNA) profile in mice applied to 2 different CR protocols; chronic (CCR) and intermittent (ICR) and follow the MT development. In addition, the roles of miRNAs involved in adiponectin and/or leptin signaling pathways were investigated. Mice were divided into 3 groups: ad-libitum (AL), CCR, or ICR, which comprised 3 weeks of AL feeding followed by 1 week of 60% CR in a cyclic manner. Blood and tissue collection were performed at weeks 10, 17/18, 49/50 and 81/82. Long-term CCR provided better protection compared with ICR for MT development with a delay in the MT occurrence. Adiponectin expression in mammary fat pad were significantly higher in CCR group compared with AL. Using GeneChip Array, 250 of 3195 miRNAs were differentially expressed among the dietary groups. Thirteen of 250 miRNAs were related to adiponectin and/or leptin signaling genes. Results were verified by reverse transcription polymerase chain reaction. Specifically, miR-326-3p, miR-500-3p and miR-129-5p, which are related to adiponectin and/or leptin signaling, may play important roles in the preventive effects of CR in MT development and in ageing. Thus, these miRNAs might be putative biomarkers to target for diagnostic and treatment purposes. Novelty: Type of CR and micro RNA interaction is related to ageing. miR-326-3p, miR-500-3p and miR-129-5p expression levels were differentially expressed in MT development and in ageing. The genes associated with adiponectin and/or leptin signaling pathways are regulated by certain miRNAs in the protective effects of CR.

Leptin Signaling in Liver Tissue of a Transgenic Breast Cancer Mouse Model.

Leptin, an adipocytokine, is secreted from various tissues including the liver. The roles of both leptin and leptin receptor (ObR) in numerous pathophysiological conditions including mammary tumor (MT) development have been reported. However, the roles of leptin signaling-related proteins in the liver have not been reported previously in MT development. The objective of this study was to examine the expression levels of leptin and ObR in liver tissue of a transgenic breast cancer mouse model to investigate whether the roles of leptin in MT development are systemic or local. MMTV-TGF-α transgenic female mice were fed ad-libitum from week 10 up to week 74. Protein expression levels of leptin and ObR were measured in liver tissues of 74-week-old MMTV-TGF-α mice with and without MT by western blot. Serum leptin and insulin levels were measured using a enzyme-linked immunosorbent assay. Protein expression levels of leptin and ObR were similar in mice with MT compared to the ones without MT. Serum leptin and insulin levels were also not significantly different between the two groups. These results indicate that the effects of leptin signaling in MT development might be important at a local tissue level, such as mammary fat pad, and not as important at a systemic level.

Effects of leptin on the viability of MCF-7 and T47D cells at different glucose concentrations.

Obesity is associated with increased risk of breast cancer. Leptin is a well-known factor involved in obesity and its serum levels are increased in breast cancer. Hyperglycemia is another significant risk factor for breast cancer. Consistently, high glucose induces proliferation and invasion of breast cancer cells and in-vivo calorie restriction reduce tumorigenesis in rodent models. The aim of this study was to investigate the effect of leptin on the viability and mode of cell death in breast cancer cells incubated in different glucose concentrations to represent caloric restriction. For this purpose, MCF-7 and T47D breast cancer cells incubated in different glucose concentrations for a total of 72 hours were treated with or without leptin either for one hour or 24 hours and the ratio of apoptotic, necrotic and alive cells were analyzed by flow cytometry. Our data revealed that glucose incubation significantly decreased apoptosis and necrosis, while increasing viability in both cell lines in a dose dependent manner. One-hour leptin treatment significantly decreased viability, and increased apoptosis but did not significantly affect necrosis in T47D cells incubated in 2.5 mM glucose. In MCF-7 cells, one-hour leptin incubation significantly increased necrosis but its effects on apoptosis and viability were not significant. In conclusion, although glucose induces cell death by apoptosis and necrosis in T47D and MCF-7 cells respectively in a dose dependent manner, the overallviability is still increased in both cell lines. One-hour leptin treatment reverses the effect of low glucose incubation on apoptosis of T47D and necrosis of MCF-7 cells. Moreover, the effect of one-hour leptin treatment on apoptosis or necrosis is significantly higher than that of 24-hour leptin treatment.

Effects of long-term intermittent versus chronic calorie restriction on oxidative stress in a mouse cancer model.

Calorie restriction (CR) is one of the most effective methods to prevent many diseases including cancer in preclinical models. However, the molecular mechanism of how CR prevents cancer is unclear. The aim of this study was to understand the role of oxidative stress (OS) in the preventive effects of different types of CR in aging mouse mammary tumor virus-transforming growth factor-alpha (MMTV-TGF-α) female mice. Mice were enrolled in ad libitum (AL), chronic CR (CCR, 15% CR) or intermittent CR [ICR, 3 weeks AL (ICR-Refeed, ICR-RF) and 1 week 60% CR (ICR-Restriction, ICR-R) in cyclic periods] groups started at the age of 10 weeks and continued until 81/82 weeks of age. Blood samples were collected to measure malondialdehyde (MDA), glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD) levels. There was no significant difference for MDA levels among the dietary groups although the chronic calorie restriction (CCR) group had lower MDA levels compared to intermittent calorie restriction (ICR) and AL group at different time points. There was also no change in MDA levels of CCR group with aging. On the other hand, the CCR group had higher CAT and SOD activity compared to ICR-R, ICR-RF, and AL groups. Moreover, GSH level was higher in CCR compared to ICR group at week 49/50 (p < .05). CAT and SOD activities were also positively correlated (p < .05). Here, for the first time, the long-term (72 weeks) effects of different types of CR on OS parameters were reported. In conclusion, moderate that is, 15%, CCR is more likely to be protective compared to the same overall calorie deficit implemented by ICR against OS that may play role in the preventive effects of CR.

Circulating Adipose Fatty Acid Binding Protein Is a New Link Underlying Obesity-Associated Breast/Mammary Tumor Development.

It is clear that obesity increases the risk of many types of cancer, including breast cancer. However, the underlying molecular mechanisms by which obesity is linked to cancer risk remain to be defined. Herein, we report that circulating adipose fatty acid binding protein (A-FABP) promotes obesity-associated breast cancer development. Using clinical samples, we demonstrated that circulating A-FABP levels were significantly increased in obese patients with breast cancer in comparison with those without breast cancer. Circulating A-FABP released by adipose tissue directly targeted mammary tumor cells, enhancing tumor stemness and aggressiveness through activation of the IL-6/STAT3/ALDH1 pathway. Importantly, genetic deletion of A-FABP successfully reduced tumor ALHD1 activation and obesity-associated mammary tumor growth and development in different mouse models. Collectively, these data suggest circulating A-FABP as a new link between obesity and breast cancer risk, thereby revealing A-FABP as a potential new therapeutic target for treatment of obesity-associated cancers.

Stearic Acid Induces CD11c Expression in Proinflammatory Macrophages via Epidermal Fatty Acid Binding Protein.

Obesity is associated with elevated levels of free fatty acids (FAs) and proinflammatory CD11c+ macrophages. However, whether and how free FAs contribute to CD11c+ macrophage differentiation and proinflammatory functions remain unclear. Here we report that dietary saturated FAs, but not unsaturated FAs, promoted the differentiation and function of CD11c+ macrophages. Specifically, we demonstrated that stearic acid (SA) significantly induced CD11c expression in monocytes through activation of the nuclear retinoid acid receptor. More importantly, cytosolic expression of epidermal FA binding protein (E-FABP) in monocytes/macrophages was shown to be critical to the mediation of the SA-induced effect. Depletion of E-FABP not only inhibited SA-induced CD11c upregulation in macrophages in vitro but also abrogated high-saturated-fat diet-induced skin lesions in obese mouse models in vivo. Altogether, our data demonstrate a novel mechanism by which saturated FAs promote obesity-associated inflammation through inducing E-FABP/retinoid acid receptor-mediated differentiation of CD11c+ macrophages.

Epidermal FABP Prevents Chemical-Induced Skin Tumorigenesis by Regulation of TPA-Induced IFN/p53/SOX2 Pathway in Keratinocytes.

Skin lipids (e.g., fatty acids) are essential for normal skin functions. Epidermal FABP (E-FABP) is the predominant FABP expressed in skin epidermis. However, the role of E-FABP in skin homeostasis and pathology remains largely unknown. Herein, we utilized the 7,12-dimethylbenz(a)anthracene and 12-O-tetradecanolyphorbol-13-acetate-induced skin tumorigenesis model to assess the role of E-FABP in chemical-induced skin tumorigenesis. Compared to their wild-type littermates, mice deficient in E-FABP, but not adipose FABP, developed more skin tumors with higher incidence. 12-O-tetradecanolyphorbol-13-acetate functioning as a tumor promoter induced E-FABP expression and initiated extensive flaring inflammation in skin. Interestingly, 12-O-tetradecanolyphorbol-13-acetate -induced production of IFN-ß and IFN-λ in the skin tissue was dependent on E-FABP expression. Further protein and gene expression arrays demonstrated that E-FABP was critical in enhancing IFN-induced p53 responses and in suppressing SOX2 expression in keratinocytes. Thus, E-FABP expression in skin suppresses chemical-induced skin tumorigenesis through regulation of IFN/p53/SOX2 pathway. Collectively, our data suggest an unknown function of E-FABP in prevention of skin tumor development, and offer E-FABP as a therapeutic target for improving skin innate immunity in chemical-induced skin tumor prevention.

Induction of the p53 Tumor Suppressor in Cancer Cells through Inhibition of Cap-Dependent Translation.

The p53 tumor suppressor plays a critical role in protecting normal cells from malignant transformation. Development of small molecules to reactivate p53 in cancer cells has been an area of intense research. We previously identified an internal ribosomal entry site (IRES) within the 5' untranslated region of p53 mRNA that mediates translation of the p53 mRNA independent of cap-dependent translation. Our results also show that in response to DNA damage, cells switch from cap-dependent translation to cap-independent translation of p53 mRNA. In the present study, we discovered a specific inhibitor of cap-dependent translation, 4EGI-1, that is capable of inducing the accumulation of p53 in cancer cells retaining wild-type p53. Our results show that 4EGI-1 causes an increase in p53 IRES activity, leading to increased translation of p53 mRNA. We also observed that 4EGI-1 induces cancer cell apoptosis in a p53-dependent manner. Furthermore, 4EGI-1 induces p53 in cancer cells without causing DNA double-strand breaks. In conclusion, we discovered a mechanistic link between inhibition of cap-dependent translation and enhanced p53 accumulation. This leads to apoptosis of cancer cells without causing collateral damage to normal cells, thus providing a novel and effective therapeutic strategy for cancer.

Expression of Adipocyte/Macrophage Fatty Acid-Binding Protein in Tumor-Associated Macrophages Promotes Breast Cancer Progression.

Tumor-associated macrophages (TAM) play a critical role in cancer development and progression. However, the heterogeneity of TAM presents a major challenge to identify clinically relevant markers for protumor TAM. Here, we report that expression of adipocyte/macrophage fatty acid-binding protein (A-FABP) in TAM promotes breast cancer progression. Although upregulation of A-FABP was inversely associated with breast cancer survival, deficiency of A-FABP significantly reduced mammary tumor growth and metastasis. Furthermore, the protumor effect of A-FABP was mediated by TAM, in particular, in a subset of TAM with a CD11b+F4/80+MHCII-Ly6C- phenotype. A-FABP expression in TAM facilitated protumor IL6/STAT3 signaling through regulation of the NFκB/miR-29b pathway. Collectively, our results suggest A-FABP as a new functional marker for protumor TAM.Significance: These findings identify A-FABP as a functional marker for protumor macrophages, thus offering a new target for tumor immunotherapy. Cancer Res; 78(9); 2343-55. ©2018 AACR.

The potential role of leptin in tumor invasion and metastasis.

The adipocyte-released hormone-like cytokine/adipokine leptin behaves differently in obesity compared to its functions in the normal healthy state. In obese individuals, elevated leptin levels act as a pro-inflammatory adipokine and are associated with certain types of cancers. Further, a growing body of evidence suggests that higher circulating leptin concentrations and/or elevated expression of leptin receptors (Ob-R) in tumors may be poor prognostic factors. Although the underlying pathological mechanisms of leptin's association with poor prognosis are not clear, leptin can impact the tumor microenvironment in several ways. For example, leptin is associated with a number of biological components that could lead to tumor cell invasion and distant metastasis. This includes interactions with carcinoma-associated fibroblasts, tumor promoting effects of infiltrating macrophages, activation of matrix metalloproteinases, transforming growth factor-ß signaling, etc. Recent studies also have shown that leptin plays a role in the epithelial-mesenchymal transition, an important phenomenon for cancer cell migration and/or metastasis. Furthermore, leptin's potentiating effects on insulin-like growth factor-I, epidermal growth factor receptor and HER2/neu have been reported. Regarding unfavorable prognosis, leptin has been shown to influence both adenocarcinomas and squamous cell carcinomas. Features of poor prognosis such as tumor invasion, lymph node involvement and distant metastasis have been recorded in several cancer types with higher levels of leptin and/or Ob-R. This review will describe the current scenario in a precise manner. In general, obesity indicates poor prognosis in cancer patients.

The influence of different calorie restriction protocols on serum pro-inflammatory cytokines, adipokines and IGF-I levels in female C57BL6 mice: short term and long term diet effects.

Calorie restriction (CR) is an effective intervention to prevent chronic diseases including cancer. Although many factors, i.e., sex hormones, IGF-I and mTOR have been studied in response to CR, the molecular mechanisms of CR remain to be identified. Our objective was to determine the short and long-term effects of different CR protocols on pro-inflammatory cytokines. Our hypothesis was that Intermittent CR (ICR) would result in greater inhibition of pro-inflammatory serum cytokines compared to Chronic CR (CCR) as we previously found ICR to be more protective in the prevention of mammary tumor development. From ten weeks of age female C57BL6 mice were maintained on either ad libitum (AL) fed, ICR or CCR protocols (overall CR of ~75% of AL) for up to 74 weeks of age. Blood samples were collected for measurements of serum interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), adiponectin, leptin, IGF-I and insulin at specified ages. For ICR mice samples were collected following 3 weeks of restriction (ICR-R) and after one week of refeeding (ICR-RF). In general, both modes of CR significantly reduced serum IL-6, TNF-α, IGF-I and leptin levels compared to AL with IL-6 levels 24 and 3.5 fold and TNF-α levels t 11 and 1.5 fold lower in ICR and CCR groups, respectively at study termination. There was a trend for adiponectin and insulin to be highest in ICR-RF mice. Body weights were positively correlated with IL-6, TNF-α, insulin and leptin but negatively correlated with adiponectin-to-leptin ratio. Moreover, there was a positive correlation between IL-6 and TNF-α. Beneficial effects of ICR may function through pro-inflammatory cytokine pathways.

Targeting IRES-Mediated p53 Synthesis for Cancer Diagnosis and Therapeutics.

While translational regulation of p53 by the internal ribosome entry site (IRES) at its 5'-untranslated region following DNA damage has been widely accepted, the detailed mechanism underlying the translational control of p53 by its IRES sequence is still poorly understood. In this review, we will focus on the latest progress in identifying novel regulatory proteins of the p53 IRES and in uncovering the functional connection between defective IRES-mediated p53 translation and tumorigenesis. We will also discuss how these findings may lead to a better understanding of the process of oncogenesis and open up new avenues for cancer diagnosis and therapeutics.

Adipose Fatty Acid Binding Protein Promotes Saturated Fatty Acid-Induced Macrophage Cell Death through Enhancing Ceramide Production.

Macrophages play a critical role in obesity-associated chronic inflammation and disorders. However, the molecular mechanisms underlying the response of macrophages to elevated fatty acids (FAs) and their contribution to metabolic inflammation in obesity remain to be fully elucidated. In this article, we report a new mechanism by which dietary FAs, in particular, saturated FAs (sFAs), are able to directly trigger macrophage cell death. We demonstrated that excess sFAs, but not unsaturated FAs, induced the production of cytotoxic ceramides (Cers) in macrophage cell lines. Most importantly, expression of adipose FA binding protein (A-FABP) in macrophages facilitated metabolism of excess sFAs for Cer synthesis. Inhibition or deficiency of A-FABP in macrophage cell lines decreased sFA-induced Cer production, thereby resulting in reduced cell death. Furthermore, we validated the role of A-FABP in promoting sFA-induced macrophage cell death with primary bone marrow-derived macrophages and high-fat diet-induced obese mice. Altogether, our data reveal that excess dietary sFAs may serve as direct triggers in induction of Cer production and macrophage cell death through elevated expression of A-FABP, thus establishing A-FABP as a new molecular sensor in triggering macrophage-associated sterile inflammation in obesity.

Inhibiting breast cancer by targeting the thromboxane A2 pathway.

Targeting the estrogen receptor as a strategy has been the gold standard for breast cancer chemoprevention or breast cancer recurrence, but its benefit is limited to estrogen receptor-positive tumors. Cyclooxygenases have been implicated in mammary tumorigenesis. We sought to identify the key prostaglandin responsible for the pro-neoplastic effect of cyclooxygenases and develop prostaglandin-targeted strategies for breast cancer chemoprevention or therapy. Immunohistochemical analysis revealed that either thromboxane A2 synthase 1 or the thromboxane A2 receptor is highly expressed in human breast tumors as well as premalignant lesions, but not in normal mammary tissues. Clinically, the thromboxane A2 pathway might be associated with HER2-positive and axillary lymph node metastasis in human breast cancer. We found that the thromboxane A2 pathway was required for breast cancer cell growth, anchorage-independent growth and invasion capabilities. Importantly, we discovered that switching off thromboxane A2 biosynthesis effectively suppressed either MMTV-HER2-driven mammary tumorigenesis or breast cancer metastasis in preclinical animal models. Taken together, this study established a critical pathophysiological role of the thromboxane A2 pathway in breast cancer, and provided a rationale for introducing a strategy targeting thromboxane A2 for breast cancer chemoprevention and therapy.

Measuring relative utilization of aerobic glycolysis in breast cancer cells by positional isotopic discrimination.

The ability of cancer cells to produce lactate through aerobic glycolysis is a hallmark of cancer. In this study, we established a positional isotopic labeling and LC-MS-based method that can specifically measure the conversion of glucose to lactate in glycolysis. We show that the rate of aerobic glycolysis is closely correlated with glucose uptake and lactate production in breast cancer cells. We also found that the production of [3-(13) C]lactate is significantly elevated in metastatic breast cancer cells and in early stage metastatic mammary tumors in mice. Our findings may enable the development of a biomarker for the diagnosis of aggressive breast cancer.

Breast cancers from black women exhibit higher numbers of immunosuppressive macrophages with proliferative activity and of crown-like structures associated with lower survival compared to non-black Latinas and Caucasians.

Racial disparities in breast cancer incidence and outcome are a major health care challenge. Patients in the black race group more likely present with an early onset and more aggressive disease. The occurrence of high numbers of macrophages is associated with tumor progression and poor prognosis in solid malignancies. Macrophages are observed in adipose tissues surrounding dead adipocytes in "crown-like structures" (CLS). Here we investigated whether the numbers of CD163+ tumor-associated macrophages (TAMs) and/or CD163+ CLS are associated with patient survival and whether there are significant differences across blacks, non-black Latinas, and Caucasians. Our findings confirm that race is statistically significantly associated with the numbers of TAMs and CLS in breast cancer, and demonstrate that the highest numbers of CD163+ TAM/CLS are found in black breast cancer patients. Our results reveal that the density of CD206 (M2) macrophages is a significant predictor of progression-free survival univariately and is also significant after adjusting for race and for HER2, respectively. We examined whether the high numbers of TAMs detected in tumors from black women were associated with macrophage proliferation, using the Ki-67 nuclear proliferation marker. Our results reveal that TAMs actively divide when in contact with tumor cells. There is a higher ratio of proliferating macrophages in tumors from black patients. These findings suggest that interventions based on targeting TAMs may not only benefit breast cancer patients in general but also serve as an approach to remedy racial disparity resulting in better prognosis patients from minority racial groups.

Deregulation of Internal Ribosome Entry Site-Mediated p53 Translation in Cancer Cells with Defective p53 Response to DNA Damage.

Synthesis of the p53 tumor suppressor and its subsequent activation following DNA damage are critical for its protection against tumorigenesis. We previously discovered an internal ribosome entry site (IRES) at the 5' untranslated region of the p53 mRNA. However, the connection between IRES-mediated p53 translation and p53's tumor suppressive function is unknown. In this study, we identified two p53 IRES trans-acting factors, translational control protein 80 (TCP80), and RNA helicase A (RHA), which positively regulate p53 IRES activity. Overexpression of TCP80 and RHA also leads to increased expression and synthesis of p53. Furthermore, we discovered two breast cancer cell lines that retain wild-type p53 but exhibit defective p53 induction and synthesis following DNA damage. The levels of TCP80 and RHA are extremely low in both cell lines, and expression of both proteins is required to significantly increase the p53 IRES activity in these cells. Moreover, we found cancer cells transfected with a shRNA against TCP80 not only exhibit decreased expression of TCP80 and RHA but also display defective p53 induction and diminished ability to induce senescence following DNA damage. Therefore, our findings reveal a novel mechanism of p53 inactivation that links deregulation of IRES-mediated p53 translation with tumorigenesis.