Guermarie Velázquez-Torres

Aurora B is a mitotic checkpoint kinase that plays a pivotal role in the cell cycle, ensuring correct chromosome segregation and normal progression through mitosis. Aurora B is overexpressed in many types of human cancers, which has made it an attractive target for cancer therapies. Tumor suppressor p53 is a genome guardian and important negative regulator of the cell cycle. Whether Aurora B and p53 are coordinately regulated during the cell cycle is not known. We report that Aurora B directly interacts with p53 at different subcellular localizations and during different phases of the cell cycle (for instance, at the nucleus in interphase and the centromeres in prometaphase of mitosis). We show that Aurora B phosphorylates p53 at S183, T211, and S215 to accelerate the degradation of p53 through the polyubiquitination-proteasome pathway, thus functionally suppressing the expression of p53 target genes involved in cell cycle inhibition and apoptosis (e.g., p21 and PUMA). Pharmacologic inhibition of Aurora B in cancer cells with WT p53 increased p53 protein level and expression of p53 target genes to inhibit tumor growth. Together, these results define a mechanism of p53 inactivation during the cell cycle and imply that oncogenic hyperactivation or overexpression of Aurora B may compromise the tumor suppressor function of p53. We have elucidated the antineoplastic mechanism for Aurora B kinase inhibitors in cancer cells with WT p53.

BACKGROUND: Obesity increases the risk of cancer death among postmenopausal women with estrogen receptor-positive (ER+) breast cancer, but the direct evidence for the mechanisms is lacking. The purpose of this study is to demonstrate direct evidence for the mechanisms mediating this epidemiologic phenomenon. METHODS: We analyzed transcriptomic profiles of pretreatment biopsies from a prospective cohort of 137 ER+ breast cancer patients. We generated transgenic (MMTV-TGFα;A (y) /a) and orthotopic/syngeneic (A (y) /a) obese mouse models to investigate the effect of obesity on tumorigenesis and tumor progression and to determine biological mechanisms using whole-genome transcriptome microarrays and protein analyses. We used a coculture system to examine the impact of adipocytes/adipokines on breast cancer cell proliferation. All statistical tests were two-sided. RESULTS: Functional transcriptomic analysis of patients revealed the association of obesity with 59 biological functional changes (P < .05) linked to cancer hallmarks. Gene enrichment analysis revealed enrichment of AKT-target genes (P = .04) and epithelial-mesenchymal transition genes (P = .03) in patients. Our obese mouse models demonstrated activation of the AKT/mTOR pathway in obesity-accelerated mammary tumor growth (3.7- to 7.0-fold; P < .001; n = 6-7 mice per group). Metformin or everolimus can suppress obesity-induced secretion of adipokines and breast tumor formation and growth (0.5-fold, P = .04; 0.3-fold, P < .001, respectively; n = 6-8 mice per group). The coculture model revealed that adipocyte-secreted adipokines (eg, TIMP-1) regulate adipocyte-induced breast cancer cell proliferation and invasion. Metformin suppress adipocyte-induced cell proliferation and adipocyte-secreted adipokines in vitro. CONCLUSIONS: Adipokine secretion and AKT/mTOR activation play important roles in obesity-accelerated breast cancer aggressiveness in addition to hyperinsulinemia, estrogen signaling, and inflammation. Metformin and everolimus have potential for therapeutic interventions of ER+ breast cancer patients with obesity.

BACKGROUND: Aurora B kinase is an important mitotic kinase involved in chromosome segregation and cytokinesis. It is overexpressed in many cancers and thus may be an important molecular target for chemotherapy. AZD1152 is the prodrug for AZD1152-HQPA, which is a selective inhibitor of Aurora B kinase activity. Preclinical antineoplastic activity of AZD1152 against acute myelogenous leukemia, multiple myeloma and colorectal cancer has been reported. However, this compound has not been evaluated in breast cancer, the second leading cause of cancer deaths among women. RESULTS: The antineoplastic activity of AZD1152-HQPA in six human breast cancer cell lines, three of which overexpress HER2, is demonstrated. AZD1152-HQPA specifically inhibited Aurora B kinase activity in breast cancer cells, thereby causing mitotic catastrophe, polyploidy and apoptosis, which in turn led to apoptotic death. AZD1152 administration efficiently suppressed the tumor growth in a breast cancer cell xenograft model. In addition, AZD1152 also inhibited pulmonary metastatic nodule formation in a metastatic breast cancer model. Notably, it was also found that the protein level of Aurora B kinase declined after inhibition of Aurora B kinase activity by AZD1152-HQPA in a time- and dose-dependent manner. Investigation of the underlying mechanism suggested that AZD1152-HQPA accelerated protein turnover of Aurora B via enhancing its ubiquitination. CONCLUSIONS: It was shown that AZD1152 is an effective antineoplastic agent for breast cancer, and our results define a novel mechanism for posttranscriptional regulation of Aurora B after AZD1152 treatment and provide insight into dosing regimen design for this kinase inhibitor in metastatic breast cancer treatment.

Nuclear factor of activated T cell (NFAT1, NFATC2) is a transcription factor that binds and positively regulates IL2 expression during T-cell activation. NFAT1 has important roles in both innate and adaptive immune responses, but its involvement in cancer is not completely understood. We previously demonstrated that NFAT1 contributes to melanoma growth and metastasis by regulating the autotaxin gene (Enpp2). Here, we report a strong correlation between NFAT1 expression and metastatic potential in melanoma cell lines and tumor specimens. To elucidate the mechanisms underlying NFAT1 overexpression during melanoma progression, we conducted a microarray on a highly metastatic melanoma cell line in which NFAT1 expression was stably silenced. We identified and validated two downstream targets of NFAT1, IL8, and MMP3. Accordingly, NFAT1 depletion in metastatic melanoma cell lines was associated with reduced IL8 and MMP3 expression, whereas NFAT1 overexpression in a weakly metastatic cell line induced expression of these targets. Restoration of NFAT1 expression recovered IL8 and MMP3 expression levels back to baseline, indicating that both are direct targets of NFAT1. Moreover, in vivo studies demonstrated that NFAT1 and MMP3 promoted melanoma tumor growth and lung metastasis. Collectively, our findings assign a new role for NFAT1 in melanoma progression, underscoring the multifaceted functions that immunomodulatory factors may acquire in an unpredictable tumor microenvironment. Cancer Res; 76(11); 3145-55. ©2016 AACR.