The triple-negative breast cancer (TNBC) is an aggressive form of breast cancer frequently seen in African American women and BRCA1 mutation carriers. The TNBC tumors often relapse with distant metastases following standard chemotherapy. It is now evident that discoveries of new mechanisms and approaches that explain and target breast cancer biology are urgently needed for durable intervention of metastatic disease. Earlier, we have demonstrated that BLID, BH-3 Like motif containing Inducer of cell Death, is a strong prognostic factor in invasive breast cancer. Frequent lack of BLID has been associated with TNBC, African American ethnicity and younger women. Significant correlations exist between BLID negative breast cancer and declines in overall survival, local relapse-free survival and distant metastasis-free survival. Recently, BLID has been shown to inhibit breast cancer cell growth and metastasis. The purpose of this study was to investigate the role of BLID in response of breast cancer cells to chemotherapeutic drugs. In the dose response and time course studies, BLID mRNA expression was found to be induced by chemotherapeutic drugs. Expression of BLID cDNA nanocomplex (scLBLID) resulted in significant increase in chemosensitivity in SKBr3 and MDA-MB-231 cells, and a comparison of BLID with p53 showed that the chemosensitization effect of BLID was significantly greater than that of p53. Consistently, BLID knockdown led to reversal of drug-induced cytotoxicity. In the ChIP-PCR and ChIP-qPCR assays, drug treatment of breast cancer cells resulted in an increased binding of pro-apoptotic transcription factor FOXO3a to the BLID promoter, and the reversal of drug-induced BLID reporter activity was seen in presence of FOXO3a siRNA. Furthermore, siRNA silencing of FOXO3a was found to be associated with decrease in endogenous BLID mRNA expression. Remarkably, we found that expression of central tumor suppressor microRNA miR34a also resulted in increased BLID mRNA expression and drug toxicity in breast cancer cells. Because lack of BLID expression has been associated with poor prognosis in breast cancer patients, we reasoned that the silencing of BLID may reveal as yet unknown changes in gene expression that may drive breast cancer cell proliferation and therapy resistance. In this context, the mRNA array profiling studies showed that BLID knockdown in MDA-MB-231 cells was associated with increased expression of the oncogenic/anti-apoptotic molecules CYP1B1, BIRC3 and CSF1, and decreased expression of the anti-oncogenic/apoptotic molecules AKAP12, DFNA5 and CHRDL1. Our data suggest that chemotherapeutic drugs induce BLID expression via activation of FOXO3a, and the BLID signaling axis downstream of FOXO3a and miR34a is a novel integrative mechanism of breast cancer response to chemotherapy. SY and RH are equal contributors in this study.

Citation Format: Sivaramakrishna Yadavalli, Rong Hu, Antonina Rait, Xin Li, Esther Chang, Robert Clarke, Usha Kasid. BLID is a novel drug-inducible apoptotic molecule: Identification of an integrative mechanism of chemosensitivity in breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2164. doi:10.1158/1538-7445.AM2017-2164