Studying on the Mechanism and Translational Application of Blocking the Protein-Protein Interaction between Galpha-h and PLC-delta1 in Combating Drug-Resistance and Metastasis of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is the population of which does not express estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor-2 (HER2). Due to the loss of these receptors, the hormone (e.g. tamoxifen) and targeted (e.g. Herceptin) therapies are less effective to treat TNBC patients. So far, the treatment of clinical TNBC patients merely relies on the traditional chemotherapy. Several studies demonstrated that the evolution of TNBC is highly aggressive but poorly differentiated. In addition, the prognosis and survival rate of patients with TNBC are relatively unfavorable to other breast cancer types. Moreover, TNBC is highly metastatic and tends to recur after chemotherapy. Although the mechanisms remain unknown, the development of drug-resistance has been thought to be the main cause for the failure of using chemotherapy to treat TNBC. Therefore, it is urgently needed to dissect the molecular mechanisms for drug-resistance and metastatic progression, thereby providing a basis of developing targeted therapies to combating TNBC in the future. Our previous report has elucidated that the protein-protein interaction (PPI) of Gαh with PLC-δ1 regulates the action of follicle-stimulating hormone (FSH) in testicular Sertoli cells via elevating the level of intracellular Ca2+ and inositol triphosphate (IP3). Based on the results of recent reports showing that Gαh overexpression (OE) might be associated with the molecular mechanism for drug resistance and metastasis in breast cancer, we thus performed a globally meta-analysis of Gαh gene, TGM2. Our data showed that Gαh-OE extensively occurs in TNBC and metastatic cancer tissues and significantly correlates with poorer prognosis, presumably owing to cancer metastasis and recurrence, in cancer patients. Moreover, our preliminary results revealed that Gαh is up-regulated in the drug-resistant and highly metastatic TNBC cell lines, e.g. MDA-MB231, MDA-MB436, HS578T and HCC38 but down-regulated in the drug-sensitive and less metastatic cell lines, e.g. MDA-MB468, HCC1143, HCC1599 and HCC70. According to our previous report that PLC-δ1 peptide fragment (TIPWNSLKQGYRHVHLL) is capable of effectively blocking the binding of PLC-δ1 with Gαh and thereby ultimately inhibits FSH action in Sertoli cells, therefore we are prompted to investigate if the treatment with this peptide fragment is able to reverse drug-resistance and inhibit metastasis in breast cancer cells with Gαh-OE. To achieve this goal, in this proposed 3-year study, we will investigate the following Specific Aims: (1) To validate the association of Gαh/PLC-δ1 PPI with the development of drug-resistance in TNBC; (2) To determine the relevance of Gαh/PLC-δ1 PPI with the metastatic progression in TNBC; (3) To estimate the possibility of blocking Gαh/PLC-δ1 PPI to reverse drug resistance in TNBC with Gαh-OE in vitro and in vivo; (4) To evaluate the effectiveness of blocking Gαh/PLC-δ1 PPI on inhibiting the metastasis of TNBC with Gαh-OE in vitro and in vivo. The data obtained from this proposed study will unveil the role of Gαh/PLC-δ1 PPI in the molecular mechanisms for drug resistance and metastatic progression in TNBC with Gαh-OE. Moreover, the result of utilizing the PLC-δ1 peptide fragment to reverse drug resistance and inhibit metastasis in TNBC with Gαh-OE will provide solid evidence that the binding interface of Gαh in PLC-δ1 can be used as a target to discover the small-molecule PPI blocker for Gαh/PLC-δ1 complex by computational virtual screening.