Inhibition of Inositol 1, 4, 5-Trisphosphate Receptor Induce Breast Cancer Cell Death Through Deregulated Autophagy and Cellular Bioenergetics.

Inositol 1,4,5-trisphosphate receptors (IP3 Rs) regulate autophagy in normal cells and are associated with metastasis in cancer cells. In breast cancer, however, the regulation and role of IP3 Rs is not clear. To study this, we used MCF-7 breast cancer cell line and mouse model of breast cancer. Inhibiting IP3 R sub types resulted in compromised bioenergetics both in terms of glucose and mitochondrial metabolism. The siRNA mediated silencing of IP3 R or its blocking by its inhibitors Xestospongin C and 2-Amino-ethoxy diphenyl borate increased cell death and LC3II expression in MCF-7 cells as well as attenuated cellular bioenergetics. The level of Autophagy related gene, Atg5 was found to be up regulated after pharmacological as well as siRNA blocking of IP3 R. The specificity of its role in autophagy was confirmed through specific shRNA knockdown of the Atg5 along with IP3 R inhibitor. Inhibiting as well as silencing of IP3 R receptor also resulted in increase in ROS production which was abolished after pretreatment with N-acetyl cysteine. Its role in autophagy was confirmed through decrease in the levels of LC3 II after pretreatment with IP3 R inhibitor and N acetyl cysteine.Moreover, inhibiting as well as silencing IP3 R-induced cell death in MCF-7 cells was attenuated by autophagic inhibitors (Bafilomycin A1 or 3-Methyladeneine). In mice, blocking of IP3 Rs by 2-Amino-ethoxy diphenyl borate arrested tumor growth. Overall our findings indicate that IP3 R blocking resulted in autophagic cell death in breast cancer cells and provides a role of IP3 Rs in determining the breast cancer cell fate. J. Cell. Biochem. 118: 2333-2346, 2017.