TRIM8 regulated autophagy modulates the level of cleaved Caspase-3 subunit to inhibit genotoxic stress induced cell death.

In cancer patients, treatment modalities like chemotherapy and radiation exert their anticancer effects by inducing DNA damage. The cancer cells can survive under genotoxic stress by inducing DNA damage response (DDR) or can undergo cell death. The process of autophagy is emerging as crucial regulator of cell survival during different stress conditions. Post translational modification through ubiquitin plays an essential role in DDR during genotoxic stress conditions. Ubiquitin ligases regulate autophagy and cell death pathways however their role during genotoxic stress conditions is not understood. In the current study we identified TRIM8, RING E3 Ligase, as a novel regulator of autophagy during DDR. TRIM8 regulates lysosomal biogenesis and autophagy flux. The turnover of TRIM8 is high and is stabilized during genotoxic stress conditions. TRIM8 regulated autophagy is essential for its cytoprotective role during genotoxic stress induced cell death. TRIM8 stabilizes the turnover of XIAP during genotoxic stress and forms complex with XIAP and caspase-3 to inhibit its activation in presence of etoposide. TRIM8 mediated autophagy promotes degradation of cleaved caspase-3 subunits. This study described TRIM8, as a novel regulator of DDR-autophagy crosstalk, which may play role in survival of cancer cells in presence of genotoxic agents.

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. © 2017 Wiley Periodicals, Inc.

TRIM4; a novel mitochondrial interacting RING E3 ligase, sensitizes the cells to hydrogen peroxide (H2O2) induced cell death.

The emerging evidences suggest that posttranslational modification of target protein by ubiquitin (Ub) not only regulate its turnover through ubiquitin proteasome system (UPS) but is a critical regulator of various signaling pathways. During ubiquitination, E3 ligase recognizes the target protein and determines the topology of ubiquitin chains. In current study, we studied the role of TRIM4, a member of the TRIM/RBCC protein family of RING E3 ligase, in regulation of hydrogen peroxide (H2O2) induced cell death. TRIM4 is expressed differentially in human tissues and expressed in most of the analyzed human cancer cell lines. The subcellular localization studies showed that TRIM4 forms distinct cytoplasmic speckle like structures which transiently interacts with mitochondria. The expression of TRIM4 induces mitochondrial aggregation and increased level of mitochondrial ROS in the presence of H2O2. It sensitizes the cells to H2O2 induced death whereas knockdown reversed the effect. TRIM4 potentiates the loss of mitochondrial transmembrane potential and cytochrome c release in the presence of H2O2. The analysis of TRIM4 interacting proteins showed its interaction with peroxiredoxin 1 (PRX1), including other proteins involved in regulation of mitochondrial and redox homeostasis. TRIM4 interaction with PRX1 is critical for the regulation of H2O2 induced cell death. Collectively, the evidences in the current study suggest the role of TRIM4 in regulation of oxidative stress induced cell death.