| Breast Cancer remains the second leading cause of cancer-related deaths among American women mainly because of resistance to anti-estrogen therapies. Recently we reported that G1P3, an immuno-endocrine induced anti-apoptotic protein, is a mediator of anti-estrogen resistance in breast cancer. However, anti-apoptotic mechanisms of G1P3 in mitochondria remain unclear. Based upon its localization into mitochondria, we hypothesized that G1P3 augments ROS levels in mitochondria to regulate mitochondrial biogenesis to suppress apoptosis. Since localization within the mitochondria regulates the activity of a protein, submitochondrial localization of G1P3 was determined.In fractionation studies, G1P3 localized into inner mitochondrial membrane (IMM), suggesting a role for G1P3 in inner mitochondrial permeabilization by preventing the opening of mitochondrial permeability transition pore, the critical steps of intrinsic apoptosis process. ROS levels in G1P3 overexpressing cells were significantly higher than that of vector control cells (3.3 fold, P < 0.0001). Additionally, Ca2+ ionophore ionomycin markedly increased ROS levels and mitochondrial fission in MCF-7vector cells. However, in G1P3 overexpressing cells ionomycin resulted in mitochondrial fusion.Moreover, cyclosporine A (CSA), an inhibitor of MPTP, reversed mitochondrial fission in vector and fusion in G1P3 overexpressing cells. Taken together, our results suggest that G1P3 inhibits MPTP opening and leads to mitochondrial fusion to antagonize apoptosis. Further delineation of molecular mechanism by which G1P3 regulates mitochondrial biogenesis and MPTP opening would allow us to design novel strategies to inhibits its activity in cancer cells. |
