REGULATORY MECHANISMS OF DYNAMIN-RELATED PROTEIN 1 (DRP1) AND ITS INFLUENCE ON APOPTOSIS IN BREAST CANCER

Our study examined the regulation of dynamin-related protein 1 (Drp1) and its influence on apoptosis in breast cancer. Mitochondrial length analyses determined that HTB-22 adenocarcinoma cells displayed fragmented mitochondrial morphology. Western blot analyses of mitochondrial dynamics proteins showed increased endogenous Drp1 and Opa1 expression. This suggests that Drp1 function may be upregulated and/or the balance to fission is lost by the overexpression of Opa1, thus creating a hyper-fused morphology that resembles a pro-fission state. Multiple techniques revealed the majority of Drp1 protein is sequestered in the cytoplasm of these cells. Also, cytochrome c protein expression was predominantly localized to the mitochondria in HTB-22 cells, which upholds a hallmark of cancer, showing apoptotic resistance. To better understand which part of the intrinsic apoptotic pathway is impeded in HTB-22 cells, we examined Drp1 regulatory mechanisms. Post-translational modifications of Drp1, such as phosphorylation of serine residue 637, inhibit its translocation to the mitochondria to initiate fission and begin early stages of apoptosis. Our phosphopurification data suggest that HTB-22 cells have increased phosphorylation at Drp1 S637.  The negative regulation of Drp1-dependent fission by phosphorylation could be the mechanism by which HTB-22 cells can prohibit mitochondrial membrane changes that subsequently promote apoptosis.