Non-canonical functions of the mitochondrial fission protein Drp1 in ovarian cancer

About This Grant

PROJECT SUMMARY High grade serous ovarian cancer (HGSOC) is the most common histologic subtype of ovarian cancer and remains a deadly malignancy facing women. Late-stage diagnosis, development of chemoresistance and high rates of recurrence all contribute to the low five-year survival rate of advanced stage patients. Thus, identifying novel drivers of tumor progression and heterogeneity continue to be high research priorities. We find that enhanced mitochondrial fusion driven by a splice variant of the mitochondrial fission protein Drp1/DNM1L is a phenotype of HGSOC. Loss of exon 16 in the Exon16/17 variable domain, denoted as Drp1(-/17), leads to Drp1 redistribution from mitochondria to microtubules (MTs), and consequentially to dampened fission, a fused mitochondrial network and enhanced mitochondrial metabolism. Importantly, Drp1(-/17) expression drives proliferation, metastasis and chemoresistance, and this is of clinical significance as Drp1(-/17) high HGSOC tumors are associated with poor patient outcome. In the present proposal we will test the hypothesis that the extra-mitochondrial function of Drp1(-/17) contributes to HGSOC tumor progression and heterogeneity. Our preliminary data suggest that microtubules are not simply reservoirs for Drp1(-/17) to drive mitochondrial fusion, but that Drp1(-/17) has localized microtubule functions associated with its interaction and recruitment of the multi amino acyl tRNA synthase complex (MSC) to centrosomes. Based on observations that Drp1(-/17) high tumors display greater aneuploidy and copy number alterations leads us to predict that localized centrosome protein synthesis facilitated by the MSC interaction with Drp1(-/17) at centrosomes leads to centrosome amplification and chromosome segregation defects. Intriguingly, many of the amino acids that are required for tRNA charging by the MSC are derived from the TCA cycle. Coincidentally, we find that Drp1(-/17) cells display increased levels of TCA cycle metabolites and downstream amino acid. This leads us to predict that increased mitochondrial fusion due to Drp1(-/17) microtubule association drives TCA cycle flux, and that this works in concert with the MT-dependent function of Drp1(-/17) by supplying amino acids for the MSC. We further propose that de novo amino acid synthesis provides survival advantages to Drp1(-/17) under amino acid deprivation and that this contributes to tumor progression. Our work is conceptually innovative as it investigates the unique interplay between mitochondrial morphology, amino acid metabolism, and localized regulation of protein synthesis at the centrosome to chromosome instability, a common feature of HGSOC. The results from this work will have major impacts on our understanding of HGSOC tumor heterogeneity. Moreover, our research is the first demonstration that a splice variant of Drp1 has unique extra-mitochondrial functions in a pathophysiologic context.