Role of myoferlin in mitochondrial dynamics and metabolic fitness of Pancreatic Ductal Adenocarcinoma

Pancreatic cancer is the 7th most common cause of cancer mortality in the world. It is predicted to become the 2nd leading cause of cancer-related death in 2030. In the majority of cases, due to a late diagnosis, the tumor is not resectable and already disseminated. Therefore, new specific biomarkers providing early diagnosis for pancreatic cancer are needed. In addition to the lack of specific and early biomarkers, chemotherapies (gemcitabine and folfirinox) poorly improve the overall survival of Pancreatic Ductal Adenocarcinoma (PDAC) patients. Hence, a better understanding of physiopathological processes underlying PDAC is required in order to offer more effective treatments.

Myoferlin is a 230 kDa protein with multiple C2 domains known to interact, through calcium binding, with negatively charged phospholipids. This protein was first described in myoblast fusion. Interestingly, Myoferlin is also overexpressed in several cancers, including pancreatic cancer, where it plays a role in endocytosis, exocytosis, and has been located in exosomes. Recently, our team showed a fragmentation of the mitochondrial network in PDAC cells when myoferlin was depleted using siRNA. Understanding the mechanism underlying this mitochondrial disruption would be of great interest as mitochondria are major actors in cancer development, progression and resistance.

Owing to the known role of myoferlin in membrane fusion, we assessed its direct involvement in the mitochondrial fusion machinery. Indeed, if myoferlin is a part of the mitochondrial fusion machinery, its silencing together with an unopposed fission would lead to mitochondrial fragmentation. First, we performed immunofluorescence to colocalize myoferlin and a mitochondrial outer membrane 65kDa protein. Colocalization studies showed no significant colocalization. We then performed immunofluorescence to stained myoferlin and the main factor of mitochondrial fusion mitofusin-1/2 (MFN1/2). Colocalization image analysis revealed a 60% colocalization between both proteins. Those results were further confirmed by PLA (Proximity Ligation Assay). Finally, to evaluate a direct protein-protein interaction, we performed a co-immunoprecipitation assay. The main isoform of myoferlin appeared to coimmunoprecipitate with MFN1/2, suggesting a direct interaction between these proteins.