Loss of Rnf43 accelerates Kras-mediated pancreatic neoplasia
The ring finger protein 43 (RNF43) is a gene that encodes for an E3 ubiquitin ligase and is mutated recurrently in cystic neoplasms and approximately 10% of ductal adenocarcinomas of pancreas with oncogenic activation of KRAS. Mutations identified in RNF43 are predominantly loss-of-function mutations suggesting that RNF43 is a putative tumor suppressor in pancreatic cancer. To date, no mouse model has been developed to better understand the role of Rnf43 in the context of pancreatic cancer. Using a conditional mouse model with pancreas-specific loss of Rnf43, we investigated and characterized the functional importance of Rnf43 in pancreatic cancer development and progression. We observed that loss of Rnf43 alone has no discernible effect on normal pancreas development and is not sufficient to develop any neoplastic lesions. Disruption of Rnf43 accelerated the development of Kras-driven pancreatic precursor lesions that eventually progressed to PDAC resulting in decreased survival. Similar to humans, higher incidence of intraductal papillary mucinous neoplasms of pancreas was observed in Rnf43 knockout mice compared to wild type in presence of a concomitant oncogenic Kras mutation.
To understand the molecular mechanisms by which Rnf43 regulates pancreatic cancer progression, cell lines were established from mouse tumors. In-vitro functional assays demonstrated increased growth and invasion with loss of Rnf43 compared to control. Pathway analysis of differentially expressed genes revealed oxidative phosphorylation as one of the significantly upregulated pathways in Rnf43 knockout cells. We also found that there is increase in mitochondrial respiration in Rnf43 deficient cells, as evidenced by increased oxygen consumption rate. In addition, metabolomics analysis has demonstrated increased TCA cycle metabolites in cells with Rnf43 loss compared to control. The viability of Rnf43 depleted cells decreased significantly by inhibiting the oxidative phosphorylation pathway using IACS10759. These results provide confirmation that Rnf43 acts as a tumor suppressor in pancreatic cancer by impeding the progression of Kras-mediated neoplasms potentially through suppression of mitochondrial activity.