Molecular determinants of SEC61A1 mutant R236C in two patient-derived cellular platforms

Abstract

Background & objectivesSEC61A1 encodes a central protein of the mammalian translocon machinery residing in the ER. Mutations ofSEC61A1are implicated to result in various severe diseases. Recently, mutation R236C was identified in patients having autosomal dominant polycystic liver disease (ADPLD), which originates from defects of cholangiocytes in the liver. The molecular phenotype of R236C was assessed.MethodsTwo cellular platforms were established from the same cell source of an ADPLD patient by different methodology. Cells were immortalized by retroviral transduction of an oncogene (UCi) or reprogrammed to induced pluripotent stem cells (iPSC) that were differentiated to cholangiocyte progenitor-like cells (CPLC). UCi and CPLC were subjected to several analyses of molecular pathways that were previously associated with development of polycystic disease.ResultsUCi displayed markers of epithelial cells, while CPLCs expressed typical markers of both cholangiocytes and hepatocytes. Cells encoding R236C showed a stable, continuous proliferation in both platforms, however growth rates were reduced as compared to wildtype control. Autophagy, cAMP synthesis, and secretion of important marker proteins were reduced in R236C-expressing cells. In addition, R236C induced increased calcium leakiness from the ER to the cytoplasm. Upon oxidative stress, R236C led to a high induction of apoptosis and necrosis.ConclusionAlthough the grade of aberrant cellular functions differed between the two platforms, overall the molecular phenotype of R236C was shared suggesting that the mutation, regardless of the cell type, has a dominant impact on disease-associated pathways that cause ADPLD. Our approach may be valuable to decipher the molecular pathways of other rare genetic diseases using patient-specific cell models.