Sortilin knock-down effects the processing and expression of cathepsin d in epidymal cells

Abstract

The intense secretory activity of epididymal cells contributes to sperm maturation. Lysosomal enzymes are highly secreted by the epithelium into the epididymal lumen, and they can participate in remodeling the sperm surface during their maturation process. In most eukaryotic cells, the intracellular transport of these enzymes is mostly regulated by mannose 6 phosphate receptors (MPRs). The lysosomal protease cathepsin D (CatD) is mostly transported by MPRs, although the receptor sortilin (Sort) has also been implicated in this transport since CatD is complexed with prosaposin (Psap), the natural ligand for Sort. In this study, we evaluated the incidence of the Sort expression on transport and processing of CatD in cultured epididymal cells. In a rat epididymal cell line (RCE-1) the sortilin knock-down was induced by transfection with a sortilin pSilencer. Then, we observed by western blot that this Sort silencing increases the expression of other proteins, such as the cation-dependent MPR (CD-MPR) and Psap. In turn, CatD is decreased under these conditions, where the immature form of the enzyme (proCathepsin D) prevailed. Meanwhile, a similar distribution of wild type RCE-1 was observed by IFI. These preliminary results suggest that proCathepsin D could be transported by sortilin and CD-MPR alternatively, but its processing is affected by the silincig of sortilin in this cell type.