Regulation of cell polarity by controlled proteolytic systems

Epithelial and neuronal cells are highly asymmetric, with discrete regions responsible for different roles that underlie the generation of specific compartments within cells that are distinct in biochemical composition, structure, and morphology that ultimately lead to distinct functions. Controlled and specific molecular targeting and sorting have been studied to understand the generation of asymmetric domains inside cells. Recently, a new and complementary explanation has emerged to account for the generation of domains that are enriched by a subset of proteins or polarization determinants: local proteolysis. In this review, we discuss the most conspicuous proteolytic systems that may contribute to the generation of cell polarity, namely the ubiquitin-proteosome and the calpain systems. Specifically, we focus this review on two cellular processes that depend on the acquisition of cell polarity; cell migration and the establishment of an axon in a neuronal cell.