Protein targeting: the molecular basis of vectorial transport in the kidney

The renal tubular epithelium maintains different sets of transport proteins in plasma membrane domains facing the lumenal and mucosal fluids and limits diffusion between these two compartments. This asymmetry is generated by directing transporters to the appropriate membrane domain, a process that requires both an intracellular machinery that sorts out proteins destined for different domains and cues that create the addresses to which these proteins are sorted. Interactions with the extracellular environment convey the positional information that creates the plasma membrane domains. These interactions are mediated by macromolecular assemblies of cell adhesion molecules, cytoskeleton, and signaling molecules. This review focuses on the mechanisms by which these complexes create polarized membrane domains.