Joav Prives

We are studying the regulation of surface expression of the nicotinic acetylcholine receptor (AChR). This receptor is a ligand-gated ion channel that mediates neuromuscular transmission. The binding of the neurotransmitter acetylcholine to AChR results in a conformational change that leads to the opening of a transmembrane ion channel. The muscle AChR comprises four distinct homologous subunit polypeptides expressed as separate gene products and assembled in the stoichiometry of a2:b 1:g1:d1. Our current research is focused on the regulation of AChR biogenesis (subunit folding and assembly) and topogenesis (formation and dispersal of AChR-rich membrane domains). These aspects of AChR expression appear to be regulated by cellular mechanisms that involve covalent modifications of AChR subunits and interactions with other cellular constituents. In our studies we are using primary chick muscle cells that express endogenous AChR and cells transfected with all four AChR subunits. AchR assembly occurs in the endoplasmic reticulum (ER) and it involves interactions of subunits with ER-resident proteins. We have observed that nascent AChR a-subunits form complexes with the molecular chaperone calnexin in the ER, which facilitates its folding and assembly. We are studying the role of post-translational modifications that occur in the ER, such as N-linked glycosylation, disulfide bond formation, and phosphorylation of nascent subunits, in the regulation of AChR biogenesis. With respect to AChR topogenesis, we are analyzing the contribution of phosphorylation-dephosphorylation to the surface aggregation and cytoskeletal attachment of AChR, as well as of glutamate receptors transfected into embryonic muscle cells. It is anticipated that these studies will further our understanding of key features common to the regulated expression of neurotransmitter receptors in muscle cells and neurons.