A Role for the Calmodulin Kinase II-Related Anchoring Protein (alpha kap) in Maintaining the Stability of Nicotinic Acetylcholine Receptors

作者：Mouslim Chakib; Aittaleb Mohamed; Hume Richard I; Akaaboune Mohammed^*

来源：Journal of Neuroscience, 2012, 32(15): 5177-5185.

DOI：10.1523/JNEUROSCI.6477-11.2012

alpha kap, a muscle specific anchoring protein encoded within the Camk2a gene, is thought to play a role in targeting multiple calcium/calmodulin kinase II isoforms to specific subcellular locations. Here we demonstrate a novel function of alpha kap in stabilizing nicotinic acetylcholine receptors (AChRs). Knockdown of alpha kap expression with shRNA significantly enhanced the degradation of AChR alpha-subunits (AChR alpha), leading to fewer and smaller AChR clusters on the surface of differentiated C2C12 myotubes. Mutagenesis and biochemical studies in HEK293T cells revealed that alpha kap promoted AChR alpha stability by a ubiquitin-dependent mechanism. In the absence of alpha kap, AChR alpha was heavily ubiquitinated, and the number of AChR alpha was increased by proteasome inhibitors. However, in the presence of alpha kap, AChR alpha was less ubiquitinated and proteasome inhibitors had almost no effect on AChR alpha accumulation. The major sites of AChR alpha ubiquitination reside within the large intracellular loop and mutations of critical lysine residues in this loop to arginine increased AChR alpha stability in the absence of alpha kap. These results provide an unexpected mechanism by which alpha kap controls receptor trafficking onto the surface of muscle cells and thus the maintenance of postsynaptic receptor density and synaptic function.

• 出版日期2012-4-11