Differential ubiquitination and proteasome regulation of Ca(V)2.2 N-type channel splice isoforms

Ca(V)2.2 (N-type) calcium channels control the entry of calcium into neurons to regulate essential functions but most notably presynaptic transmitter release. Ca(V)2.2 channel expression levels are precisely controlled, but we know little of the cellular mechanisms involved. The ubiquitin proteasome system (UPS) is known to regulate expression of many synaptic proteins, including presynaptic elements, to optimize synaptic efficiency. However, we have limited information about ubiquitination of Ca(V)2 channels. Here we show that Ca(V)2.2 proteins are ubiquitinated, and that elements in the proximal C terminus of Ca(V)2.2 encoded by exon 37b of the mouse Cacna1b gene predispose cloned and native channels to downregulation by the UPS. Ca(V)2.2 channels containing e37b are expressed throughout the mammalian nervous system, but in some cells, notably nociceptors, sometimes e37a--not e37b--is selected during alternative splicing of Ca(V)2.2 pre-mRNA. By a combination of biochemical and functional analyses we show e37b promotes a form of ubiquitination that is coupled to reduced Ca(V)2.2 current density and increased sensitivity to the UPS. Cell-specific alternative splicing of e37a in nociceptors reduces Ca(V)2.2 channel ubiquitination and sensitivity to the UPS, suggesting a role in pain processing.