The BTB-MATH protein BATH-42 interacts with RIC-3 to regulate maturation of nicotinic acetylcholine receptors

RIC-3 is a member of a conserved family of proteins that affect nicotinic acetylcholine receptor maturation. In yeast and in vitro, BATH-42, a BTB- and MATH-domain-containing protein, interacts with RIC-3. BATH-42 is also known to interact with the CUL-3 ubiquitin ligase complex. Loss of BATH-42 function leads to increased RIC-3 expression and decreased activity of nicotinic acetylcholine receptors in Caenorhabditis elegans vulva muscles. Increased expression of RIC-3 is deleterious for activity and distribution of nicotinic acetylcholine receptors, and thus the effects of BATH-42 loss of function on RIC-3 expression explain the associated reduction in receptor activity. Overexpression of BATH-42 is also detrimental to nicotinic acetylcholine receptor function, leading to decreased pharyngeal pumping. This effect depends on the C-terminus of RIC-3 and on CUL-3. Thus, our work suggests that BATH-42 targets RIC-3 to degradation via CUL-3-mediated ubiquitylation. This demonstrates the importance of regulation of RIC-3 levels, and identifies a mechanism that protects cells from the deleterious effects of excess RIC-3.