The cysteine-rich with EGF-Like domains 2 (CRELD2) protein interacts with the large cytoplasmic domain of human neuronal nicotinic acetylcholine receptor α4 and β2 subunits

Using a yeast two-hybrid screening we report the isolation of a novel human protein, hCRELD2 beta, that interacts specifically with the large cytoplasmic regions of human nicotinic acetylcholine receptor (nAChR) alpha 4 and beta 2 subunits, both in yeast cells and in vitro. This interaction is not detected with nAChR alpha 7 and alpha 3 subunits. The hCRELD2 gene encodes for multiple transcripts, likely to produce multiple protein isoforms. A previously reported one has been renamed as CRELD2 alpha. Isoforms alpha and beta are expressed in all tissues examined and have the same N-terminal and central regions but alternative C-terminal regions. Both isoforms interact with the alpha 4 subunit. Within this subunit the interaction was localized to the N-terminal region of the large cytoplasmic loop. The CRELD2 beta protein is present at the endoplasmic reticulum where colocalized with alpha 4 beta 2 nAChRs upon cell transfection. Immunohistochemistry experiments demonstrated the presence of CRELD2 in the rat brain at sites where alpha 4b2 receptors have been previously detected. Labeling was restricted to neuronal perikarya. Finally, CRELD2 decreases the functional expression and impairs membrane transport of alpha 4 beta 2 nAChRs in Xenopus leavis oocytes, without affecting alpha 3 beta 4 and alpha 7 nAChR expression. These results suggest that CRELD2 can act as a specific regulator of alpha 4 beta 2 nAChR expression.