Interaction of serotonin 5-hydroxytryptamine type 2C receptors with PDZ10 of the multi-PDZ domain protein MUPP1

By using the yeast two-hybrid system, we previously isolated a cDNA clone e ncoding a novel member of the multivalent PDZ protein family called MUPP1 c ontaining 13 PDZ domains. Here we report that the C terminus of the Fi-hydr oxytryptamine type 2C (5-HT2C) receptor selectively interacts with the 10th PDZ domain of MUPP1. Mutations in the extreme C terminal SSV sequence of t he 5-HT2C receptor confirmed that the SXV motif is critical for the interac tion, Co-immunoprecipitations of MUPP1 and 5-HT2C receptors from transfecte d COS-7 cells and from rat choroid plexus verified this interaction in vivo . Immunocytochemistry revealed an SXV motif-dependent co-clustering of both proteins in transfected COS-7 cells as well as a colocalization in rat cho roid plexus. A 5-HT2C receptor-dependent unmasking of a C-terminal vesicula r stomatitis virus epitope of MUPP1 suggests that the interaction triggers a conformational change within the MUPP1 protein. Moreover, 5-HT2A and 5-HT 2B, sharing the C-terminal EX(V/I)SXV sequence with 5-HT2C receptors, also bind MUPP1 PDZ domains in vitro. The highest MUPP1 mRNA levels were found i n all cerebral cortical layers, the hippocampus, the granular layer of the dentate gyrus, as well as the choroid plexus, where 5-HT2C receptors are hi ghly enriched. We propose that MUPP1 may serve as a multivalent scaffold pr otein that selectively assembles and targets signaling complexes.