The serotonin 5-HT2A and 5-HT2C receptors interact with specific sets of PDZ proteins

The 5-hydroxytryptamine type 2A (5-HT2A) receptor and the 5-HT2C receptor are closely related members of the G-protein-coupled receptors activated by serotonin that share very similar pharmacological profiles and cellular signaling pathways. These receptors express a canonical class I PDZ ligand (SXV) at their C-terminal extremity. Here, we have identified proteins that interact with the PDZ ligand of the 5-HT2A and 5-HT2C receptors by a proteomic approach associating affinity chromatography using immobilized synthetic peptides encompassing the PDZ ligand and mass spectrometry. We report that both receptor C termini interact with specific sets of PDZ proteins in vitro. The 5-HT2C receptor but not the 5-HT2A receptor binds to the Veli-3.CASK.Mint1 ternary complex and to SAP102. In addition, the 5-HT2C receptor binds more strongly to PSD-95 and MPP-3 than the 5-HT2A receptor. In contrast, a robust interaction between the 5-HT2A receptor and the channel-interacting PDZ protein CIPP was found, whereas CIPP did not significantly associate with the 5-HT2C receptor. We also show that residues located at the -1 position and upstream the PDZ ligand in the C terminus of the 5-HT2A and 5-HT2C receptors are major determinants in their interaction with specific PDZ proteins. Immunofluorescence and electron microscopy studies strongly suggested that these specific interactions also take place in living cells and that the 5-HT2 receptor-PDZ protein complexes occur in intracellular compartments. The interaction of the 5-HT2A and the 5-HT2C receptor with specific sets of PDZ proteins may contribute to their different signal transduction properties.