A SINGLE MUTATION OF THE NEUROKININ-2 (NK2) RECEPTOR PREVENTS AGONIST-INDUCED DESENSITIZATION - DIVERGENT CONFORMATIONAL REQUIREMENTS FOR NK2 RECEPTOR SIGNALING AND AGONIST-INDUCED DESENSITIZATION IN XENOPUS OOCYTES

Receptor activation and agonist induced desensitization of the human n eurokinin-2 (NK2) receptor expressed in Xenopus oocytes have been inve stigated, When neurokinin A (NKA) was applied repeatedly at 5-min inte rvals, the second and subsequent applications gave no responses. This desensitization was not observed with the specific agonists (Lys(3), G ly(8)-R-gamma-lactam-Leu(9))MCA(3-10) (GR64349) or (Nle(10))-NKA(4-10) . However, in the presence of the protein kinase inhibitor staurospori ne, stimulation with GR64349 or (Nle(10))-NKA(4-10) induced receptor d esensitization. In contrast, the protein kinase C inhibitor Ro-31-8220 was not able to enhance GR64349-mediated desensitization. We created a mutation (F248S) in the third cytoplasmic loop of NK2 that impairs N KA-induced desensitization. In the presence of either staurosporine or Ro-31-8220, the mutant receptor was desensitized in response to NKA a pplication but not to GR64349. Also, truncation mutants Delta 62 and D elta 87, lacking serine and threonine residues in the cytoplasmic COOH -terminal tail, were functionally active and were partially resistant to desensitization. These observations indicate that 1) there are diff erent conformational requirements for NK2 receptor signaling and agoni st-induced desensitization, 2) the third intracellular loop and the cy toplasmic tail of NK2 are functional domains important for agonist-ind uced desensitization, and 3) some agonists at the NK2 receptor cause m uch more desensitization than others and suggest that this might resul t from phosphorylation by receptor-specific kinases and other non-iden tified protein kinases.