IMPORTANCE OF THE CARBOXY-TERMINUS OF THE CXGR2 FOR SIGNAL-TRANSDUCTION

The CXCR2 is phosphorylated at the C-terminal intracytoplasmic portion within 15 sec following the addition of IL-8 or MGSA. Cells transfect ed with a truncated form of the receptor missing the last 12 amino aci ds (T3) showed normal binding affinity, but were no longer phosphoryla ted; individual alanine replacement indicated that Ser346 and 348 were the primary sites of phosphorylation, In studies of the importance of phosphorylation in CXCR2 desensitization, cells expressing wild type CXCR2 lost GTP Psi gamma S binding above basal rate after the first ex posure to IL-8, while cells with the T3 mutant retained 60% of their c apacity to induce GTP gamma S exchange upon a second exposure to IL-8. In contrast, receptor internalization was not affected by the loss of phosphorylation of the T3 mutant. Further receptor truncation led to decreasing binding affinities for IL-8 and MGSA and a decreased rate o f GTP gamma S exchange following addition of excess ligand which sugge sts involvement of this region in G-protein coupling. (C) 1998 Academi c Press.