Point mutation causing constitutive signaling of CXCR2 leads to transforming activity similar to Kaposi's sarcoma herpesvirus-G protein-coupled receptor

The chemokine receptor CXCR2 is the closest homologue to Kaposi's sarcoma h erpesvirus-G protein-coupled receptor (KSHV-GPCR), which is known to be con stitutively activated and able to cause oncogenic transformation. Among G p rotein-coupled receptors, a DRY sequence in the second intracellular loop i s highly conserved. However, the KSHV-GPCR shows a VRY sequence instead. In this study, we exchanged Asp(138) of the DRY sequence in the CXCR2 with a Val (D138V), the corresponding amino acid in KSHV-GPCR, or with a Gin (D138 Q), and investigated the functional consequences of these mutations. In foc us formation and soft agar growth assays in NIH 3T3 cells, the D138V mutant exhibited transforming potential similar to the KSHV-GPCR, Surprisingly, t he CXCR2 wild type itself showed transforming activity, although not as pot ently, due to continuous autocrine stimulation, whereas the D138Q mutant fo rmed no foci, In agreement with these results were high levels of inositol phosphate accumulation in the D138V mutant and the KSHV-GPCR, indicating co nstitutive activity. These data emphasize the importance of the DRY sequenc e for G protein-coupled signaling of the CXCR2, Either constitutive activat ion or persistent autocrine stimulation of the CXCR2 causes transformation similar to KSHV-GPCR-transfected cells, probably activating the same signal transduction cascade that can abrogate normal growth control mechanisms.