Desensitization and functional interaction of the five-TM chemokine receptor with receptor kinases and arrestins. HEK293 cells transiently expressing the wild-type or mutant chemokine receptors were pretreated with PBS (as control), 10 nM indicated chemokine (A), or 1 μM PMA (B) for 15 min at 37°C. After rinsing with PBS, the cells were challenged with 10 nM chemokine (RANTES for CCR5 and SDF-1α for CXCR4) and forskolin-stimulated cAMP formation was determined. The cells were transiently transfected with the wild-type or mutant CCR5 (C) or CXCR4 receptors (D) alone (control) or cotransfected with GRK2, GRK5, β-arrestin 1, or β-arrestin 2 as indicated. The inhibition of the cAMP formulation induced by 10 nM chemokines (RANTES for CCR5 and SDF-1α for CXCR4) was determined. (A) The untreated forskolin-stimulated cAMP levels were in the range of 123 ± 12 pmol/mg protein. Data presented are averages and error ranges of two separate experiments performed in duplicate. ∗∗, P < 0.01 compared with controls.