beta-arrestin differentially regulates the chemokine receptor CXCR4-mediated signaling and receptor internalization, and this implicates multiple interaction sites between beta-arrestin and CXCR4

The chemokine receptor CXCR4 has recently been shown to be a co-receptor in volved in the entry of human immunodeficiency virus type 1 into target cell s. This study shows that coexpression of beta-arrestin with CXCR4 in human embryonic kidney 293 cells attenuated chemokine-stimulated G protein activa tion and inhibition of cAMP production. Truncation of the C-terminal 34 ami no acids of CXCR4 (CXCR4-T) abolished the effects of beta-arrestin on CXCR4 /G protein signaling, indicating the functional interaction of the receptor C terminus with beta-arrestin. On the other hand, receptor internalization and the subsequent activation of extracellular signal-regulated kinases we re significantly promoted by coexpression of beta-arrestin with CXCR4, wher eas the C-terminal truncation of CXCR4 did not affect this regulation of be ta-arrestin, suggesting that beta-arrestin can functionally interact with C XCR4 with or without the C terminus. Moreover, beta(2)V54D, the dominant in hibitory mutant of beta-arrestin 2, exerted no effects on CXCR4/G protein s ignaling, but strongly influenced receptor internalization and extracellula r signal-regulated kinase activation. Further cross-linking experiments dem onstrated that beta-arrestin as well. as beta(2)V54D could physically conta ct both CXCR4. and CXCR4-T. Glutathione S-transferase pub-down assay showed that beta-arrestin was able to bind efficiently In vitro to both the third intracellular loop and the 34-amino acid C terminus of CXCR4. Taken togeth er, our data clearly establish that beta-arrestin can effectively regulate different functions of CXCR4 and that this is mediated through its distinct interactions with the C terminus and other regions including the third loo p of CXCR4.