Interaction of soluble CD4 with the chemokine receptor CCR5

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Abstract

The chemokine receptor CCR5 is constitutively associated with the T cell co-receptor CD4 in plasma cell membranes. The CD4–CCR5 complex exhibits distinct binding properties for macrophage inflammatory protein 1β (MIP-1β) and enhanced G-protein signaling as compared with those of CCR5 alone. Here we report that recombinant soluble CD4, when refolded into its dimeric form, allosterically modulates CCR5 and decreases the affinity for its natural ligand MIP-1β. Monomeric soluble CD4 had little inhibitory effect on CCR5. In contrast, the two-domain amino-terminal fragment of soluble CD4 was able to completely inhibit the interaction of CCR5 with MIP-1β. Thus, we suggest that various conformational states of CD4 exist, which differ markedly with regard to inhibiting the interaction of CCR5 with its ligand MIP-1β. R5-tropic HIV-1 glycoprotein 120, but not interleukin-16, the natural agonist, or X4-tropic glycoprotein 120, inhibited MIP-1β binding to CCR5 in the presence of monomeric and dimeric soluble CD4.

Section snippets

Materials and methods

Materials. [125I]-MIP-1β and sCD4 were from Perkin–Elmer Life Sciences (Boston, MA). MIP-1β was purchased from Peprotech (Rocky Hill, NJ). Gp120LAI was obtained from Progenics (Tarrytown, NY) and gp120ADA was from Immunodiagnostics (Woburn, MA). The first two-domain fragment of sCD4 (D1D2-sCD4) was kindly provided by Dr. Dimiter Dimitrov.

Cell culture. The human osteosarcoma cell line, transfected with CCR5 (HOS-CCR5), was kindly provided by Dr. Dan Littman. Cells were grown in DMEM containing

Results

It was shown earlier that the two-domain CD4 (D1D2-sCD4) was able to interact with CCR5 and inhibit MIP-1β binding completely, while full-length sCD4 had only little effect. It was suggested that the conformation of the D1D2-fragment of sCD4 exposes a CCR5-interactive region more efficiently than full-length sCD4 [19], [20]. Interestingly, co-expression of CD4 decreases the affinity of CCR5 for its ligand MIP-1β [15]. Since cellular CD4 exists mostly in higher order oligomers, whereas

Discussion

CCR5 and CD4 functionally associate on the plasma membrane and co-expression of CD4 decreases the affinity of CCR5 for MIP-1β [13], [14], [15]. Although full-length sCD4 has little effect on CCR5, its fragment containing only the first two domains interacts efficiently with CCR5 and can inhibit MIP-1β binding completely [13], [19], [20]. Since cellular CD4 exists mostly as homodimers and tetramers and refolded dimeric sCD4 modulates CCR5 potently, we suggest that various conformational forms or

Acknowledgements

This work was supported by a Veterans Affairs Advanced Career Development Award to R.S.

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