The B-oligomer of pertussis toxin deactivates CC chemokine receptor 5 and blocks entry of M-tropic HIV-1 strains

Infection of target cells by HIV-1 requires initial binding interactions be tween the viral envelope glycoprotein gp120, the cell surface protein CD4, and one of the members of the seven-transmembrane G protein-coupled chemoki ne receptor family, Most primary isolates (R5 strains) use chemokine recept or CCR5, but some primary syncytium-inducing, as well as T cell line-adapte d, strains (X4 strains) use the CXCR4 receptor. Signaling from both CCR5 an d CXCR4 is mediated by pertussis toxin (PTX)-sensitive G(i) proteins and is not required for HIV-1 entry. Here, we show that the PTX holotoxin as well as its binding subunit, B-oligomer, which lacks G(i)-inhibitory activity, blocked entry of R5 but not X4 strains into primary T lymphocytes. interest ingly, B-oligomer inhibited virus production by peripheral blood mononuclea r cell cultures infected with either R5 or X4 strains, indicating that it c an affect HIV-1 replication at both entry and post-entry levels. T cells tr eated with B-oligomer did not initiate signal transduction in response to m acrophage inflammatory protein (MIP)-1 beta or RANTES (regulated upon activ ation, normal T cell expressed and secreted); however, cell surface express ion of CCR5 and binding of MIP-1 beta or HIV-1 to such cells were not impai red. The inhibitory effect of B-oligomer on signaling from CCR5 and on entr y of R5 HIV-1 strains was reversed by protein kinase C (PKC) inhibitors, in dicating that B-oligomer activity is mediated by signaling events that invo lve PKC. B-oligomer also blocked cocapping of CCR5 and CD4 induced by R5 HI V-1 in primary T cells, but did not affect cocapping of CXCR 4 and CD4 afte r inoculation of the cultures with X4 HIV-1. These results suggest that the B-oligomer of PTX cross-deactivates CCR5 to impair its function as a corec eptor for HIV-1.