Anti-HIV agent trichosanthin enhances the capabilities of chemokines to stimulate chemotaxis and G protein activation, and this is mediated through interaction of trichosanthin and chemokine receptors

Trichosanthin (TCS), an active protein component isolated from a traditiona l Chinese medicinal herb Trichosanthes kirilowii, has been shown to inhibit HIV infection and has been applied in clinical treatment of AIDS. The rece nt development that chemokines and chemokine receptors play important roles in HIV infection led us to investigate the possible functional interaction of TCS with chemokines and their receptors. This study demonstrated that T CS greatly enhanced both RANTES (regulated upon activation, normal T cell e xpressed and secreted)- and stromal cell-derived factor (SDF)-1 alpha-stimu lated chemotaxis (EC50 congruent to 1 nM) in leukocytes (THP-1,Jurkat, and peripheral blood lymphocyte cells) and activation of pertussis toxin-sensit ive G proteins (EC50 congruent to 20 nM). TCS also significantly augmented chemokine-stimulated activation of chemokine receptors CCR5 and CXCR4 as we ll as CCR1, CCR2B, CCR3, and CCR4 transiently expressed in HEK293 cells. A mutant TCS with 4,000-fold lower ribosome-inactivating activity showed simi lar augmentation activity as wild-type TCS. Moreover, now cytometry demonst rated that the specific association of TCS to the cell membranes required t he presence of chemokine receptors, and laser confocal microscopy reveals t hat TCS was colocalized with chemokine receptors on the membranes. The resu lts from TCS-Sepharose pull-down and TCS and chemokine receptor coimmunopre cipitation and cross-linking experiments demonstrated association of TCS wi th CCR5. Thus, our data clearly demonstrated that TCS synergizes activities of chemokines to stimulate chemotaxis and G protein activation, and the ef fects of TCS are likely to be mediated through its interaction with chemoki ne receptors.