CD4 CROSS-LINKING (CD4XL) INDUCES RAS ACTIVATION AND TUMOR-NECROSIS-FACTOR-ALPHA SECRETION IN CD4(-CELLS() T)

CD4 molecules are the primary receptors for human immunodeficiency vir us (HIV) and bind the envelope glycoprotein gp120 of HIV with high-aff inity. We have previously shown that cross-linking of CD4 molecules (C D4XL) in normal peripheral blood mononuclear cells (PBMC) results in s ecretion of cytokines tumor necrosis factor-alpha (TNF-alpha) and inte rferon-gamma (IFN-gamma), but not of interleukin-2 (IL-2) or IL-4. To investigate the intracellular signaling events associated with CD4-gp1 20 interaction, we incubated CD4(+) T cells from peripheral blood of H IV-negative healthy donors with HIV envelope protein gp160 alone or pe rformed CD4XL with gp160 and anti-gp160 antibody. This procedure resul ted in tyrosine phosphorylation of intracellular substrates p59(fyn), zap 70, and p95(vav) and also led to ras activation, as assessed by co nversion of rasGDP to rasGTP. The role of res in CD4 signaling was fur ther investigated using CD4(+) Jurkat cells transfected with a dominan t negative ras mutant. CD4(+) T cells expressing dn-ras secreted signi ficantly reduced levels of TNF-alpha in response to CD4XL. These studi es indicate that interaction of HIV gp160 with CD4 molecules activates the ras pathway in T cells, which may result in the cells becoming un responsive to subsequent stimulation. (C) 1997 by The American Society of Hematology.