NITRIC OXIDE-STIMULATED GUANINE-NUCLEOTIDE EXCHANGE ON P21(RAS)

The protooncogene p21(ras), a monomeric G protein family member, plays a critical role in converting extracellular signals into intracellular biochemical events. Here, we report that nitric oxide (NO) activates p21(ras) in human T cells as evidenced by an increase in GTP-bound p21(ras). In vitro studies using pure recombinant p21(ras) demonstrate that the activation is direct and reversible. Circular dichroism analysis reveals that NO induces a profound conformational change in p21(ras) in association with GDP/GTP exchange. The mechanism of activation is due to S-nitrosylation of a critical cysteine residue which stimulates guanine nucleotide exchange. Furthermore, we demonstrate that p21(ras) is essential for NO-induced downstream signaling, such as NF-KB activation, and that endogenous NO can activate p21(ras) in the same cell. These studies identify p21(ras) as a target of NO in T cells and suggest that NO activates p21P(ras) by an action which mimics that of guanine nucleotide exchange factors.