Inhibitory heterotrimeric GTP-binding proteins (Gi proteins) mediate a variety of signaling pathways by coupling receptors and effectors to regulate cellular proliferation, differentiation, and apoptosis. However, the role of Gi proteins in the modulation of hydrogen peroxide-induced apoptosis is not clearly understood. Thus, we investigated the effect of Gi proteins oil hydrogen peroxide-induced apoptosis and the underlying mechanisms in H1299 human lung cancer cells. The stable expression Of constitutively active alpha subunits of Gil (G alpha i1QL), Gi2, or Gi3 inhibited hydrogen peroxide-induced apoptosis. The expression of G alpha i1QL Lip-regulated BcI-2 expression, and the knockdown of Bcl-2 with siRNA abolished the anti-apoptotic effect of G alpha i1QL Call induced the transcription of Bcl-2 by activation of NF kappa B, which resulted from an increase in NF-kappa B p50 protein. We conclude that G alpha i1 inhibits hydrogen peroxide-induced apoptosis of H1299 lung cancer cells by Lip-regulating the transcription of BcI-2 through a p50-mediated NF-kappa B activation. (C) 2009 Elsevier Inc. All rights reserved.