A role for Akt in the activation of NF-kappa B to suppress apoptosis

The regulation of the transcription factor NF-κB is crucial to understanding its biological function because it regulates genes involved in protecting cells from apoptosis and can also contribute to the transformation potential of cells. The canonical mechanism of NF-κB activation involves the stimulation of signaling pathways that lead to the cytoplasmic phosphorylation of the NF-κB interacting protein called IκB. Phosphorylation of IκB leads to its degradation allowing liberated NF-κB to translocate to the nucleus where it regulates responsive genes. Recently, this mechanism of NF-κB activation has been challenged by a process that involves phosphorylation and activation of the transactivation subunit of NF-κB independent of nuclear translocation.; My studies have focused on a serine/threonine protein kinase, known as Akt, which leads to the activation of NF-κB by stimulating the transactivation subunit of NF-κB. My first project demonstrates that oncogenic H-Ras requires Akt to stimulate the transcriptional activity of NF-κB. Akt stimulates NF-κB-dependent transcription by targeting the TA1 transactivation domain of the RelA/p65 subunit rather than inducing NF-κB nuclear translocation via IκB degradation. Additionally, inhibition of endogenous Akt activity sensitizes cells to H-Ras(V12)-induced apoptosis. Finally, Akt-transformed cells require NF-κB to suppress the ability of the chemotherapeutic drug etoposide to induce apoptosis.; My second and third projects further delineates the mechanisms of Akt-mediated NF-κB activation. These results demonstrate that Akt targets the transactivation function of NF-κB in a manner dependent on IKKβ and the mitogen activated protein kinase p38. IKKβ nullizygous mouse embryo fibroblasts are deficient in Akt mediated transactivation of NF-κB and a known IKKβ phosphorylation site on RelA/p65, serine 536, is required for this activation. The inflammatory cytokine IL-1β requires Akt to activate the p38 MAPK. Furthermore, the p38 MAPK is also required for efficient stimulation of RelA/p65 in response to Akt. p38 does not directly modulate RelA/p65, but requires the co-activator CBP/p300. IKKϵ, a related kinase to IKKα and IKKβ, interacts in vivo with Akt. Furthermore, we demonstrate that Akt in conjunction with IKKϵ stimulates the RelA/p65 transactivation domain in a manner dependent on IKKϵ kinase function and interestingly, the Akt consensus phosphorylation site, threonine 501 of IKKϵ.