Akt Suppresses Apoptosis by Stimulating the Transactivation Potential of the RelA/p65 Subunit of NF-κB

TLDR

Cell survival signals from growth factors, cytokines, and oncoproteins are initiated by PI3K‑ and Akt‑dependent pathways, and oncogenic Ras requires NF‑κB to suppress transformation‑associated apoptosis. The study investigates whether oncogenic H‑Ras depends on PI3K and Akt to enhance NF‑κB transcriptional activity. Activated Ras and MEKK promote NF‑κB nuclear translocation and DNA binding, whereas PI3K or Akt activate NF‑κB transcription by stimulating the transactivation domain 1 of the p65 subunit through an IKK‑dependent mechanism. Loss of Akt activity sensitizes cells to Ras‑induced apoptosis and reduces NF‑κB activity, and Akt‑transformed cells require NF‑κB to block etoposide‑induced apoptosis, showing that Akt mainly upregulates p65 transactivation.

Abstract

It is well established that cell survival signals stimulated by growth factors, cytokines, and oncoproteins are initiated by phosphoinositide 3-kinase (PI3K)- and Akt-dependent signal transduction pathways. Oncogenic Ras, an upstream activator of Akt, requires NF-κB to initiate transformation, at least partially through the ability of NF-κB to suppress transformation-associated apoptosis. In this study, we show that oncogenic H-Ras requires PI3K and Akt to stimulate the transcriptional activity of NF-κB. Activated forms of H-Ras and MEKK stimulate signals that result in nuclear translocation and DNA binding of NF-κB as well as stimulation of the NF-κB transactivation potential. In contrast, activated PI3K or Akt stimulates NF-κB-dependent transcription by stimulating transactivation domain 1 of the p65 subunit rather than inducing NF-κB nuclear translocation via IκB degradation. Inhibition of IκB kinase (IKK), using an IKKβ dominant negative protein, demonstrated that activated Akt requires IKK to efficiently stimulate the transactivation domain of the p65 subunit of NF-κB. Inhibition of endogenous Akt activity sensitized cells to H-Ras(V12)-induced apoptosis, which was associated with a loss of NF-κB transcriptional activity. Finally, Akt-transformed cells were shown to require NF-κB to suppress the ability of etoposide to induce apoptosis. Our work demonstrates that, unlike activated Ras, which can stimulate parallel pathways to activate both DNA binding and the transcriptional activity of NF-κB, Akt stimulates NF-κB predominantly by upregulating of the transactivation potential of p65.