Suppression of PTEN Expression by NF-κB Prevents Apoptosis

Abstract

NF-κB is a heterodimeric transcription activator consisting of the DNA binding subunit p50 and the transactivation subunit p65/RelA. NF-κB prevents cell death caused by tumor necrosis factor (TNF) and other genotoxic insults by directly inducing antiapoptotic target genes. We report here that the tumor suppressor PTEN, which functions as a negative regulator of phosphatidylinositol (PI)-3 kinase/Akt-mediated cell survival pathway, is down regulated by p65 but not by p50. Moreover, a subset of human lung or thyroid cancer cells expressing high levels of endogenous p65 showed decreased expression of PTEN that could be rescued by specific inhibition of the NF-κB pathway with IκB overexpression as well as with small interfering RNA directed against p65. Importantly, TNF, a potent inducer of NF-κB activity, suppressed PTEN gene expression in IKKβ^+/+ cells but not in IKKβ^−/− cells, which are deficient in the NF-κB activation pathway. These findings indicated that NF-κB activation was necessary and sufficient for inhibition of PTEN expression. The promoter, RNA, and protein levels of PTEN are down-regulated by NF-κB. The mechanism underlying suppression of PTEN expression by NF-κB was independent of p65 DNA binding or transcription function and involved sequestration of limiting pools of transcriptional coactivators CBP/p300 by p65. Restoration of PTEN expression inhibited NF-κB transcriptional activity and augmented TNF-induced apoptosis, indicating a negative regulatory loop involving PTEN and NF-κB. PTEN is, thus, a novel target whose suppression is critical for antiapoptosis by NF-κB.