p65 Negatively regulates transcription of the cyclin E gene.

ABSTRACT

NF-kappaB family members play a pivotal role in many cellular and organismal functions, including the cell cycle. As an activator of cyclin D1 and p21(Waf1) genes, NF-kappaB has been regarded as a critical modulator of cell cycle. To study the involvement of NF-kappaB in G(1)/S phase regulation, the levels of selected transcriptional regulators were monitored following overexpression of NF-kappaB or its physiological induction by tumor necrosis factor-alpha. Cyclin E gene was identified as a major transcriptional target of NF-kappaB. Recruitment of NF-kappaB to the cyclin E promoter was correlated with the transrepression of cyclin E gene. Ligation-mediated PCR and micrococcal nuclease-Southern assays suggested the nucleosomal nature of this region while chromatin immunoprecipitation analysis confirmed the exchange of cofactors following tumor necrosis factor-alpha treatment or release from serum starvation. There was a progressive reduction in cyclin E transcription along with the accumulation of catalytically inactive cyclin E-cdk2 complexes and arrest of cells in G(1)/S-phase. Thus, our study clearly establishes NF-kappaB as a negative regulator of cell cycle through transcriptional repression of cyclin E.