Repression of NF-kappa B impairs HeLa cell proliferation by functional interference with cell cycle checkpoint regulators

NF-kappa B is an inducible transcription factor, which is regulated by inte raction with inhibitory I kappa B proteins. Previous studies linked the act ivity of NF-kappa B to the proliferative state of the cell, Here we have an alysed the function of NF-kappa B in the cell cycle. Inhibition of NF-kappa B in HeLa cells by stable overexpression of a transdominant negative I kap pa B-alpha protein reduced cell growth. A kinetic analysis of the cell cycl e revealed a retarded G1/S transition. The I kappa B-alpha overexpressing c ell clones show ed a decreased percentage of cells in the S phase and an im paired incorporation of bromodeoxyuridine (BrdU), The amounts of cyclins A, B1, D1, D3, and E were unchanged, but the G1-specific proteins cyclin D2 a nd cdk2 were strongly elevated in the I kappa B-alpha overexpressing cell c lones. These cell clones also displayed an increase in cyclin D1-dependent kinase activity, pointing to a cell ca de arrest at the late G1 phase. I ka ppa B-alpha overexpression crosstalked to cell cycle checkpoints via a redu ction of transcription factor p53 and elevation of p21(WAF). Surprisingly, the I kappa B-alpha overexpressing cells showed an enrichment of c-Myc in t he nucleoli, although the total amount of c-Myc protein was unchanged. Thes e experiments identify an important contribution of the NF-kappa B/I kappa B system for the growth of HeLa cells.