Differential effects of transforming growth factor on cell cycle regulatory molecules in human myeloid leukemia cells

In this report we have studied the mechanism by which Transforming Growth F actor beta (TGF beta) inhibits growth of human myeloid leukemia cell lines. TGF beta1 arrested cells in G1 phase and significantly downregulated the e xpression of cyclin D2, cyclin D3, cdk4, cyclin A, and cdk2. The downregula tion of the molecules resulted in approximately 50-90% decrease of the mole cule-dependent kinase activity, varying with each molecule. Although treatm ent of cells with TGF beta1 upregulated accumulation of p27(kip1) in both n ucleus and cytoplasm, the association of the p27(kip1) with cdk2, cyclin A, cyclin D2, cyclin D3, and cdk4 was markedly downregulated, suggesting that p27(kip1) is not responsible for the downregulation of the kinase activity . In contrast, TGF beta1 upregulated cyclin E-associated p27(kip1) with no effect on the expression of cyclin E. p27(kip1)-immunodepletion upregulated cyclin E-dependent kinase activity by more than 10-fold in TGF beta1-treat ed cells but not in proliferating cells; whereas immunodepletion of p27(kip 1) from cdk2-immunoprecipitates markedly downregulated cdk2 kinase activity in the lysates extracted from both proliferating and TGF beta -treated cel ls. Consistent with this observation, TGF beta1 and p27(kip1) antisense cDN A had a synergistic or additive inhibitory effect on cdk2 but not cyclin E- dependent kinase activity. Our data suggest that (1) TGF beta1-mediated gro wth inhibition is accomplished through multiple pathways and (2) p27(kip1) has opposing effects on cdk2 and cyclin E activity in response to TGF beta1 .