The Cyclin-Dependent Kinase Inhibitor p21 Is a Crucial Target for Histone Deacetylase 1 as a Regulator of Cellular Proliferation

Abstract

Histone deacetylases (HDACs) are chromatin-modifying enzymes that are involved in the regulation of proliferation, differentiation and development. HDAC inhibitors induce cell cycle arrest, differentiation, or apoptosis in tumor cells and are therefore promising antitumor agents. Numerous genes were found to be deregulated upon HDAC inhibitor treatment; however, the relevant target enzymes are still unidentified. HDAC1 is required for mouse development and unrestricted proliferation of embryonic stem cells. We show here that HDAC1 reversibly regulates cellular proliferation and represses the cyclin-dependent kinase inhibitor p21 in embryonic stem cells. Disruption of the p21 gene rescues the proliferation phenotype of HDAC1^−/− embryonic stem cells but not the embryonic lethality of HDAC1^−/− mice. In the absence of HDAC1, mouse embryonic fibroblasts scarcely undergo spontaneous immortalization and display increased p21 expression. Chromatin immunoprecipitation assays demonstrate a direct regulation of the p21 gene by HDAC1 in mouse embryonic fibroblasts. Transformation with simian virus 40 large T antigen or ablation of p21 restores normal immortalization of primary HDAC1^−/− fibroblasts. Our data demonstrate that repression of the p21 gene is crucial for HDAC1-mediated control of proliferation and immortalization. HDAC1 might therefore be one of the relevant targets for HDAC inhibitors as anticancer drugs.

We thank E. Pineda for help with the proliferation assays and N. Foeger for helpful discussions. We are grateful to E. F. Wagner for kindly providing the p21-deficient mice, D. J. McCance for the HPV16 E6/E7 constructs, and I. Mudrak for the pBABE SV40 LT vector.

C.S. was supported by the Austrian Science Fund (FWF P16443 and P18746) and the Herzfelder Family Foundation and the GEN-AU project Epigenetic Plasticity of the Mammalian Genome (Federal Ministry for Education, Science, and Culture), and S.C. was supported by the Associazione Italiana Ricerca sul Cancro. R.G., G.Z., and S.L. were fellows of the Vienna Biocenter PhD program (Austrian Science Fund), and R.B. was a fellow of the Ernst Schering Foundation.