p21Cip1 gene expression is modulated by Egr1 -: A novel regulatory mechanism involved in the resveratrol antiproliferative effect

Epidemiological observations indicate that resveratrol, a natural antioxidant stilbene, exerts cardioprotective and chemopreventive effects. Moreover, the molecule induces in vitro cell growth inhibition and differentiation. Using human erythroleukemic K562 cells as model system, we demonstrated that resveratrol induces a remarkable gamma-globin synthesis, the erythroid differentiation being linked to impairment of cell proliferation, increased p21(Cip1) expression and inhibition of cdk2 activity. The up-regulation of p21(Cip1) transcription is prevented by cycloheximide, indicating the requirement of intermediate protein(s), which, in turn, regulate gene expression. The quantitative analysis of some transcription factors involved in the erythroid lineage, namely GATA-1, GATA-2, and Egr1, indicated that resveratrol selectively up-regulates Egr1 by an Erk1/2-dependent mechanism. The presence of an Egr1 consensus sequence in the p21(Cip1) promoter suggested the hypothesis that this transcription factor directly regulates the expression of the cdk inhibitor. Transfection studies with deleted gene promoter constructs, as well as EMSA, pull-down, and chromatin immunoprecipitation experiments substantiated this view, demonstrating that Egr1 binds in vitro and in vivo to the identified consensus sequence of the p21(Cip1) promoter. Moreover, an Egr1 phosphorothioate antisense hinders p21(Cip1) accumulation and the antiproliferative effects of resveratrol. In conclusion, this is the first demonstration that Egr1 controls p21(Cip1) expression by directly interacting with a specific sequence on its gene promoter. The identified regulatory mechanism also contributes to the clarification of the complex chemopreventive and antiproliferative properties of resveratrol.