p21-mediated the down-regulation of genes involved in cell cycle.

<p>A.The expression of p21 was induced in Kp21-4 cells by 75 µM ZnSO₄ and 3, 6 and 12 h later, total RNA was prepared and expression of the indicated genes was determined by RT-qPCR. In some cases an alternative name is given into brackets. Cyc., cyclin. The values are means ±S.E.M. from two independent experiments and two determinations for each RNA. B. Kp21-4 cells were treated for 6 h with 75 µM ZnSO₄ to induce p21. Chromatin immunoprecipitation was carried out with anti-histone H3 and anti-acetylated-histone H3 antibodies and (as specificity control) rabbit IgG. The DNA in the immunoprecipitated chromatin was measured by quantitative PCR. The amplicons encompass the transcription start site of the indicated genes. A regulatory sequence of the promoter of rDNA was used as a control. The results are expressed as the ratio of DNA enrichment in chromatin immunoprecipitated with anti-H3 versus acetylated-H3 (“Ac-H3”) and normalized to the values obtained in uninduced cells. The values are the means ±S.E.M of two independent ChIP experiments with two PCR determinations each.