Histone deacetylase inhibitors upregulate p57Kip2 level by enhancing its expression through Sp1 transcription factor

Histone deacetylase inhibitors (HDACIs) represent a new class of targeted anticancer agents. Here, we evaluate the effects of butyrate (BuA) and other HDACIs on p57Kip2, a cyclin-dependent kinase inhibitor (cki). We observed that inhibitors of class I/II histone deacetylases (HDACs), but not of class III HDACs, induce a remarkable accumulation of p57Kip2 in several cells. The cki upregulation is associated with an increased gene expression that was not prevented by cycloheximide, indicating that HDACIs affect directly p57Kip2 transcription. The characterization of p57Kip2 promoter indicates that the first 165 bp are mostly involved in the BuA effects. Chromatin immunoprecipitation studies demonstrated that the BuA treatment causes the recruitment of Sp1 transcription factor. The Sp1 importance was confirmed by the reduction of BuA effects by mithramycin A (an Sp1 antagonist) and, most stringently, by Sp1 downregulation due to Sp1 siRNA. Moreover, both the treatments reduce the p57Kip2 transcription in untreated cells, suggesting that Sp1 is required for the constitutive cki expression. Studies employing plasmids containing parts of the 165 bp of p57Kip2 promoter indicate that the promoter region between −87 and −113 bp, which includes two putative Sp1 consensus sequences, plays a critical role in the response to HDACIs. Since this p57Kip2 promoter region also embraces the consensus sequence for the transcriptional repressor chicken ovalbumin upstream promoter transcription factor-interacting protein 2 (CTIP2), we evaluated whether this factor is involved into the BuA effect. When CTIP2 was downregulated by a specific siRNA, we observed the enhancement of BuA activity on p57Kip2 expression suggesting that CTIP2 might also be involved in HDACIs effects.