Our data demonstrate that miR-200a is frequently down-regulated in HCC tissues in comparison with the adjacent noncancerous hepatic tissues, a finding that is consistent with other reports.35, 36 Reduced levels of the histone H3 acetylation at the mir-200a promoter and increased levels of HDAC4 mRNA were also observed in HCCs. Because HDAC4 alone is enzymatically inactive, CCI-779 in vitro it may suppress the transcription of miR-200a and induce the histone H3 deacetylation at the mir-200a promoter by recruiting catalytically active HDACs into transcriptional

corepressor complexes.37 Therefore, further investigations are required to fully elucidate the nature of HDAC4-containing repressor complexes at the mir-200a promoter. In addition to miR-200a, the miR-200 family also includes miR-200b, miR-200c, miR-141, and miR-429, with miR-200b, miR-200a, and miR-429 being located on chromosome 1 and miR-200c and miR-141 being located on chromosome 12. Both clusters are encoded

as polycistronic transcripts. Our results show that HDAC4 regulates the expression of the miR-200b, miR-200a, miR-429 cluster, but does not regulate the other cluster. Other reports have demonstrated that HDAC inhibitors induce up-regulation of miR-200c,15, 17 and therefore we speculated that other HDACs may participate in the regulation of the miR-200c and miR-141 cluster. Interestingly, we observed that miR-200a, in turn, negatively regulated HDAC4 expression by directly targeting the complementary sites in the 3′-UTR selleck products of HDAC4 mRNA, generating a double negative feedback loop. Feedback loops are common in many genetic pathways involving miRNAs, and they seem to enhance the robustness of gene networks.38 A significant inverse correlation was also observed between HDAC4 and miR-200a in human HCC tissues. Copy number alterations of

miR-200a and HDAC4 were not found in HCC tissues compared with matched controls. Other proteins such as ZEB1,24 SIRT1,22 p53,39 and gata-binding factors23 can also regulate the expression of miR-200a. Therefore, there is an intricate mechanism regulating the expression of miR-200a and HDAC4 in HCCs. Further investigations are required to elucidate whether the up-regulation of HDAC4 or the down-regulation of miR-200a is the initial 上海皓元 factor of this loop in HCC. Recently, many studies have demonstrated that miRNAs may affect the epigenetic mechanism. For instance, miR-152 induced aberrant DNA methylation in HCC by targeting the DNA methyltransferase 1, as demonstrated in our previous study.40 Other miRNAs, such as miR-148a/b,41 miR-1,20 and miR-449a19, have also been reported to target epigenetic modifying enzymes and modulate the epigenetic transcriptional-regulatory process. However, whether miRNAs can affect the histone acetylation level in HCC remains largely unknown.