The Regulatory Mechanisms Of Histone H3 Acetylation On Hsp70 Gene Transcription

Histone acetylation at gene's promoter and coding region correlates with transcriptional activation. However, the detailed mechanisms by which histone acetylation regulates hsp genes are still unclear. This study intended to elucidate the involvement of histone acetylation in transcriptional regulation of hsp70 gene in yeast. Our results indicated that histone acetylation was required for both ssa3 and ssa4 transcription activation, regardless of the occurrence of nucleosome disassembly. Histone acetyltransferases (HATs) Gcn5 and Elp3 affected hsp70 gene transcription and their HAT activity was required for their function of regulating transcription. The transcriptional regulatory function of Gcn5 and Elp3 was direct because they could be recruited to hsp70 gene. The two HATs modulated the transcription of ssa3 and ssa4 genes through affecting the acetylation status of histone H3 and they could also affect the loss of histone-DNA contacts in ssa3 gene. Although the two HATs had an overlapping function of acetylating histone H3, they affected hsp70 gene transcription through different ways. Namely, Gcn5 was present at gene's promoter and the recruitment of Gcn5 was Swi/Snf-dependent, it was required for HSF recruitment and affected RNAPII recruitment; whereas Elp3 exerted its roles mainly through affecting RNAPII elongation that was dependent on histone methylation by Set2. Our data also showed that the mRNA level of hsp70 gene was increased in the cells treated with TSA or the cells with the deletion of histone deacetylases (HDACs), indicating that HDACs were involved in the transcription of hsp70 gene. One of the HDACs, Rpd3, could be recruited to the coding region of hsp70 gene and it deacetylated histone H3 to inhibite the transcription. These data provide insights into the effects of Gcn5 and Elp3 in hsp70 gene transcription and underscore the importance of the histone acetylation for transcriptional initiation and elongation in hsp genes.The human Elongator complex is remarkably similar to its yeast counterpart in several aspects. In a previous study, we analyzed the functions of the hElp3 subunit of the human Elongator by using an in vivo yeast complementation system. However, direct evidence for hElp3 functions in regulating gene expression in human cells had not been obtained. In this study, we used the help3 antisense oligonucleotide inhibitors to knock down the help3 gene expression to investigate its function in human 293T cells. The results showed that specific reduction of help3 mRNA and protein caused a significant suppression of hsp70-2 gene expression, and this was accompanied by histone H3 hypoacetylation and a decreased RNAPII density at hsp70-2 gene. Moreover, the data also demonstrated that hElp3 exerted the transcriptional regulatory function directly through its presence at the hsp70-2 gene. Data presented in this report provide further insight into and direct evidence of the functions of hElp3 in hsp70-2 gene transcriptional elongation in human cells.