Influence Of Histone Acetyltransferase P300 On Regulation Of PTTG Gene Expression And Its Molecular Mechanisms

The remodeling of chromatin structure mediated by histone post-translationalmodifications plays a crucial role in the regulation of eukaryotic gene expression. Among thevarious types of histone post-translational modifications, the histone acetylation catalyzed byhistone acetyltransferases (HATs) and histone deacetylases (HDACs) play a critical role ingene regulation, and hence have been intensively studied. The reversibleacetylation/deacetylation modifications of lysine residues in core histone tails mediated bythese two enzymes modulate the initiation of transcription, thus lead to theactivation/suppression of gene expression. Transcriptional co-activators p300/CBP andP/CAF, which possess histone acetyltransferase activities, are involved in transcriptionalregulation of many genes through distinct mechanisms.The aim of this study was to clarify whether the reversible histoneacetylation/deacetylation modifications participate in the regulation of hPTTG genetranscription, and to explore its molecular mechanisms under these processes. By applying aseries of transient transfection and relative luciferase activity assays, as well assemi-quantitative RT-PCR and Western Blotting assays, we discovered that histoneacetyltransferases p300/CBP not only promoted the activities of the hPTTG promoter, butalso increased the expression of endogenous hPTTG mRNA and protein. Meanwhile, E1Aprotein repressed the promotive effect of p300 on hPTTG transcription. This results furthervalidated the effects of p300/CBP in promoting the hPTTG gene expression. Our results alsoindicated that p300/CBP and transcription factors NF-YA/YB synergistically activatedhPTTG reporter gene transcription. In addition, by using the HAT domain-deleted p300mutant, we showed that the histone acetyltransferase activity of p300/CBP was important inregulation of hPTTG gene expression. By using the chromatin immunoprecipitation assay(ChIP), we determined that p300/CBP were able to enhance the acetylation of the histone H3at the hPTTG promoter. Furthermore, our results demonstrated that another histoneacetyltransferase P/CAF could also activate hPTTG reporter gene expression. The histoneacetyltransferase activities of P/CAF and p300/CBP were both important in the activation ofhPTTG reporter gene expression. With regard to histone deacetylases, we tested theinfluences of the six human histone deacetylases (HDAC1～6) on hPTTG gene expression.The results showed that among these HDACs, HDAC3 and HDAC6 were able to repress theactivity of the hPTTG promoter/luciferase reporter gene.Data presented in this thesis demonstrated, for the first time, that the reversible histone acetylation/deacetylation modification was involved in the transcriptional regulation ofhPTTG gene. The molecular mechanisms of histone acetylation in hPTTG gene regulationwere briefly exploited. This study provides further insight into the mechanisms oftranscriptional regulation of hPTTG gene and the basis for studies of hPTTG-associateddiseases.