Studies On The Molecular Mechanisms Of INI1/hSNF5/BAF47 Involving In The Regulation Of Gene Transcription

Eukaryotic genome exists in the form of chromatin. Chromatin structure isinextricably linked to transcriptional regulation. The modification and remodeling of thechromatin structure is a precondition for the initiation and elongation of genetranscription. The most widely characterized chromatin-modifying complexes can beclassified into two major groups, one is the histone acetyltransferase (HAT) and histonedeacetylase (HDAC) complexes, which regulate the transcriptional activation orsuppression of genes by regulating the level of acetylation of the aminoterminaldomains of nucleosomal histones. Another is the ATP-dependent complexes, which usethe energy of ATP hydrolysis to locally disrupt or alter the association of histones withDNAThe hSWI/SNF ATP-dependent chromatin-remodeling complex plays a crucial rolein gene transcriptional regulation by remodeling chromatin, and through the way itfunctions in cell proliferation and differentiation, cellular antiviral activities andinhibition of tumor formation. INI1/hSNF5/BAF47 is a core component of thehSWI/SNF complex. It has been suggested that INI1/hSNF5/BAF47 contributes to theregulation of many genes. Howover, the mechanism by which INI1/hSNF5/BAF47exerts its regulator properties remains to be elucidated.The aim of this study was to clarify whether INI1/hSNF5/BAF47 involves in theregulation of CSF1 and c-fos gene transcription and to explore its molecularmechanisms. By applying a series of transient transfection and relative luciferaseactivity assays, semiquantitative RT-PCR, as well as Realtime RT-PCR, we investigatedwhether INI1/hSNF5/BAF47 functions in the regulation of CSF1 gene transcription inHeLa cells. The results showed that the overexpression of INI1/hSNF5/BAF47activated the CSF1 promoter and promoted endogenous CSF1 gene transcription. ThesiRNA targeting INI1/hSNF5/BAF47 (siINI1) strongly inhibited the activity of theCSF1 promoter and endogenous CSF1 gene transcription. We demonstrated that theintegrity of INI1/hSNF5/BAF47 is required for activating the CSF1 promoter, and theactivation of CSF1 promoter by INI1/hSNF5/BAF47 requires the formation of properchromatin and Z-DNA structure. In addition, ChIP experiment showed thatINI1/hSNF5/BAF47 is recruited to the region of the CSF1 promoter. Taken together,these results indicate that INI1/hSNF5/BAF47 is involved in activation of the CSF1promoter.On the other hand, we showed that the overexpression of INI1/hSNF5/BAF47repressed c-fos promoter activity and endogenous c-fos transcription in 293T cells, andthe siRNA targeting INI1/hSNF5/BAF47 (siINI1) reversed the inhibitory effect. Theanalysis of INI1/hSNF5/BAF47 truncations indicated that the two imperfect repeatsregions (Rpt1 and Rpt2) are involved in the repression of c-fos gene transcription.Histone deacetylation by histone deacetylases (HDACs) was required for the repressionof c-fos transcription by INI1/hSNF5/BAF47. In addition, the association andinteraction of HDAC4 with INI1/hSNF5/BAF47 is necessary for the repression of c-fostranscription, and HDAC and INI1/hSNF5/BAF47 functioned together to suppress c-fostranscription. ChIP experiments demonstrated that INI1/hSNF5/BAF47 could berecruited to the region of c-fos promoter to reduce histone acetylation. Altogether, thesedata show that INI1/hSNF5/BAF47 represses c-fos transcription via a histonedeacetylases (HDACs)-dependent manner.In summary, for the first time, data presented in this study indicated thatINI1/hSNF5/BAF47 could promote CSF1 gene transcription and repress c-fostranscription via a histone deacetylases (HDACs)-dependent manner. The molecularmechanisms of INI1/hSNF5/BAF47 as a dual functional transcriptional co-regulatorwere briefly exploited, and the data presented here have provided evidence for furtherinsight into the role and mechanisms of transcriptional regulation ofINI1/hSNF5/BAF47.