The Molecular Study Of Nuclear Actin Involving In The Regulation Of Gene Transcription

Actin is a highly conserved protein which is known to act on many crucial evens not only in the cytoplasm but also in the nuclei of eukaryotic cells. The studies on the structure and function have indicated that nuclear actin may take part in the process and transport of mRNA, the chromotin contraction and chromosome formation, the chromatin remodeling, the regulation of gene transcription and the cell senescence. Nuclear actin was tentatively implicated in transcription by earlier experiments showing the injection of anti-actin antibodies or actin-binding proteins into amphibian oocyte nuclei. But until today, there is no report for the nuclear actin directly participate the regulation of gene transcription.Recently, that actin was found to be a component of the human chromatin remodeling complex (BAF) interests the researchers. It is necessary for facilitating transcription to disrupt nucleosome structure by the ATP-dependent nucleosome remodeling complexes. Biochemical analysis indicates that actin is tightly bound to BRG1 during gene activation processes in the BAF complex, and the actin subunit is required for optimal ATPase activity of BRG1. So nuclear actin is likely to play a role in transcription, but the precise mechanisms are still to be revealedIn this study, we overexpressed actin in nuclei using a transient transfection method to investigate whether it directly takes part in the transcription of CSF-1 and c-fos. The dual-luciferase assay and RT-PCR results showed that nuclear actin augments CSF-1 while represses c-fos gene transcription, implying that nuclear actin plays an complex role on the regulation of gene transcription. And both of the regulations require the formation of chromatin and Z-DNA structure. We built three actin mutants, (the deletion of ammo- terminus, the deletion of carboxy- terminus and the deletion of carboxy- terminus with ATPase binding site), and found that themutants have lower capacity for regulating and the deletion of carboxy-terminus with ATPase binding site has nearly lost the capacity of regulation. Furthermore, the overexpressed actin can increase the nuclear ATPase activity while the mutants can not. The reduction of increasing nuclear ATPase activity is correspond to that of regulating gene transcrption, indicating that the activity of ATPase is important for actin in the regulation of gene transcription.Results presented in this paper has prove that nuclear actin takes part in regulating gene transcription and these original results will be helpful for understanding the mechanism of nuclear actin playing roles in gene transcripition.