Studies On The Molecular Mechanism Of Nuclear Actin And Actin-related Protein, BAF53, In The Regulation Of P53-mediated P21 Gene Transcription

Actin and actin-binding factors have been implicated in nuclear processes, such as chromatin remodelling, mRNA processing and export, and transcription. Various lines of evidence suggest that nuclear actin is required for efficient transcription by RNA polymerases I, II and III. Nuclear actin seems to function in several steps of the transcription process, particularly during initiation complex assembly and transcription elongation. However, the mechanisms involved are not understood, and so far, there is no evidence that the interaction between transcriptional regulator and actin may function in transcription.The P53 tumor suppressor protein is a key regulator of cellular functions including responses to numerous stress signals, and triggers cell cycle arrest or apoptosis. Because of the short half-life of the P53 protein, P53 activity is maintained at low levels in the absence of stress. Upon exposure to a variety of stress conditions, the stability of P53 increases and the protein accumulates in the nucleus, where it is activated as a transcription factor. The stabilization and activation of P53 is largely mediated through posttranslational modifications, such as phosphorylation and acetylation, as well as by protein-protein interactions.Here, we demonstrated that nuclear actin critically interacts with P53 in vivo and in vitro. Dual luciferase assays showed that the interaction between the two proteins results in the repression of P53-mediated p21, mdm-2 and pG13 genes transcription. We employed EMSA and ChIP assays to demonstrate thatβ-actin is in the P53-mediated transcriptional regulation complex dependent on P53 and inhibits the binding of P53 to p21 promoter and decreases actyl-H3 or H4 level. Finally, we demonstrated that overexpression of nuclear actin has no effect on the posttranslational modifications of P53, however, treatment with CD to P53+/+ cells can activate the transactivation of P53.BAF53, one actin-related protein, has been shown to be essential for cell survival in human cells and play roles in P53-dependent gene transcription, but the information concerned in the process is still limited. In this study, we showed that BAF53 is associated with P53 both in vivo and in vitro, and BAF53 represses P53-dependent p21 gene transcription by interaction with P53. By chromatin immunoprecipitation, dual-luciferase and western-blotting assays, we demonstrated that BAF53 can impair the binding ability of P53 through existing in the PREs dependent on P53, which might be due to the decrease of acetylation of P53-Lys382. Furthermore, we showed that BAF53 represses p21 promoter activity in a BRG1 or P53-independent manner.Our study towards the elucidation of the interaction between actin/BAF53 and P53 may provide valuable information for further insights into the mechanisms of nuclear actin/BAF53 in transcriptional regulation factor transcription, and provide essential basis for future studies on how the nuclear actin/BAF53 control the activity of transcriptional regulation factors.