The Influence Of P53on The Transcription Regulation Of PA28γ Gene

Tumor suppressor p53exerts its role as a transcription factor. In normal cells, p53is present at low abundance. Under conditions of cellular stress such as DNA damage, hypoxia or oncogenic stimuli, p53accumulates in the cell and becomes activated. It then regulates the transcription of various target genes, leading cell cycle arrest, apoptosis or senescence.PA28γ (also known as REGy,11Sy, PSME3) is one of the activators of20S proteasome, can combine with20S proteasome and activate the ubiquitin-and ATP-independent proteolytic function of the20S proteasome. Additionally, PA28y can promote the MDM2-mediated mono-ubiquitylation and/or multi-ubiquitylation of p53, leading to its nuclear export and/or degradation. PA28y play important roles in various physiological or pathogenic processes such as DNA replication, cell proliferation, carcinogenesis and degenerative nerve diseases. However, the regulatory mechanism of PA28y gene expression is unknown. To elucidate the regulatory mechanism, we investigated the transcription start site, promoter and transcriptional regulation of PA28y gene.In this paper, by using RLM-RACE (RNA ligase-mediated rapid amplification of cDNA ends) method, we identified the transcription start site of PA28y gene. Luciferase assay showed that the sequence-193to+16is the basal promoter. Three p53response elements (i.e. P53binding sites) were found within the PA28y promoter utilizing a bioinformatics approach. Chromatin immunoprecipitation and biotinylated DNA affinity precipitation experiments confirmed that p53protein can bind to these response elements. Luciferase assay and Western blotting experiments demonstrated that over-expression of p53gene promotes the promoter activity and expression of PA28y, while silencing of p53gene inhibits its promoter activity and expression. Moreover, p53-stimulated transcription of PA28y can be suppressed by PA28y itself. The results show that P53and PA28y can form a negative feedback loop to maintain their balance within cells.These results not only elucidate primarily transcriptional regulation mechanism of PA28y, but also are helpful to enhance our understanding of p53function.