Adenosine Promotes GATA-2-Regulated p53 Gene Transcription to Induce HepG2 Cell Apoptosis

Abstract

Background/Aims: In our earlier study, adenosine induced apoptosis in HepG2 human hepatoma cells by tuning of apoptosis-mediator gene transcription. The present study aimed at understanding the regulatory mechanism underlying the apoptosis-mediator gene transcription under the control of adenosine. Methods: For HepG2 cells with and without knocking-down p53 or GATA-2, cell viability, mitochondrial membrane potentials, caspase activity, and transcriptional activity were monitored, and Western blotting, RT-PCR, electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP) assay were carried out. Results: Extracellular adenosine upregulated expression of the p53 mRNA and protein in HepG2 human hepatoma cells. Adenosine induced apoptosis, disrupted mitochondrial membrane potentials, and activated caspase-3, -8 and -9 in HepG2 cells, and those effects were inhibited by silencing the p53-targetd gene. In the assay of transcriptional activity using full-length p53 gene promoter and 5’ deletion mutants combined with the luciferase reporter vector, adenosine enhanced transcriptional activity for full-length p53 gene promoter, that was prevented by deleting from -240 to -146 bp on the promoter. In the EMSA using a ³²P-labeled DNA probe to detect binding to the putative GATA-2 biding site on the p53 gene promoter, adenosine produced ³²P-positive signals in nuclear extracts from HepG2 cells. In the Western blot analysis, adenosine increased presence of GATA-2 in nuclear extracts. In the ChIP assay, adenosine increased PCR products for the p53 gene promoter in chromosomal extracts from HepG2 cells, immunoprecipitated using an anti-GATA-2 antibody. Adenosine-induced upregulation of the p53 mRNA expression was suppressed by knocking-down GATA-2. Conclusion: The results of the present study show that p53 is a transcriptional target of GATA-2 and that adenosine upregulates GATA-2-regulated p53 expression, thereby activating caspase-3, -8, and -9 to induce HepG2 cell apoptosis.