p53 may positively regulate hepatocyte proliferation in rats

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Abstract
P53, known as a tumor suppressor gene, is a transcription factor that regulates various cellular functions. Recently, several growth factor gene promoters, including that of transforming growth factor α (TGF-α), were shown to be direct targets of p53-mediated transcription. Hepatic p53 mRNA is up-regulated during liver regeneration in rats. The aim of this study is to examine the role of p53 in hepatocyte proliferation. p53 protein levels were examined in rat hepatocytes cultured in the medium containing hepatocyte growth factor (HGF). p53 levels began to increase after 6 hours of incubation, reached a maximum at 18 hours, and decreased thereafter. DNA synthesis increased at 12 hours and peaked at 30 hours. When hepatocytes were incubated with p53 antisense oligonucleotide in addition to HGF, increases of p53 and TGF-α levels were suppressed, and DNA synthesis was reduced. The increases of TGF-α levels and DNA synthesis were also suppressed by a chemical inhibitor of p53, pifithrin-α. In rats after two-thirds partial hepatectomy, hepatic p53 increased and reached maximal levels around 16 hours when hepatic HGF levels have been shown to reach a maximum followed by an increase in hepatic TGF-α levels or hepatocyte proliferation. In contrast, sham-operated rats showed minor elevations of hepatic p53 levels. In conclusion, p53 production is stimulated by HGF and may contribute to the proliferation of rat hepatocytes. Considering previous findings indicating the importance of endogenous TGF-α for the proliferation of hepatocytes stimulated by HGF, TGF-α might play a role in HGF-p53 mediated hepatocyte proliferation.