Differences in Yes-associated protein and mRNA levels in regenerating liver and hepatocellular carcinoma.

Yes-associated protein (YAP) has been identified as an oncoprotein that regulates organ size by modulating proliferative and apoptotic activities. The aim of this study was to measure YAP gene expression and protein levels during rat liver regeneration and in liver cancer, and to explore possible correlations between YAP levels and cancer cell proliferation following partial hepatectomy. We examined YAP expression in rat regenerating liver using real-time PCR, Western blotting and immunohistochemical methods. YAP mRNA and protein levels were measured in human hepatocellular carcinoma. The results demonstrated that YAP protein levels were markedly increased in the regenerating liver (2.5-3 times), while YAP mRNA levels decreased slightly (1.47-2.17 times) (P=0.017). YAP mRNA and protein levels were both higher in hepatocellular carcinoma than in para-cancerous tissue. In conclusion, liver regeneration alone elevated YAP protein levels without elevating YAP mRNA levels. YAP mRNA and protein levels were both elevated in liver cancer cells.