Identification of Pirh2E and Pirh2F,two additional novel isoforms of Pirh2 ubiquitin ligase from human hepatocellular liver carcinoma cell line

Abstract

Hepatocellular carcinoma (HCC) is one of the most common malignancies in the world, especially in China. Recent researches have shown that E3 ubiquitin ligases Pirh2 (p53-induced RING-H2 protein) is highly expressed in HCC cell lines and is correlated with poor survival and prognostic in patients with HCC; however, the function of Pirh2 in the genesis and the development of HCC remains unclear. Pirh2, a member of the RING finger family, can target p53 for degradation and thereby repress a diverse group of biological activities and involved in many signalling pathways related to the genesis and evolution of cancer. Up to now, four Pirh2 variants had been reported and named Pirh2A, Pirh2B, Pirh2C and Pirh2D. Here we report the existence of two additional isoforms from human hepatocellular liver carcinoma cell line (HepG2 cell) and named as Pirh2E and Pirh2F. Compared to full-length Pirh2A, Pirh2E lacks amino acids 235–261, while Pirh2F is missing C-terminal amino acids 227–261 and both isoforms harbor the RING domain; therefore, we speculate that ubiquitin ligase activity maybe reversed by them. Further studies are required to determine whether Pirh2E and Pirh2F functions in a manner similar to Pirh2A.