EPS15R, TASP1, and PRPF3 are novel disease candidate genes targeted by HNF4α splice variants in hepatocellular carcinomas

Background Aims: The orphan nuclear receptor HNF4 alpha is a member of the hepatic transcription factor network. This protein plays a pivotal role in liver development and hepatocellular differentiation. Nine splice variants have been identified, some of which are specifically regulated in disease. The role of HNF4a splice variants in hepatocellular carcinomas (HCC) is unknown. Here, we report an identification of novel candidate genes targeted by splice variants of HNF4a. Methods: We used chromatin immunoprecipitation followed by cloning and sequencing of DNA. Expression of HNF4a P1 and P2 promoter-driven isoforms and of genes targeted by HNF4a were analyzed by quantitative reverse-transcription polymerase chain reaction, Western blotting, electrophoretic mobility shift assay, and immunohistochemistry. Results: We observed a remarkable switch in gene and protein expression from P1 to P2 promoter-driven fetal isoforms of HNF4a in transgenic livers and HCCs of epidermal growth factor (EGF) over-expressing mice and in human HCCs. We further identified EGF-receptor substrate (EPS 15 R), related EPS15, the premessenger RNA processing factor 3 (PRPF3), and taspase 1 (TASP1) as novel HNF4a disease regulated genes with induced expression in mouse and in human HCCs. We suggest EPS15 and EPS15R mediated internalization of activated EGF receptor to result in receptor recycling as to reinforce the proliferative response to EGF. Regulation of the type 2 asparaginase TASP1 and of the splicing factor PRPF3 further documents a switch to fetal liver programs in HCC. Conclusions: We report induction of P2 promoter-driven HNF4a splice variants and regulation of disease candidate genes in EGF-induced mouse and human HCC.