Two mRNA isoforms of homeobox transcription factor Prox1 in human liver cirrhosis, in hepatocellular and in cholangiocellular carcinoma

Aims: Prospero-related homeobox 1 (Prox1) transcription factor is a hepatocellular differentiation marker, and is absent from biliary epithelial cells. In this study Prox1-gene-expression was investigated at mRNA and at protein levels in normal human liver tissue, in histologically normal liver surrounding primary liver tumours, in cirrhotic human liver samples, in hepatocellular (HCC) and cholangiocellular carcinomas (CCC), and in HCC- and biliary adenocarcinoma- cell lines.

Methods: mRNA and protein expression of Prox1 was analysed by PCR methods using exon-specific primers, by northern blot analysis, by western blot and immunohistochemical methods.

Results: Prox1 mRNA expression was detected in all liver samples, and in HCC cell lines. The average amounts of Prox1-specific-transcripts contained in total RNA of histologically normal liver surrounding primary liver tumours, of cirrhotic liver samples and of HCC/CCC were lower compared to normal liver tissue. In contrast, in several HCC samples the expression was higher than in normal liver. In grade 3 HCC high Prox1, high Hepatocyte Nuclear Factor 4-Alpha steady-state-levels and low albumin levels were found. Two mRNA isoforms of Prox1 were detected in human liver samples, determining the same single protein translate. The dominance of the longer isoform was found in more HCC samples and cell lines, and the short isoform was more frequent in the CCC samples. In contrast to the normal bile duct epithelial cells, cells with bile duct morphology in cirrhotic liver samples and tumor cells of intrahepatic cholangiocellular carcinomas were Prox1+.

Conclusions: The regulation of Prox1 might be changed under pathological conditions, which is identified by neoexpression in cells with bile duct markers, and by alteration of the quantitative relation of mRNA isoforms.