The Role of CREG1 as a Master Regulator of Liver Function

The liver is known as the chemical factory of the body because it performs a wide range of biochemical functions required for life. Since the liver has such an important role in regulation of normal physiological processes, liver diseases cause a high rate of morbidity and mortality. Therefore, understanding the mechanisms of liver development will shed light on the causes of liver disease. In this study, a cell line model that utilizes rat hepatoma cells (Fg14) and hepatoma variant cells (H11) was used to identify master regulators of liver gene expression. Whole genome expression studies identified the gene CREG1 (Cellular repressor of E1A-stimulated genes-1) as a potential master regulator of liver gene expression. The ability of CREG1 to restore liver gene expression in the H11 variant cell line was determined by forced overexpression of this gene via transfection of H11 cells with a CREG1 expression vector. Rescue of the liver-specific gene SERPINA1 (which produces a protein that plays a role in regulatory functions in the inflammatory, complement, coagulation, and fibrinolytic cascades and whose expression is used as a marker for liver function) was tested using RT-PCR. Results show that SERPINA1 gene expression was fully rescued. Importantly, genes encoding liver-specific transcription factors were also rescued, including Hepatocyte Nuclear Factors HNF1α and HNF4. In subsequent experiments, it was found that CREG1 expression also activated several additional genes located in the SERPIN locus which have been suggested to be controlled by the SERPIN Locus Control Region (LCR). This was surprising considering most serpin genes have not been shown to be activated by the HNF4/HNF1 pathway. Because HNF6 (Onecut) has been previously shown to bind to the serpin LCR, we measured its expression and found it to be rescued as well with CREG1 overexpression. We next asked whether HNF6 alone could rescue serpin locus gene expression by transfecting H11 cells with an HNF6 expression vector. The H11-HNF6 cells showed rescue of many of the serpin locus genes, although only partial rescue was observed. Likewise, a partial rescue of HNF4 and HNF1 genes was observed in the H11-HNF6 cells, but not to the level observed in the H11-CREG1 cells. We conclude that CREG1 can fully rescue expression of several liver-specific genes, including transactivation genes, suggesting its role as a master regulator of liver function. CREG1 action appears to act at least partially through HNF6 gene activation as well as through activation of the HNF4/HNF1 pathway, both of which act to increase expression of the serpin locus through both LCR activation (through HNF6) and individual serpin gene activation (through HNF4/HNF1)