Regucalcin/SMP‐30 is regulated by β‐catenin in the liver

Abstract

Our laboratory has identified regucalcin as a novel target of β‐catenin in the liver. We show that regucalcin mRNA levels were downregulated in β‐catenin conditional knockout mice (KO), as compared to their wild‐type (WT) controls. Immunohistochemistry (IHC) and Western blotting (WB) confirms that regucalcin protein expression is also decreased in these mice. Analysis of HepG2 and Hep3B hepatoma cell lines demonstrates that HepG2 (active β‐catenin) have higher levels of regucalcin as compared to Hep3B (normal β‐catenin). Further, we find a correlation between the presence of β‐catenin in the nucleus or cytoplasm of human hepatocellular carcinomas (HCC) and an increase in regucalcin by IHC and WB. An analysis of the promoter region of the mouse regucalcin gene reveals at least 11 putative Tcf‐binding sites. Use of multiple deletion mutants identifies the specific sites, which might be regulating regucalcin expression by β–catenin. Finally, we examine the regucalcin expression in methionine‐choline‐deficient (MCD) diet‐induced steatohepatitis. IHC identifies an increase in regucalcin levels in MCD‐fed mice, as compared to control diet‐fed mice. In conclusion, regucalcin is a novel target of β‐catenin levels in liver and may have a biological function in liver diseases such as steatohepatitis and HCC.