ACTIVATION OF WNT/beta-CATENIN SIGNALING PATHWAY IN THE LIVER OF TRANSGENIC MICE OVEREXPRESSING GROWTH HORMONE

MIQUET JG; MARTINEZ C; GONZALEZ L; DIAZ ME; ZOTTA E; BARTKE A; TURYN D; SOTELO AI

Berlin

Congreso; The International Liver Congress 2011; 2011

European Society for the study of the Liver

BACKGROUND AND Aims: Transgenic mice overexpressing growth hormone (GH) exhibit hepatomegaly due to hypertrophy and hyperplasia. Throughout lifespan, transgenic mice present high levels of hepatocellular replication and at advanced ages develop liver tumors, mainly hepatocellular carcinoma (HCC). Wnt/b-catenin signaling regulates cell proliferation, apoptosis and differentiation, and is believed to play a role in carcinogenesis. A high percentage of human HCC show high levels of â-catenin, usually located at the cytoplasm or nucleus rather than at the plasma membrane. Control of â-catenin stability is regulated by GSK-3b, which phosphorylates b-catenin, promoting its degradation. The objective of this work was to evaluate if Wnt/b-catenin signaling is dysregulated in the liver of GH-transgenic mice to assess its possible association with the liver pathology observed in these animals.Methods: Young adult transgenic mice overexpressing GH, which present preneoplastic liver pathology, were studied; non-transgenic siblings were used as controls. Liver samples were subjected to qRT-PCR, Western-blotting and immunohistochemistry to evaluate gene expression, protein content and cellular localization of the mediators under study. Results: b-catenin protein content was 2-fold increased in the liver of GH-overexpressing mice, although its mRNA levels were lower compared to normal siblings (P< 0.002). Immunohistochemical analyses revealed that b-catenin was mainly located in the nucleus or in the cytoplasm in transgenic mice. Transgenic mice presented GSK-3b mRNA levels similar to those observed for control mice, but its protein content was elevated, with a parallel increase in its phosphorylation levels at serine-9, which renders GSK-3b inactive (P< 0.001). The expression of the b-catenin target genes cyclin D1, c-myc and c-jun was increased in transgenic mice liver (P< 0.005). Conclusions: Wnt/b-catenin signaling is dysregulated in the liver of GH-transgenic mice. The increased protein levels and nuclear/cytoplasmic localization of â-catenin, without an increase in its mRNA levels, suggest that the upregulation of b-catenin may be associated with increased protein stability, in accordance with the overexpression of inactive GSK-3b found in these mice. Elevated levels of inactive GSK-3b were previously reported in HCC harboring b-catenin accumulation. We propose aberrant Wnt/b-catenin signaling may be involved in the preneoplastic liver pathology observed in GH-overexpressing transgenic mice.