Gankyrin Promotes Tumor-Suppressor Protein Degradation to Drive Hepatocyte Proliferation

Abstract

Background & AimsUncontrolled liver proliferation is a key characteristic of liver cancer; however, the mechanisms by which this occurs are not well understood. Elucidation of these mechanisms is necessary for the development of better therapy. The oncogene Gankyrin (Gank) is overexpressed in both hepatocellular carcinoma and hepatoblastoma. The aim of this work was to determine the role of Gank in liver proliferation and elucidate the mechanism by which Gank promotes liver proliferation.MethodsWe generated Gank liver-specific knock-out (GLKO) mice and examined liver biology and proliferation after surgical resection and liver injury.ResultsGlobal profiling of gene expression in GLKO mice showed significant changes in pathways involved in liver cancer and proliferation. Investigations of liver proliferation after partial hepatectomy and CCl4 treatment showed that GLKO mice have dramatically inhibited proliferation of hepatocytes at early stages after surgery and injury. In control LoxP mice, liver proliferation was characterized by Gank-mediated reduction of tumor-suppressor proteins (TSPs). The failure of GLKO hepatocytes to proliferate is associated with a lack of down-regulation of these proteins. Surprisingly, we found that hepatic progenitor cells of GLKO mice start proliferation at later stages and restore the original size of the liver at 14 days after partial hepatectomy. To examine the proliferative activities of Gank in cancer cells, we used a small molecule, cjoc42, to inhibit interactions of Gank with the 26S proteasome. These studies showed that Gank triggers degradation of TSPs and that cjoc42-mediated inhibition of Gank increases levels of TSPs and inhibits proliferation of cancer cells.ConclusionsThese studies show that Gank promotes hepatocyte proliferation by elimination of TSPs. This work provides background for the development of Gank-mediated therapy for the treatment of liver cancer. RNA sequencing data can be accessed in the NCBI Gene Expression Omnibus: GSE104395.

Liver Proliferation Is an Essential Driver of Fibrosis in Mouse Models of Nonalcoholic Fatty Liver Disease

“…Our previous work found that the HFD protocol initiates liver proliferation at very early stages . Because livers of GLKO mice have reduced capabilities to proliferate, we used this animal model to examine the role of proliferation in NAFLD and show a strategy for these studies in Fig. A.…”

“…Liver‐specific GLKO mice were generated by crossing Cre‐Alb mice with LoxP‐Gank mice. These GLKO mice have been characterized . CUGBP1‐S302A KI mice have also been described.…”

“…Because Gank promotes liver proliferation and CUGBP1 promotes steatosis, we generated mice with a liver‐specific deletion of Gank (Gank liver‐specific knockout [GLKO] mice) and CUGBP1‐S302A knockin (KI) mice, which have reduced levels of CUGBP1 and increased proliferation . Using these animal models, we examined the role of proliferation and steatosis in HFD‐mediated NAFLD.…”

Small‐Molecule Inhibitors of the Proteasome's Regulatory Particle

“…Cjoc42 was also observed to enhance p53 levels in vitro. Further studies showed that cell proliferation in liver cancer cell lines was halted through cjoc42 inhibition, and in vivo characterization of this small‐molecule compound is ongoing …”

Tumor Suppressor Down-Regulation Promotes Hepatocyte Proliferation: A New GANKster on the Block

“…Here, D’Souza et al 3 treated human and mouse liver cancer cells, Huh6 and Hepa1c1c7, with cjoc42. CUGBP1, C/EBPα, p53, and HNF4α levels were increased significantly by cjoc42 treatment.…”