Investigation of the Role of Glypican 3 in Liver Regeneration and Hepatocyte Proliferation

Abstract

Glypicans are heparan sulfate proteoglycans (HSPGs) that are bound to the cell surface through a glycosylphosphatidylinositol (GPI) anchor. Six members of glypican family have been identified in mammals. Our study focused on glypican 3 (GPC3) which is mutated in the Simpson‐Golabi‐Behmel (SGB) syndrome, an X‐linked disorder characterized by pre‐ and postnatal overgrowth. GPC3 is reported to be over‐expressed in human hepatocellular carcinoma (HCC). Whether GPC3 is involved in liver regeneration and hepatocyte proliferation is still unknown. We investigated its role in regenerative liver using the 2/3rd partial hepatectomy (PHx) model in rats. Results showed that GPC3 is up‐regulated in liver starting from day 2 after PHx. GPC3 is also up‐regulated from day 7 in primary hepatocyte cultures, when the process of proliferation slows down. We hypothesize that GPC3 negatively regulate liver regeneration. In vitro study showed that hepatocyte growth is promoted at the end of proliferation when GPC3 is blocked by Morpholino oligos. Further study will include GPC3 transgenic mice screening and study, and in vivo function and growth study. To investigate the signaling pathway involving GPC3, yeast two hybrid assay was performed. The assay results revealed that GPC3 might interact with CD81, a member of tetraspanin and reported to involve in HCV infection and cell proliferation. Our study showed that CD81 level increased from day 2 after PHx, corresponding to the changes of GPC3. Immunofluorescence showed that CD81 and GPC3 co‐localize at day 2 and day 6 after PHx. Co‐immunoprecipitation also showed that CD81 protein co‐precipitates with GPC3. So we hypothesize that GPC3 may be a negative regulator in liver regeneration and hepatocyte proliferation, and may interact with CD81.