Role of Glycanation and Convertase Maturation of Soluble Glypican-3 in Inhibiting Proliferation of Hepatocellular Carcinoma Cells.

Glypican 3 (GPC3) is a complex heparan sulfate proteoglycan associated with the outer surface of the plasma membrane by a glycosylphosphatidylinositol (GPI) anchor. It is also N-glycosylated and processed by a furin-like convertase. GPC3 has numerous biological functions. Although GPC3 is undetectable in normal liver tissue, it is abnormally and highly overexpressed in hepatocellular carcinoma (HCC). Interestingly, proliferation of HCC cells such as HepG2 and HuH7 is inhibited when they express a soluble form of GPC3 after lentiviral transduction. To obtain more insight into the role of some of its post-translational modifications, we designed a mutant GPC3, sGPC3m, without its GPI anchor, convertase cleavage site, and glycosaminoglycan chains. The highly pure sGPC3m protein strongly inhibited HuH7 and HepG2 cell proliferation in vitro and induced a significant increase in their cell doubling time. It changed the morphology of HuH7 cells but not that of HepG2. It induced the enlargement of HuH7 cell nuclear area and the restructuration of adherent cell junctions. Unexpectedly, for both cell types, the levels of apoptosis, cell division, and β-catenin were not altered by sGPC3m, although growth inhibition was very efficient. Overall, our data show that glycanation and convertase maturation are not required for sGPC3m to inhibit HCC cell proliferation.