P0981 - Proteolytic Cleavage of Glypican 3 Promotes Hepatoblastoma Cell Proliferation In Vitro

Background: Hepatoblastoma (HB) is the most common primary pediatric liver malignancy, treated with multimodal therapy including chemotherapy, surgical resection, and sometimes hepatic transplantation. Curative therapy greatly impacts long-term quality of life and still, disease recurrence must often be addressed. Therefore, a significant need exists to develop novel treatment options, especially for more aggressive and relapsed tumors. Glypican 3 (GPC3) is a 70 kDa heparin sulfate proteoglycan overexpressed in HB tumors. Post translational modification of GPC3 can include cleavage into 40 kDa N-terminal and 30 kDa C-terminal protein fragments by enzymes including Furin.

Methods: GPC3 protein and gene expression were quantified in HB patient tumors and background livers from 12 patients. In vitro studies were conducted in HepG2 and SK-HEP1 cells to analyze the effect of (1) Furin inhibition and (2) treatment with recombinant protein on cell proliferation in GPC3 expressing and non-GPC3 expressing cell lines, respectively.

Results: We have demonstrated that high levels of GPC3 isoforms, in addition to full-length (FL) GPC3, are present in ten human HB samples. Using the HepG2 cell line, administration of a competitive Furin inhibitor demonstrated decreased levels of both GPC3 fragments and cellular proliferation. Furthermore, in vitro treatment of SK-HEP1 with recombinant C-terminal GPC3 demonstrates increased cellular proliferation.

Conclusions: Higher levels of GPC3 isoforms are associated with increased proliferation in vitro. Not only does the addition of exogenous GPC3 isoforms increase proliferation, but the inhibition of endogenous FL GPC3 cleavage has the inverse effect on proliferation. Given the elevated levels in most human samples analyzed, further studies are needed to elicit the oncogenic potential of the GPC3 isoforms.