Journal of Stem Cell Research & Therapy

Abstract

Glypican-3-Mediates Autophagy and Promotes Self-Renewal and Tumor Initiation of Hepatocellular Carcinoma Cells

Sun CK, Chua MS, Wei W and So SK

Objective: Understanding the biological functions of cancer stem cells (CSCs) provide new avenues for therapeutic interventions, which is especially important in hepatocellular carcinoma (HCC), an often fatal malignancy. We aim to determine whether glypican-3 (GPC3), an over-expressed membrane protein in HCC, mediates CSC properties in HCC cells.
Design: We determined the cell surface expression of GPC3 in HCC patients and HCC cell lines, and isolated GPC3-high/low sub-populations to study their abilities to self-renew. Additionally, we used HCC cell-based systems where GPC3 expression was either suppressed or induced, to validate the stem-like properties (spheroid formation, cell cycle progression, tumor initiation) that may be mediated by GPC3.
Results: We observed highly specific cell surface expression of GPC3 in HCC cells only (and not in normal hepatocytes or tumor-associated fibroblasts). The GPC3-high sub-populations isolated from HCC cells possess higher levels of self-renewing ability, have lower percentages of cells in the G0/G1 phase, and promoted tumor formation in vivo. These observations were confirmed in HCC cell-based systems where GPC3 expression was either suppressed or induced. The effects of GPC3 (and EpCAM and CD133) on spheroid formation and cell cycle were nullified by the starvation-induced autophagy inhibitor, 3-methyladenine (3-MA), indicating that these processes are partially regulated by autophagy.
Conclusion: We provide first evidence that GPC3 is a novel CSC marker in HCC, and that it mediates selfrenewal, cell cycle progression, and tumor formation partly via autophagy induction. We also suggest that autophagy inhibition may be a general approach for intervening with liver CSC functions, regardless of cell surface marker expression.