Glypican-3 (GPC3) is a proteoglycan involved in proliferation and cell survival. Several reports demonstrated that GPC3 is downregulated in some tumors, such as breast cancer. Previously, we determined that GPC3 reexpression in the murine mammary adenocarcinoma LM3 cells induced an impairment of their invasive and metastatic capacities, associated with a decrease of their motility and an increase of their cell death. We demonstrated that GPC3 inhibits canonical Wnt signaling, as well as it activates non canonical pathway. Now, we identified signaling pathways responsible for the pro-apoptotic role of GPC3 in LM3 cells. We found for the first time that GPC3 inhibits the PI3K/Akt anti-apoptotic pathway while it stimulates the p38MAPK stress-activated one. We report a concomitant modulation of CDK inhibitors as well as of pro- and anti-apoptotic molecules. Our results provide new clues regarding the mechanism involved in the modulation induced by GPC3 of mammary tumor cell growth and survival.

Tumor metastasis is a main contributor to death in cancer patients. In the last years, a new class of molecules that reduces the metastatic propensity has been identified: metastasis suppressors. These proteins regulate multiple steps in the metastatic cascade, including cell invasion, survival in the vascular and lymphatic circulation, and colonization of distant organ sites. As a consequence, they are very important therapeutic targets. This review discusses our current understanding of metastasis suppressors and how this knowledge might be useful to improve the treatment of cancer patients.

Background: The in vitro culture of insulinomas provides an attractive tool to study cell proliferation and insulin synthesis and secretion. However, only a few human beta cell lines have been described, with long-term passage resulting in loss of insulin secretion. Therefore, we set out to establish and characterize human insulin-releasing cell lines.

The Wnt pathway is involved in regulating cell proliferation and differentiation. Alterations of this pathway have been identified as key event in neoplastic development. Previously, we have demonstrated that the restatement of Glypican-3 (GPC3), a proteoglycan downregulated in breast cancer, is able to induce an inhibition of the canonical Wnt pathway in the murine mammary adenocarcinoma LM3 cells. We also reported that GPC3 reexpression induces an inhibition of the in vivo metastatic capacity and an in vitro reversion of the epithelial to mesenchymal transition (EMT). GPC3 reexpressing clones are less viable in stress conditions, more senescent, more homotypic adherent, less migrants and their actin is mainly localized in cortical position. The aim of this study was to analyze whether the effects of GPC3 on these cellular parameters are dependent on the inhibition of canonical Wnt pathway. As a strategy, two LM3-GPC3 clones and two LM3-vector ones were treated with LiCl (activator of the Wnt pathway canonical) or NaCl as control. We determined that LiCl was able to partially reverse the LM3-GPC3 cell senescence (X-gal positive senescent cells: LM3-GPC3+NaCl=85% vs +LiCl=65%, ANOVA-Bonferroni p <0.05). In contrast, no changes were observed on the susceptibility to death by serum starving (ANOVA, ns). Although there were no effects on the actin cytoskeleton organization, we established by a wound healing assays that LM3-GPC3 cells treated with LiCl regain their ability to migrate (Wound coverage: LM3-GPC3+NaCl=15% vs +LiCl=75%, ANOVA-Bonferroni p<0.05). Interestingly, LiCl significantly reduced the homotypic adhesion of LM3-GPC3 cells, reaching control levels (ANOVA-Bonferroni p<0.05). These results suggest that inhibition of the canonical Wnt pathway induced by GPC3 mediates the effects of this glypican on senescence, migration and cell aggregation, while survival and actin cytoskeleton organization would be modulated through other pathways. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1958. doi:10.1158/1538-7445.AM2011-1958