Signaling network involved in the GPC3-induced inhibition of breast cancer progression

CERCATO MAGALÍ CECILIA; GUEREÑO, MACARENA; PETERS, MARÍA GISELLE; FERNÁNDEZ, DOLORES

Congreso; LXIII Reunión anual de la Sociedad Argentina de Investigaciones Clínicas (SAIC); 2018

We showed that GPC3 overexpression in breast cancer cells prevents metastatic dissemination, as well as it inhibits canonical Wnt and Akt pathways, while non-canonical Wnt and p38MAPK cascades are activated. However, the hierarchical sequence through which GPC3 modulates these pathways has not been determined.In this study, we aimed to investigate the mechanism involved in the GPC3 effect on breast tumor progression, focusing on Wnt pathway. We employed the murine mammary LM3 cancer cell line (ER -, PR -, GPC3 -), overexpressing GPC3. We confirmed by cytoplasmic β-Catenin levels and its transcriptional activity, that GPC3 inhibits autocrine and paracrine canonical Wnt signaling. We demonstrated by qPCR microarrays that GPC3 can modulate Wnt pathway in a genomic way. Out of the 84 evaluated genes, only Wnt 5b (non-canonical) was upregulated, 66 genes were downregulated (several Fz), and the expression of 17 genes -including several Wnt factors- was not modified by GPC3 overexpression (3-fold change, p≤0.05). Our WB from conditioned media indicated that GPC3 is secreted, suggesting that it competes with Wnt factors and thus prevents their binding to Fz.In the cross-talk studies, we demonstrated that the GPC3-induced inhibition of Akt is necessary for the non-canonical Wnt activation, and for the canonical inhibition, but it has no effect on p38MAPK. The p38MAPK activation was required for the non-canonical Wnt upregulation and for the canonical Wnt and Akt pathways inhibition. The canonical Wnt inhibition was crucial for the Akt downregulation as well as for the p38MAPK and non-canonical Wnt pathways activation. The non-canonical Wnt activity regulated canonical Wnt and p38MAPK pathways, although it had no effect on Akt.In conclusion, our data indicate that GPC3 is secreted and it operates through an intricate signaling network. From the balance of these interactions, the inhibition of breast metastatic spread induced by GPC3 emerges.