Abstract 553: Interactions among JNK, p38, Akt and canonical Wnt pathways in murine mammary adenocarcinoma cells reexpressing Glypican-3 (GPC3).
Authors: Peters Maria Giselle , Tascon Rocio , Castillo Lilian F. , Bal de Kier Joffe Elisa 
Published: August 2014

GPC3 is expressed in normal mammary tissues, but it disappears in tumors. We have transfected the GPC3 gene into the murine mammary adenocarcinoma LM3 cells, demonstrating that it acts as a metastasis suppressor. We have also reported that LM3-GPC3 cells exhibit an inhibition of Akt and canonical Wnt pathways, while they show an activation of non-canonical Wnt (JNK) and p38 signaling.

The aim of this work was to study the interactions among GPC3 modulated pathways. For this, subconfluent LM3-GPC3 cells were treated with SB203589 or SP600125 (p38 and JNK pharmacological inhibitors, respectively), or with the vehicle. Also, we introduced by viral infection a constitutively active variant of Akt1 (CA Akt), or the empty vector, into LM3-GPC3 cells. The effect of the different treatments on the activity of the other pathways was evaluated by WB.

We demonstrated that in addition to the central role of JNK in the non-canonical Wnt pathway, it also regulates canonical signaling. We found that SP600125 induced a 2 to 5-fold increase in the cytoplasmic β-Catenin levels, as well it reduced 2 to 6 times E-Cadherin expression. Therefore, our results suggest that JNK activation would be required for the canonical Wnt signaling inhibition induced by GPC3. On the other side, p38 pathway is considered independent of Wnt signaling. In association, SB203589 did not modulate either cytoplasmic β-Catenin or E-Cadherin levels, suggesting that p38 activation would not participate in the canonical Wnt pathway inhibition induced by GPC3. We also observed that LM3-GPC3 cells expressing CA Akt, showed less E-Cadherin than controls. So, Akt inhibition would be essential to increase of E-Cadherin expression induced by GPC3.

In relation with the non-canonical Wnt pathway, we found that SB203589 induced a partial decrease in phospho-JNK levels. Therefore, p38 would be involved in the non-canonical Wnt signaling activation induced by GPC3.

Inhibitors actions on Akt pathway were analyzed. We determined that SP600125 had no effect on Akt activation, suggesting that Akt inhibition induced by GPC3 is independent of non-canonical Wnt signaling. On the other hand, although without reaching LM3-vector levels, SB203589 caused a 2-fold increase in phospho-Akt levels. This indicates that the activation of p38 would be necessary to induce the inhibition of Akt signaling detected in GPC3 reexpressing cells.

In sum, we have dissected some of the functional and hierarchical interactions between the pathways modulated by GPC3 that may contribute to the metastasis suppressing activity of this proteoglycan.

Citation Format: Maria Giselle Peters, Rocio Tascon, Lilian F. Castillo, Elisa Bal de Kier Joffe. Interactions among JNK, p38, Akt and canonical Wnt pathways in murine mammary adenocarcinoma cells reexpressing Glypican-3 (GPC3). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 553. doi:10.1158/1538-7445.AM2013-553