The interaction of galectin-3 with TAM receptors in activating signalling pathways for human cancer cell survival and migration.


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Nour Al Kafri1,Sassan Hafizi1
1University of Portsmouth

Abstract

Background

Galectin-3 (Gal-3) is a beta-galactoside-binding protein that has been shown to influence various properties of cancer cells. Gal-3 has also been shown to be a novel ligand for the TAM sub-family of receptor tyrosine kinases (RTKs), which have been shown to promote tumour growth and spread in different cancers as well as mediating tumour chemoresistance. However, it is not known whether and to what extent Gal-3 influences TAM signalling in carcinogenesis. The aim of this project is to determine the impact of Gal-3 and TAM RTKs on cancer cells, downstream signalling and malignant cell behaviours.

Method

A variety of human cancer cell lines were grown in culture, and analysed for proteins and mRNAs of interest by western blotting and qRT-PCR respectively. Activation of TAM RTKs and downstream kinases was analysed by western blot detection of phosphorylated proteins. The effect of recombinant Gal-3, TAM ligands (Gas6, ProS1) and inhibitors on cell viability was determined by MTS assay. Cell migration rate was measured by scratch wound assay with microscopy. All experiments were performed a minimum of three times.

Results

Gal-3 was expressed in a range of human cancer cell lines from different sources. Recombinant Gal-3 rapidly stimulated ERK1/2 and Akt phosphorylation in cells by two-fold, as did Gas6, whilst ProS1 only stimulated ERK. Out of the three TAM ligands, only Gas6 conferred a significant positive effect on cell survival following long-term serum starvation, whereas all three ligands significantly protected cells from acute apoptosis induced by staurosporine. In addition, exogenous Gal-3 significantly hindered the suppressive effect on cell migration observed when Axl was selectively inhibited with the small molecule inhibitor BGB324. 

Conclusion

Our results so far show that Gal-3 stimulates cancer-promoting signalling pathways and associated functions in cancer cells as do TAM receptor ligands. Further work will determine the extent to which these pathways are shared.