Differential Expression of TKS4 Isoforms and Their Role in Cellular Processes in Breast Cancer

The scaffold protein TKS4 plays a role in the development of several cancers. Alternative splicing of the TKS4 gene generates two isoforms, TKS4L and TKS4b; however, their distinct expression patterns and functional roles have not yet been characterized. We have shown that TKS4 isoforms were differentially expressed across human cell lines and breast cancer (BC) tumor samples. Both TKS4L and TKS4L/TKS4b mRNA ratios were significantly altered in tumors compared with adjacent tissues. We identified six novel binding SH3-domain-containing partners for TKS4L, none of which interact with TKS4b, suggesting their functional differences. Tyrosine phosphorylation of both isoforms was induced by Src(Y527F) kinase overexpression, enabling binding to the SH2 domains of signaling proteins. Interestingly, TKS4b significantly accumulated in the nucleus, while TKS4L was primarily present in the cytosol in MCF-7 cells. TKS4b overexpression enhanced MCF-7 cell migration. Both TKS4 isoforms exhibit oncogenic properties by promoting epithelial-mesenchymal transition in BC cells, highlighting their potential as targets for therapeutic intervention.