Tubulin-dependent secretion of S100A6 and cellular signaling pathways activated by S100A6-integrin β1 interaction

S100A6 is a calcium binding protein expressed mainly in fibroblasts and epithelial cells. Interestingly, S100A6 is also present in extracellular fluids. Recently we have shown that S100A6 is secreted by WJMS cells and binds to integrin beta 1 (Jurewicz et al., 2014). In this work we describe for the first time the mechanism of S100A6 secretion and signaling pathways activated by the S100A6-integrin beta 1 complex. We show that colchicine suppressed the release of S100A6 into the cell medium, which indicates that the protein might be secreted via a tubulin-dependent pathway. By applying double immunogold labeling and immunofluorescence staining we have shown that S100A6 associates with microtubules in WJMS cells. Furthermore, results obtained from im-munoprecipitation and proximity ligation assay (PLA), and from in vitro assays, reveal that S100A6 is able to form complexes with alpha and beta tubulin in these cells, and that the S100A6-tubulin interaction is direct. We have also found that the S100A6 protein, due to binding to integrin beta 1, activates integrin-linked kinase (ILK), focal adhesion kinase (FAK) and p21-activated kinase (PAK). Our results suggest that binding of S100A6 to integrin beta 1 affects cell adhesion/proliferation due to activation of ILK and FAK signaling pathways.