Src family kinase activity regulates adhesion, spreading and migration of pancreatic endocrine tumour cells

Abstract

Pancreatic endocrine tumours (PETs) are rare and ‘indolent’ neoplasms that usually develop metastatic lesions and exhibit poor response to standard medical treatments. Few studies have investigated pathways responsible for PET cell growth and invasion and no alternative therapeutic strategies have been proposed. In a recent microarray analysis for genes up-regulated in PETs, we have described the up-regulation of soluble Src family tyrosine kinases in this neoplasia, which may represent potentially promising candidates for therapy. Herein, we have investigated the expression and function of Src family kinases in PETS and PET cell lines. Western blot analysis indicated that Src is highly abundant in the PET cell lines CM and QGP-1. Immunohistochemistry and Western blot analyses showed that Src is up-regulated also in human PET lesions. Pharmacological inhibition of Src family kinases by the specific inhibitor PP2 strongly interfered with adhesion, spreading and migration of PET cell lines. Accordingly, the actin cytoskeleton was profoundly altered after inhibition of Src kinases, whereas even prolonged incubation with PP2 exerted no effect on cell cycle progression and/or apoptosis of PET cells. A transient increase in tyrosine phosphorylation of a subset of proteins was observed in QGP-1 cells adhering to the plate, with a peak at 75 min after seeding, when approximately 80% of cells were attached. Inhibition of Src kinases caused a dramatic reduction in the phosphorylation of proteins with different molecular weight that were isolated from the cell extracts by anti-phosphotyrosine immunoprecipitation or pull-down with the SH2 domain of Src. Among them, the docking protein p130Cas interacted with Src and is a major substrate of the Src kinases in QGP-1 cells undergoing adhesion. Our results suggest that Src kinases play a specific role during adhesion, spreading and migration of PET cells and may indicate therapeutical approaches directed to limiting the metastatic potential of these cells.