Soft tissue and visceral leiomyosarcoma account for 15% of all sarcomas in adults. Molecular alterations in LMS are not well characterized, with often complex gains and losses of chromosome segments. We investigated the expression or phosphorylation of kinases and downstream signalling molecules in a series of fresh frozen LMS and cell lines with the aim to identify potential targets for targeted therapy. Four proteins were found differentially expressed including Tyro3, a receptor tyrosine kinase. The functional activity of Tyro3 was investigated in 2 LMS cell lines, SK-LMS-1 and CNIO AA. Four proteins and phosphoproteins were found differentially expressed in LMS samples as compared to NSM: an hypophosphorylation of FAK Y397 was observed in all samples while Tyro3, MSH2, and PKC theta were found overexpressed in LMS samples. Gas6, the ligand of Tyro3 was found expressed in 8 of the 13 samples, and the coexpression of Gas6 and Tyro3 was found exclusively associated with Akt phosphorylation. Both SK-LMS-1 and CNIO AA LMS cell lines were found to express Tyro3, while Gas6 expression was only observed in CNIO AA cells. P-Akt was expressed spontaneously in CNIO AA, but not in SKLMS-1, while the opposite figure was observed for phosphorylated FAK Y397. Exposure of SKLMS-1 to exogenous Gas6 induced P-Akt, and resulted in a reduction of FAK Y397 phosphorylation. Transfection of CNIO AA with siRNA directed against, Tyro3 and Axl genes induced a reduction of the expression of the specific proteins, and when combined, significantly reduced CNIO AA cell viability. Gas 6 a ligand of Tyro3 is expressed in a subset of LMS tumors and cell lines, and may exert autocrine activities in a subset of LMS
