Posters— Basic Science/Biology

INSULIN AND IGFs SIGNALING IN SOFT TISSUE SARCOMAS: ROLE OF IRS-1 AND IRS-2 PROTEINS

Bogetto L, Cervi M, Spessotto P, Mucignat MT, Canzonieri V, De Paoli A, Perris R, Colombatti A. Centro di Riferimento Oncologico -National Cancer Institute- Aviano, Italy (33081)

Insulin is a pleiotrophic hormone with both metabolic and mitogenic effects on cells. Insulin receptor substrate 1 and 2 proteins (IRS-1/2) are the principal intracellular substrates of insulin (and IGFs) receptor(s) that undergo tyrosine phosphorylation immediately after ligand stimulation. They act as docking proteins transmitting the receptor signal to downstream effector proteins containing SRC homology 2 domains, such the p85 regulatory subunit of phosphatidyl-inositol 3-kinase (PI 3K), and the growth factor receptor binding protein 2 (Grb2). Together these intermediate signals stimulate a variety of different biological effects, including glucose transport, glicogen synthesis, gene expression, cell migration, and cell proliferation. Although IRS-1 and IRS-2 contain common functional units and share some unique signaling pathways, it is not clear yet if they play redundant or selective roles in insulin action in different tissues, even if data provide evidence that they are not functionally interchangeable substrates. These two proteins show differential expression in several carcinoma tissues and cell lines; IRS-1 results highly expressed in hepatocellular and breast carcinomas, whereas pancreatic carcinomas overexpress IRS-2. Little is known about the role of IRS-1 and 2 in soft tissue sarcomas (STS) as well as about the insulin and IGFs signaling in the biology of these tumours. We have analyzed the expression pattern of IRS-1, IRS-2, IR, and IGF-1R in a number of cell lines derived from our patients and have selected two malignant fibrous histiocytoma-like (MFH) sarcoma cell lines (97441 and 98337) for their differential expression of IRS-1 and IRS-2 molecules and their different behaviour in vitro under basal conditions or under stimulation with insulin. From each tumours three morphologically different sub-lines, named with A, B and C, were obtained. 97441 A and 98337 A cells show high expression of IRS-1, whereas IRS-2 predominates in 97441 B cells; 98337 B cells lack both IRS-1 and IRS-2. The C populations of 97441 and 98337 show only a weak IRS-1 expression and no IRS-2. The IGF-1R expression is almost the same among the different sub-lines, whereas a slight increase of IR appears only in 97441 B cells. Extending our study on in vitro migration and invasion of these cells, we found that insulin does not modify the migration activity of 98337 A and B (on different ECM molecules), whereas it considerably increases the invasive capability of 98337 A. These results indicate a possible role of insulin in dissociating the migration and the invasion signaling pathways. To study the effect of IRS molecules that are differentially expressed we are transfecting these cell lines with vectors containing sense or antisense IRS-1/2.