Galectins and their ligands have been implicated in cell transformation and cancer metastasis, and found to have prognostic value. Mac-2 BP, also known as 90K, is a highly glycosylated, secreted protein extensively studied in human cancer, which binds galectin-1, galectin-3 and galectin-7. High expression levels of 90K are associated with a shorter survival, the occurrence of metastasis or a reduced response to chemotherapy in patients with different types of malignancy. The mechanisms underlying the prognostic significance of 90K and galectins in cancer are far from being understood, although they may be related to the ability of these proteins to interact and, to some extent, modulate cell-cell and cell-matrix adhesion and apoptosis. The resulting scenario is even more complex, as data have been presented that all these proteins might be associated with either a positive or a negative outcome of the patients. It is hypothesised that different galectins and galectin ligands with overlapping or opposite functions, expressed in different tumors during the different steps of the metastatic cascade might play a crucial role in tumor progression.

Phosphatidylinositol-3-phosphate (PtdIns-3-P) is considered as a lipid constitutively present on endosomes; it does not seem to have a dynamic role in signalling. In contrast, phosphatidylinositol-3,4,5-trisphosphate (PtdIns-3,4,5-P 3 ) plays a crucial role in different signalling pathways including translocation of the glucose transporter protein GLUT4 to the plasma membrane upon insulin receptor activation. GLUT4 translocation requires activation of two distinct pathways involving phosphatidylinositol 3-kinase (PI 3-K) and the small GTP-binding protein TC10, respectively. The contribution of each pathway remains to be elucidated. Here we show that insulin speci®cally induces the formation of PtdIns-3-P in insulinresponsive cells. The insulin-mediated formation of PtdIns-3-P occurs through the activation of TC10 at the lipid rafts subdomain of the plasma membrane. Exogenous PtdIns-3-P induces the plasma membrane translocation of both overexpressed and endogenous GLUT4. These data indicate that PtdIns-3-P is specifically produced downstream from insulin-mediated activation of TC10 to promote the plasma membrane translocation of GLUT4. These results give a new insight into the intracellular role of PtdIns-3-P and shed light on some aspects of insulin signalling so far not completely understood. Keywords: GLUT4/insulin/phosphatidylinositol 3-kinase/ phosphatidylinositol-3-phosphate/TC10 Introduction Phosphatidylinositol 3-kinases (PI 3-Ks) phosphorylate position D-3 of phosphoinositides leading to the formation of 3¢-phosphorylated phosphoinositides. Different PI 3-Ks have been identi®ed and grouped in three classes on the basis of their sequence homology and in vitro substrate speci®city (Vanhaesebroeck et al., 2001). Among the different products of PI 3-Ks, resting mammalian cells contain detectable levels of phosphatidylinositol-3-phosphate (PtdIns-3-P) mainly localized on endosomes (Gillooly et al., 2001) that do not change upon cellular stimulation. On the contrary, phosphatidylinositol-3,4,5-trisphosphate (PtdIns-3,4,5-P 3 ) is barely detected in resting cells but its intracellular concentration rapidly increases upon stimulation by growth factors and cytokines and it plays a pivotal role in many different physiological events, including cell proliferation, motility, receptor internalization and glucose transport (Rameh and Cantley, 1999).Disposal of glucose into fat and muscle cells requires the insulin-induced translocation of the GLUT4 glucose transporter protein from intracellular storage sites to the plasma membrane ). The signalling pathway that links the insulin receptor to GLUT4 translocation is still controversial. It has been well established that activation of a PI 3-Kdependent pathway is necessary for this traf®cking event (Shepherd et al., 1998) but several lines of evidence suggest that it is not suf®cient and a second signalling pathway is also required (Isakoff et al., 1995;Wiese et al., 1995;Jiang et al., 1998;Czech and Corvera, 1999). Apparently, this additional pathway is PI 3-K-independen...

The purpose of this study was to investigate the antiangiogenic and in vivo properties of the recently identified phosphatidylinositol 3-kinase (PI3K)/Akt inhibitor Inositol(1,3,4,5,6) pentakisphosphate [Ins(1,3,4,5,6)P 5 ]. Because activation of the PI3K/Akt pathway is a crucial step in some of the events leading to angiogenesis, the effect of Ins(1,3,4,5,6)P 5 on basic fibroblast growth factor (FGF-2)-induced Akt phosphorylation, cell survival, motility, and tubulogenesis in vitro was tested in human umbilical vein endothelial cells (HUVEC). The effect of Ins(1,3,4,5,6)P 5 on FGF-2-induced angiogenesis in vivo was evaluated using s.c. implanted Matrigel in mice. In addition, the effect of Ins(1,3,4,5,6)P 5 on growth of ovarian carcinoma SKOV-3 xenograft was tested. Here, we show that FGF-2 induces Akt phosphorylation in HUVEC resulting in antiapoptotic effect in serum-deprived cells and increase in cellular motility. Ins(1,3,4,5,6)P 5 blocks FGF-2-mediated Akt phosphorylation and inhibits both survival and migration in HUVEC. Moreover, Ins(1,3,4,5,6)P 5 inhibits the FGF-2-mediated capillary tube formation of HUVEC plated on Matrigel and the FGF-2-induced angiogenic reaction in BALB/c mice. Finally, Ins(1,3,4,5,6)P 5 blocks the s.c. growth of SKOV-3 xenografted in nude mice to the same extent than cisplatin and it completely inhibits Akt phosphorylation in vivo. These data definitively identify the Akt inhibitor Ins(1,3,4,5,6)P 5 as a specific antiangiogenic and antitumor factor. Inappropriate activation of the PI3K/Akt pathway has been linked to the development of several diseases, including cancer, making this pathway an attractive target for therapeutic strategies. In this respect, Ins(1,3,4,5,6)P 5 , a water-soluble, natural compound with specific proapoptotic and antiangiogenic properties, might result in successful anticancer therapeutic strategies. (Cancer Res 2005; 65(18): 8339-49)

Phosphoinositide 3-kinase (PI 3-K) is implicated in a wide array of biological and pathophysiological responses, including tumorigenesis, invasion and metastasis, therefore specific inhibitors of the kinase may prove useful in cancer therapy. We propose that specific inositol polyphosphates have the potential to antagonize the activation of PI 3-K pathways by competing with the binding of PtdIns(3,4,5)P 3 to pleckstrin homology (PH) domains. Here we show that Ins(1,3,4,5,6)P 5 inhibits the serine phosphorylation and the kinase activity of Akt/PKB. As a consequence of this inhibition, Ins(1,3,4,5,6)P 5 induces apoptosis in ovarian, lung and breast cancer cells. Overexpression of constitutively active Akt protects SKBR-3 cells from Ins(1,3,4,5,6)P 5 -induced apoptosis. Furthermore, Ins(1,3,4,5,6)P 5 enhances the proapoptotic effect of cisplatin and etoposide in ovarian and lung cancer cells, respectively. These results support a role for Ins(1,3,4,5,6)P 5 as a specific inhibitor of the PI 3-K/Akt signalling pathway, that may sensitize cancer cells to the action of commonly used anticancer drugs.