THE SERINE/THREONINE KINASE AKT ACTIVATED BY FIBROBLAST GROWTH FACTOR RECEPTORS FROM OESTROGEN-INDEPENDENT BREAST CANCER CELLS REGULATES THE G sub(2)/M CHEKPOINT

• Published in: Anticancer research Vol. 28; no. 5C
• Main Authors: Browaeys-Poly, E, Lescuyer, A, Perdereau, D, Vilain, J P, Burnol, A-F, Cailliau-Maggio, K
• Format: Journal Article
• Language: English
• Published: 01-10-2008
• Subjects: Xenopus
• ISSN: 0250-7005

Hormone-independent breast cancers proliferate in response to "fibroblast growth factor". The oestrogen-independent breast cancer cell line, MDA-MB-231, expresses fibroblast growth factor receptors (FGFRs), and secretes FGF1 that exerts an autocrine mitogenic effect. Analysis of FGFRs signalling is rendered difficult by the concomitant expression of several tyrosine kinase receptors and their shared transduction cascades. To specifically investigate FGFR signalling, we used a biological system the Xenopus oocyte, a giant cell, devoid of endogenous FGFRs, that allows microinjections and expression of various RNAs. This paradigm offers a powerful experimental approaches to question cascade transduction regulation in relation to the cell cycle G sub(2)/M checkpoint. Oocytes expressing FGFRs from MDA-MB-231 enter in M phase, after stimulation by exogenous FGF1. This G sub(2)/M transition involves Ras-dependent and Ras-independent cascades. The phospholipase C gamma (PLC gamma ) and the serine/threonine kinase (Akt), two enzymatic effectors activated by FGFRs, are involved in breast cancer growth. In oocytes expressing FGFRs from MDA-MB-231, inhibitors of PI3Kinase-Akt pathway (Wortmannin, LY 294002, N terminal SH2 domain of p85 PI3Kinase) and an inhibitor of PLC gamma (a mimetic peptide of the SH2 domain) block FGF1-FGFR transduction. Activation of PLC gamma is the result of a direct binding to the FGFRs p(Y)766 site. A PLC gamma /calcium dependent chlorure current, measured by electrophysiological techniques, starts 2 to 4 minutes after FGF1 addition, and displays a duration of 20 minutes. A kinetic analysis shows that PLC gamma is phosphorylated on tyrosine 5 minutes and on serine 30 minutes after FGFRs activation. PLC gamma immunoprecipitations show that the serine phosphorylated PLC gamma is associated with active phosphorylated Akt (serine 473). A PLC gamma mimetic peptide of the SH3 domain disrupts the PLC gamma -Akt interaction, the serine phosphorylation of PLC gamma and favours Akt binding to an other downstream target: Chfr, a mitotic checkpoint protein deregulated in breast cancers. Moreover, an acceleration of the G sub(2)/M transition occurs when the Akt-PLC gamma interaction is substituted for the Akt-Chfr interaction. In conclusion, in the oestrogen-independent breast cancer line, MDA-MB-231, cell cycle progression in the M phase induced by FGF receptors is controlled by a time regulated interaction of activated Akt with two partners PLC gamma and Chfr.