Dicty News Electronic Edition Volume 20, number 1 January 18, 2003 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at DictyBase--http://dictybase.org. ============= Abstracts ============= Receptor Mediated Regulation of PI3Ks Confines PI(3,4,5)P3 to the Leading Edge of Chemotaxing Cells Yi Elaine Huang1, Miho Iijima1, Carole A. Parent,2 Satoru Funamoto3, Richard A. Firtel3, and Peter Devreotes1 1Department of Cell Biology Johns Hopkins University School of Medicine Baltimore, MD 21205 2Laboratory of Cellular and Molecular Biology Division of Basic Sciences NCI, NIH 37 Convent Drive, MSC 4255 Bldg. 37/Rm. 1E24 Bethesda, MD 20892-4255 3Section of Cell and Developmental Biology Division of Biology University of California, San Diego 9500 Gillman Drive La Jolla, CA 92093 Molecular Biology of the Cell, In Press Abstract Recent studies have demonstrated that PH domains specific for PI(3,4,5)P3 accumulate at the leading edge of a number of migrating cells and that PI3Ks and PTEN associate with the membrane at the front and back, respectively, of chemotaxing D. discoideum cells. However, the dependence of chemoattractant induced changes in PI(3,4,5)P3 on PI3K and PTEN activities have not been defined. We find that bulk PI(3,4,5)P3 levels increase transiently upon chemoattractant stimulation, and the changes are greater and more prolonged in pten- cells. PI3K activation increases within 5 seconds of chemoattractant addition and then declines to a low level of activity identically in wild type and pten- cells. Reconstitution of the PI3K activation profile can be achieved by mixing membranes from stimulated pi3k1-/pi3k2- cells with cytosolic PI3Ks from unstimulated cells. These studies show that significant control of chemotaxis occurs upstream of the PI3Ks and that regulation of the PI3Ks and PTEN cooperate to shape the temporal and spatial localization of PI(3,4,5)P3. submitted by Pam Antol [pjantol@jhmi.edu] ---------------------------------------------------------------------------- Dictyostelium differentiation-inducing factor-3 activates glycogen synthase kinase-3b and degrades cyclin D1 in mammalian cells Fumi Takahashi-Yanaga, Yoji Taba, Yoshikazu Miwa, Yuzuru Kubohara, Yutaka Watanabe, Masato Hirata, Sachio Morimoto, and Toshiyuki Sasaguri Dept. of Clinical Pharmacology, Graduate school of Med. Sciences, Kyushu University Dept. of Mol. Cell. Biochem., Graduate School of Dental Sciences, Kyushu University, Fukuoka 812-8582 Biosignal Research Center, IMCR, Gunma University, Mabashi 371-8512 Dept. of Applied Chem. Ehime University, Matsuyama 790-8577, Japan J. Biol. Chem. In press. In search of chemical substances applicable for the treatment of cancer and other proliferative disorders, we studied the signal transduction of Dictyostelium differentiation-inducing factors (DIFs) in mammalian cells mainly using HeLa cells. Although DIF-1 and DIF-3 both strongly inhibited cell proliferation by inducing G0/G1 arrest, DIF-3 was more effective than DIF-1. DIF-3 suppressed cyclin D1 expression at both mRNA and protein levels, while the overexpression of cyclin D1 overrode DIF-3-induced cell cycle arrest. The DIF-3-induced decrease in the amount of cyclin D1 protein preceded the reduction in the level of cyclin D1 mRNA. The decrease in cyclin D1 protein seemed to be caused by accelerated proteolysis, since it was abrogated by ALLN, a proteasome inhibitor. DIF-3-induced degradation of cyclin D1 was also prevented by treatment with lithium chloride, an inhibitor of glycogen synthase kinase-3b (GSK-3b, suggesting that DIF-3 induced cyclin D1 proteolysis through the activation of GSK-3b. Indeed, DIF-3 dephosphorylated Ser9 and phosphorylated tyrosine on GSK-3b, and it stimulated GSK-3b activity in an in vitro kinase assay. Moreover, DIF-3 was revealed to induce the nuclear translocation of GSK-3b by immunofluorescent microscopy and immunoblotting of subcellular protein fractions. These results suggested that DIF-3 activates GSK-3b to accelerate the proteolysis of cyclin D1 and this mechanism is involved in the DIF-3-induced G0/G1 arrest in mammalian cells. submitted by: kubohara@pop.showa.gunma-u.ac.jp ---------------------------------------------------------------------------- [End Dicty News, volume 20, number 1]