Molecular and Cellular Pathobiology Phosphatidylinositol 4-Phosphate in the Golgi Apparatus Regulates Cell–Cell Adhesion and Invasive Cell Migration in Human Breast Cancer

Downregulation of cell–cell adhesion and upregulation of cell migration play critical roles in the conversion of benign tumors to aggressive invasive cancers. In this study, we show that changes in cell–cell adhesion and cancer cell migration/invasion capacity depend on the level of phosphatidylinositol 4-phosphate [PI(4)P] in the Golgi apparatus in breast cancer cells. Attenuating SAC1, a PI(4)P phosphatase localized in theGolgi apparatus, resulted in decreased cell–cell adhesion and increased cell migration in weakly invasive cells. In contrast, silencing phosphatidylinositol 4-kinase IIIb, which generates PI(4)P in the Golgi apparatus, increased cell–cell adhesion and decreased invasion in highly invasive cells. Furthermore, a PI(4)P effector, Golgi phosphoprotein 3, was found to be involved in the generation of these phenotypes in a manner that depends on its PI(4)P-binding ability. Our results provide a newmodel for breast cancer cell progression inwhich progression is controlled by PI(4)P levels in the Golgi apparatus. Cancer Res; 74(11); 1–13. 2014 AACR. Introduction Phosphoinositides are lipid constituents of plasma and organelle membranes and comprise seven different phosphorylated versions. The levels of various phosphorylated phosphoinositides within the cell are regulated by multiple phosphoinositide kinases and phosphoinositide phosphatases (1, 2). Phosphatidylinositol 4-phosphate [PI(4)P] is a relatively abundant phosphoinositide required for the maintenance and function of the Golgi apparatus, including intracellular trafficking (3). The PI(4)P level at the Golgi apparatus is controlled by phosphatidylinositol 4-kinases (PI4K) and SAC1 phosphoinositide phosphatase. The PI4K isoforms phosphatidylinositol 4-kinase IIa (PI4KIIa) and PI4KIIIb are known to localize to the Golgi apparatus and to be involved in membrane transport from the trans-Golgi network to the plasmamembrane (4, 5). In contrast, SAC1, which dephosphorylates PI(4)P at the Golgi apparatus, is involved in the same membrane transport pathway and in protein glycosylation (6). Several PI(4)P-binding proteins, including FAPP, OSBP, CERT, and GGA, have been identified (7). One PI(4)P effector, Golgi phosphoprotein 3 (GOLPH3), maintains a tensile force on the Golgi apparatus and plays a role in the Golgi secretory pathway (8, 9). Recently, GOLPH3 was shown to be involved in cancer progression. Human chromosome 5p13, on which the GOLPH3 gene is located, is amplified in several cancers (10), and expression of GOLPH3 is increased in several cancer cell lines and in some patients with cancer (11–14). GOLPH3 enhances cell proliferation and tumorigenicity (10, 15). However, its role in cell migration and invasion remains unknown. Tometastasize from their locationwithin a primary tumor to the surrounding tissue, tumor cells undergo several processes, including loss of cell–cell adhesion and gains in motile and invasive potential (16). This temporary and reversible phenotype is referred to as epithelial–mesenchymal transition (EMT). Following invasion or distal metastasis, metastatic tumor cells revert to an epithelial phenotype in the so-calledmesenchymal– epithelial transition (MET). EMT/MET conversions are recognized as critical events in cancer progression (17). To identify the physiologic role of PI(4)P in the Golgi apparatus during tumor progression, we investigated the effects of PI(4)P metabolism on cell–cell adhesion and cell migration in breast cancer cells. PI(4)P in the Golgi apparatus was found to regulate cell–cell adhesion, cell migration, invasion, and metastasis, which are essential for breast cancer progression through regulation of GOLPH3 localization to the Golgi apparatus. On the basis of these results, we propose a novel mechanism for the development of cancer progression. Authors' Affiliations: IntegratedCenter forMassSpectrometry; Division of Membrane Biology; and Department of Evidence-based Laboratory Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Hyogo, Japan Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Current address for T. Itoh: Biosignal Research Center, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, Hyogo 657-8501, Japan; and current address for J. Hasegawa, Laboratory of Intracellular Membrane Dynamics, Graduate School of Frontier Biosciences, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. Corresponding Author: Tadaomi Takenawa, Integrated Center for Mass Spectrometry, Kobe University, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, Hyogo 650-0017, Japan. Phone: 81-78-382-5410; Fax: 81-78-382-5419; E-mail: [email protected] doi: 10.1158/0008-5472.CAN-13-2441 2014 American Association for Cancer Research. Cancer Research www.aacrjournals.org OF1 Research. on July 25, 2017. © 2014 American Association for Cancer cancerres.aacrjournals.org Downloaded from Published OnlineFirst April 4, 2014; DOI: 10.1158/0008-5472.CAN-13-2441