Focal adhesion-localization of START-GAP1/DLC1 is essential for cell motility and morphology

• Published in: Genes to cells : devoted to molecular & cellular mechanisms 2009-02, Vol.14 (2), p.227-241
• Main Authors: Kawai, Katsuhisa, Iwamae, Yui, Yamaga, Masaki, Kiyota, Minoru, Ishii, Hiroko, Hirata, Hajime, Homma, Yoshimi, Yagisawa, Hitoshi
• Format: Article
• Language: English
• Subjects: cdc42 GTP-Binding Protein - metabolism; Cell Movement - physiology; Cell Shape - physiology; Cells, Cultured; Focal Adhesions - metabolism; Focal Adhesions - physiology; GTPase-Activating Proteins; HeLa Cells; Humans; Models, Biological; Protein Structure, Tertiary - genetics; Protein Structure, Tertiary - physiology; rhoA GTP-Binding Protein - metabolism; Tissue Distribution; Transfection; Tumor Suppressor Proteins - chemistry; Tumor Suppressor Proteins - genetics; Tumor Suppressor Proteins - metabolism; Tumor Suppressor Proteins - physiology
• ISSN: 1356-9597; 1365-2443
• DOI: 10.1111/j.1365-2443.2008.01265.x

There is a class of GTPase activating proteins for the Rho family GTPases (RhoGAPs) that contain the steroidogenic acute regulatory protein (STAR)-related lipid transfer (START) domain. In mammals three genes encode such proteins and they are designated START-GAP1-3 or deleted in liver cancer 1-3 (DLC1-3). In this study, we examined the intracellular localization and roles of START-GAP1/DLC1 in cell motility. Immunofluorescence microscopic analysis of NRK cells and HeLa cells revealed that START-GAP1 was localized in focal adhesions. Amino acid residues 265-459 of START-GAP1 were found to be necessary for focal adhesion targeting and we name the region "the focal adhesion-targeting (FAT) domain." It was previously known that ectopic expression of START-GAP1 induced cell rounding. We demonstrated that the FAT domain of START-GAP1 was partially required for this morphological change. Furthermore, expression of this domain in HeLa cells resulted in dissociation of endogenous START-GAP1 from focal adhesions as a dominant negative modulator, reducing cell migration and spreading. Taken together, START-GAP1 is targeted to focal adhesions via the FAT domain and regulates actin rearrangement through down-regulation of active RhoA and Cdc42. Its absence from focal adhesions could, therefore, cause abnormal cell motility and spreading.