title: S6K is a morphogenic protein with a mechanism involving Filamin-A phosphorylation and phosphatidic acid binding.
abstract: Change of cell shape in vivo plays many roles that are central to life itself, such as embryonic development, inflammation, wound healing, and pathologic processes such as cancer metastasis. Nonetheless, the spatiotemporal mechanisms that control the concerted regulation of cell shape remain understudied. Here, we show that ribosomal S6K, which is normally considered a protein involved in protein translation, is a morphogenic protein. Its presence in cells alters the overall organization of the cell surface and cell circularity [(4π × area)/(perimeter)(2)] from 0.47 ± 0.06 units in mock-treated cells to 0.09 ± 0.03 units in S6K-overexpressing macrophages causing stellation and arborization of cell shape. This effect was partially reversed in cells expressing a kinase-inactive S6K mutant and was fully reversed in cells silenced with small interference RNA. Equally important is that S6K is itself regulated by phospholipids, specifically phosphatidic acid, whereby 300 nM 1,2-dioleoyl-sn-glycero-3-phosphate (DOPA), but not the control 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), binds directly to S6K and causes an ∼ 2.9-fold increase in S6K catalytic activity. This was followed by an increase in Filamin A (FLNA) functionality as measured by phospho-FLNA (S(2152)) expression and by a subsequent elevation of actin nucleation. This reliance of S6K on phosphatidic acid (PA), a curvature-inducing phospholipid, explained the extra-large perimeter of cells that overexpressed S6K. Furthermore, the diversity of the response to S6K in several unrelated cell types (fibroblasts, leukocytes, and invasive cancer cells) that we report here indicates the existence of an underlying common mechanism in mammalian cells. This new signaling set, PA-S6K-FLNA-actin, sheds light for the first time into the morphogenic pathway of cytoskeletal structures that are crucial for adhesion and cell locomotion during inflammation and metastasis.
authors.affiliation: *Wright State University School of Medicine, Department of Biochemistry and Molecular Biology, Dayton, Ohio, USA; and Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, USA.
authors.forename: Karen M
authors.initials: KM
authors.lastname: Henkels
authors.affiliation: *Wright State University School of Medicine, Department of Biochemistry and Molecular Biology, Dayton, Ohio, USA; and Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, USA.
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Mallets
authors.affiliation: *Wright State University School of Medicine, Department of Biochemistry and Molecular Biology, Dayton, Ohio, USA; and Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, USA.
authors.forename: Patrick B
authors.initials: PB
authors.lastname: Dennis
authors.affiliation: *Wright State University School of Medicine, Department of Biochemistry and Molecular Biology, Dayton, Ohio, USA; and Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, USA julian.cambronero@wright.edu.
authors.forename: Julian
authors.initials: J
authors.lastname: Gomez-Cambronero
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002465:Cell Movement; D048430:Cell Shape / Q000235:genetics / Q000502:physiology*; D022081:Cell Surface Extensions / Q000378:metabolism; D002522:Chlorocebus aethiops; D064448:Filamins / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D010712:Phosphatidic Acids / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D064448:Filamins; C529499:FlnA protein, mouse; D010712:Phosphatidic Acids; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse
keywords: breast cancer; cell invasion; cell morphology; cytoskeleton signaling; morphogenesis