title: Inhibition of Focal Adhesion Kinase Signaling by Integrin α6β1 Supports Human Pluripotent Stem Cell Self-Renewal.
abstract: Self-renewal of human embryonic stem cells and human induced pluripotent stem cells (hiPSCs)-known as pluripotent stem cells (PSC)-is influenced by culture conditions, including the substrate on which they are grown. However, details of the molecular mechanisms interconnecting the substrate and self-renewal of these cells remain unclear. We describe a signaling pathway in hPSCs linking self-renewal and expression of pluripotency transcription factors to integrin α6β1 and inactivation of focal adhesion kinase (FAK). Disruption of this pathway results in hPSC differentiation. In hPSCs, α6β1 is the dominant integrin and FAK is not phosphorylated at Y397, and thus, it is inactive. During differentiation, integrin α6 levels diminish and Y397 FAK is phosphorylated and activated. During reprogramming of fibroblasts into iPSCs, integrin α6 is upregulated and FAK is inactivated. Knockdown of integrin α6 and activation of β1 integrin lead to FAK phosphorylation and reduction of Nanog, Oct4, and Sox2, suggesting that integrin α6 functions in inactivation of integrin β1 and FAK signaling and prevention of hPSC differentiation. The N-terminal domain of FAK, where Y397 is localized, is in the nuclei of hPSCs interacting with Oct4 and Sox2, and this immunolocalization is regulated by Oct4. hPSCs remodel the extracellular microenvironment and deposit laminin α5, the primary ligand of integrin α6β1. Knockdown of laminin α5 resulted in reduction of integrin α6 expression, phosphorylation of FAK and decreased Oct4. In conclusion, hPSCs promote the expression of integrin α6β1, and nuclear localization and inactivation of FAK to supports stem cell self-renewal. Stem Cells 2016;34:1753-1764.
authors.affiliation: Department of Biologic & Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan, USA.
authors.forename: Luis G
authors.initials: LG
authors.lastname: Villa-Diaz
authors.affiliation: Department of Biologic & Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan, USA.
authors.forename: Jin Koo
authors.initials: JK
authors.lastname: Kim
authors.affiliation: Department of Biomedical Engineering, University of Michigan School of Dentistry, Ann Arbor, Michigan, USA.
authors.forename: Alex
authors.initials: A
authors.lastname: Laperle
authors.affiliation: Department of Chemical & Biological Engineering, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Sean P
authors.initials: SP
authors.lastname: Palecek
authors.affiliation: Department of Biologic & Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan, USA.|Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Krebsbach
mesh_terms: D002454:Cell Differentiation; D002467:Cell Nucleus / Q000378:metabolism; D000066673:Cell Self Renewal; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000737:chemistry / Q000378:metabolism*; D022001:Focal Adhesions / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D039121:Integrin alpha6beta1 / Q000378:metabolism*; D007797:Laminin / Q000378:metabolism; D010766:Phosphorylation; D039904:Pluripotent Stem Cells / Q000166:cytology* / Q000378:metabolism*; D011485:Protein Binding; D000072417:Protein Domains; D020033:Protein Isoforms / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D039121:Integrin alpha6beta1; D007797:Laminin; D020033:Protein Isoforms; D014157:Transcription Factors; C097043:laminin alpha5; D051416:Focal Adhesion Protein-Tyrosine Kinases
keywords: Differentiation; Integrins; Molecular signaling; Pluripotent stem cells; Self-renewal