title: Integrin alpha4beta1 promotes focal adhesion kinase-independent cell motility via alpha4 cytoplasmic domain-specific activation of c-Src.
abstract: The fibronectin binding integrins alpha5beta1 and alpha4beta1 generate signals pivotal for cell migration through distinct yet undefined mechanisms. For alpha5beta1, beta1-mediated activation of focal adhesion kinase (FAK) promotes c-Src recruitment to FAK and the formation of a FAK-Src signaling complex. Herein, we show that FAK expression is essential for alpha5beta1-stimulated cell motility and that exogenous expression of human alpha4 in FAK-null fibroblasts forms a functional alpha4beta1 receptor that promotes robust cell motility equal to the alpha5beta1 stimulation of wild-type and FAK-reconstituted fibroblasts. alpha4beta1-stimulated FAK-null cell spreading and motility were dependent on the integrity of the alpha4 cytoplasmic domain, independent of direct paxillin binding to alpha4, and were not affected by PRNK expression, a dominant-negative inhibitor of Pyk2. alpha4 cytoplasmic domain-initiated signaling led to a approximately 4-fold activation of c-Src which did not require paxillin binding to alpha4. Notably, alpha4-stimulated cell motility was inhibited by catalytically inactive receptor protein-tyrosine phosphatase alpha overexpression and blocked by the p50Csk phosphorylation of c-Src at Tyr-529. alpha4beta1-stimulated cell motility of triple-null Src(-/-), c-Yes(-/-), and Fyn(-/-) fibroblasts was dependent on c-Src reexpression that resulted in p130Cas tyrosine phosphorylation and Rac GTPase loading. As p130Cas phosphorylation and Rac activation are common downstream targets for alpha5beta1-stimulated FAK activation, our results support the existence of a novel alpha4 cytoplasmic domain connection leading to c-Src activation which functions as a FAK-independent linkage to a common motility-promoting signaling pathway.
authors.affiliation: The Scripps Research Institute, Department of Immunology, IMM21, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Datsun A
authors.initials: DA
authors.lastname: Hsia
authors.forename: Ssang-Taek
authors.initials: ST
authors.lastname: Lim
authors.forename: Joie A
authors.initials: JA
authors.lastname: Bernard-Trifilo
authors.forename: Satyajit K
authors.initials: SK
authors.lastname: Mitra
authors.forename: Sakae
authors.initials: S
authors.lastname: Tanaka
authors.forename: Jeroen
authors.initials: J
authors.lastname: den Hertog
authors.forename: Daniel N
authors.initials: DN
authors.lastname: Streblow
authors.forename: Dusko
authors.initials: D
authors.lastname: Ilic
authors.forename: Mark H
authors.initials: MH
authors.lastname: Ginsberg
authors.forename: David D
authors.initials: DD
authors.lastname: Schlaepfer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D002460:Cell Line; D002465:Cell Movement / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism / Q000502:physiology*; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D039041:Integrin alpha4beta1 / Q000235:genetics / Q000502:physiology*; D039081:Integrin alpha5beta1 / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D051076:Proto-Oncogene Proteins c-fyn / Q000235:genetics / Q000378:metabolism; D051575:Proto-Oncogene Proteins c-yes / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D019061:src-Family Kinases
chemical_list: D039041:Integrin alpha4beta1; D039081:Integrin alpha5beta1; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D051416:Focal Adhesion Protein-Tyrosine Kinases; D051076:Proto-Oncogene Proteins c-fyn; D051575:Proto-Oncogene Proteins c-yes; D019061:src-Family Kinases; C000631346:CSK protein, human