title: Brk activates rac1 and promotes cell migration and invasion by phosphorylating paxillin.
abstract: Brk (for breast tumor kinase) is a nonreceptor tyrosine kinase containing SH3, SH2, and tyrosine kinase catalytic domains. Brk was originally identified from a human metastatic breast tumor, and its overexpression is frequently observed in breast cancer and several other cancer types. However, the molecular mechanism by which this kinase participates in tumorigenesis remains poorly characterized. In the present study, we not only identified paxillin as the binding partner and substrate of Brk but also discovered a novel signaling pathway by which Brk mediates epidermal growth factor (EGF)-induced paxillin phosphorylation. We show that EGF stimulation activates the catalytic activity of Brk, which in turn phosphorylates paxillin at Y31 and Y118. These phosphorylation events promote the activation of small GTPase Rac1 via the function of CrkII. Through this pathway, Brk is capable of promoting cell motility and invasion and functions as a mediator of EGF-induced migration and invasion. In accordance with these functional roles, Brk translocates to membrane ruffles, where it colocalizes with paxillin during cell migration. Together, our findings identify novel signaling and biological roles of Brk and indicate the first potential link between Brk and metastatic malignancy.
authors.affiliation: Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Hsin-Yi
authors.initials: HY
authors.lastname: Chen
authors.forename: Che-Hung
authors.initials: CH
authors.lastname: Shen
authors.forename: Yuh-Tyng
authors.initials: YT
authors.lastname: Tsai
authors.forename: Feng-Chi
authors.initials: FC
authors.lastname: Lin
authors.forename: Yuan-Ping
authors.initials: YP
authors.lastname: Huang
authors.forename: Ruey-Hwa
authors.initials: RH
authors.lastname: Chen
mesh_terms: D000818:Animals; D019556:COS Cells; D020134:Catalytic Domain; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D002465:Cell Movement; D002633:Chemotaxis / Q000187:drug effects; D002522:Chlorocebus aethiops; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009363:Neoplasm Proteins; D051419:Paxillin; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D050737:Proto-Oncogene Proteins c-crk; D034741:RNA, Small Interfering / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013379:Substrate Specificity; D020830:rac1 GTP-Binding Protein / Q000032:analysis / Q000378:metabolism*
chemical_list: D015815:Cell Adhesion Molecules; D003598:Cytoskeletal Proteins; D009363:Neoplasm Proteins; C496061:PXN protein, human; D051419:Paxillin; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D050737:Proto-Oncogene Proteins c-crk; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D004815:Epidermal Growth Factor; D005982:Glutathione Transferase; D011505:Protein-Tyrosine Kinases; C088375:PTK6 protein, human; D020830:rac1 GTP-Binding Protein