title: Protein-tyrosine phosphatase alpha regulates Src family kinases and alters cell-substratum adhesion.
abstract: The roles of protein-tyrosine phosphatases (PTPs) in processes such as cell growth and adhesion are poorly understood. To explore the ability of specific PTPs to regulate cell signaling pathways initiated by stimulation of growth factor receptors, we expressed the receptor-like PTP, PTPalpha, in A431 epidermoid carcinoma cells. These cells express high levels of the epidermal growth factor (EGF) receptor and proliferate in response to the autocrine production of transforming growth factor-alpha. Conversely, EGF stimulation of A431 cells in vitro leads to growth inhibition and triggers the rapid detachment of these cells from the substratum. Although PTPalpha expression did not alter the growth characteristics of either unstimulated or EGF-stimulated cells, this phosphatase was associated with increased cell-substratum adhesion. Furthermore, PTPalpha-expressing A431 cells were strikingly resistant to EGF-induced cell rounding. Overexpression of PTPalpha in A431 cells was associated with the dephosphorylation/activation of specific Src family kinases, suggesting a potential mechanism for the observed alteration in A431 cell-substratum adhesion. Src kinase activation was dependent on the D1 catalytic subunit of PTPalpha, and there was evidence of association between PTPalpha and Src kinase(s). PTPalpha expression also led to increased association of Src kinase with the integrin-associated focal adhesion kinase, pp125(FAK). In addition, paxillin, a Src and/or pp125(FAK) substrate, displayed increased levels of tyrosine phosphorylation in PTPalpha-expressing cells and was associated with elevated amounts of Csk. In view of these alterations in focal adhesion-associated molecules in PTPalpha-expressing A431 cells, as well as the changes in adhesion demonstrated by these cells, we propose that PTPalpha may have a role in regulating cell-substratum adhesion.
authors.affiliation: Centre for Molecular Medicine and Therapeutics and the Department of Medicine, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada.
authors.forename: K W
authors.initials: KW
authors.lastname: Harder
authors.forename: N P
authors.initials: NP
authors.lastname: Moller
authors.forename: J W
authors.initials: JW
authors.lastname: Peacock
authors.forename: F R
authors.initials: FR
authors.lastname: Jirik
mesh_terms: D000595:Amino Acid Sequence; D002294:Carcinoma, Squamous Cell; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects / Q000502:physiology; D019976:Cloning, Organism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology / Q000502:physiology; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D051419:Paxillin; D010446:Peptide Fragments / Q000737:chemistry; D010748:Phosphopeptides / Q000737:chemistry; D010750:Phosphoproteins / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011972:Receptor, Insulin / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012394:Rosaniline Dyes / Q000378:metabolism; D013379:Substrate Specificity; D014162:Transfection; D016211:Transforming Growth Factor alpha / Q000494:pharmacology / Q000502:physiology; D014407:Tumor Cells, Cultured; D018909:src Homology Domains
chemical_list: D015815:Cell Adhesion Molecules; D003598:Cytoskeletal Proteins; C496061:PXN protein, human; D051419:Paxillin; D010446:Peptide Fragments; D010748:Phosphopeptides; D010750:Phosphoproteins; D011994:Recombinant Proteins; D012394:Rosaniline Dyes; D016211:Transforming Growth Factor alpha; C005095:malachite green; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D017027:Protein Tyrosine Phosphatases