Protein-tyrosine Phosphatase α Regulates Src Family Kinases and Alters Cell-Substratum Adhesion*
- From the ‡Centre for Molecular Medicine and Therapeutics and the Department of Medicine, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada and ¶Novo Nordisk, Novo Alle, DK-2880 Bagsvaerd, Denmark
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, PTPα, 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-α. Conversely, EGF stimulation of A431 cells in vitro leads to growth inhibition and triggers the rapid detachment of these cells from the substratum. Although PTPα expression did not alter the growth characteristics of either unstimulated or EGF-stimulated cells, this phosphatase was associated with increased cell-substratum adhesion. Furthermore, PTPα-expressing A431 cells were strikingly resistant to EGF-induced cell rounding. Overexpression of PTPα 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 PTPα, and there was evidence of association between PTPα and Src kinase(s). PTPα expression also led to increased association of Src kinase with the integrin-associated focal adhesion kinase, pp125FAK. In addition, paxillin, a Src and/or pp125FAK substrate, displayed increased levels of tyrosine phosphorylation in PTPα-expressing cells and was associated with elevated amounts of Csk. In view of these alterations in focal adhesion-associated molecules in PTPα-expressing A431 cells, as well as the changes in adhesion demonstrated by these cells, we propose that PTPα may have a role in regulating cell-substratum adhesion.
Footnotes
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↵* This research was supported by the National Cancer Institute of Canada (with funds from the Canadian Cancer Society) and by the Medical Research Council of Canada.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ Supported by a studentship from the Canadian Arthritis Society.
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↵‖ Recipient of a Canadian Arthritis Society Research Scientist Award. To whom correspondence should be addressed: Dept. of Medicine, University of British Columbia, Centre for Molecular Medicine and Therapeutics, 950 W. 28th Ave., Vancouver, British Columbia V5Z 4H4, Canada. Tel.: 604-875-3829; Fax: 604-875-3840; E-mail: jirikcmmt{at}ubc.ca.
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↵2 K. Harder, L. Amankwa, and F. R. Jirik, unpublished observations.
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↵3 K. Harder and F. R. Jirik, manuscript in preparation.
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↵4 K. Harder and F. R. Jirik, unpublished observations.
- Abbreviations:
- ECM
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extracellular matrix
- PTP
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protein-tyrosine phosphatase
- EGF
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epidermal growth factor
- FAK
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focal adhesion kinase
- IR
-
insulin receptor
- mAb
-
monoclonal antibody
- PIPES
-
piperazine-N, N′-bis 2-ethanesulfonic acid
- GST
-
glutathione S-transferase
- MGMP
-
malachite green microtiter plate
- MES
-
2-(N-morpholino)ethanesulfonic acid
- Ctr
-
control
- PAGE
-
polyacrylamide gel electrophoresis
- PBS
-
phosphate-buffered saline.
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- Received December 22, 1997.
- Revision received August 26, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
