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Am J Physiol Cell Physiol (January 23, 2008). doi:10.1152/ajpcell.00359.2007
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Submitted on August 10, 2007
Accepted on January 18, 2008

Tyrosine Phosphatase PTP{alpha} Regulates Focal Adhesion Remodeling Through Rac1 Activation

Maria Teresa Herrera Abreu1, Patricia Castellanos Penton2, Vivian Kwok2, Eric Vachon2, David Shalloway3, Luis Vidali4, Wilson Lee5, Christopher A. G. McCulloch5, and Gregory P. Downey2*

1 Department of Medicine, Clinical Science Division, University of Toronto, Toronto, Canada
2 Medicine, University of Toronto, Toronto, Canada
3 Department of Molecular Biology and Genetics, Cornell University, Ithica, New York, United States
4 Medicine, Brigham and Womens Hospital, Boston, Massachusetts, United States
5 MRC Group in Pediodontal Physiology, University of Toronto, Toronto, Canada

* To whom correspondence should be addressed. E-mail: downeyg{at}njc.org.

We characterized the role of protein tyrosine phosphatase (PTP){alpha} in focal adhesion formation and remodeling using wild-type and PTP{alpha}-deficient cells. Compared to wild-type cells, spreading PTP{alpha}-/- fibroblasts displayed fewer leading edges and formed elongated focal adhesions at the cell periphery that were enriched with {alpha}-actinin. These features suggest the presence of slowly remodeling cell adhesions and were phenocopied in human fibroblasts in which PTP{alpha} was knocked down using siRNA or in NIH3T3 fibroblasts expressing catalytically inactive (C433S/C723S) PTP{alpha}. Fluorescence recovery after photobleaching showed slower GFP-{alpha}-actinin recovery in the focal adhesions of PTP{alpha}-/- cells compared to wild-type cells. These alterations correlated with reduced cell spreading, adhesion, polarization, and retarded contraction of extracellular matrices in PTP{alpha}-/- cells. Activation of Rac1 and its recruitment to focal adhesions during spreading was diminished in cells expressing C433S/C723S PTP{alpha}. Rac1-/- cells also displayed abnormally elongated and peripherally distributed focal adhesions that failed to remodel. Conversely, expression of constitutively active Rac1 restored normal focal adhesion remodeling in PTP{alpha}-/- cells. We conclude that PTP{alpha} is required for remodeling of focal adhesions during cell spreading via a pathway involving Rac1.




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