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First published online 30 July 2003
doi: 10.1242/jcs.00693
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Research Article |
1 University of British Columbia, Faculty of Dentistry, Department of Oral
Biological and Medical Sciences, 2199 Wesbrook Mall, Vancouver, BC V6T 1Z3,
Canada
2 Kinexus Bioinformatics Corporation, Suite 401, 2389 Health Sciences Mall,
Vancouver, BC V6T 1Z4, Canada
3 University of Toronto, Faculty of Dentistry, Department of Biological and
Diagnostic Sciences, 150 College Street, Toronto, ON M5S 3E2, Canada
* Author for correspondence (e-mail: larjava{at}interchange.ubc.ca)
Accepted 28 May 2003
During wound healing, keratinocytes initiate migration from the wound edge
by extending lamellipodia into a fibronectin-rich provisional matrix. While
lamellipodia-like structures are also found in cultured keratinocytes exposed
to epidermal growth factor (EGF), the signaling pathway that regulates the
formation of these structures is not defined. In cultured human keratinocytes
seeded on fibronectin, we found that protein-serine/threonine kinase
inhibitors including staurosporine, induced concentration-dependent formation
of extended lamellipodia (E-lams). The formation of E-lams was inhibited by
the proteintyrosine kinase inhibitors herbimycin A and genistein and augmented
by the protein-tyrosine phosphatase inhibitor sodium orthovanadate.
Staurosporine treatment induced relocation of tyrosine phosphorylated
phospholipase C-
1 (PLC-
1) to the tips of lamellipodia where
actin assembly was initiated. Consistent with an involvement of PLC-
1
in E-lam formation, intracellular free calcium (Ca2+) was elevated
during the formation of E-lams and conversely, E-lam formation was blocked by
intracellular Ca2+ chelation with BAPTA/AM, but not by
extracellular reduction of Ca2+ by EGTA. Notably, glycogen synthase
kinase-3
/ß (GSK-3
/ß) was activated by staurosporine as
evidenced by reduced phosphorylation on Ser-21/9. Suppression of GSK-3
activity by LiCl2 or by a specific chemical inhibitor, SB-415286,
blocked E-lam formation but without altering cell spreading. Furthermore,
GSK-3 inhibitors blocked both staurosporine- and EGF-induced keratinocyte
migration in scratch-wounded cultures. We propose that GSK-3 plays a crucial
role in the formation of long lamellipodia in human keratinocytes and is
potentially a central regulatory molecule in epithelial cell migration during
wound healing.
Key words: Fibronectin, Wound healing, Calcium, EGF, Migration
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