Am. J. Respir. Cell Mol. Biol., Vol 16, No. 5, 05 1997, 613-620.
Protein tyrosine phosphatases mediate cell readhesion in alveolar epithelial cells mechanically separated from in vitro matrix
BL Oliver, C Garat, R Pytela and MA Matthay
Cardiovascular Research Institute, University of California, San Francisco 94143, USA.
Alveolar epithelial type II cells are the progenitor cells for restoring
the alveolar epithelial barrier after acute lung injury. During repair of
lung injury, the alveolar epithelial type II cells reepithelialize denuded
air spaces, a process that involves breaking and reforming cell adhesions.
A novel technique of mechanical separation of cultured alveolar epithelial
cells from in vitro matrix was used to examine the intracellular signals
that result when alveolar epithelial cell adhesions are broken. The results
show that the tyrosine phosphorylation levels of focal adhesion kinase,
paxillin, and pp60(src) decreased immediately after mechanical separation
of the cells. Levels returned to nearly normal by 24 h after mechanical
separation. Paxillin and pp60(scr) coprecipitated with focal adhesion
kinase regardless of their phosphorylation state. Interestingly, the
tyrosine phosphorylation level of the mitogen-activated protein kinase,
p42(erk2), increased 15 min after mechanical separation. Preincubation of
cell monolayers with phenylarsine oxide, a protein tyrosine phosphatase
inhibitor, blocked the decrease in tyrosine phosphorylation levels of focal
adhesion kinase, paxillin and pp60(src). Phenylarsine oxide incubation also
prevented readhesion of mechanically separated cells at 24 h, but
genistein, a tyrosine kinase inhibitor, had no effect. We conclude that
protein tyrosine phosphatases are activated immediately after cultured
alveolar epithelial cells are mechanically separated from in vitro matrix,
and their activation is required for alveolar epithelial cell readhesion.
