Am. J. Respir. Cell Mol. Biol., Vol 17, No. 4, Oct 1997, 456-461.
Adhesion of bovine airway smooth muscle cells activates extracellular signal-regulated kinases
RM Heuertz, KJ Hamann, MB Hershenson and AR Leff
Department of Medicine, University of Chicago, Illinois 60637-1470, USA.
Extracellular signal-regulated kinases (ERKs) phosphorylate and regulate
cytoskeletal components of contractile cells and have been implicated in
integrin-mediated adhesion. In this study, we examined the contributions of
adherence, cell flattening, and cytoskeletal reorganization to
adhesion-induced ERK activation in cultured bovine tracheal myocytes. We
found, as evidenced by a reduction in electrophoretic mobility, that
adhesion to fibronectin induced phosphorylation of both p44ERK1 and
p42ERK2. In-gel kinase assays confirmed activation of both p44ERK1 and
p42ERK2 in fibronectin- adherent cells, consistent with the notion that
ligand-integrin binding is required for adhesion-induced ERK activation.
However, ERK activation was maximal 2-4 h after plating, and adherence to
either polystyrene or poly-L-lysine also caused ERK activation (fold
increase 4 h after plating: fibronectin, 3.75 +/- 0.33; polystyrene, 3.95
+/- 0.78; poly-L-lysine, 2.14 +/- 0.36). Inspection of myocytes following
passage onto fibronectin showed near 100% adhesion and cell spreading after
4 h, whereas cells plated onto poly-L-lysine demonstrated adherence but
minimal spreading. To test whether the cytoskeletal reorganization
accompanying cell spreading is required for adhesion- induced ERK
activation, we assessed ERK activity following pretreatment with
cytochalasin D, an inhibitor of actin polymerization. Cytochalasin
inhibited both cell spreading and ERK activation following adhesion to
fibronectin, but had no effect on growth factor-induced ERK activation in
adherent cells. We conclude that adhesion-induced ERK activation in bovine
tracheal myocytes may occur independently of ligand-integrin binding and is
primarily related to the cell spreading that follows adhesion.
