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* From the Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, PA. This research was supported by National Institutes of Health grants AHA0150244N, HL31560, and HL10358.
Correspondence to: D. Eugene Rannels, PhD, Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, PA 17033; e-mail: grannels{at}psu.edu
Alveolar
epithelial cells (AECs) in primary cultures express gap junction (GJ)
proteins, connexins (Cxs), and establish GJ intercellular
communication. Cx expression is differentially regulated via
integrin-mediated interactions of AEC with extracellular matrix (ECM)
proteins including fibronectin (FN) and laminin, which exert reciprocal
effects. ECM FN increases the expression of Cx43 messenger RNA and
protein. Antibodies against FN,
5ß1-integrin, or the
5-integrin
subunit block FN effects on Cx43 abundance and cause the redistribution
of immunopositive Cx43 from the plasma membrane to the cytosol.
Anti-
5ß1 antibodies had no effect on the AEC expression of Cx43
mRNA over a 24-h exposure but caused the transient phosphorylation
(activation) of extracellular signal-regulated kinase (ERK)-1 and
ERK-2. These data suggest that FN-mediated integrin ligation activates
intracellular kinases that may regulate Cx expression and/or
trafficking. Cells thus were treated with the mitogen-activated protein
kinase-1 and 2 inhibitor, PD98059. PD98059 did not cause AEC detachment
or death after 24 h at concentrations up to 50 µM. The drug
reduced Cx43 expression within 24 h in a dose-dependent manner and
caused immunopositive Cx43 to redistribute from the membrane to the
cytosol. The dimethyl sulfoxide vehicle had no effect. PD98059 had no
additional effect in the presence of anti-
5 integrin antibodies,
suggesting an action through similar regulatory pathways. Although the
drug rapidly reduced ERK phosphorylation, it had little effect on the
expression of ERK-1 or ERK-2 proteins. These data suggest that the
regulation of Cx expression, and thus of GJ intercellular communication
in AECs is exerted through integrin-mediated cell-ECM interactions at
the plasma membrane, which are linked to the activation of
intracellular kinase-signaling cascades.
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