Received for publication October 31, 2007.
Revised February 26, 2008.
Accepted for publication February 27, 2008.

Lysophosphatidic acid induces rapid and sustained decreases in epidermal growth factor binding via different signaling pathways in BEAS-2B airway epithelial cells

Abstract

Lysophosphatidic acid (LPA) and epidermal growth factor (EGF) are important mediators of lung cell function and lung diseases. We showed previously that LPA decreases EGFR binding rapidly in BEAS-2B airway epithelial cells, and this decrease is sustained to at least 18 hr. The current studies investigate which LPA signaling pathways mediate the rapid vs. sustained decreases in EGFR binding in BEAS-2B cells. The G_i/o inhibitor pertussis toxin and the Rho kinase inhibitor Y-27632 had no effect on the rapid or sustained decreases. However, the MEK inhibitor U0126 decreased ERK1/2 phosphorylation, completely inhibited the rapid decrease in binding, and partially inhibited the sustained decrease. The direct PKC activator phorbol-12-myristate-13-acetate (PMA) stimulated ERK1/2 phosphorylation and decreased EGFR binding at both 15 min and 18 hr. Furthermore, inhibitors of Ca²⁺- and phospholipid-dependent protein kinase (PKC) partially inhibited ERK1/2 phosphorylation and the 15-min decrease but completely inhibited the 18-hr decrease. Inhibitor time course studies showed that PKC induction of the 18 hr decrease occurred during the first 3 hr of treatment. We showed previously that LPA-stimulated EGFR transactivation contributes to the rapid decrease. Two transactivation inhibitors partially inhibited ERK1/2 phosphorylation, and U0126 partially inhibited EGFR transactivation, indicating that MEK may be involved both upstream and downstream of EGFR activation. Together the data presented here indicate that LPA mediates the rapid decrease in EGFR binding via EGFR transactivation, MEK/ERK, and PKC, whereas the sustained decrease is regulated primarily by PKC.

Key words: EGFR, ERK, LPA, PKC, airway epithelial cells, transactivation