Epidermal growth factor receptor is activated by hyposmolarity and is an early signal modulating osmolyte efflux pathways in Swiss 3T3 fibroblasts

Abstract

Exposure of cultured Swiss 3T3 fibroblasts to 35% hyposmotic solution activated epidermal growth factor receptor (EGFR) phosphorylation to a greater extent than the ligand, EGF. Concanavalin A (Con A) and wheat-germ agglutinin (WGA) had the same effect. EGFR phosphorylation seems to be involved in the transduction signalling for hyposmotically induced taurine release, as suggested by the latter's reduction when EGFR phosphorylation was blocked by 50 microM AG213 or AG112 and, conversely, its potentiation by EGF (200 ng/ml). The relationship between hyposmotically induced taurine efflux and reduced osmolarity showed saturable kinetics, following a sigmoidal function. EGF shifted the relationship to the left, implying an increase in sensitivity to hyposmolarity. EGF increased taurine efflux only marginally under isosmotic conditions. EGF and agglutinins also potentiated the hyposmotically induced release of 86Rb but, in contrast to taurine, the efflux was unaffected by EGFR inhibition. EGF and agglutinins markedly increased 86Rb release under isosmotic conditions. The EGF-evoked isosmotic 86Rb release, together with the hyposmotic efflux, accounted fully for the observed potentiation by EGF, raising the possibility of an overlapping of these two effects, rather than a true potentiation. A link between EGFR, phosphatidylinositide-3-kinase (PI3K) and hyposmotically induced taurine (but not 86Rb) release is suggested by the increase in PI3K activity elicited by hyposmolarity, which was fully prevented by EGFR inhibition, and by a marked reduction of hyposmotically induced taurine (but not 86Rb) release, by wortmannin. The present findings, together with results showing EGF activation of osmosensitive Cl- fluxes implicate EGFR as an important modulator of osmolyte efflux pathways.

Functional and molecular characterization of multiple K–Cl cotransporter isoforms in corneal epithelial cells

“…11 and 12). Tyrosine kinase receptors can be activated by membrane stretch induced by hypotonic swelling, which in turn, activates the EGF receptor (Franco et al, 2004). Such a rationale could explain how, in CEC, both hypotonic swelling and EGF receptor stimulation produce the same effect, i.e., MAPK pathway activation.…”

“…One of the pathways wellstudied in CEC is the signaling cascade of epidermal growth factor (EGF)-induced p44/42 and p38MAPK activation (Kang et al, 2000;Kang et al, 2001;Lu et al, 2001;Mergler et al, 2005;Roderick et al, 2003;Tao et al, 1995;Yang et al, 2005;Yang et al, 2003;Yang et al, 2001). It has also been shown that membrane stretch, induced by hypotonic swelling, is capable of activating tyrosine kinase receptors, which, in turn, activate the EGF receptor (Franco et al, 2004).…”

Physiology of Cell Volume Regulation in Vertebrates

“…The EGF rececptor in Swiss 3T3 fibroblasts (247) and keratocytes (449) and other cell types (771), and the ErbB4 EGF receptor in cerebellar granular neurons (548), are activated by hypotonic cell swelling, resulting in activation of the PI3K-PKB and MEK1/2-ERK1/2 pathways and volume regulatory taurine efflux (247).…”

“…A role for tyrosine phosphorylation events in modulation of swelling-induced taurine release is suggested by the inhibitory effect of tyrosine kinase blockers (genistein, tyrphostins) and potentiating effect of tyrosine phosphatase inhibitors on the efflux (492,662,670,920). Pharmacological evidence indicates that the tyrosine kinases regulating the taurine efflux pathway include receptor tyrosine kinases (247,492), FAK, and members of the Src family (391, 492).…”

Potassium-Chloride Cotransporter Mediates Cell Cycle Progression and Proliferation of Human Corneal Epithelial Cells

“…This result is in agreement with another study that showed hypotonicity-induced mechanical stretch of the plasma membrane can activate tyrosine kinase receptors, which, in turn, activates the EGF receptor. 45 Taken together, these studies suggest that the signaling pathway that is induced by EGF receptor stimulation or hypotonicity exposure converge to induce coordinated activation of ion transport mechanisms and p44/42MAPK activation, presumably through a tyrosine kinase receptor.…”