Epidermal growth factor disrupts gap-junctional communication and induces phosphorylation of connexin43 on serine.

Abstract

Growth factors regulate cellular proliferation and differentiation by activating plasma membrane tyrosine kinase receptors and triggering a cascade of events mediated by intracellular signaling proteins. The mechanism underlying growth factor modification of cellular functions, such as gap-junctional communication (gjc), has not been established clearly. Addition of epidermal growth factor (EGF) to T51B rat liver epithelial cells resulted in the rapid activation of EGF receptor tyrosine kinase activity followed by a transient dose-dependent disruption of gjc. This change did not result from the gross disturbance of membrane gap junction plaques as measured by immunofluorescence microscopy, but instead correlated with markedly elevated phosphorylation of the connexin43 (cx43) gap junction protein, a profound shift to predominantly phosphorylated forms of cx43, and the appearance of a novel phosphorylated cx43 protein. These changes in cx43 phosphorylation involved only serine residues. On restoration of gjc, these alterations in cx43 phosphorylation reverted to the pre-EGF treatment state. Both events were inhibited by the serine/threonine protein phosphatase inhibitor, okadaic acid. Therefore, unlike the case for pp60v-src, EGF-induced disruption of gjc is not associated with tyrosine phosphorylation of cx43, but instead may result from phosphorylation of cx43 by activated intracellular signaling serine protein kinase(s).

Epidermal growth factor receptor mutation type iii transfected into a small cell lung cancer cell line is predominantly localized at the cell surface and enhances the malignant phenotype

“…These proteins includes ZO-1, ZO-2, ZO-3, cingulin, occludin, connexin43, nectin-2delta, cytoskeletal proteins and vinculin, actin and cadherins. [51][52][53][54][55][56] From these studies it is apparent that the EGFR has a major role in disrupting tight junctions, adherence junctions and gap-junctional communication. It was therefore interesting that gap junction communication in gliomas was recently found to be inversely correlated to cell motility.…”

Disruption of Gap Junctional Communication by the Platelet-derived Growth Factor Is Mediated via Multiple Signaling Pathways

“…Cell Culture and Materials-T51B is a non-neoplastic epithelial cell line derived from rat liver, the origin of which has been described (35), and has been widely used for various studies (23,36,37). The cells were grown to confluence in a complete medium consisting of 90% Eagle's basal medium and 10% bovine calf serum (Colorado Serum Co., Denver, CO) and were maintained in Eagle's basal medium alone for 18 h before treatment with PDGF (5 ng/ml, unless specified).…”

“…(19 -22). Since opening and closure of these channels will regulate the intercellular levels of these yet to be identified signals, inhibition of GJC by mitogens (15,16,23), tumor promoters (24 -26), and oncogenes (27,28) and enhancement of GJC by antineoplastic agents (29,30) are considered to be critical for augmenting their respective effects.…”

Lysophosphatidic acid inhibits gap-junctional communication and stimulates phosphorylation of connexin-43 in WB cells: possible involvement of the mitogen-activated protein kinase cascade

“…There is considerable evidence that junctional permeability can be modulated by phosphorylation of the connexin proteins (see [17][18][19] [20] and cells were cultured as described previously [18]. In Partial purification and assay of MAP kinase Cells (from 100 mm dishes) were rinsed with Ca2+/Mg2+-free PBS and incubated with LPA, PMA or EGF.…”