Multiple actions of epidermal growth factor and TGF-alpha on rabbit gastric parietal cell function

Parietal cells in primary culture and freshly isolated parietal cells were used to compare acute and chronic effects of epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) on acid-secretory related activity, measured as accumulation of the weak base, [14C]aminopyrine (AP). EGF and TGF-alpha chronically enhanced basal and agonist-stimulated AP accumulation (mean effective concentration 0.6-0.8 nM) but acutely inhibited responses to histamine and carbachol (half-maximal inhibitory concentration approximately 4 nM). Pertussis toxin (250 ng/ml, 4 h) suppressed acute EGF inhibition of histamine-stimulated AP accumulation but not the chronic enhancement. A subclass of tyrosine kinase inhibitors suppressed chronic EGF effects (genistein > tyrphostin B56 >>> tyrphostin B42), whereas tyrphostin A25, lavendustin A, and the inactive genistein analogue, daidzein, had no significant effect. In contrast, histamine-stimulated AP accumulation was acutely potentiated by genistein, daidzein, and tyrphostin B42, but not tyrphostin B56. Reduced phosphorylation of a 44- to 45-kDa protein with an isoelectric point of approximately 7 [phosphoprotein (pp) 44] was correlated with chronic inhibition but not with acute potentiation by specific tyrosine kinase inhibitors. Preliminary data indicate that pp44 is a member of the mitogen-activated protein kinase family of tyrosine/threonine kinases (also known as extracellular signal-related kinases). We propose that 1) EGF and/or TGF-alpha modulates parietal cell function by multiple signaling pathways, 2) a soluble tyrosine kinase may be involved in the mediation of the chronic effects of EGF, and 3) acute potentiation of histamine-stimulated AP accumulation by certain tyrosine kinase inhibitors and daidzein is probably not mediated by receptor-associated tyrosine kinases.