Orogastric EGF enhances c-neu and EGF receptor phosphorylation in suckling rat jejunum in vivo.

Epidermal growth factor (EGF) in rat milk stimulates intestinal growth. We examined the role of EGF-stimulated tyrosine kinase activity in vivo in this process using an affinity-purified anti-phosphotyrosine antibody in Western blot. Jejunal sacs from fasted 8-day-old rat pups were incubated with intraluminal EGF and were then assayed for phosphotyrosyl proteins (p-Tyr) by Western blot. A 170-kDa p-Tyr was present in EGF-treated sacs but not in control. A 190-kDa p-Tyr was constitutively present in control but increased in abundance in EGF-treated sacs. Dose-response experiments demonstrated that the increase in p-Tyr was present at 100 ng/ml EGF, which is within the physiological range. The 170- and 190-kDa p-Tyr was confirmed by immunoprecipitation to be the EGF receptor and c-neu, respectively. A similar response was also observed in the jejunum after orogastric gavage feeding of EGF. By use of indirect immunofluorescence, the EGF receptor was localized primarily to the basolateral membrane of both the crypt and villus epithelium. c-neu was localized primarily in the villus enterocyte basolateral membrane. These data demonstrate that intraluminal EGF stimulates rapid tyrosine phosphorylation of the EGF receptor in vivo and that c-neu is a major substrate of the EGF receptor in suckling jejunum. The basolateral membrane localization of the EGF receptor and c-neu suggests that EGF is rapidly transported across the intestinal epithelium in suckling rat jejunum.