EGF rapidly stimulates tyrosine phosphorylation in cultured endometrial cells

Recent increasing evidence suggests that EGF has a role in modulating the differentiated functions of human endometrial cells in an autocrine/paracrine fashion. To explore the signal transduction pathway of EGF in endometrial cells, we used cultured human endometrial cells to examine whether EGF induces tyrosine-phosphorylation. EGF phosphorylated the 175 kDa protein on tyrosine residues within 10 seconds of stimulation. EGF induced tyrosine phosphorylation at as low as 0.1 ng/ml with the maximal effect occurring at 10 ng/ml. Estradiol was shown to enhance the phosphorylation by EGF in this system. These results thus suggest that tyrosine-phosphorylation might be an important step in the signal transduction of EGF in human endometrial cells. Furthermore, the observed stimulatory action of estradiol on tyrosine-phosphorylation by EGF might provide a clue in the elucidation of the cellular mechanism of estrogen action in endometrium.