ANALYSIS OF EPIDERMAL GROWTH-FACTOR ACTION IN HUMAN MYOMETRIAL SMOOTH-MUSCLE CELLS

The present study investigated the mechanisms involved in the mitogeni c action of epidermal growth factor (EGF) in cultured human myometrial smooth muscle cells. The cells contained EGF/transforming growth fact or-alpha (TGF-alpha) receptors as well as EGF and TGF-alpha mRNA trans cripts and the corresponding proteins. Culturing with human EGF result ed in concentration- and time-dependent increases in cell density. The maximal increase was seen at 1 nM followed by a decrease to control l evels at 100 nM EGF. The EGF increased cell density from 4 to 8 days f ollowed by a plateau coinciding with the cells reaching confluence. EG F treatment concomitantly decreased the average size of cells. TGF-alp ha mimicked EGF and there was no synergism between the two, suggesting a common mechanism of action. Although the presence of 10% fetal bovi ne serum enhanced overall cell growth, it was not required for EGF and TGF-alpha action. The receptor antibody, which is directed against th e extracellular domain and can inhibit ligand binding to the receptors , dramatically inhibited the basal cell growth and exogenous EGF rever sed the antibody effect. While TGF-alpha antibody was only marginally effective, EGF antibody had no effect on basal cell growth. Lavendusti n (a tyrosine kinase inhibitor), calphostin (a protein kinase C inhibi tor), but not H-89 (a protein kinase A inhibitor), inhibited EGF actio n. Indomethacin, a cyclo-oxygenase inhibitor, completely inhibited, wh ereas nordihydroguaiaretic acid, a lipoxygenase inhibitor, slightly in hibited EGF action. While estradiol-17 beta modestly inhibited basal a s well as EGF-stimulated myometrial smooth muscle cell density, proges terone had no effect. In summary, mitogenic action of EGF in human myo metrial smooth muscle cells does not require serum components and it i nvolves tyrosine kinase and protein kinase C signaling and eicosanoids from the cycleoxygenase pathway of arachidonic acid metabolism.