Genistein and erbstatin inhibition of normal mammary epithelial cell proliferation is associated with EGF-receptor down-regulation.
Epidermal growth factor (EGF) is a potent mitogen for normal mouse mammary epithelial cells grown in primary culture. EGF activation of the EGF-receptor (EGF-R) induces intrinsic tyrosine kinase activity which results in EGF-R autophosphorylation and tyrosine phosphorylation of other intracellular substrates involved in EGF-R signal transduction. Genistein and erbstatin are anticancer agents which have been shown to be potent tyrosine kinase inhibitors. However, the effects of these compounds in modulating EGF-dependent normal mammary epithelial cell proliferation is presently unknown. Therefore, studies were conducted to determine the effects of genistein and erbstatin on EGF-dependent proliferation, and EGF-R levels and autophosphorylation in normal mouse mammary epithelial cells grown in primary culture and maintained in serum-free media. Chronic treatment with 6.25-100 microM genistein or 1-16 microM erbstatin significantly decreased EGF-dependent mammary epithelial cell proliferation in a dose-responsive manner. However, the highest doses of genistein (100 microM) and erbstatin (16 microM) were found to be cytotoxic. Additional studies showed that acute treatment with 6.25-400 microM genistein did not affect EGF-R levels or EGF-induced EGF-R autophosphorylation, while acute treatment with 1-64 microM erbstatin caused a slight reduction in EGF-R levels, but had no effect on EGF-dependent EGF-R autophosphorylation in these cells. In contrast, chronic treatment with similar doses of genistein or erbstatin resulted in a large dose-responsive decrease in EGF-R levels, and a corresponding decrease in total cellular EGF-R autophosphorylation intensity. These results demonstrate that the inhibitory effects of chronic genistein and erbstatin treatment on EGF-dependent mammary epithelial cell proliferation is not due to a direct inhibition of EGF-R tyrosine kinase activity, but results primarily from a down-regulation in EGF-R levels and subsequent decrease in mammary epithelial cell mitogenic-responsiveness to EGF stimulation.
McIntyre
B S
BS
Department of Zoology, Washington State University, Pullman 99164-4236, USA.
Sylvester
P W
PW
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D015536:Down-Regulation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism*; D005260:Female; D019833:Genistein / Q000494:pharmacology*; D006131:Growth Inhibitors / Q000494:pharmacology*; D006873:Hydroquinones / Q000494:pharmacology*; D008321:Mammary Glands, Animal; D051379:Mice; D008807:Mice, Inbred BALB C
D006131:Growth Inhibitors; D006873:Hydroquinones; D004815:Epidermal Growth Factor; D019833:Genistein; D066246:ErbB Receptors; C048212:erbstatin