title: Glucocorticoids coordinately disrupt a transforming growth factor alpha autocrine loop and suppress the growth of 13762NF-derived Con8 rat mammary adenocarcinoma cells.
abstract: We have demonstrated previously that the synthetic glucocorticoid dexamethasone suppresses the growth of Con8 rat mammary tumor cells, which are derived from the 13762NF transplantable, hormone-responsive rat mammary adenocarcinoma. Dexamethasone inhibited [3H]thymidine incorporation into Con8 cells at high cell density under both serum and serum-free conditions. Fractionation in nonreducing sodium dodecyl sulfate-polyacrylamide gels of proteins secreted from dexamethasone-treated and untreated Con8 mammary tumor cells revealed two size classes of glucocorticoid inhibited mitogenic activities; a larger M(r) 27,000-33,000 and a smaller M(r) 5,000-12,000 activity. Both size classes of mitogens restimulated the growth of glucocorticoid-suppressed Con8 cells suggesting that they can act in an autocrine fashion. The smaller mitogen was identified as transforming growth factor alpha (TGF-alpha) since this activity competed with 125I-epidermal growth factor (EGF) for EGF receptor binding and was selectively immunodepleted with monoclonal TGF-alpha antibodies but not with EGF antibodies. Western blots and radioreceptor assay of Con8-secreted proteins revealed that glucocorticoids inhibited the production of a M(r) 5500 immunoreactive TGF-alpha protein by 10-fold. Consistent with a steroid effect on the level of TGF-alpha production, rather than on its activity, the specific mitogenic activities of the TGF-alpha s secreted by dexamethasone-treated and untreated Con8 cells were identical to that of recombinant human TGF-alpha. Treatment of intact cells with suramin, which dissociates ligand-receptor complexes, revealed that the EGF receptor-mediated mitogenic response is functional in both glucocorticoid-treated and untreated cells. Taken together, our results demonstrate that glucocorticoids suppress Con8 mammary tumor cell growth and disrupt a potential TGF-alpha autocrine loop which results in a dramatic reduction in the level of extracellular TGF-alpha.
authors: Department of Molecular and Cell Biology, University of California, Berkeley 94720.
authors: D B
authors: DB
authors: Alexander
authors: L
authors: L
authors: Goya
authors: M K
authors: MK
authors: Webster
authors: T
authors: T
authors: Haraguchi
authors: G L
authors: GL
authors: Firestone
mesh_terms: D016475:3T3 Cells; D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D016895:Culture Media, Serum-Free; D004247:DNA / Q000096:biosynthesis; D003907:Dexamethasone / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008934:Mitogens / Q000037:antagonists & inhibitors / Q000302:isolation & purification; D008970:Molecular Weight; D009368:Neoplasm Transplantation; D051381:Rats; D011916:Rats, Inbred F344; D016211:Transforming Growth Factor alpha / Q000037:antagonists & inhibitors* / Q000302:isolation & purification / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D016895:Culture Media, Serum-Free; D008934:Mitogens; D016211:Transforming Growth Factor alpha; D003907:Dexamethasone; D004247:DNA; D066246:ErbB Receptors