Polyamines and autocrine control of N-nitrosomethylurea-induced rat mammary tumor growth in vitro by progesterone.
These experiments were designed to test whether autocrine/paracrine mechanisms are involved in the growth-promoting action of progesterone (Pg) in the N-nitrosomethylurea-induced rat mammary tumor cultured in vitro in soft agar clonogenic assay. In support of our hypothesis, we observed that conditioned media obtained from Pg-treated tumors (Pg-CM), consistently stimulated colony formation in our system to the same degree as Pg itself (approximately 140% of control). Treatment with heat, trypsin, and concanavalin A abolished the colony-stimulating effect of Pg-CM, thus suggesting the possible glycoprotein nature of the Pg-inducible growth factor(s). The growth-promoting action of Pg-CM was rather specific since CMs obtained from tumors exposed to a variety of other steroid hormones rarely stimulated colony formation and usually only to a modest degree. Administration of the polyamine biosynthetic inhibitor, alpha-difluoromethylornithine, abolished the colony-stimulating effect of Pg-CM. The inhibitory effect of alpha-difluoromethylornithine was reversed in a dose-dependent fashion by exogenous administration of spermidine, which entirely restored the growth-promoting action of Pg-CM. Addition of increasing amounts of spermidine, however, did not potentiate Pg-CM action under our experimental conditions. Our results indicate that autocrine/paracrine mechanisms may mediate, at least in part, the colony-stimulating effect of Pg in our system. The polyamine pathway plays an essential role in the expression of such control of tumor growth by Pg.
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D003208:Concanavalin A / Q000494:pharmacology; D003470:Culture Media; D000518:Eflornithine / Q000494:pharmacology*; D008325:Mammary Neoplasms, Experimental / Q000473:pathology*; D008770:Methylnitrosourea; D011073:Polyamines / Q000502:physiology*; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D013095:Spermidine / Q000494:pharmacology*; D013256:Steroids / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology; D014410:Tumor Stem Cell Assay
D003470:Culture Media; D011073:Polyamines; D013256:Steroids; D003208:Concanavalin A; D011374:Progesterone; D008770:Methylnitrosourea; D014357:Trypsin; D013095:Spermidine; D000518:Eflornithine