Author/Editor		Lenasi, Helena; Breskvar, Katja
Title		Specific interactions of steroids, arylhydrocarbons and flavonoids with progesterone receptors from the cytosol of the fungus Rhizopus nigricans
Type		članek
Source		J Steroid Biochem Mol Biol
Vol. and No.		Letnik 91
Publication year		2004
Volume		str. 273-84
Language		eng
Abstract		Rhizopus nigricans (R. nigricans) transforms fungitoxic progesterone into the less toxic 11alpha-hydroxyprogesterone which is then able to exit the mycelia into the surrounding water. Hydroxylation of progesterone is an inducible process in which cytosolic progesterone receptors could be involved. In the present study, we characterised receptors with respect to ligand specificity and to their involvement in progesterone induction of hydroxylase. EC50 values of different ligands (steroids, xenobiotic arylhydrocarbons and natural flavonoids) were determined by competition studies using 40 nM (3H)progesterone. C21 and C19 3-oxo-4-ene steroids were good competitors (EC50 of progesterone 2.3 +- 0.1 x 10-7 M, EC50 of androsten-3,17-dione 24 +- 2 x 10-7 M). The presence of hydroxyl groups in steroids significantly decreased the affinity for receptors. The arylhydrocarbons a-naphthoftavone and ketoconazole exhibited EC50 values of 0.3 +- 0.01 x 10-7 M and 27 +- 5 x 10-7 M, respectively, whereas (3-naphthoftavone and benzo(a)pyrene were not able to displace labelled progesterone completely. The competition curves obtained by natural flavonoids also did not reach the bottom level of non-labelled progesterone, indicating the interaction at some allosteric binding site(s) of progesterone receptors. All ligands were examined for their involvement in progesterone-hydroxylase induction. Steroid agonists induced the enzyme in a dose-dependent manner in accordance with their affinity for receptors, whereas arylhydrocarbons and natural flavonoids did not induce the enzyme. The agonistic action of steroids, together with the antagonistic action of alpha-naphthoftavone, strongly suggests the involvement of progesterone receptors in progesterone signalling resulting in the induction of progesterone-hydroxylase.
Descriptors		RHIZOPUS PROGESTERONE RECEPTORS, PROGESTERONE FLAVONES KETOCONAZOLE STEROIDS BETA-NAPHTHOFLAVONE BENZOPYRENES CYTOSOL RADIOLIGAND ASSAY BINDING SITES BINDING, COMPETITIVE