Disease relevance of CYP17

• Flavodoxin and NADPH-flavodoxin reductase from Escherichia coli support bovine cytochrome P450c17 hydroxylase activities [1].
• Expression of bovine 17 alpha-hydroxylase cytochrome P450 (P450c17) in insect Sf9 cells using baculovirus is the fourth heterologous expression system developed for studying this enzyme [2].

High impact information on CYP17

• In order to investigate the possible role of the AF-2 domain of SF-1 in cAMP-dependent transcriptional regulation of the bovine steroid hydroxylase gene CYP17, mutations were introduced and the effects were characterized [3].
• A cAMP-responsive sequence (CRS1) from bovine CYP17 has previously been shown to be a binding site for Pbx1 [4].
• Indeed, supplying cells with steroid precursors revealed that TGF-beta1 inhibited two steps in the steroid synthesis pathway, one prior to pregnenolone production and another corresponding to P450c17 [5].
• We have reported the localization on yeast microsomes for a modified P450c27 (mic-P450c27) that contains the microsomal targeting signal of bovine P450c17 in front of the mature form of rat mitochondrial P450c27 (Sakaki, T., Akiyoshi-Shibata, M., Yabusaki, Y., and Ohkawa, H. (1992) J. Biol. Chem. 267, 16497-16502) [6].
• Utilizing the cAMP-regulatory sequence CRS1 of the bovine CYP17 gene as an affinity ligand, four CRS1-binding proteins have been purified from nuclear extracts of mouse adrenocortical Y1 cells and shown to enhance the in vitro transcription of a reporter gene promoted by CRS1 [7].

Chemical compound and disease context of CYP17

• When intact E. coli cells were used for analysis, the truncated P450c17 showed the typical cytochrome P450 CO-difference spectrum and type I substrate binding spectra for pregnenolone, 17 alpha-hydroxypregnenolone, progesterone, and 17 alpha-hydroxyprogesterone [8].
• Escherichia coli flavodoxin sepharose as an affinity resin for cytochromes P450 and use to identify a putative cytochrome P450c17/3beta-hydroxysteroid dehydrogenase interaction [9].

Biological context of CYP17

• The gene contains eight exons with exon/intron boundaries which are identical to those determined previously for the human CYP17 gene [10].
• Considerable sequence homology (58.7%) is found when approximately 500 bp of the 5'-flanking sequences of the bovine and human CYP17 genes are compared [10].
• Regions within the 5'-flanking sequence of the bovine CYP17 (P-450(17)alpha) gene which are required for cAMP-dependent regulation of transcription have been localized by transient transfection of chimeric reporter gene constructs into mouse adrenal tumor Y1 cells [11].
• Regulation of CYP11A (P450SCC) and CYP17 (P450(17) alpha) gene expression in bovine luteal cells in primary culture [12].
• The first and only functional Pbx1 binding site has been localized in bovine CYP17 to a sequence (CRS1) that participates in cAMP-dependent transcription of this gene encoding the steroid hydroxylase, 17 alpha-hydroxylase cytochrome P450 [13].

Anatomical context of CYP17

• In bovine adrenal cortex, transcription of the CYP17 gene is regulated by the peptide hormone adrenocorticotropin via cAMP [10].
• On the other hand, expression of the CYP17 gene in bovine luteal cells appears to be completely repressed, due to the absence of specific positive transcription factor(s) or the presence of negative regulatory factor(s) [12].
• Analysis of the delta 4-lyase activity of mutant rat CYP17 cDNA expressed in nonsteroidogenic COS-1 cells revealed that substitution of Phe at position 343 in the rat with Ile of the human/bovine sequence resulted in a reduction in delta 4-lyase activity to levels in the range of the delta 5-supported reaction [14].
• Dexamethasone treatment of the cells cultured in the presence of ACTH or forskolin resulted in about 50% suppression of both CYP11A and CYP17 mRNA accumulation, with a concomitant fall in cortisol secretion to about 60% of the stimulated value [15].
• These results show that AII is able to modulate the expression of CYP17 in adrenal glomerulosa cells following ACTH stimulation [16].

Associations of CYP17 with chemical compounds

• Cytochrome P450c17 encoded by CYP17, whose expression is regulated by peptide hormones via cAMP, is required for cortisol and sex hormone biosynthesis thereby playing a key role in biological processes including sexual differentiation [7].
• Requirement of phenylalanine 343 for the preferential delta 4-lyase versus delta 5-lyase activity of rat CYP17 [14].
• Dexamethasone inhibits corticotropin-induced accumulation of CYP11A and CYP17 messenger RNAs in bovine adrenocortical cells [15].
• Mutually exclusive interactions of two nuclear orphan receptors determine activity of a cyclic adenosine 3',5'-monophosphate-responsive sequence in the bovine CYP17 gene [17].
• The effects of dexamethasone on accumulation of CYP11A and CYP17 mRNAs and cortisol secretion were blocked by pretreatment of the cells with RU 486 (100 nM), while RU 486 had no effect on forskolin-induced accumulation of either mRNA or cortisol secretion [15].

Enzymatic interactions of CYP17

• Cytochrome P450c17 from porcine and bovine adrenal catalyses the formation of 5,16-androstadien-3 beta-ol from pregnenolone in the presence of cytochrome b5 [18].

Regulatory relationships of CYP17

• We also demonstrated that in H295R cells TGF-beta inhibited both basal and forskolin-stimulated accumulation of CYP17 mRNA [19].

Other interactions of CYP17

• The expression of negative regulators of CYP17 gene expression: DAX-1, COUP-TF and N-CoR was investigated in bovine adrenocortical cells in primary culture [20].
• The ratio of CYP17 messenger RNA (mRNA) to 18S ribosomal RNA was also significantly higher in fetal adrenals ofthe N-POMC-(1-77)-infused group (49.1+/-4.7) compared with that in either the N-POMC-(1-49)-infused (20.4+/-6.4) or saline-infused (15.2+/-4.4) group [21].
• It is concluded that in bovine and human adrenocortical cells, androgens inhibit basal CYP17 expression probably at the transcriptional level and independently of the effect of TGF-beta [19].
• Cyp19 transcript variants, derived from different promoters, as well as transcripts of Hsd3b, Cyp11A1, and Cyp17, encoding the steroidogenic enzymes P450arom, 3beta-HSD, P450SCC, and P450C17, respectively, were quantified by newly developed real-time PCR assays [22].
• Differences in expression of mRNA for LH receptor, FSH receptor, cytochrome P450 side-chain cleavage, 3beta-hydroxysteroid dehydrogenase, cytochrome P450 17alpha-hydroxylase (P450c17) and cytochrome P450 aromatase were determined in large follicles using in situ hybridization [23].

Analytical, diagnostic and therapeutic context of CYP17

• Site-directed mutagenesis of a domain (amino acids 343-348) within the conserved region of rat CYP17 was performed to investigate species-specific differences between rat and human/bovine delta 4-versus delta 5-lyase activity [14].
• The accumulation of CYP11A and CYP17 mRNAs was evaluated by Northern blot analysis with the use of [alpha-32P]deoxy-CTP-labeled bovine CYP11A and CYP17 cDNAs [15].
• Expression of mRNAs encoding P450scc, P450c17, and P450arom was detected by in situ hybridization and quantified by image analysis [24].
• Immunocytochemistry confirmed a marked reduction in cellular content of P450c17 protein after BMP treatment (P < 0.001) [25].
• Semiquantitative RT-PCR showed that all three BMPs markedly reduced steady-state levels of mRNA for P450c17 [25].

References