Human cholesterol side-chain cleavage enzyme, P450scc: cDNA cloning, assignment of the gene to chromosome 15, and expression in the placenta

Comparative mapping of IGHG1, IGHM, FES, and FOS in domestic cattle

The immunoglobulin genes have not been genetically characterized as thoroughly in cattle as in other mammals, particularly humans and mice. Comparative gene mapping in mammals suggests that the bovine immunoglobulin heavy chain genes, IGHG4 and IGHM might be syntenic with the FOS oncogene. Interestingly, however, when these genes were assigned to bovine syntenic groups utilizing a panel of bovine: hamster hybrid somatic cells, IGH genes were shown to be syntenic with the FES oncogene rather than FOS. In this study IGH and FES were assigned to Bos taurus chromosome 21 while FOS was assigned to chromosome 10. In addition, bovine-specific immunoglobulin-like sequences were observed in the hybrid somatic cells, and one, IGHML1, was mapped to bovine syntenic group U16. The probes used for somatic-cell mapping were also used to screen a small number of cattle of several different breeds for restriction fragment length polymorphisms. IGHG4 and IGHM were shown to be highly polymorphic, while FOS and FES were not.

Normal genes for the cholesterol side chain cleavage enzyme, P450scc, in congenital lipoid adrenal hyperplasia

Congenital lipoid adrenal hyperplasia is the most severe form of congenital adrenal hyperplasia. Affected individuals can synthesize no steroid hormones, and hence are all phenotypic females with a severe salt-losing syndrome that is fatal if not treated in early infancy. All previous studies have suggested that the disorder is in the cholesterol side chain cleavage enzyme (P450scc), which converts cholesterol to pregnenolone. A newborn patient was diagnosed by the lack of significant concentrations of adrenal or gonadal steroids either before or after stimulation with corticotropin (ACTH) or gonadotropin (hCG). The P450scc gene in this patient and in a previously described patient were grossly intact, as evidenced by Southern blotting patterns. Enzymatic (polymerase chain reaction) amplification and sequencing of the coding regions of their P450scc genes showed these were identical to the previously cloned human P450scc cDNA and gene sequences. Undetected compound heterozygosity was ruled out in the new patient by sequencing P450scc cDNA enzymatically amplified from gonadal RNA. Northern blots of gonadal RNA from this patient contained normal sized mRNAs for P450scc and also for adrenodoxin reductase, adrenodoxin, sterol carrier protein 2, endozepine, and GRP-78 (the precursor to steroidogenesis activator peptide). These studies show that lipoid CAH is not caused by lesions in the P450scc gene, and suggest that another unidentified factor is required for the conversion of cholesterol to pregnenolone, and is disordered in congenital lipoid adrenal hyperplasia.

cDNAs encoding members of a family of proteins related to human sterol carrier protein 2 and assignment of the gene to human chromosome 1 p21----pter

Sterol carrier protein 2 (SCP2) is believed to play a key role in intracellular lipid movement. Here we report the cloning and nucleotide sequences of cDNAs encoding SCP2-related proteins of 58.85 kD and 30.8 kD and the assignment of the SCP2 gene to human chromosome 1 p21-pter. The SCP2-related proteins share common deduced carboxyl amino acid sequences with SCP2 and the cDNAs have a common 3' untranslated nucleotide sequence. The mRNAs encoding these proteins increased in a coordinate fashion as human placental cytotrophoblasts differentiated into syncytiotrophoblasts in culture. Our observations document the existence of a family of related proteins encoded by the human SCP2 gene.

Analysis of the polyadenylation consensus sequence context in the genes of nuclear encoded mitochondrial proteins

A compilation of the pre-mRNA ends of the genes of nuclear encoded mitochondrial proteins resulted in a consensus sequence of the type (T/A)NTTNNNNNTTTNAATAAA. Nucleotide positions +8, +13, +14, +16 and +17 downstream of the AATAAA sequence show also a predominance of nucleotide T. This consensus sequence suggests the importance of the immediate surroundings of the cannonical polyadenylation signal sequence AATAAA on the efficiency of the cleavage and polyadenylation of this specific group of pre-mRNAs.

Primary and secondary structural patterns in eukaryotic cytochrome P-450 families correspond to structures of the helix-rich domain of Pseudomonas putida cytochrome P-450cam. Indications for a similar overall topology

An extensive sequence analysis of the eukaryotic cytochrome P-450 (P-450) protein families was conducted with a view to identifying conserved regions that might be related to secondary structural features in the Pseudomonas putida camphor hydroxylase (P-450cam). All sequences available on-line were collected, classified and aligned within families. Distinctively different sequences were chosen from each of seven eukaryotic families, and an unbiased multi-alignment was constructed. Profile patterns of the most conserved regions were generated and screened against the sequence of P-450cam, the structure of which has been elucidated by X-ray crystallography. While some of these profiles did not map on the P-450cam sequence, the structurally most important helices were clearly identified and the correlations were found to be statistically significant. Our analysis suggests that the helix-rich domain with the cysteine pocket and the oxygen-binding site is conserved in all P-450 forms. Helices I and L from P-450cam can be easily identified in all eukaryotic P-450 forms. Other helices which seem to exist in all P-450 forms include helices C, D, G and J. K. In the helix-poor domain of P-450cam, only structures b3/b4 seem to have been conserved. The obvious sequence conservation throughout the helix-rich domain of the P-450cam protein might be expected for a molecular class whose overall topology is preserved. Additional support for the conservation of structure between eukaryotic cytochromes P-450 and P-450cam comes from secondary structure prediction of the eukaryotic sequences.

Regional mapping of genes encoding human steroidogenic enzymes: P450scc to 15q23-q24, adrenodoxin to 11q22; adrenodoxin reductase to 17q24-q25; and P450c17 to 10q24-q25

Steroid hormones are synthesized by a complex array of 10 enzymes. The genes for each of these have now been cloned, and previous work has determined the regional chromosomal assignments of six of these. We used in situ hybridization to determine the regional chromosomal assignments of the four remaining enzymes. The CYP11A1 gene encodes mitochondrial P450scc, which converts cholesterol to pregnenolone, and is located on 15q23-q24. The gene for adrenodoxin, which receives electrons from adrenodoxin reductase and transfers them to P450scc, is on 11q22 while its pseudogenes are on 20q11-q12. The gene for adrenodoxin reductase is on 17q24-q25. The CYP17 gene encodes P450c17, which has both 17 alpha-hydroxylase and 17,20-lyase activities, and is located on 10q24-q25. None of the 10 genes involved in human steroidogenesis is closely linked to another gene for a steroidogenic enzyme.

Regulated expression of cytochrome P-450scc (cholesterol-side-chain cleavage enzyme) in cultured cell lines detected by antibody against bacterially expressed human protein

The first step in the synthesis of steroids is catalysed by cytochrome P-450ssc (cholesterol-side-chain cleavage enzyme). We have investigated the synthesis of this enzyme in three cultured cell lines at the protein and hormone secretion levels. Hormone levels were measured by an enzyme immunoassay using a monoclonal antibody against progesterone. The protein level was detected using polyclonal antibodies directed against a P-450scc fusion protein overproduced in Escherichia coli. Utilizing a bacteriophage T7 promoter expression system, a large amount of human P-450scc fusion protein was produced and easily purified. P-450scc was synthesized in the mouse adrenal tumour cell line Y1 and human choriocarcinoma cell line JEG-3, but not in monkey kidney cell line COS-1. The production of P-450scc in Y1 and JEG-3 cells was stimulated by 8-bromo cyclic AMP, the effect of which was not observed until 6 h after induction and was more pronounced at 24 h. Y1 and JEG-3 cells exhibited a difference in progesterone secretion after induction.

Human P450scc gene transcription is induced by cyclic AMP and repressed by 12-O-tetradecanoylphorbol-13-acetate and A23187 through independent cis elements

Long-term regulation of mammalian steroid hormone synthesis occurs principally by transcriptional regulation of the gene for the rate-limiting cholesterol side-chain cleavage enzyme P450scc. Adrenal steroidogenesis is regulated primarily by two hormones: adrenocorticotropin, which works via cyclic AMP (cAMP) and protein kinase A, and angiotensin II, which works via Ca2+ and protein kinase C. Forskolin and 8-bromo-cAMP stimulated, while prolonged treatment with a phorbol ester (12-O-tetradecanoylphorbol-13-acetate [TPA]) and a calcium ionophore (A23187) additively suppressed accumulation of endogenous P450scc mRNA in transformed murine adrenal Y1 cells. In Y1 cells transfected with 2,327 base pairs of the human P450scc promoter fused to the bacterial gene for chloramphenicol acetyltransferase (CAT), forskolin increased CAT activity 900% while combined TPA plus A23187 reduced CAT activity to 15% of the control level. Forskolin induced the P450scc promoter as rapidly as a promoter containing two cAMP-responsive elements fused to a simian virus 40 promoter, a system known to respond directly to cAMP. Basal expression was increased by sequences between -89 and -152 and was increased further by sequences between -605 and -2327. This upstream region also conferred inducibility by cAMP. TPA plus A23187 transiently increased CAT activity before repressing it, reflecting the complex actions of angiotensin II in vivo. Repression by prolonged treatment with TPA plus A23187 was mediated by multiple elements between -89 and -343. Induction of CAT activity by forskolin was not diminished by treatment with TPA plus A23187, nor were the regions of the promoter responsible for regulation by the two pathways coisolated. Thus, the human gene for P450scc is repressed by TPA plus A23187 by mechanisms and sequences independent of those that mediate induction by cAMP.

Human P450scc gene transcription is induced by cyclic AMP and repressed by 12-O-tetradecanoylphorbol-13-acetate and A23187 through independent cis elements

Long-term regulation of mammalian steroid hormone synthesis occurs principally by transcriptional regulation of the gene for the rate-limiting cholesterol side-chain cleavage enzyme P450scc. Adrenal steroidogenesis is regulated primarily by two hormones: adrenocorticotropin, which works via cyclic AMP (cAMP) and protein kinase A, and angiotensin II, which works via Ca2+ and protein kinase C. Forskolin and 8-bromo-cAMP stimulated, while prolonged treatment with a phorbol ester (12-O-tetradecanoylphorbol-13-acetate [TPA]) and a calcium ionophore (A23187) additively suppressed accumulation of endogenous P450scc mRNA in transformed murine adrenal Y1 cells. In Y1 cells transfected with 2,327 base pairs of the human P450scc promoter fused to the bacterial gene for chloramphenicol acetyltransferase (CAT), forskolin increased CAT activity 900% while combined TPA plus A23187 reduced CAT activity to 15% of the control level. Forskolin induced the P450scc promoter as rapidly as a promoter containing two cAMP-responsive elements fused to a simian virus 40 promoter, a system known to respond directly to cAMP. Basal expression was increased by sequences between -89 and -152 and was increased further by sequences between -605 and -2327. This upstream region also conferred inducibility by cAMP. TPA plus A23187 transiently increased CAT activity before repressing it, reflecting the complex actions of angiotensin II in vivo. Repression by prolonged treatment with TPA plus A23187 was mediated by multiple elements between -89 and -343. Induction of CAT activity by forskolin was not diminished by treatment with TPA plus A23187, nor were the regions of the promoter responsible for regulation by the two pathways coisolated. Thus, the human gene for P450scc is repressed by TPA plus A23187 by mechanisms and sequences independent of those that mediate induction by cAMP.

Cloning and sequence of the human adrenodoxin reductase gene

Adrenodoxin reductase (ferrodoxin:NADP+ oxidoreductase, EC 1.18.1.2) is a flavoprotein mediating electron transport to all mitochondrial forms of cytochrome P450. We cloned the human adrenodoxin reductase gene and characterized it by restriction endonuclease mapping and DNA sequencing. The entire gene is approximately 12 kilobases long and consists of 12 exons. The first exon encodes the first 26 of the 32 amino acids of the signal peptide, and the second exon encodes the remainder of signal peptide and the apparent FAD binding site. The remaining 10 exons are clustered in a region of only 4.3 kilobases, separated from the first two exons by a large intron of about 5.6 kilobases. Two forms of human adrenodoxin reductase mRNA, differing by the presence or absence of 18 bases in the middle of the sequence, arise from alternate splicing at the 5' end of exon 7. This alternately spliced region is directly adjacent to the NADPH binding site, which is entirely contained in exon 6. The immediate 5' flanking region lacks TATA and CAAT boxes; however, this region is rich in G + C and contains six copies of the sequence GGGCGGG, resembling promoter sequences of "housekeeping" genes. RNase protection experiments show that transcription is initiated from multiple sites in the 5' flanking region, located about 21-91 base pairs upstream from the AUG translational initiation codon.

Isolation of two developmentally regulated genes involved in spore wall maturation in Saccharomyces cerevisiae

During sporulation of Saccharomyces cerevisiae, the four haploid nuclei generated by meiosis are encapsulated within multilayered spore walls. Taking advantage of the natural fluorescence imparted to yeast spores by the presence of a dityrosine-containing macromolecule in the spore wall, we identified and cloned two genes, termed DIT1 and DIT2, which are required for spore wall maturation. Mutation of these genes has no effect on the efficiency of spore formation or spore viability. The mutant spores, however, fail to accumulate the spore wall-specific dityrosine and lack the outermost layer of the spore wall. The absence of this cross-linked surface layer reduces the resistance of the spores to lytic enzymes, to ether, and to elevated temperature. Expression of the DIT and DIT2 genes is restricted to sporulating cells, with the DIT1 transcripts accumulating at the time of prospore enclosure and just prior to the time of dityrosine biosynthesis. Both genes act in a spore-autonomous manner implying that at least some of the activities responsible for forming the outermost layer of the spore wall reside within the developing spore rather than in the surrounding ascal cytoplasm. As the DIT2 gene product has significant homology with cytochrome P-450s, DIT2 may be responsible for catalyzing the oxidation of tyrosine residues in the formation of dityrosine.

cAMP regulates P450scc gene expression by a cycloheximide-insensitive mechanism in cultured mouse Leydig MA-10 cells

Mouse MA-10 Leydig tumor cells synthesize and secrete progesterone in response to human chorionic gonadotropin, luteinizing hormone, and cAMP but may not synthesize androgens. Maximal doses of human chorionic gonadotropin, ovine luteinizing hormone, forskolin, or 8-bromoadenosine 3',5'-cyclic monophosphate, stimulated cytochrome P450scc mRNA accumulation 1.5- to 3-fold and progesterone secretion 10- to 100-fold in MA-10 cells. P450scc mRNA increased by 2 hr and was maximal by 8 hr; polymerase run-on experiments showed this was due to increased P450scc gene transcription. MA-10 cells are a hormonally homogeneous population, as all cells expressed P450scc mRNA and responded to cAMP equally. cAMP-stimulated accumulation of P450scc mRNA continued in the presence of cycloheximide. Gonadotropins stimulated testicular steroidogenesis by coordinate cAMP-induced increases in P450scc gene transcription, mRNA accumulation, and P450scc activity. We cloned rat P450c17 cDNA and showed it detected no P450c17 mRNA in control or cAMP-stimulated MA-10 cells by RNA transfer blots or RNase protection assays. Similarly, HPLC detected no 17 alpha-hydroxyprogesterone or testosterone synthesis in MA-10 cells. Thus MA-10 cells, unlike untransformed Leydig cells, do not express detectable amounts of P450c17 mRNA or P450c17 activity.

Isolation of human cDNA clones of ski and the ski-related gene, sno

cDNA clones of ski and the ski-related gene, sno, were obtained by screening human cDNA libraries. The predicted open reading frame of h-ski could encode a protein of 728 amino acid residues. The h-ski protein is highly homologous with the v-ski protein. The overall homology between h-ski and v-ski is 91% at the amino acid level. DNA sequencing analysis revealed two types of cDNA clones from the sno (ski-related novel gene) gene, possibly due to alternative splicing. The first type, named snoN (non Alu-containing), encoded a protein of 684 amino acid residues. The second type, named snoA (Alu-containing), encoded a protein of 415 amino acid residues. The first 366 amino acid residues of snoN and snoA are the same, but subsequent amino acids show divergence. Several transcripts of h-ski (6.0, 4.7, 3.8, 3.0, 2.1 and 1.8 kb) were detected. The mRNAs of h-sno were 6.2, 4.4 and 3.2kb.

Immunohistochemical demonstration of cholesterol side-chain cleavage cytochrome P-450 in bovine and human adrenals

Cytochrome P-450 specific for cholesterol side-chain cleavage (P-450SCC) was purified from the bovine adrenal and a specific antibody was raised in rabbits. The antiserum was applied for immunohistochemical visualization of the P-450SCC in the bovine and human adrenal cortex. The immunoreactivity was intense in the zona fasciculata (ZF) and reticularis (ZR) while weak in the zona glomerulosa (ZG) in the normal adrenals. In adrenocortical hyperplasia, a marked immunoreactivity was observed in the ZG in idiopathic hyperaldosteronism and the inner ZF and reticularis particularly in cells of micronodules in Cushing's disease, corresponding to cells with active steroidogenesis. In aldosteronoma and adenoma with Cushing's syndrome, P-450SCC was generally present in compact cells of adenomas.

The P450 superfamily: updated listing of all genes and recommended nomenclature for the chromosomal loci

In this update we provide a list of the 71 P450 genes and the four P450 pseudogenes that have been characterized as of September 30, 1988. The chromosomal locations of many of these genes are also summarized. A modest revision of the initially proposed nomenclature of the P450 superfamily (Nebert et al., DNA 6, 1-11, 1987) is described specifically for the human and mouse chromosomal loci. The motivation for this revision is to conform to the rules of nomenclature for human and mouse genes. Recommendations for the naming of chromosomal loci include the root symbol "CYP" for human ("Cyp" for mouse), denoting "cytochrome P450." We recommend that this root also be used for other organisms. For a chromosomal locus, the root symbol is followed by an Arabic numeral designating the P450 family, a letter indicating the subfamily, and an Arabic numeral representing the individual gene within the family or subfamily. Numbers of the individual genes usually will be assigned in the order the genes are identified. This system is consistent with our earlier proposed nomenclature for P450 families and gene products from all eukaryotes and prokaryotes.

Regulation of steroid hydroxylase gene expression is multifactorial in nature

In summary, regulation of steroid hydroxylase gene expression is complex and multifactorial, involving cAMP-dependent and -independent mechanisms required for maintenance of optimal steroidogenic capacity, tissue-specific mechanisms which lead to different steroidogenic pathways in different tissues, and developmental mechanisms which lead to fetal imprinting of steroid hydroxylase expression and which probably overlap with both maintenance and tissue-specific mechanisms. Future studies will involve identification of the trans-acting factors associated with each of these aspects of the multifactorial regulation and characterization of the cis-regulatory elements to which they bind. Such studies will inevitably lead to the identification of genes encoding these trans-acting factors and investigation of their regulation. In this way, it will be possible to work outward from the steroid hydroxylase genes toward the cell surface receptors in order to elucidate the series of events which lead to cAMP-dependent and -independent regulation of steroid hydroxylase gene expression.

Regulation of mRNAs for human steroidogenic enzymes

Steroid hormone synthesis is controlled by two classes of mechanisms. "Acute" regulation entails rapid increases or decreases of steroid synthesis and secretion, principally mediated by rapid changes in the activities of the steroidogenic enzymes and by the availability of the substrate, free cholesterol. "Chronic" regulation entails increases or decreases in the amounts of the steroidogenic enzymes as well as their activities. The amounts of the enzymes are regulated principally by the amounts of the specific mRNAs encoding them. These, in turn, are regulated both transcriptionally and post-transcriptionally. The mRNAs are regulated by hormonal induction, by an ontogenic program, and in a tissue-specific fashion.

Isolation of human cDNA clones of myb-related genes, A-myb and B-myb

cDNA clones of the myb-related genes A-myb and B-myb were obtained by screening human cDNA libraries. The predicted open reading frame of B-myb could encode a protein of 700 amino acid residues. Although the C-terminal end has not been cloned yet, an almost entire coding region of A-myb, which is 745 amino acid long, was determined. The A-myb and B-myb proteins are highly homologous with the myb protein in three regions. Domain I, which is 161 amino acid long, is well conserved in the myb gene family. The homology between human-myb and A-myb in domain I is 90% at the amino acid level. Domain II, which is about 85 amino acid long, is less well conserved. Although it is a short stretch, domain III is found in the C-terminal region. The mRNAs of A-myb and B-myb were 5.0 and 2.6 kb, respectively. The mRNA expression pattern of the myb gene family in various tumors is presented.

Control mechanisms of testicular differentiation

In this paper the importance of unknown factors responsible for the initial differentiation of a gonadal primordium is stressed. The hypothesis that in the absence of testis determining genes (TDG) the indifferent gonad is programmed to become an ovary is considered further. The TDG(s) are expressed only among cells already marked as gonadal cells, and they seem mainly to change the chronological sequence and intensity of expression of processes common to both sexes. The chronology of the normal events necessary for testicular differentiation and the fact that some of these events can be dissociated from one another under experimental conditions in vitro, suggest that many genes are involved in testicular differentiation and that the so-called testis-determining genes are probably regulatory genes.

Human adrenodoxin reductase: two mRNAs encoded by a single gene on chromosome 17cen----q25 are expressed in steroidogenic tissues

Adrenodoxin reductase is a mitochondrial flavoprotein that receives electrons from NADPH, thus initiating the electron-transport chain serving mitochondrial cytochromes P450. We have cloned and sequenced two human adrenodoxin reductase cDNAs that differ by the presence of six additional codons in the middle of one clone. The sequence in this region indicates that these six extra codons arise by alternative splicing of the pre-mRNA. Southern blot hybridization patterns of human genomic DNA cut with four restriction enzymes indicate that the human genome has only one gene for adrenodoxin reductase. Analysis of a panel of mouse-human somatic cell hybrids localized this gene to chromosome 17cen----q25. The alternatively spliced mRNA containing the six extra codons represents 10-20% of all adrenodoxin reductase mRNA. The expression of the adrenodoxin reductase gene may be stimulated by pituitary tropic hormones acting through cAMP, but its response is quantitatively much less than the responses of P450scc and adrenodoxin.

Assignment of the functional gene for human adrenodoxin to chromosome 11q13----qter and of adrenodoxin pseudogenes to chromosome 20cen----q13.1

Adrenodoxin is a small iron/sulfur protein serving as an electron-transport intermediate for all mitochondrial forms of cytochrome P450. Southern blots of normal genomic DNA cleaved with six restriction endonucleases probed with full-length human adrenodoxin cDNA revealed complex patterns indicating the presence of multiple adrenodoxin genes. Southern blots of DNA from a panel of mouse/human somatic cell hybrids identified cross-hybridizing adrenodoxin DNA in two loci, chromosome 11q13----qter and chromosome 20cen----q13.1. Examination of adrenodoxin clones from a genomic DNA library in phage lambda revealed some clones bearing gene fragments interrupted by introns and other clones bearing processed pseudogenes. By probing the mouse/human hybrids with unique intronic DNA and by correlating restriction maps of the phage clones with that of uncloned genomic DNA, we show that the authentic transcribed adrenodoxin gene lies on chromosome 11, while pseudogenes lie on chromosome 20.

Developmental and hormonal regulation of mRNAs for insulin-like growth factor II and steroidogenic enzymes in human fetal adrenals and gonads

Insulin-like growth factor II (IGF-II) is regulated developmentally and hormonally in human fetal gonads and adrenals. The abundance of IGF-II mRNA is greatest in RNA from human fetal adrenals, followed by fetal liver, testis, placenta, and ovaries. Fetal testicular IGF-II mRNA decreases significantly with increasing gestational age, in parallel with our previous measurements of the mRNAs for the steroidogenic enzymes P450scc (cholesterol side-chain cleavage enzyme) and P450c17 (17 alpha-hydroxylase/17,20 lyase) (J. Clin. Endocrinol. Metab. 63, 1145, 1986). The abundances of P450scc and P450c17 mRNAs in cultured fetal testis cells rose 2.5-fold (p less than 0.01) and 9.2-fold (p less than 0.001), respectively, in response to 0.5 mM cAMP, but the abundance of IGF-II mRNA was not affected. This suggests that the IGF-II gene is regulated differently in fetal testes than it is in fetal adrenals, placenta, or adult granulosa cells, where we have previously shown that ACTH, cAMP, and gonadotropins, respectively, increase IGF-II mRNA accumulation (Proc. Natl. Acad. Sci. USA 84, 1590, 1987). Exogenously added IGF-I and IGF-II had no effect on mRNAs for P450c17 or P450c21 (21-hydroxylase), but decreased IGF-II mRNA in ACTH-stimulated fetal adrenal cells. Thus, the IGFs appear to exert short-loop feedback inhibition on accumulation of IGF-II mRNA.

Human aromatase: cDNA cloning, Southern blot analysis, and assignment of the gene to chromosome 15

The amino acid sequence of human placental aromatase was determined in part (about 40%) by microsequencing methods. Using a region of overlapping peptide sequences, synthetic oligonucleotide probes were constructed and used to screen a human placental lambda gt-11 cDNA library. Of a number of positive clones, one containing a 2.4-kb insert was characterized further by restriction mapping and determination of its nucleotide sequence. The cDNA-deduced amino acid sequence is in perfect agreement with the peptide sequence data, confirming that the clone encodes for aromatase. The sequence contains a 3' untranslated region of 1.2 kb, and an open-reading frame of 1.25 kb; approximately 0.3 kb is missing from the 5' end of the coding region. While exhibiting no more than 20-30% sequence homology with other mammalian cytochromes P450, it contains the highly conserved heme-binding domain, thus confirming the essential structural requirements for this class of protein. Two cDNA fragments containing sequences coding for the amino- and carboxy-portions of the protein were used to probe for the human aromatase gene by Southern blotting. The results of these studies suggest the existence of at least two human aromatase genes. The gene encoding the aromatase cDNA we cloned was assigned to human chromosome 15 using somatic cell hybrids. This gene was mapped to band 15q21.1 by in situ hybridization studies.

Isolation of a cDNA for adrenodoxin reductase (ferredoxin-NADP+ reductase). Implications for mitochondrial cytochrome P-450 systems

Using specific antibodies against adrenodoxin reductase (AR), we screened lambda gt11 cDNA expression libraries constructed from bovine adrenal cortex mRNA, and isolated several putative clones coding for this enzyme. Concurrently we determined the amino acid sequences of fragments from it. A deoxyinosine-containing oligonucleotide probe, generated for one of the sequences, reacted specifically with one of the cloned cDNAs of about 1600 base pairs. The codon sequence of this cDNA matched the peptide sequences, further confirming its identity as a copy of AR mRNA. RNA blot analysis indicates that in the adrenal cortex and corpus luteum there is only one major mRNA (approximately 2000 bp) for AR. The levels of this mRNA are at least 40-fold lower in the liver and kidney which are also known to contain in homologue of AR. As compared to adrenodoxin and cytochrome P-450scc mRNAs, AR mRNA levels in the adrenal cortex appear to be about 10-fold lower. Southern blot analysis of bovine and human genomic DNAs reveals that in both of these species there is only one gene for AR. These results indicate that only a single reductase serves the different mitochondrial P-450 systems in steroidogenic tissues.

Cloning of cDNA encoding steroid 11 beta-hydroxylase (P450c11)

We have isolated bovine and human adrenal cDNA clones encoding the adrenal cytochrome P-450 specific for 11 beta-hydroxylation (P450c11). A bovine adrenal cDNA library constructed in the bacteriophage lambda vector gt10 was probed with a previously isolated cDNA clone corresponding to part of the 3' untranslated region of the 4.2-kilobase (kb) mRNA encoding P450c11. Several clones with 3.2-kb cDNA inserts were isolated. Sequence analysis showed that they overlapped the original probe by 300 base pairs (bp). Combined cDNA and RNA sequence data demonstrated a continuous open reading frame of 1509 bases. P450c11 is predicted to contain 479 amino acid residues in the mature protein in addition to a 24-residue amino-terminal mitochondrial signal sequence. A bovine clone was used to isolate a homologous clone with a 3.5-kb insert from a human adrenal cDNA library. A region of 1100 bp was 81% homologous to 769 bp of the coding sequence of the bovine cDNA except for a 400-bp segment presumed to be an unprocessed intron. Hybridization of the human cDNA to DNA from a panel of human-rodent somatic cell hybrid lines and in situ hybridization to metaphase spreads of human chromosomes localized the gene to the middle of the long arm of chromosome 8. These data should be useful in developing reagents for heterozygote detection and prenatal diagnosis of 11 beta-hydroxylase deficiency, the second most frequent cause of congenital adrenal hyperplasia.

Cloning and sequence of the human gene for P450c17 (steroid 17 alpha-hydroxylase/17,20 lyase): similarity with the gene for P450c21

P450c17 is a single cytochrome P450 enzyme mediating both 17 alpha-hydroxylase and 17,20 lyase activities in the biosynthesis of steroid hormones. We have cloned and sequenced the human P450XVIIA1 gene lying on chromosome 10, which encodes P450c17. The gene spans 6569 bp and is divided into eight exons by seven introns. This intron/exon structure closely resembles that of the P450XXI genes encoding P450c21 (steroid 21-hydroxylase), which contain 10 exons, except that the introns dividing exons 1 and 2 and exons 4 and 5 in the P450XXI gene are absent in the P450XVII gene. Furthermore, computer modeling studies indicate the conformations of P450c17 and P450c21 are very similar. The structures of the P450XXVII and P450XXI genes are very different from other classes of P450 genes. Although the production of P450c17 is under different hormonal, ontogenic, and tissue-specific controls in various types of steroidogenic cells, the adrenal and testis transcribe the P450XVIIA1 gene into P450c17 mRNAs having the same cap sites. S1 nuclease protection experiments locate the principal cap sites as a G residue lying 22 bases 3' to an atypical TTTAAA promoter, and 82 bases 3' to a typical CAAT box. The 5'-flanking DNA contains sequences similar to consensus sequences regulated by cAMP and glucocorticoids.

Human chorionic gonadotropin and 8-bromo cyclic adenosine monophosphate promote an acute increase in cytochrome P450scc and adrenodoxin messenger RNAs in cultured human granulosa cells by a cycloheximide-insensitive mechanism

Treatment of human granulosa cells with human chorionic gonadotropin (hCG) or an analogue of its second messenger, cyclic AMP (cAMP), promotes a rapid accumulation of the messenger RNAs (mRNAs) for cytochrome P450 side-chain cleavage (scc) and adrenodoxin. A twofold increase in the cellular content of these mRNAs was observed within 4 h of exposure to 8-bromo-cAMP, and was maintained for up to 48 h. Inhibition of protein synthesis by cycloheximide did not prevent the hCG- or 8-bromo-cAMP-stimulated accumulation of either cytochrome P450scc or adrenodoxin mRNAs. We conclude that human granulosa cells respond rapidly to hCG and cAMP analogues with a coordinate increase in levels of the mRNAs encoding two key proteins of the steroidogenic machinery, and that this stimulation does not require synthesis of a protein intermediate.

P450XXI (steroid 21-hydroxylase) gene deletions are not found in family studies of congenital adrenal hyperplasia

Congenital adrenal hyperplasia (CAH) is a common genetic disorder due to defective 21-hydroxylation of steroid hormones. The human P450XXIA2 gene encodes cytochrome P450c21 [steroid 21-monooxygenase (steroid 21-hydroxylase), EC 1.14.99.10], which mediates 21-hydroxylation. The P450XXIA2 gene may be distinguished from the duplicated P450XXIA1 pseudogene by cleavage with the restriction endonuclease Taq I, with the XXIA2 gene characterized by a 3.7-kilobase (kb) fragment and the XXIA1 pseudogene characterized by a 3.2-kb fragment. Restriction endonuclease mapping by several laboratories has suggested that deletion of the P450XXIA2 gene occurs in about 25% of patients with CAH, as their genomic DNA lacks detectable 3.7-kb Taq I fragments. We have cloned human P450c21 cDNA and used it to study genomic DNA prepared from 51 persons in 10 families, each of which includes 2 or more persons with CAH. After Taq I digestion, apparent deletions are seen in 7 of the 20 alleles of the probands; using EcoRI, apparent deletions are seen in 9 of the 20 alleles. However, the apparently deleted alleles seen with Taq I do not coincide with those seen with EcoRI. Furthermore, studies with Bgl II, EcoRI, Kpn I, and Xba I yield normal patterns with at least two enzymes in all cases. Since all probands yielded normal patterns with at least two of the five enzymes used, we conclude that the P450XXIA2 gene "deletions" widely reported in CAH patients probably represent gene conversions, unequal crossovers, or polymorphisms rather than simple gene deletions.

Coordinate tropic hormone regulation of mRNAs for insulin-like growth factor II and the cholesterol side-chain-cleavage enzyme, P450scc [corrected], in human steroidogenic tissues

Insulin-like growth factors (IGFs) are single-chain polypeptides important for cell proliferation and growth. IGFs are produced in several tissues, suggesting that they function in a paracrine or autocrine fashion as well as functioning as endocrine hormones. We studied the hormonal regulation of IGF-I and IGF-II mRNA in human steroidogenic tissues. In cultured human ovarian granulosa cells, follicle-stimulating hormone, human chorionic gonadotropin, and dibutyryl cAMP increased IGF-II mRNA, but corticotropin [adrenocorticotropic hormone (ACTH)], chorionic somatomammotropin, growth hormone, prolactin, dexamethasone, estradiol, and progesterone had no effect. In cultured human fetal adrenal cells, ACTH and dibutyryl cAMP increased IGF-II mRNA accumulation, but human chorionic gonadotropin and angiotensin II did not. The same five size species of IGF-II mRNA were detected in transfer blots of RNA from granulosa cells and fetal adrenal cells, and all of these increased after hormonal stimuli. Dibutyryl cAMP also increased IGF-II mRNA accumulation in cultured human placental cells. Accumulation of mRNA for the cholesterol side-chain-cleavage monooxygenase [P450scc [corrected]; cholesterol, reduced-adrenal-ferredoxin:oxygen oxidoreductase (side-chain-cleaving), EC 1.14.15.6] was regulated in parallel with IGF-II mRNA in all these steroidogenic tissues. IGF-I mRNA was not detected in transfer blots of these RNAs, and the minimal amounts detected in dot blots showed no detectable change after any of the hormonal stimuli studied. The data indicate that the IGF-II gene is expressed in human steroidogenic tissues and is regulated by cAMP. These data suggest that IGF-II may act in an autocrine or paracrine fashion to stimulate the adrenal and gonadal growth stimulated by ACTH and gonadotropins, respectively.

Cytochrome P450c17 (steroid 17 alpha-hydroxylase/17,20 lyase): cloning of human adrenal and testis cDNAs indicates the same gene is expressed in both tissues

P450c17 is the single enzyme mediating both 17 alpha-hydroxylase (steroid 17 alpha-monooxygenase, EC 1.14.99.9) and 17,20 lyase activities in the synthesis of steroid hormones. It has been suggested that different P450c17 isozymes mediate these activities in the adrenal gland and testis. We sequenced 423 of the 509 amino acids (83%) of the porcine adrenal enzyme; based on this partial sequence, a 128-fold degenerate 17-mer was synthesized and used to screen a porcine adrenal cDNA library. This yielded a 380-base cloned cDNA, which in turn was used to isolate several human adrenal cDNAs. The longest of these, lambda hac17-2, is 1754 base pairs long and includes the full-length coding region, the complete 3'-untranslated region, and 41 bases of the 5'-untranslated region. This cDNA encodes a protein of 508 amino acids having a predicted molecular weight of 57,379.82. High-stringency screening of a human testicular cDNA library yielded a partial clone containing 1303 identical bases. RNA gel blots and nuclease S1-protection experiments confirm that the adrenal and testicular P450c17 mRNAs are indistinguishable. These data indicate that the testis possesses a P450c17 identical to that in the adrenal. The human amino acid sequence is 66.7% homologous to the corresponding regions of the porcine sequence, and the human cDNA and amino acid sequences are 80.1 and 70.3% homologous, respectively, to bovine adrenal P450c17 cDNA. Both comparisons indicate that a central region comprising amino acid residues 160-268 is hypervariable among these species of P450c17. Comparison of the amino acid sequence of P450c17 with two other human steroidogenic cytochromes P450 show much greater homology with P450c21 (28.9%), another microsomal enzyme, than with P450scc (12.3%), a mitochondrial enzyme.