Masaaki Kagimoto

Identification of a common molecular basis for combined 17α-hydroxylase/17,20-lyase deficiency in two Mennonite families

SummaryDuring the course of studies to characterize mutations of the CYP17 gene that cause the 17α-hydroxylase-deficient form of congenital adrenal hyperplasia we have discovered two ostensibly unrelated Mennonite families in which affected individuals are homozygous for the same mutation. The defect is a four-base duplication in exon 8 of the CYP17 gene, which alters the reading frame encoding the C-terminal 26 animo acids of cytochrome P45017α.

Molecular basis of apparent isolated 17,20-lyase deficiency: compound heterozygous mutations in the C-terminal region (Arg(496) → Cys, Gln(461) → Stop) actually cause combined 17α-hydroxylase/17,20-lyase deficiency

The molecular defect in a reported case of isolated 17,20-lyase deficiency in a 46XY individual has been elucidated. The patient was found to be a compound heterozygote, carrying two different mutant alleles in the CYP17 gene. One allele contains a point mutation of arginine (CGC) to cysteine (TGC) at amino acid 496 in exon 8. The second allele contains a stop codon (TAG) in place of glutamine (CAG) at position 461 in exon 8 which is located 19 amino acids to the carboxy-terminal side of the P-450(17) alpha heme binding cysteine. COS-1 cells transfected with cDNAs containing one or the other of these mutations showed dramatically reduced 17 alpha-hydroxylase and 17,20-lyase activities relative to cells transfected with the wild type P-450(17) alpha cDNA. While the in vitro data in COS 1 cells can explain the patients physical phenotype, with female external genitalia, it was somewhat discordant with the clinical expression of isolated 17,20-lyase deficiency with relative preservation of 17 alpha-hydroxylase activity in vivo. In addition to the expression studies of these two examples of mutants in the C-terminal region of cytochrome P-450(17) alpha, a third mutant cDNA construct containing a 4-base duplication at codon 480 previously found in patients with combined 17 alpha-hydroxylase/17,20-lyase deficiency was also expressed in COS-1 cells. This expressed protein was completely inactive with respect to both activities, supporting the biochemical findings in serum and in vitro biochemical data obtained using a testis from the patient. The results from these patients clearly indicate the importance of the C-terminal region of human P-450(17) alpha in its enzymatic activities.

Structural characterization of the bovine CYP17 (17α-hydroxylase) gene

Abstract The complete exonic and partial intronic sequence of the bovine CYP17 (P450 17α ) gene has been determined. The gene contains eight exons with exon/intron boundaries which are identical to those determined previously for the human CYP17 gene. The site of initiation of transcription of this gene is located within a 6-base sequence 52 bp from the initiation of translation. Considerable sequence homology (58.7%) is found when ~500 bp of the 5′-flanking sequences of the bovine and human CYP17 genes are compared. A computer-based search of this region of bovine CYP17 for consensus sequences associated with binding of transcription factors (i.e., GR, PR, CREB/ATF, AP1, AP2, AP3, AP4, AP5, OTF, CTF/NF1, SP1) shows only the consensus CREB/ATF sequence TGACGT which is also found to be at approximately the same position in the human CYP17 gene. In bovine adrenal cortex, transcription of the CYP17 gene is regulated by the peptide hormone adrenocorticotropin via cAMP. Whether the consensus CREB/ATF sequence is associated with the cAMP-mediated transcription of the CYP17 gene remains to be elucidated.

Nucleotide sequence of a cDNA encoding porcine testis 17α-hydroxylase cytochrome P-450

We describe the isolation and characterization of a cDNA encoding the complete porcine neonatal testis 17α-hydroxylase/C-17,20-lyase cytochrome P -450. The deduced amino acid sequence is 509 amino acids in length.

Deduced amino acid sequence of mature chicken testis ferredoxin

The cDNA sequence encoding the complete mature form of the steroidogenic ferredoxin from chicken testis has been determined and the amino acid sequence deduced therefrom has been compared with the sequences of bovine, human and porcine steroidogenic ferredoxins. The chicken sequence is between 84% and 88% identical with those of the other mitochondrial iron-sulfur proteins. Thus, the amino acid structure of steroidogenic ferredoxins which transfer electrons to mitochondrial forms of cytochrome P-450 has been very highly conserved over evolutionary time.