Probing structural and functional domains of human P450c17

A novel communication role for CYP17A1 in the progression of castration-resistant prostate cancer

BACKGROUND

CYP17A1 is currently a target for total androgen blockade in advanced prostate cancer (CaP) patients. After castration, or removal of testicular androgens, CYP17A1 can act as a rate-limiting enzyme in androgen synthesis from cholesterol or other adrenal precursors within the tumor microenvironment ultimately contributing to disease progression. Herein we provide evidence that CYP17A1 could also be a mediator of cell-to-cell communication within the CaP tumor microenvironment.

METHODS

CYP17A1 expression was evaluated by immunohistochemical analysis of human tumor sections and Western blot analysis of CaP patients' serum and exosome isolates. CYP17A1 activity assays were conducted in human serum (and positive control human liver and kidney microsomes) using progesterone as a precursor and an LC-MS endpoint.

RESULTS

These studies revealed that the expression pattern of CYP17A1 is typical of a secretory protein as it is localized to the luminal pole of the cells in exocrine secretory mode. CYP17A1 is expressed in human serum and in fact is elevated in the serum of CaP patients as compared to healthy controls. Serum CYP17A1 activity could not be confirmed, however, verification of CYP17A1 expression in exosomes suggests a role in cell-to-cell communication within the tumor microenvironment.

CONCLUSIONS

CYP17A1 is a crucial enzyme for de novo androgen synthesis within the tumor microenvironment after removal of testicular androgens by castration. We provide evidence for a novel role for CYP17A1 in serum and further reiterate the importance of targeting this enzyme in CaP progression.

Mutagenesis of putative serine-threonine phosphorylation sites proximal to Arg255 of human cytochrome P450c17 does not selectively promote its 17,20-lyase activity

OBJECTIVE

To investigate the role of serine-threonine phosphorylation on the activity of human P450c17.

DESIGN

In vitro study.

SETTING

Academic basic research laboratory.

PATIENT(S)

None.

INTERVENTION(S)

P450c17 expression constructs with a FLAG-tag on either the C-terminus or N-terminus of the protein were generated. Human C-terminal FLAG-tagged P450c17 chromosomal DNA was subjected to site-directed mutagenesis. Serine 258 and threonine 260 each were mutated to alanine and aspartic acid. The mutant P450c17s were expressed in COS-7 cells, and the enzymatic activities were measured.

MAIN OUTCOME MEASURE(S)

17alpha-Hydroxylase and C(17-20) lyase activities of human P450c17.

RESULT(S)

C-terminal FLAG-tagged P450c17 functioned indistinguishably from the wild-type P450c17. Mutants S258A, S258D, and T260D had significantly less 17alpha-hydroxylase and C(17-20) lyase activities than the wild type.

CONCLUSION(S)

Adding an epitope tag to the C-terminus of the P450c17 protein does not interfere with its activities and will be a useful tool to isolate human P450c17 protein from cultured cells. Phosphorylation of serine 258 but not threonine 260 may act as a physiologic regulator of both enzymatic activities through interaction with obligatory redox partners.

Novel mutation of the CYP17 gene in two unrelated patients with combined 17alpha-hydroxylase/17,20-lyase deficiency: demonstration of absent enzyme activity by expressing the mutant CYP17 gene and by three-dimensional modeling

The CYP17 gene, located on chromosome 10q24-q25, encodes the cytochrome P450c17 enzyme. Mutations of this gene cause the 17alpha-hydroxylase/17,20-lyase deficiency, which is a rare, autosomal recessive form of congenital adrenal hyperplasia. Approximately 50 different mutations of the CYP17 gene have been described, of which some mutations have been identified in certain ethnic groups. In this study, we present the clinical history, hormonal findings and mutational analysis of two patients from unrelated families, who were evaluated for hypertension, hypokalemia and sexual infantilism. In the first patient, who was a 37-year-old female, additional studies showed a large myelolipoma in the left adrenal gland, and a smaller tumor in the right adrenal gland. In the second patient, who was a 31-year-old phenotypic female, clinical work-up revealed a 46,XY kariotype, absence of ovaries and presence of testes located in the inner opening of both inguinal canals. Analysis of the CYP17 gene by polymerase chain reaction amplification and direct sequencing demonstrated a novel homozygous mutation of codon 440 from CGC (Arg) to TGC (Cys) in both patients. The effect of this novel mutation on 17alpha-hydroxylase/17,20-lyase activity was assessed by in vitro studies on the mutant and wild-type P450c17 generated by site-directed mutagenesis and transfected in nonsteroidogenic COS-1 cells. These studies showed that the mutant P450c17 protein was produced in transfected COS-1 cells, but it had negligible 17alpha-hydroxylase and 17,20-lyase activities. In addition, three-dimensional computerized modeling of the heme-binding site of the P450c17 enzyme indicated that replacement of Arg by Cys at amino acid position 440 predicts a loss of the catalytic activity of the enzyme, as the mutant enzyme containing Cys440 fails to form a hydrogen bond with the propionate group of heme, which renders the mutant enzyme unable to stabilize the proper position of heme. Based on these findings we conclude that expressing the CYP17 gene with functional analysis, combined with three-dimensional computerized modeling of the heme-binding site of the protein provide feasible tools for molecular characterizing of functional consequences of the novel CYP17 mutation on enzyme function.

P450c17 deficiency in Brazilian patients: biochemical diagnosis through progesterone levels confirmed by CYP17 genotyping

P450c17 deficiency is an autosomal recessive disorder and a rare cause of congenital adrenal hyperplasia characterized by hypertension, hypokalemia, and impaired production of sex hormones. We performed a clinical, hormonal, and molecular study of 11 patients from 6 Brazilian families with the combined 17alpha-hydroxylase/17,20-lyase deficiency phenotype. All patients had elevated basal serum levels of progesterone (1.8-38 ng/ml; 0.57-12 pmol/liter) and suppressed plasma renin activity. CYP17 genotyping identified 5 missense mutations. The compound heterozygous mutation R362C/W406R was found in 1 family, whereas the homozygous mutations R96W, Y329D, and P428L were seen in the other 5 families. The R96W mutation has been described as the cause of p450c17 deficiency in Caucasian patients. The other mutations were not found in 50 normal subjects screened by allele-specific oligonucleotide hybridization (Y329D, R362C, and W406R) or digestion with HphI (P428L) and were recently found in other Brazilian patients. Therefore, we elucidated the genotype of 11 individuals with p450c17 deficiency and concluded that basal progesterone measurement is a useful marker of p450c17 deficiency and that its use should reduce the misdiagnosis of this deficiency in patients presenting with male pseudohermaphroditism, primary or secondary amenorrhea, and mineralocorticoid excess syndrome.

Familial partial 17,20-desmolase and 17alpha-hydroxylase deficiency presenting as infertility

PURPOSE

Females with 17alpha-hydroxylase/17,20-desmolase deficiency normally present with amenorrhea, sexual infantilism, hypertension, and hypokalemia. We report on a new clinical presentation of this combined enzymatic defect.

METHODS

Four Jewish women from two unrelated families presented with primary infertility. All patients exhibited a normal phenotype, blood pressure, and serum potassium levels with abnormally high follicular phase serum progesterone and low E2 levels. In order to characterize the underlying defect, the following steps were undertaken: 1) ovarian suppression by GnRH agonist, 2) adrenal suppression by dexamethasone, 3) ovarian stimulation by gonadotropins, 4) adrenal stimulation by ACTH, 5) hormonal assessment of follicular fluid aspirates, and 6) assessment of in vitro E2 production by luteinized granulosa cells.

RESULTS

The clinical characteristics and endocrine testing results support the diagnosis of a partial deficiency in 17alpha-hydroxylase/17,20-desmolase activities, shared by the adrenal gland and the ovaries

CONCLUSIONS

Female infertility can be the first and sole clinical manifestation of this enzymatic defect. Its exact nature and prevalence remain to be determined.

Baboon cytochrome P450 17alpha-hydroxylase/17,20-lyase (CYP17)

Human cytochrome P450 17alpha-hydroxylase (CYP17) catalyses not only the 17alpha-hydroxlation of pregnenolone and progesterone and the C17,20-side chain cleavage (lyase) of 17alpha-hydroxypregnenolone, necessary for the biosynthesis of C21-glucocorticoids and C19-androgens, but also catalyses the 16alpha-hydroxylation of progesterone. In efforts to understand the complex enzymology of CYP17, structure/function relationships have been reported previously after expressing recombinant DNAs, encoding CYP17 from various species, in nonsteroidogenic mammalian or yeast cells. A major difference between species resides in the lyase activity towards the hydroxylated intermediates and in the fact that the secretion of C19-steroids take place, in some species, principally in the gonads. Because human and higher primate adrenals secrete steroids, CYP17 has been characterized in the Cape baboon, a species more closely related to humans, in an effort to gain a further understanding of the reactions catalysed by CYP17. Baboon and human CYP17 cDNA share 96% homology. Baboon CYP17 has apparent Km and V values for pregnenolone and progesterone of 0.9 micro m and 0.4 nmol.h-1.mg protein-1 and 6.5 micro m and 3.9 nmol.h-1.mg protein-1, respectively. Baboon CYP17 had a significantly higher activity for progesterone hydroxylation relative to pregnenolone. No 16alpha-hydroxylase and no lyase activity for 17alpha-hydroxyprogesterone. Sequence analyses showed that there are 28 different amino acid residues between human and baboon CYP17, primarily in helices F and G and the F-G loop.