The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
David W. Russell - One of the best experts on this subject based on the ideXlab platform.
-
Cell type specific expression of steroid 5 alpha-Reductase 2.
The Journal of urology, 1994Co-Authors: R I Silver, Anice E. Thigpen, E L Wiley, J M Guileyardo, J D Mcconnell, David W. RussellAbstract:Isozymes of steroid 5 alpha-Reductase (5 alpha-Reductase) have crucial roles in androgen physiology by synthesizing the potent hormone dihydrotestosterone. The expression pattern of the 5 alpha-Reductase type 2 isozyme was determined in genital and extragenital tissues by developing an immunohistochemical assay using formalin-fixed tissue and affinity purified polyclonal antibodies that specifically recognize this isozyme. Expression was detected in basal epithelial and stromal cells of the normal prostate but not in luminal epithelial cells. Stromal cells of the seminal vesicle also expressed the type 2 isozyme. In contrast, staining was detected in epithelial cells of the epididymis but not in the surrounding stroma. Myofibroblasts in foreskin samples of normal and hypospadiac individuals expressed antigen and were distributed in bands throughout the prepuce, suggesting a clonal origin. In most cells the type 2 isozyme exhibited a perinuclear subcellular distribution. However, in liver hepatocytes the protein was distributed throughout the intracellular membrane compartment.
-
Expression and regulation of steroid 5 alpha-Reductase 2 in prostate disease.
The Journal of urology, 1994Co-Authors: R I Silver, Daphne L. Davis, Anice E. Thigpen, David W. Russell, E L Wiley, J D McconnellAbstract:The androgen dihydrotestosterone is synthesized by the enzyme steroid 5 alpha-Reductase, and it is required for growth and development of the prostate. We used immunohistochemistry to examine the expression of the type 2 isozyme of 5 alpha-Reductase in benign prostatic hyperplasia and prostate cancer. The type 2 isozyme is highly expressed within stromal cells in both disease states. No type 2 isozyme is detectable in a lymph node metastasis. Immunoblotting studies show that androgen ablation therapies substantially decrease isozyme expression in the epididymis but have a lesser effect on expression in the prostate. Finasteride therapy (2 weeks to 3 years) did not abolish expression of the prostatic type 2 isozyme nor did this drug treatment induce expression of the type 1 isozyme.
-
Steroid 5 alpha-Reductase 2 deficiency.
Endocrine Reviews, 1993Co-Authors: Jean D Wilson, James E. Griffin, David W. RussellAbstract:Abstract In the 20 yr since it was established that impairment of dihydrotestosterone formation is the cause of a rare form of human intersex, a wealth of information has accumulated about the genetics, endocrinology, and variable phenotypic manifestations, culminating in the cloning of cDNAs encoding two 5 alpha-Reductase genes and documentation that mutations in the steroid 5 alpha-Reductase 2 gene are the cause of 5 alpha-Reductase deficiency. Perplexing and difficult problems remain unresolved, e.g. whether the variability in manifestations is due to variable expressions of steroid 5 alpha-Reductase 1 or to effects of testosterone itself. It is also imperative to establish whether defects in steroid 5 alpha-Reductase 2, perhaps in the heterozygous state, are responsible for a portion of cases of sporadic hypospadias, to determine whether 5 alpha-Reductase plays a role in progesterone action in women, and to elucidate the relation between androgen action and gender role behavior.
-
tissue distribution and ontogeny of steroid 5 alpha Reductase isozyme expression
Journal of Clinical Investigation, 1993Co-Authors: Anice E. Thigpen, Richard I Silver, Joseph M Guileyardo, M L Casey, John D Mcconnell, David W. RussellAbstract:The synthesis of dihydrotestosterone is catalyzed by steroid 5 alpha-Reductase isozymes, designated types 1 and 2. Mutation of type 2 results in male pseudohermaphroditism, in which the external genitalia are phenotypically female at birth. Two striking and unexplained features of this disorder are that external genitalia of affected males undergo virilization during puberty and that these individuals have less temporal hair regression. The tissue-specific and developmental expression patterns of the 5 alpha-Reductase isozymes were investigated by immunoblotting. The type 1 isozyme is not detectable in the fetus, is transiently expressed in newborn skin and scalp, and permanently expressed in skin from the time of puberty. There was no qualitative difference in 5 alpha-Reductase type 1 expression between adult balding vs. nonbalding scalp. The type 2 isozyme is transiently expressed in skin and scalp of newborns. Type 2 is the predominant isozyme detectable in fetal genital skin, male accessory sex glands, and in the prostate, including benign prostatic hyperplasia and prostate adenocarcinoma tissues. Both isozymes are expressed in the liver, but only after birth. These results are consistent with 5 alpha-Reductase type 1 being responsible for virilization in type 2-deficient subjects during puberty, and suggest that the type 2 isozyme may be an initiating factor in development of male pattern baldness.
-
ly191704 a selective nonsteroidal inhibitor of human steroid 5 alpha Reductase type 1
Proceedings of the National Academy of Sciences of the United States of America, 1993Co-Authors: Kenneth Steven Hirsch, Charles David Jones, James E Audia, Stefan Andersson, Loretta Ames Mcquaid, Nancy B Stamm, Blake Lee Neubauer, Pam Pennington, Richard E Toomey, David W. RussellAbstract:Abstract Androgens, in particular dihydrotestosterone (DHT), play a key role in differentiation, growth, and maintenance of the mammalian prostate. Production of DHT from testosterone is catalyzed by two distinct membrane-bound steroid 5 alpha-Reductase [5 alpha-Reductase; 3-oxo-5 alpha-steroid delta 4-dehydrogenase; 3-oxo-5 alpha-steroid:(acceptor) delta 4-oxidoReductase, EC 1.3.99.5] isozymes designated types 1 and 2. Benign prostatic hyperplasia (BPH), a disease that occurs almost universally in males, is characterized by obstructive and irritative urinary voiding symptoms and has been associated with an overproduction of DHT. Recently, steroidal inhibitors of 5 alpha-Reductase type 2 have been used successfully for treatment of BPH. Described here is a nonsteroidal inhibitor of 5 alpha-Reductase type 1, LY191704 (8-chloro-4-methyl-1,2,3,4,4a,5,6,10b-octaahydro-benzo[f]quinol in-3(2H)-one). This compound was identified based on its capacity to inhibit 5 alpha-Reductase activity in a human genital skin fibroblast cell line (Hs68). Surprisingly, LY191704 is inactive when tested in freshly isolated prostate cells obtained from subjects with BPH, whereas previously described 4-azasteroids are active. LY191704 is, however, a potent inhibitor of the 5 alpha-Reductase activity of BPH cells that have been maintained in culture. Analysis of human and rat 5 alpha-Reductases expressed from transfected cDNAs in simian COS cells indicates that LY191704 is a specific noncompetitive inhibitor of the human 5 alpha-Reductase type 1. Taken together, the results suggest that prostate cells have the capacity to express both 5 alpha-Reductase isozymes and that LY191704 may be useful in treatment of human endocrine disorders associated with overproduction of DHT by 5 alpha-Reductase type 1.
Dagmar Struve - One of the best experts on this subject based on the ideXlab platform.
-
Nonisotopic single strand conformation analysis of the 5 alpha-Reductase type 2 gene for the diagnosis of 5 alpha-Reductase deficiency.
The Journal of Clinical Endocrinology and Metabolism, 1996Co-Authors: Olaf Hiort, Gernot H G Sinnecker, Holger Willenbring, A. Lehners, Alfred Zollner, Dagmar StruveAbstract:5 alpha-Reductase deficiency is a rare autosomal recessive disorder of defective virilization in karyotypic males due to reduced conversion of testosterone to dihydrotestosterone. The gene encoding the affected 5 alpha-Reductase type 2 enzyme has recently been cloned, and mutations within the coding region have been discovered as the cause of this disease. We address the possibility of a rapid nonradioactive molecular genetic screening technique for initial diagnosis and report different point mutations in this gene in eight unrelated patients with clinical features of 5 alpha-Reductase deficiency. For molecular genetic analysis, DNA from peripheral blood leukocytes was studied. The coding region of the 5 alpha-Reductase type 2 gene was characterized by exon-specific PCR amplification, nonradioactive single strand conformation analysis, and direct sequencing. In seven patients, homozygous point mutations were identified (Leu55-Gln, delta Met157, Gly196-Ser, Arg227-Gln, Ala228-Thr, and His231-Arg). One ind...
-
nonisotopic single strand conformation analysis of the 5 alpha Reductase type 2 gene for the diagnosis of 5 alpha Reductase deficiency
The Journal of Clinical Endocrinology and Metabolism, 1996Co-Authors: Olaf Hiort, Gernot H G Sinnecker, Holger Willenbring, A. Lehners, Alfred Zollner, Dagmar StruveAbstract:5 alpha-Reductase deficiency is a rare autosomal recessive disorder of defective virilization in karyotypic males due to reduced conversion of testosterone to dihydrotestosterone. The gene encoding the affected 5 alpha-Reductase type 2 enzyme has recently been cloned, and mutations within the coding region have been discovered as the cause of this disease. We address the possibility of a rapid nonradioactive molecular genetic screening technique for initial diagnosis and report different point mutations in this gene in eight unrelated patients with clinical features of 5 alpha-Reductase deficiency. For molecular genetic analysis, DNA from peripheral blood leukocytes was studied. The coding region of the 5 alpha-Reductase type 2 gene was characterized by exon-specific PCR amplification, nonradioactive single strand conformation analysis, and direct sequencing. In seven patients, homozygous point mutations were identified (Leu55-Gln, delta Met157, Gly196-Ser, Arg227-Gln, Ala228-Thr, and His231-Arg). One individual was a compound heterozygote carrier of two mutations (Ile112-Asn and Gln126-Arg). We conclude that molecular genetic characterization of point mutations in the 5 alpha-Reductase type 2 gene may be used as an additional valuable procedure for the diagnosis of this disorder.
Olaf Hiort - One of the best experts on this subject based on the ideXlab platform.
-
Nonisotopic single strand conformation analysis of the 5 alpha-Reductase type 2 gene for the diagnosis of 5 alpha-Reductase deficiency.
The Journal of Clinical Endocrinology and Metabolism, 1996Co-Authors: Olaf Hiort, Gernot H G Sinnecker, Holger Willenbring, A. Lehners, Alfred Zollner, Dagmar StruveAbstract:5 alpha-Reductase deficiency is a rare autosomal recessive disorder of defective virilization in karyotypic males due to reduced conversion of testosterone to dihydrotestosterone. The gene encoding the affected 5 alpha-Reductase type 2 enzyme has recently been cloned, and mutations within the coding region have been discovered as the cause of this disease. We address the possibility of a rapid nonradioactive molecular genetic screening technique for initial diagnosis and report different point mutations in this gene in eight unrelated patients with clinical features of 5 alpha-Reductase deficiency. For molecular genetic analysis, DNA from peripheral blood leukocytes was studied. The coding region of the 5 alpha-Reductase type 2 gene was characterized by exon-specific PCR amplification, nonradioactive single strand conformation analysis, and direct sequencing. In seven patients, homozygous point mutations were identified (Leu55-Gln, delta Met157, Gly196-Ser, Arg227-Gln, Ala228-Thr, and His231-Arg). One ind...
-
nonisotopic single strand conformation analysis of the 5 alpha Reductase type 2 gene for the diagnosis of 5 alpha Reductase deficiency
The Journal of Clinical Endocrinology and Metabolism, 1996Co-Authors: Olaf Hiort, Gernot H G Sinnecker, Holger Willenbring, A. Lehners, Alfred Zollner, Dagmar StruveAbstract:5 alpha-Reductase deficiency is a rare autosomal recessive disorder of defective virilization in karyotypic males due to reduced conversion of testosterone to dihydrotestosterone. The gene encoding the affected 5 alpha-Reductase type 2 enzyme has recently been cloned, and mutations within the coding region have been discovered as the cause of this disease. We address the possibility of a rapid nonradioactive molecular genetic screening technique for initial diagnosis and report different point mutations in this gene in eight unrelated patients with clinical features of 5 alpha-Reductase deficiency. For molecular genetic analysis, DNA from peripheral blood leukocytes was studied. The coding region of the 5 alpha-Reductase type 2 gene was characterized by exon-specific PCR amplification, nonradioactive single strand conformation analysis, and direct sequencing. In seven patients, homozygous point mutations were identified (Leu55-Gln, delta Met157, Gly196-Ser, Arg227-Gln, Ala228-Thr, and His231-Arg). One individual was a compound heterozygote carrier of two mutations (Ile112-Asn and Gln126-Arg). We conclude that molecular genetic characterization of point mutations in the 5 alpha-Reductase type 2 gene may be used as an additional valuable procedure for the diagnosis of this disorder.
Julianne Imperato-mcginley - One of the best experts on this subject based on the ideXlab platform.
-
5 alpha-Reductase-2 gene mutations in the Dominican Republic.
The Journal of Clinical Endocrinology and Metabolism, 1996Co-Authors: M. D. Katz, Cedric H.l. Shackleton, Julián Báez, M. Defillo-ricart, C. Herrera, Julianne Imperato-mcginleyAbstract:Male pseudohermaphroditism due to 5 alpha-Reductase deficiency was clinically and biochemically described in a large Dominican kindred of 23 families with 38 affected subjects in 1974. Recently, the 5 alpha-Reductase-2 gene defect in the large Dominican kindred was found to be due to a single base substitution of thymidine (TGG) for cytosine (CGG) on exon 5 of the 5 alpha-Reductase-2 gene, causing a tryptophan replacement of arginine at amino acid 246 (R246W) of the enzyme. In the present report, affected subjects from four additional Dominican families were studied to determine whether they carried the same 5 alpha-Reductase-2 gene defect as the large kindred, suggesting a common ancestry for the gene defect within this small country. Using single strand conformational polymorphism and DNA sequencing, two other mutations of the 5 alpha-Reductase-2 gene were found in affected subjects from two of the four families. A point mutation on exon 2 of the 5 alpha-Reductase-2 gene, in which substitution of adenin...
-
The biochemical and phenotypic characterization of females homozygous for 5 alpha-Reductase-2 deficiency.
The Journal of clinical endocrinology and metabolism, 1995Co-Authors: Melissa D. Katz, Cedric H.l. Shackleton, M. Defillo-ricart, Li-qun Cai, Yuan-shan Zhu, Cecilia Herrera, Julianne Imperato-mcginleyAbstract:The biochemical and physiologic manifestations of decreased 5 alpha-dihydrotestosterone (DHT) in females are characterized. Three females from the large Dominican kindred with 5 alpha-Reductase-2 deficiency were identified as homozygous for a point mutation (R246W, C-->T) on exon 5 of the 5 alpha-Reductase-2 gene by single strand DNA conformational polymorphism analysis and DNA sequence analysis. Body hair was decreased; there was no history of acne. Despite delayed menarche, all were fertile, and two had twins. Urinary 5 beta/5 alpha C19 and C21 steroid metabolite ratios were elevated. Plasma testosterone was normal to elevated, with low DHT, resulting in an increased testosterone/DHT ratio. 3 alpha,5 alpha-Androstanediol glucuronide was low. Menstrual cycle profiling performed in two subjects showed ovulatory gonadotropin peaks. Sebum production was normal. 5 alpha-Reductase-2-deficient homozygotic females demonstrate the importance of DHT in the physiology and pathophysiology of body hair growth. Normal sebum implies regulation by the 5 alpha-Reductase-1 isoenzyme. Delayed puberty suggests involvement of 5 alpha-Reductase-2 in menarche at the hypothalamic/pituitary and/or ovarian level. As two had nonidentical twins, DHT and/or the DHT/estradiol ratio may regulate follicular development, with lower levels permitting more than one dominant follicle per cycle and higher levels impairing follicular development and ovulation. Thus, females with 5 alpha-Reductase-2 deficiency highlight a role for DHT in hirsutism and/or menstrual disorders.
-
5 alpha-Reductase deficiency: human and animal models.
European urology, 1994Co-Authors: Julianne Imperato-mcginleyAbstract:The syndrome of male pseudohermaphroditism secondary to 5 alpha-Reductase deficiency is reviewed, as are hormonal evaluation and tissue studies documenting the enzyme deficiency. These studies reveal that the 5 alpha-metabolite dihydrotestosterone is essential for differentiation of the external genitalia and prostate. Studies of male rat fetuses treated with 5 alpha-Reductase inhibitors during the critical period of sexual differentiation in utero reveal incomplete masculinization of the external genitalia and impaired prostate growth and development. Thus, conclusive evidence is provided for the hypothesis that 5 alpha-Reductase activity and dihydrotestosterone formation are essential for normal differentiation of the male external genitalia and the prostate.
-
Prostate visualization studies in males homozygous and heterozygous for 5 alpha-Reductase deficiency.
The Journal of Clinical Endocrinology and Metabolism, 1992Co-Authors: Julianne Imperato-mcginley, Teofilo Gautier, K Zirinsky, O Palomo, John A. Markisz, E. Ramirez De Arellano, E.d. Vaughan, Evan A Stein, Elias KazamAbstract:Male pseudohermaphrodites with 5 alpha-Reductase deficiency have ambiguous genitalia and nonpalpable prostates on rectal examination, suggesting the dihydrotestosterone dependency of these structures. To clearly delineate the status of the prostate, male pseudohermaphrodites with 5 alpha-Reductase deficiency had transrectal sonography of the prostate performed, and the results were compared to that of age-matched male controls. In six male pseudohermaphrodites, magnetic resonance imaging studies of the prostate were also performed. Heterozygote fathers also had transrectal sonography of the prostate performed and the results compared to age-matched controls. The prostates of the male pseudohermaphrodites appeared as platelike soft tissue structures posterior to the urethra on both prostatic ultrasound and magnetic resonance imaging. Prostatic volume, as determined on prostatic ultrasound by two different methods, was significantly smaller (approximately one-tenth) than the volume of age-matched controls. ...
-
Molecular genetics of steroid 5 alpha-Reductase 2 deficiency.
Journal of Clinical Investigation, 1992Co-Authors: Anice E. Thigpen, Jean D Wilson, James E. Griffin, Daphne L. Davis, Athena Milatovich, Julianne Imperato-mcginley, Uta Francke, Berenice B. Mendonca, David W. RussellAbstract:Two isozymes of steroid 5 alpha-Reductase encoded by separate loci catalyze the conversion of testosterone to dihydrotestosterone. Inherited defects in the type 2 isozyme lead to male pseudohermaphroditism in which affected males have a normal internal urogenital tract but external genitalia resembling those of a female. The 5 alpha-Reductase type 2 gene (gene symbol SRD5A2) was cloned and shown to contain five exons and four introns. The gene was localized to chromosome 2 band p23 by somatic cell hybrid mapping and chromosomal in situ hybridization. Molecular analysis of the SRD5A2 gene resulted in the identification of 18 mutations in 11 homozygotes, 6 compound heterozygotes, and 4 inferred compound heterozygotes from 23 families with 5 alpha-Reductase deficiency. 6 apparent recurrent mutations were detected in 19 different ethnic backgrounds. In two patients, the catalytic efficiency of the mutant enzymes correlated with the severity of the disease. The high proportion of compound heterozygotes suggests that the carrier frequency of mutations in the 5 alpha-Reductase type 2 gene may be higher than previously thought.
Anice E. Thigpen - One of the best experts on this subject based on the ideXlab platform.
-
Cell type specific expression of steroid 5 alpha-Reductase 2.
The Journal of urology, 1994Co-Authors: R I Silver, Anice E. Thigpen, E L Wiley, J M Guileyardo, J D Mcconnell, David W. RussellAbstract:Isozymes of steroid 5 alpha-Reductase (5 alpha-Reductase) have crucial roles in androgen physiology by synthesizing the potent hormone dihydrotestosterone. The expression pattern of the 5 alpha-Reductase type 2 isozyme was determined in genital and extragenital tissues by developing an immunohistochemical assay using formalin-fixed tissue and affinity purified polyclonal antibodies that specifically recognize this isozyme. Expression was detected in basal epithelial and stromal cells of the normal prostate but not in luminal epithelial cells. Stromal cells of the seminal vesicle also expressed the type 2 isozyme. In contrast, staining was detected in epithelial cells of the epididymis but not in the surrounding stroma. Myofibroblasts in foreskin samples of normal and hypospadiac individuals expressed antigen and were distributed in bands throughout the prepuce, suggesting a clonal origin. In most cells the type 2 isozyme exhibited a perinuclear subcellular distribution. However, in liver hepatocytes the protein was distributed throughout the intracellular membrane compartment.
-
Expression and regulation of steroid 5 alpha-Reductase 2 in prostate disease.
The Journal of urology, 1994Co-Authors: R I Silver, Daphne L. Davis, Anice E. Thigpen, David W. Russell, E L Wiley, J D McconnellAbstract:The androgen dihydrotestosterone is synthesized by the enzyme steroid 5 alpha-Reductase, and it is required for growth and development of the prostate. We used immunohistochemistry to examine the expression of the type 2 isozyme of 5 alpha-Reductase in benign prostatic hyperplasia and prostate cancer. The type 2 isozyme is highly expressed within stromal cells in both disease states. No type 2 isozyme is detectable in a lymph node metastasis. Immunoblotting studies show that androgen ablation therapies substantially decrease isozyme expression in the epididymis but have a lesser effect on expression in the prostate. Finasteride therapy (2 weeks to 3 years) did not abolish expression of the prostatic type 2 isozyme nor did this drug treatment induce expression of the type 1 isozyme.
-
tissue distribution and ontogeny of steroid 5 alpha Reductase isozyme expression
Journal of Clinical Investigation, 1993Co-Authors: Anice E. Thigpen, Richard I Silver, Joseph M Guileyardo, M L Casey, John D Mcconnell, David W. RussellAbstract:The synthesis of dihydrotestosterone is catalyzed by steroid 5 alpha-Reductase isozymes, designated types 1 and 2. Mutation of type 2 results in male pseudohermaphroditism, in which the external genitalia are phenotypically female at birth. Two striking and unexplained features of this disorder are that external genitalia of affected males undergo virilization during puberty and that these individuals have less temporal hair regression. The tissue-specific and developmental expression patterns of the 5 alpha-Reductase isozymes were investigated by immunoblotting. The type 1 isozyme is not detectable in the fetus, is transiently expressed in newborn skin and scalp, and permanently expressed in skin from the time of puberty. There was no qualitative difference in 5 alpha-Reductase type 1 expression between adult balding vs. nonbalding scalp. The type 2 isozyme is transiently expressed in skin and scalp of newborns. Type 2 is the predominant isozyme detectable in fetal genital skin, male accessory sex glands, and in the prostate, including benign prostatic hyperplasia and prostate adenocarcinoma tissues. Both isozymes are expressed in the liver, but only after birth. These results are consistent with 5 alpha-Reductase type 1 being responsible for virilization in type 2-deficient subjects during puberty, and suggest that the type 2 isozyme may be an initiating factor in development of male pattern baldness.
-
Molecular genetics of steroid 5 alpha-Reductase 2 deficiency.
Journal of Clinical Investigation, 1992Co-Authors: Anice E. Thigpen, Jean D Wilson, James E. Griffin, Daphne L. Davis, Athena Milatovich, Julianne Imperato-mcginley, Uta Francke, Berenice B. Mendonca, David W. RussellAbstract:Two isozymes of steroid 5 alpha-Reductase encoded by separate loci catalyze the conversion of testosterone to dihydrotestosterone. Inherited defects in the type 2 isozyme lead to male pseudohermaphroditism in which affected males have a normal internal urogenital tract but external genitalia resembling those of a female. The 5 alpha-Reductase type 2 gene (gene symbol SRD5A2) was cloned and shown to contain five exons and four introns. The gene was localized to chromosome 2 band p23 by somatic cell hybrid mapping and chromosomal in situ hybridization. Molecular analysis of the SRD5A2 gene resulted in the identification of 18 mutations in 11 homozygotes, 6 compound heterozygotes, and 4 inferred compound heterozygotes from 23 families with 5 alpha-Reductase deficiency. 6 apparent recurrent mutations were detected in 19 different ethnic backgrounds. In two patients, the catalytic efficiency of the mutant enzymes correlated with the severity of the disease. The high proportion of compound heterozygotes suggests that the carrier frequency of mutations in the 5 alpha-Reductase type 2 gene may be higher than previously thought.
-
four amino acid segment in steroid 5 alpha Reductase 1 confers sensitivity to finasteride a competitive inhibitor
Journal of Biological Chemistry, 1992Co-Authors: Anice E. Thigpen, David W. RussellAbstract:Abstract The 4-azasteroid 17 beta-(N-t-butyl)carbamoyl-4-aza-5 alpha-androst-1-en-3-one (finasteride) is 100-fold more potent as a competitive inhibitor of the rat NADPH:delta 4-3-oxosteroid-5-Alpha- oxidoReductase (steroid 5 alpha-Reductase) type 1 enzyme (Ki = 3-5 nM) than of the human type 1 enzyme (Ki greater than or equal to 300 nM). In this study, we exploit this differential sensitivity to map a major determinant of finasteride sensitivity in steroid 5 alpha-Reductase. Chimeric steroid 5 alpha-Reductase cDNAs composed of different combinations of rat and human exon sequences were created by genetic engineering, expressed in human embryonic kidney 293 cells, and assayed for their sensitivity to finasteride. Hybrid proteins containing sequences encoded by rat exon 1 were found to be as sensitive to finasteride as the parental enzyme. The exchange of progressively smaller protein segments encoded within exon 1 identified a tetrapeptide sequence (Val-Ser-Ile-Val) in the rat enzyme that conferred sensitivity to finasteride. The analogous sequence in the human enzyme (Ala-Val-Phe-Ala) conferred partial resistance to the drug. Finasteride was a competitive inhibitor of the native and all chimeric enzymes tested, suggesting that the tetrapeptide segments form a portion of the substrate-binding domain of steroid 5 alpha-Reductase.
