Biochemical and pharmacogenetic dissection of human steroid 5??-reductase type II

Abstract

Human prostatic steroid 5alpha-reductase, encoded by the SRD5A2 gene on chromosome band 2p23, catalyses the irreversible conversion of testosterone to dihydrotestosterone (DHT), the most active androgen in the prostate, with NADPH as its cofactor. This enzyme has never been purified but a number of competitive inhibitors have been developed for this enzyme since increased steroid 5alpha-reductase activity may cause benign prostatic hypertrophy and prostate cancer. We report here the detailed biochemical and pharmacogenetic dissection of the human enzyme by analysing 10 missense substitutions and three double mutants which are all naturally found in humans. Nine of these 13 mutants reduce activity (measured as Vmax) by 20% or more, three increase steroid 5alpha-reductase by more than 15% and one results in essentially unaltered kinetic properties suggesting that it is a truly neutral ('polymorphic') amino acid substitution. Substantial pharmacogenetic variation among the mutants was also observed when three competitive inhibitors, finasteride, GG745 (dutasteride) and PNU157706, were investigated. Our studies not only define the substrate and cofactor binding sites of human steroid 5alpha-reductase, but also have significant consequences for the pharmacological usage of steroid 5alpha-reductase inhibitors in human patients treated for prostatic conditions.

Identification and characterization of somatic steroid 5α-reductase (SRD5A2) mutations in human prostate cancer tissue

“…Characterization of the apparent inhibitory constant (K i ) for three competitive 5a-reductase inhibitors (finasteride, dutasteride, and PNU-157706; Makridakis et al, 2000) indicates that there is significant pharmacogenetic variation compared to the wild-type protein for most of the somatic SRD5A2 missense substitutions (Table 4). The apparent K i for the selective 5a-reductase type II inhibitor finasteride (Stoner, 1996) varied 36-fold, from 5-180 nM (Table 4).…”

The 5α-Reductase Type II A49T and V89L High-Activity Allelic Variants are More Common in Men with Prostate Cancer Compared with the General Population

“…Interestingly, the homozygous V89L L-allele, known to have lower transcriptional activity in vitro 27 , was less common in CaP patients compared to the general population. This gives further support that the genetically predisposed conversion of T to DHT plays a role in progression of CaP to clinical disease.…”

“…The SRD5A2 gene contains three polymorphisms: a valine to leucine substitution at codon 89 (V89L), an alanine 49 to threonine transversion (A49T) and arginine to glutamine at codon 227 (R227Q). The A49T mutation seemed to have the highest impact on the enzymatic activity 5 increasing the conversion of testosterone to DHT 6-fold in vitro 6 , whereas the V89L L-allele was associated with approximately 30% lower SRD5A2 activity 7 and lower prevalence in African Americans 8 . The R227Q mutation was first reported in boys with hypospadias and micropenis 9 .…”

Nutrient selection through nutrigenomic approaches

“…As one example, steroid 5␣-reductase (designated SRD5A2), a key enzyme in androgen metabolism in the prostate, has 13 naturally occurring variants in the human population. Nine of these variants reduce SRD5A2 activity by 20% or more, and three increase activity by more than 15% (99). Since SRD5A produces dihydrotestosterone (DHT) and DHT regulates genes in the prostate, variants in steroid 5␣-reductase may affect incidence or severity of prostate cancer (123).…”