HSD3B2

HSD3B2 encodes a NAD+-dependent 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase that catalyzes the conversion of Δ5-steroids to Δ4-steroids in adrenal and gonadal steroidogenesis, and loss-of-function mutations cause 3β-HSD deficiency with a genotype–phenotype correlation in which severe salt-wasting forms reflect complete loss of catalytic activity while non-salt-losing forms retain residual activity (PMID:10599696). Catalytic competence depends on an intact NAD+-binding domain: the A10E substitution at Ala10 abolishes activity (PMID:10843183), and the G250V substitution disrupts an L239-Q251 loop adjacent to a β-sheet in this domain, lowering Vmax for progesterone synthesis without altering substrate affinity, protein level, or localization (PMID:25322271). A separate substrate-binding pocket governs substrate handling, as the Y190C and S218P mutations adjacent to this pocket impair activity in a substrate-specific manner, retaining greater residual activity toward 17-OH pregnenolone than other Δ5-steroids (PMID:24372086). Some disease alleles act through protein instability rather than direct catalytic impairment (PMID:10599696). In human adrenal cortex, HSD3B2 is co-expressed with cytochrome b5 (CYB5A) in hybrid cells at the zona fasciculata/zona reticularis border, and together they drive androstenedione production (PMID:21185375). HSD3B2 transcription is governed by multiple factors: YY1 binding at two sites within intron 1 is required for maximal basal promoter activity (PMID:15291746), GATA1 binds the promoter to activate expression and androgen biosynthesis (PMID:30650063), and cAMP-stimulated recruitment of the orphan nuclear receptor Nur77 to the promoter is suppressed by decanoic acid and metformin (PMID:26465200). Enzyme output is additionally modulated indirectly through mitochondrial complex I, since metformin and rotenone inhibit HSD3B2 activity via complex I inhibition rather than AMPK or ERK signaling (PMID:22778212).

1. 1994 Low

   Established that loss of HSD3B2 protein underlies severe salt-wasting 3β-HSD deficiency by identifying a frameshift truncating allele in affected patients.

   Evidence Direct sequencing and haplotype analysis of a homozygous 273-delta-AA frameshift producing a premature stop at codon 279

   PMID:8004103

   Open questions at the time

   • No functional expression assay was performed to confirm the predicted null
   • Does not address milder allelic forms or residual-activity mutations
2. 1999 High

   Resolved the genotype–phenotype basis of 3β-HSD deficiency by showing that disease severity tracks with quantitative residual enzyme activity, and that some mutations act through protein instability.

   Evidence Site-directed mutagenesis of 25 missense mutants, transient expression in 293 cells, [14C]-DHEA substrate assay, plus Northern/Western and in vitro translation

   PMID:10599696

   Open questions at the time

   • Activity measured in cell expression systems, not purified reconstituted enzyme
   • Does not map which structural domains each mutation perturbs
3. 2000 Medium

   Pinpointed a single NAD+-binding-domain residue (Ala10) as essential for catalysis by showing A10E abolishes all detectable activity.

   Evidence Direct sequencing and transient expression with enzymatic activity assay in Ad293 cells

   PMID:10843183

   Open questions at the time

   • Single mutation in one lab
   • No structural model linking Ala10 to cofactor binding in this study
4. 2004 Medium

   Identified the first transcriptional driver of HSD3B2 by mapping YY1 binding within intron 1 as required for maximal basal promoter activity.

   Evidence Reporter assays, gel shift with anti-YY1 supershift, competition and mutational analysis in transient transfection

   PMID:15291746

   Open questions at the time

   • Basal promoter context only; hormonal regulation not addressed
   • In vivo occupancy in adrenal tissue not demonstrated
5. 2010 Medium

   Defined a functional partnership in which HSD3B2 co-expressed with CYB5A in zona fasciculata/reticularis hybrid cells produces androstenedione.

   Evidence Immunolocalization in human adrenal plus trilostane inhibition and CYB5A siRNA knockdown with steroid measurement in H295R cells

   PMID:21185375

   Open questions at the time

   • Does not establish direct physical interaction between HSD3B2 and CYB5A
   • Functional contribution quantified only in a cell line
6. 2012 Medium

   Revealed an indirect metabolic route of enzyme regulation by linking metformin-mediated HSD3B2 inhibition to mitochondrial complex I rather than AMPK/ERK/PKC signaling.

   Evidence Activity and expression assays, rotenone pharmacological epistasis, and organic cation transporter dependency in NCI-H295R cells

   PMID:22778212

   Open questions at the time

   • Molecular link between complex I status and HSD3B2 catalysis/expression unresolved
   • Single cell-line model
7. 2014 Medium

   Distinguished substrate-binding from cofactor-binding determinants by showing Y190C and S218P mutations near the substrate pocket impair activity in a substrate-selective manner.

   Evidence In vitro enzymatic assays in transfected cells, site-directed mutagenesis, and 3D homology modeling

   PMID:24372086

   Open questions at the time

   • Pocket conformation inferred from homology model, no experimental structure
   • Only two mutations characterized
8. 2015 Medium

   Localized a catalytically critical loop in the NAD+-binding domain by showing G250V lowers Vmax for progesterone without changing Km, expression, or localization.

   Evidence Michaelis-Menten kinetics in COS-7 cells, Western blot, immunofluorescence, and homology modeling of the L239-Q251 loop

   PMID:25322271

   Open questions at the time

   • Loop importance inferred from modeling, not crystal structure
   • Single mutation
9. 2015 Medium

   Connected cAMP signaling to HSD3B2 transcription by showing decanoic acid and metformin reduce cAMP-stimulated Nur77 recruitment to the promoter.

   Evidence Dual luciferase reporter, ChIP promoter recruitment, RT-PCR, Western blot, and testosterone ELISA in NCI-H295R cells and a rat PCOS model

   PMID:26465200

   Open questions at the time

   • Whether Nur77 acts directly or via cofactors at the promoter not resolved
   • Single lab
10. 2016 Low

    Excluded DNA methylation as the mechanism of zona reticularis-specific HSD3B2 downregulation, narrowing the search for the responsible regulator.

    Evidence RT-qPCR and methylation analysis on microdissected adrenal zones showing absence of CpG islands and zone-specific methylation

    PMID:27670690

    Open questions at the time

    • Negative finding; the actual zone-specific repressor remains unidentified
    • Limited to methylation as a candidate mechanism
11. 2019 Medium

    Identified GATA1 as a promoter-binding activator of HSD3B2 driving androgen biosynthesis, targetable pharmacologically.

    Evidence Expression profiling, dual luciferase, RNAi, promoter mutagenesis, ChIP recruitment, Western blot and ELISA in NCI-H295R cells

    PMID:30650063

    Open questions at the time

    • Interplay between GATA1, YY1, and Nur77 at the locus not integrated
    • Single cell-line system

• An experimentally determined structure of HSD3B2 and the identity of the zone-specific repressor controlling its adrenal expression pattern remain unresolved.
• Catalytic-domain assignments rest on homology models, not solved structures
• The factor responsible for zona reticularis-specific downregulation is unknown