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3-oxo-5α-steroid 4-dehydrogenase 1 is an enzyme that in humans is encoded by the SRD5A1 gene.[1] It is one of three forms of 5α-reductase.

Steroid 5α-reductase (EC catalyzes the conversion of testosterone into the more potent androgen, dihydrotestosterone (DHT). There are 3 isoforms of the enzyme: SRD5A1, SRD5A2, and SRD5A3.[2][3]


ETV4 family members bind to ETS DNA-binding sites and both regulate their own expression and the transcription of a subset of genes that are dependent upon testicular luminal fluid factors, including Ggt_pr4, SRD5A1, and Gpx5.[4]

6-month dietary vitamin E (VE) deficiency in rats resulted in a twofold increase in the mRNA level of SRD5A1 gene and a twofold decrease in the mRNA level of GCLM gene but is not directly mediated by changes in promoter DNA methylation.[5]

Insulin increases the expression of 5α-reductase type 1 mRNA via Akt signalling suggest that elevated levels of 5α-reduced androgens seen in hyperinsulinemic conditions might be explained on the basis of a stimulatory effect of insulin on 5α-reductase in granulosa cells leading to impaired follicle growth and ovulation.[6]

Clinical significance

Hyperinsulinemia acutely enhances ACTH effects on both the androgen and glucocorticoid pathways leading to changes in steroid metabolites molar ratios that suggest insulin stimulation of 5 α-reductase activity. [7]

PCOS is associated with enhanced androgen and cortisol metabolite excretion and increased 5α-reductase activity that cannot be explained by obesity alone. Increased adrenal corticosteroid production represents an important pathogenic pathway in PCOS.[8]

Progression to castration-resistant prostate cancer (CRPC) is accompanied by increased expression of SRD5A1 over SRD5A2, which is otherwise the dominant isoenzyme expressed in the prostate. The dominant route of DHT synthesis in human CRPC bypasses testosterone, and instead requires 5α-reduction of androstenedione by SRD5A1 to 5α-androstanedione, which is then converted to DHT fuelling cancer growth.[9]

See also


  1. Jenkins EP, Hsieh CL, Milatovich A, Normington K, Berman DM, Francke U, Russell DW (Dec 1991). "Characterization and chromosomal mapping of a human steroid 5 alpha-reductase gene and pseudogene and mapping of the mouse homologue". Genomics. 11 (4): 1102–12. doi:10.1016/0888-7543(91)90038-G. PMID 1686016.
  2. "Entrez Gene: SRD5A1 steroid-5-alpha-reductase, alpha polypeptide 1 (3-oxo-5 alpha-steroid delta 4-dehydrogenase alpha 1)".
  3. "SRD5A3 steroid 5 alpha-reductase 3 [Homo sapiens (human)] - Gene - NCBI". Retrieved 2018-04-26.
  4. Yang L, Fox SA, Kirby JL, Troan BV, Hinton BT (Apr 2006). "Putative regulation of expression of members of the Ets variant 4 transcription factor family and their downstream targets in the rat epididymis". Biology of Reproduction. 74 (4): 714–20. doi:10.1095/biolreprod.105.044354. PMID 16394217.
  5. Fischer A, Gaedicke S, Frank J, Döring F, Rimbach G (Oct 2010). "Dietary vitamin E deficiency does not affect global and specific DNA methylation patterns in rat liver". The British Journal of Nutrition. 104 (7): 935–40. doi:10.1017/S0007114510001649. PMID 20447326.
  6. Kayampilly PP, Wanamaker BL, Stewart JA, Wagner CL, Menon KM (Oct 2010). "Stimulatory effect of insulin on 5alpha-reductase type 1 (SRD5A1) expression through an Akt-dependent pathway in ovarian granulosa cells". Endocrinology. 151 (10): 5030–7. doi:10.1210/en.2010-0444. PMC 2946143. PMID 20810561.
  7. Tosi F, Negri C, Brun E, Castello R, Faccini G, Bonora E, Muggeo M, Toscano V, Moghetti P (Feb 2011). "Insulin enhances ACTH-stimulated androgen and glucocorticoid metabolism in hyperandrogenic women". European Journal of Endocrinology / European Federation of Endocrine Societies. 164 (2): 197–203. doi:10.1530/EJE-10-0782. PMID 21059865.
  8. Vassiliadi DA, Barber TM, Hughes BA, McCarthy MI, Wass JA, Franks S, Nightingale P, Tomlinson JW, Arlt W, Stewart PM (Sep 2009). "Increased 5 alpha-reductase activity and adrenocortical drive in women with polycystic ovary syndrome". The Journal of Clinical Endocrinology and Metabolism. 94 (9): 3558–66. doi:10.1210/jc.2009-0837. PMID 19567518.
  9. Chang KH, Li R, Papari-Zareei M, Watumull L, Zhao YD, Auchus RJ, Sharifi N (Aug 2011). "Dihydrotestosterone synthesis bypasses testosterone to drive castration-resistant prostate cancer". Proceedings of the National Academy of Sciences of the United States of America. 108 (33): 13728–33. Bibcode:2011PNAS..10813728C. doi:10.1073/pnas.1107898108. PMC 3158152. PMID 21795608.

Further reading