Biology:Aromatase

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Short description: Enzyme involved in estrogen production


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example


Aromatase (EC 1.14.14.14), also called estrogen synthetase or estrogen synthase, is an enzyme responsible for a key step in the biosynthesis of estrogens. It is CYP19A1, a member of the cytochrome P450 superfamily, which are monooxygenases that catalyze many reactions involved in steroidogenesis. In particular, aromatase is responsible for the aromatization of androgens into estrogens. The enzyme aromatase can be found in many tissues including gonads (granulosa cells), brain, adipose tissue, placenta, blood vessels, skin, and bone, as well as in tissue of endometriosis, uterine fibroids, breast cancer, and endometrial cancer. It is an important factor in sexual development.

Function

Aromatase is localized in the endoplasmic reticulum where it is regulated by tissue-specific promoters that are in turn controlled by hormones, cytokines, and other factors. It catalyzes the last steps of estrogen biosynthesis from androgens (specifically, it transforms androstenedione to estrone and testosterone to estradiol). These steps include three successive hydroxylations of the 19-methyl group of androgens, followed by simultaneous elimination of the methyl group as formate and aromatization of the A-ring.

Androstenedione + 3O2 + 3NADPH + 3H+ [math]\displaystyle{ \rightleftharpoons }[/math] Estrone + Formate + 4H2O + 3NADP+
Testosterone + 3O2 + 3NADPH + 3H+ [math]\displaystyle{ \rightleftharpoons }[/math] 17β-estradiol + Formate + 4H2O + 3NADP+
General reaction for the conversion of testosterone to estradiol catalyzed by aromatase. Steroids are composed of four fused rings (labeled A-D). Aromatase converts the ring labeled "A" into an aromatic state.
Catalytic mechanism of aromatase for the conversion of androstenedione to estrone. The methyl group is oxidized and subsequently eliminated.[1]

Expression

Aromatase is expressed in the gonads, placenta, brain, adipose tissue, bone, and other tissues.[citation needed] It is almost undetectable in adult human liver.[2]

Genomics

The gene expresses two transcript variants.[3] In humans, the gene CYP19, located on chromosome 15q21.1, encodes aromatase.[4] The gene has nine coding exons and a number of alternative non-coding first exons that regulate tissue specific expression.[5]

CYP19 is present in an early-diverging chordate, the cephalochordate amphioxus (the Florida lancelet, Branchiostoma floridae), but not in the earlier diverging tunicate Ciona intestinalis. Thus, the aromatase gene evolved early in chordate evolution and does not appear to be present in nonchordate invertebrates (e.g. insects, molluscs, echinoderms, sponges, corals). However, estrogens may be synthesized in some of these organisms, via other unknown pathways.

Activity

Aromatase activity is increased by age, obesity, insulin, gonadotropins, and alcohol.[6] It also appears to be enhanced in certain estrogen-dependent local tissue next to breast tissue, endometrial cancer, endometriosis, and uterine fibroids.[6]

Aromatase activity is decreased or antagonized by prolactin, anti-Müllerian hormone and glyphosate.[6]

Role in sex-determination

Aromatase is generally highly present during the differentiation of ovaries.[7][8] It is also susceptible to environmental influences, particularly temperature. In species with temperature-dependent sex determination, aromatase is expressed in higher quantities at temperatures that yield female offspring.[7] Despite the fact that data suggest temperature controls aromatase quantities, other studies have shown that aromatase can overpower the effects of temperature: if exposed to more aromatase at a male-producing temperature, the organism will develop female and conversely, if exposed to less aromatase at female-producing temperatures, the organism will develop male (see sex reversal).[7] In organisms that develop through genetic sex determination, temperature does not affect aromatase expression and function, suggesting that aromatase is the target molecule for temperature during TSD[7] (for challenges to this argument, see temperature-dependent sex determination). It varies from species to species whether it is the aromatase protein that has different activity at different temperatures or whether the amount of transcription undergone by the aromatase gene is what is temperature-sensitive, but in either case, differential development is observed at different temperatures.[9]

Role in neuroprotection

Aromatase in the brain is usually only expressed in neurons. However, following penetrative brain injury of both mice and zebra finches, it has been shown to be expressed in astrocytes.[10] It has also been shown to decrease apoptosis following brain injury in zebra finches.[11] This is thought to be due to the neuroprotective actions of estrogens, including estradiol. Research has found that two pro-inflammatory cytokines, interleukin-1β (IL-1β) and interleukin-6 (IL-6), are responsible for the induction of aromatase expression in astrocytes following penetrative brain injury in the zebra finch.[12]

Disorders

Aromatase excess syndrome

Main page: Medicine:Aromatase excess syndrome

A number of investigators have reported on a rather rare syndrome of excess aromatase activity. In boys, it creates gynecomastia, and in girls, precocious puberty and gigantomastia. In both sexes, early epiphyseal closure leads to short stature. This condition is due to mutations in the CYP19A1 gene which encodes aromatase.[13] It is inherited in an autosomal dominant fashion.[14] It has been suggested that the pharaoh Akhenaten and other members of his family may have had from this disorder,[15] but more recent genetic tests suggest otherwise.[16] It is one of the causes of familial precocious puberty—a condition first described in 1937.[17]

Aromatase deficiency syndrome

Main page: Medicine:Aromatase deficiency

This syndrome is due to a mutation of gene CYP19 and inherited in an autosomal recessive way. Accumulations of androgens during pregnancy may lead to virilization of a female at birth (males are not affected). Females will have primary amenorrhea. Individuals of both sexes will be tall, as lack of estrogen does not bring the epiphyseal lines to closure.

Inhibition of aromatase

The inhibition of aromatase can cause hypoestrogenism (low estrogen levels). The following natural products have been found to have inhibiting effects on aromatase.


Extracts of certain (white button variety: Agaricus bisporus) mushrooms have been shown to inhibit aromatase in vitro.[28]

Pharmaceutical aromatase inhibitors

Main page: Chemistry:Aromatase inhibitor

Aromatase inhibitors, which stop the production of estrogen in postmenopausal women, have become useful in the management of patients with breast cancer whose lesion was found to be estrogen receptor positive.[29] Inhibitors that are in current clinical use include anastrozole, exemestane, and letrozole. Aromatase inhibitors are also beginning to be prescribed to men on testosterone replacement therapy as a way to keep estrogen levels from spiking once doses of testosterone are introduced to their systems.

See also

References

  1. ↑ "Chapter 1: Cytochrome activation by cytochromes P450: a role for multiple oxidants in the oxidation of substrates". Drug metabolizing enzymes: cytochrome P450 and other enzymes in drug discovery and development. Lausanne, Switzerland: FontisMedia SA. 2003. ISBN 978-0-8247-4293-5. 
  2. ↑ "Aromatase in human liver and its diseases". Cancer Med 2 (3): 305–15. June 2013. doi:10.1002/cam4.85. PMID 23930207. 
  3. ↑ "Entrez Gene: CYP19A1 cytochrome P450, family 19, subfamily A, polypeptide 1". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=1588. 
  4. ↑ "Molecular cloning of a cDNA showing alternative splicing of the 5'-untranslated sequence of mRNA for human aromatase P-450". European Journal of Biochemistry 213 (1): 383–9. April 1993. doi:10.1111/j.1432-1033.1993.tb17772.x. PMID 8477708. 
  5. ↑ "Aromatase research and its clinical significance". Endokrynologia Polska 61 (1): 126–34. 2010. PMID 20205115. 
  6. ↑ 6.0 6.1 6.2 Hussain, Aatif; Gilloteaux, Jacques (2020-09-01). "The human testes: Estrogen and ageing outlooks" (in en). Translational Research in Anatomy 20: 100073. doi:10.1016/j.tria.2020.100073. ISSN 2214-854X. 
  7. ↑ 7.0 7.1 7.2 7.3 "Ontogenesis of gonadal aromatase gene expression in atlantic silverside (Menidia menidia) populations with genetic and temperature-dependent sex determination". Journal of Experimental Zoology Part A 313 (7): 421–31. August 2010. doi:10.1002/jez.612. PMID 20623799. Bibcode: 2010JEZA..313..421D. 
  8. ↑ "Potential contributions of heat shock proteins to temperature-dependent sex determination in the American alligator". Sexual Development 4 (1–2): 73–87. 2010. doi:10.1159/000260374. PMID 19940440. 
  9. ↑ Gilbert SF (2010). Developmental biology. Sunderland, Mass: Sinauer Associates. ISBN 978-0-87893-384-6. 
  10. ↑ "Aromatase expression by astrocytes after brain injury: implications for local estrogen formation in brain repair". Neuroscience 89 (2): 567–78. March 1999. doi:10.1016/s0306-4522(98)00340-6. PMID 10077336. 
  11. ↑ "Estrogen provision by reactive glia decreases apoptosis in the zebra finch (Taeniopygia guttata)". Journal of Neurobiology 64 (2): 192–201. August 2005. doi:10.1002/neu.20147. PMID 15818556. 
  12. ↑ "Neuroinflammation induces glial aromatase expression in the uninjured songbird brain". Journal of Neuroinflammation 8 (81): 81. July 2011. doi:10.1186/1742-2094-8-81. PMID 21767382. 
  13. ↑ "Molecular bases and phenotypic determinants of aromatase excess syndrome". International Journal of Endocrinology 2012: 584807. 2012. doi:10.1155/2012/584807. PMID 22319526. 
  14. ↑ "Aromatase excess syndrome: identification of cryptic duplications and deletions leading to gain of function of CYP19A1 and assessment of phenotypic determinants". The Journal of Clinical Endocrinology and Metabolism 96 (6): E1035-43. June 2011. doi:10.1210/jc.2011-0145. PMID 21470988. 
  15. ↑ "Akhenaten and the strange physiques of Egypt's 18th dynasty". Annals of Internal Medicine 150 (8): 556–60. April 2009. doi:10.7326/0003-4819-150-8-200904210-00010. PMID 19380856. 
  16. ↑ "The breasts of Tutankhamun". Indian Journal of Endocrinology and Metabolism 16 (3): 429–30. May 2012. doi:10.4103/2230-8210.95696. PMID 22629513. 
  17. ↑ "[Familial precocious puberty -- a variant of norm or pathology?]" (in pl). Endokrynologia, Diabetologia I Choroby Przemiany Materii Wieku Rozwojowego 12 (1): 53–8. 2006. PMID 16704862. 
  18. ↑ 18.0 18.1 18.2 18.3 "Natural products as aromatase inhibitors". Anti-Cancer Agents in Medicinal Chemistry 8 (6): 646–82. August 2008. doi:10.2174/1871520610808060646. PMID 18690828. 
  19. ↑ "Inhibition of aromatase activity by green tea extract catechins and their endocrinological effects of oral administration in rats". Food and Chemical Toxicology 40 (7): 925–33. July 2002. doi:10.1016/S0278-6915(02)00066-2. PMID 12065214. 
  20. ↑ "High tea consumption diminishes salivary 17beta-estradiol concentration in Polish women". The British Journal of Nutrition 95 (5): 989–95. May 2006. doi:10.1079/BJN20061755. PMID 16611391. 
  21. ↑ "Chalcones are potent inhibitors of aromatase and 17beta-hydroxysteroid dehydrogenase activities". Life Sciences 68 (7): 751–61. January 2001. doi:10.1016/S0024-3205(00)00974-7. PMID 11205867. 
  22. ↑ "The citrus flavonone hesperetin inhibits growth of aromatase-expressing MCF-7 tumor in ovariectomized athymic mice". The Journal of Nutritional Biochemistry 23 (10): 1230–7. October 2012. doi:10.1016/j.jnutbio.2011.07.003. PMID 22209285. 
  23. ↑ "Inhibition of human aromatase by myosmine". Drug Metabolism Letters 3 (2): 83–6. April 2009. doi:10.2174/187231209788654045. PMID 19601869. 
  24. ↑ "Nicotine blocks brain estrogen synthase (aromatase): in vivo positron emission tomography studies in female baboons". Biological Psychiatry 67 (8): 774–7. April 2010. doi:10.1016/j.biopsych.2010.01.004. PMID 20188349. 
  25. ↑ "The red wine polyphenol resveratrol displays bilevel inhibition on aromatase in breast cancer cells". Toxicological Sciences 92 (1): 71–7. July 2006. doi:10.1093/toxsci/kfj190. PMID 16611627. 
  26. ↑ "Lycopene and vitamin E interfere with autocrine/paracrine loops in the Dunning prostate cancer model". FASEB Journal 18 (9): 1019–21. June 2004. doi:10.1096/fj.03-1116fje. PMID 15084515. 
  27. ↑ "Dietary zinc deficiency alters 5 alpha-reduction and aromatization of testosterone and androgen and estrogen receptors in rat liver". The Journal of Nutrition 126 (4): 842–8. April 1996. doi:10.1093/jn/126.4.842. PMID 8613886. 
  28. ↑ "Anti-aromatase activity of phytochemicals in white button mushrooms (Agaricus bisporus)". Cancer Research 66 (24): 12026–34. December 2006. doi:10.1158/0008-5472.CAN-06-2206. PMID 17178902. 
  29. ↑ "Aromatase Inhibitors". Breastcancer.org. 29 October 2020. http://www.breastcancer.org/treatment/hormonal/aromatase_inhibitors. 

Further reading

External links

  • "U.S. study of gay sheep may shed light on sexuality", via WikiNews, 15 August 2005.
  • Human CYP19A1 genome location and CYP19A1 gene details page in the UCSC Genome Browser.
  • Overview of all the structural information available in the PDB for UniProt: P11511 (Aromatase) at the PDBe-KB.



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