Biology:Cytochrome P450, family 1, member A1

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Cytochrome P450, family 1, subfamily A, polypeptide 1 is a protein[1] that in humans is encoded by the CYP1A1 gene.[2] The protein is a member of the cytochrome P450 superfamily of enzymes.[3]

Function

Metabolism of xenobiotics and drugs

CYP1A1 is involved in phase I xenobiotic and drug metabolism (one substrate of it is theophylline). It is inhibited by fluoroquinolones and macrolides and induced by aromatic hydrocarbons.[4]

CYP1A1 is also known as AHH (aryl hydrocarbon hydroxylase). It is involved in the metabolic activation of aromatic hydrocarbons (polycyclic aromatic hydrocarbons, PAH), for example, benzo(a)pyrene (BaP), by transforming it to an epoxide. In this reaction, the oxidation of benzo[a]pyrene is catalysed by CYP1A1 to form BaP-7,8-epoxide, which can be further oxidized by epoxide hydrolase (EH) to form BaP-7,8-dihydrodiol. Finally CYP1A1 catalyses this intermediate to form BaP-7,8-dihydrodiol-9,10-epoxide, which is the ultimate carcinogen.[4]

However, an in vivo experiment with gene-deficient mice has found that the hydroxylation of benzo(a)pyrene by CYP1A1 can have an overall protective effect on the DNA, rather than contributing to potentially carcinogenic DNA modifications. This effect is likely due to the fact that CYP1A1 is highly active in the intestinal mucosa, and thus inhibits infiltration of ingested benzo(a)pyrene carcinogen into the systemic circulation.[5]

CYP1A1 metabolism of various foreign agents to carcinogens has been implicated in the formation of various types of human cancer.[6][7]

Metabolism of endogenous agents

CYP1A1 also metabolizes polyunsaturated fatty acids into signaling molecules that have physiological as well as pathological activities. CYP1A1 has monoxygenase activity in that it metabolizes arachidonic acid to 19-hydroxyeicosatetraenoic acid (19-HETE) (see 20-Hydroxyeicosatetraenoic acid) but also has epoxygenase activity in that it metabolizes docosahexaenoic acid to epoxides, primarily 19R,20S-epoxyeicosapentaenoic acid and 19S,20R-epoxyeicosapentaenoic acid isomers (termed 19,20-EDP) and similarly metabolizes eicosapentaenoic acid to epoxides, primarily 17R,18S-eicosatetraenic acid and 17S,18R-eicosatetraenic acid isomers (termed 17,18-EEQ).[8] Synthesis of 12(S)-HETE by CYP1A1 has also been demonstrated.[9] 19-HETE is an inhibitor of 20-HETE, a broadly active signaling molecule, e.g. it constricts arterioles, elevates blood pressure, promotes inflammation responses, and stimulates the growth of various types of tumor cells; however the in vivo ability and significance of 19-HETE in inhibiting 20-HETE has not been demonstrated (see 20-Hydroxyeicosatetraenoic acid). The EDP (see Epoxydocosapentaenoic acid) and EEQ (see epoxyeicosatetraenoic acid) metabolites have a broad range of activities. In various animal models and in vitro studies on animal and human tissues, they decrease hypertension and pain perception; suppress inflammation; inhibit angiogenesis, endothelial cell migration and endothelial cell proliferation; and inhibit the growth and metastasis of human breast and prostate cancer cell lines.[10][11][12][13] It is suggested that the EDP and EEQ metabolites function in humans as they do in animal models and that, as products of the omega-3 fatty acids, docosahexaenoic acid and eicosapentaenoic acid, the EDP and EEQ metabolites contribute to many of the beneficial effects attributed to dietary omega-3 fatty acids.[10][13][14] EDP and EEQ metabolites are short-lived, being inactivated within seconds or minutes of formation by epoxide hydrolases, particularly soluble epoxide hydrolase, and therefore act locally. CYP1A1 is one of the main extra-hepatic cytochrome P450 enzymes; it is not regarded as being a major contributor to forming the cited epoxides[13] but could act locally in certain tissues such as the intestine and in certain cancers to do so.

Regulation

The expression of the CYP1A1 gene, along with that of CYP1A2/1B1 genes, is regulated by a heterodimeric transcription factor that consist of the aryl hydrocarbon receptor, a ligand activated transcription factor, and the aryl hydrocarbon receptor nuclear translocator.[15] In the intestine, but not the liver, CYP1A1 expression moreover depends on TOLL-like receptor 2 (TLR2),[16] which recognizes bacterial surface structures such as lipoteichoic acid.

Polymorphisms

Several polymorphisms have been identified in CYP1A1, some of which lead to more highly inducible AHH activity. CYP1A1 polymorphisms include:[17][18][19][20]

  • M1, T→C substitution at nucleotide 3801 in the 3'-non-coding region
  • M2, A→G substitution at nucleotide 2455 leading to an amino acid change of isoleucine to valine at codon 462
  • M3, T→C substitution at nucleotide 3205 in the 3'-non-coding region
  • M4, C→A substitution at nucleotide 2453 leading to an amino acid change of threonine to asparagine at codon 461

The highly inducible forms of CYP1A1 are associated with an increased risk of lung cancer in smokers. (Reference = Kellerman et al., New Eng J Med 1973:289;934-937) Light smokers with the susceptible genotype CYP1A1 have a sevenfold higher risk of developing lung cancer compared to light smokers with the normal genotype.

References

  1. ↑ "CYP1A1". IARC Scientific Publications (148): 159–72. 1999. PMID 10493257. 
  2. ↑ "Comparison of cytochrome P450 (CYP) genes from the mouse and human genomes, including nomenclature recommendations for genes, pseudogenes and alternative-splice variants". Pharmacogenetics 14 (1): 1–18. Jan 2004. doi:10.1097/00008571-200401000-00001. PMID 15128046. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=0960-314X&volume=14&issue=1&spage=1. 
  3. ↑ "Molecular genetics of the human cytochrome P450 monooxygenase superfamily". Xenobiotica 28 (12): 1129–65. Dec 1998. doi:10.1080/004982598238868. PMID 9890157. 
  4. ↑ 4.0 4.1 "CYP1A1: friend or foe?". Drug Metabolism Reviews 25 (4): 503–17. 1993. doi:10.3109/03602539308993984. PMID 8313840. 
  5. ↑ "Oral exposure to benzo[a]pyrene in the mouse: detoxication by inducible cytochrome P450 is more important than metabolic activation". Molecular Pharmacology 65 (5): 1225–37. May 2004. doi:10.1124/mol.65.5.1225. PMID 15102951. 
  6. ↑ "Role of the modulation of CYP1A1 expression and activity in chemoprevention". Journal of Applied Toxicology 34 (7): 743–53. Jul 2014. doi:10.1002/jat.2968. PMID 24532440. 
  7. ↑ "Cytochrome P450 1 family and cancers". The Journal of Steroid Biochemistry and Molecular Biology 147: 24–30. Mar 2015. doi:10.1016/j.jsbmb.2014.11.003. PMID 25448748. 
  8. ↑ "CYP-eicosanoids--a new link between omega-3 fatty acids and cardiac disease?". Prostaglandins & Other Lipid Mediators 96 (1–4): 99–108. Nov 2011. doi:10.1016/j.prostaglandins.2011.09.001. PMID 21945326. 
  9. ↑ Nguyen, CH; Brenner, S; Huttary, N; Atanasov, AG; Dirsch, VM (September 2016). "AHR/CYP1A1 interplay triggers lymphatic barrier breaching in breast cancer spheroids by inducing 12(S)-HETE synthesis". Hum Mol Genet 27. doi:10.1093/hmg/ddw329. PMID 27677308. http://hmg.oxfordjournals.org/content/early/2016/10/23/hmg.ddw329.long. 
  10. ↑ 10.0 10.1 "The pharmacology of the cytochrome P450 epoxygenase/soluble epoxide hydrolase axis in the vasculature and cardiovascular disease". Pharmacological Reviews 66 (4): 1106–40. Oct 2014. doi:10.1124/pr.113.007781. PMID 25244930. 
  11. ↑ "Stabilized epoxygenated fatty acids regulate inflammation, pain, angiogenesis and cancer". Progress in Lipid Research 53: 108–23. Jan 2014. doi:10.1016/j.plipres.2013.11.003. PMID 24345640. 
  12. ↑ "Soluble epoxide hydrolase: A potential target for metabolic diseases". Journal of Diabetes 8 (3): 305–13. Dec 2015. doi:10.1111/1753-0407.12358. PMID 26621325. 
  13. ↑ 13.0 13.1 13.2 "The role of long chain fatty acids and their epoxide metabolites in nociceptive signaling". Prostaglandins & Other Lipid Mediators 113–115: 2–12. Oct 2014. doi:10.1016/j.prostaglandins.2014.09.001. PMID 25240260. 
  14. ↑ "Dietary omega-3 fatty acids modulate the eicosanoid profile in man primarily via the CYP-epoxygenase pathway". Journal of Lipid Research 55 (6): 1150–1164. Mar 2014. doi:10.1194/jlr.M047357. PMID 24634501. 
  15. ↑ "CYP1A induction and human risk assessment: an evolving tale of in vitro and in vivo studies". Drug Metabolism and Disposition 35 (7): 1009–16. Jul 2007. doi:10.1124/dmd.107.015826. PMID 17431034. 
  16. ↑ "TLR2 controls intestinal carcinogen detoxication by CYP1A1". PLoS One 7 (3): e32309. 2012. doi:10.1371/journal.pone.0032309. PMID 22442665. PMC 3307708. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0032309. 
  17. ↑ "Human CYP1A1 gene: cosegregation of the enzyme inducibility phenotype and an RFLP". American Journal of Human Genetics 48 (4): 720–5. Apr 1991. PMID 1707592. 
  18. ↑ "Relationship between genotype and function of the human CYP1A1 gene". Journal of Toxicology and Environmental Health 40 (2–3): 309–16. 1993. doi:10.1080/15287399309531796. PMID 7901425. 
  19. ↑ "Functional significance of different human CYP1A1 genotypes". Carcinogenesis 15 (12): 2961–3. Dec 1994. doi:10.1093/carcin/15.12.2961. PMID 8001264. http://carcin.oxfordjournals.org/cgi/content/abstract/15/12/2961. 
  20. ↑ "The relationship between aryl hydrocarbon hydroxylase and polymorphisms of the CYP1A1 gene". Japanese Journal of Cancer Research 87 (1): 18–24. Jan 1996. doi:10.1111/j.1349-7006.1996.tb00194.x. PMID 8609043. 

Further reading

  • "Comparison of cytochrome P450 (CYP) genes from the mouse and human genomes, including nomenclature recommendations for genes, pseudogenes and alternative-splice variants". Pharmacogenetics 14 (1): 1–18. Jan 2004. doi:10.1097/00008571-200401000-00001. PMID 15128046. 
  • "Cytochrome P-450 1A1 gene polymorphisms and risk of breast cancer: a HuGE review". American Journal of Epidemiology 161 (10): 901–15. May 2005. doi:10.1093/aje/kwi121. PMID 15870154. 
  • "Recalling P446. P4501A1 (CYP1A1) opting for clinical application". Drug Metabolism Reviews 39 (2–3): 323–41. 2007. doi:10.1080/03602530701498026. PMID 17786624. 




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