ENOX2 explained

ENOX2 is a gene located on the long arm of the X chromosome in humans.^[1] The gene encodes the protein Ecto-NOX disulfide-thiol exchanger 2, a member of the NOX family of NADPH oxidases.^{[2] [3] [4]}

Ecto-NOX disulfide-thiol exchanger 2 is a growth-related cell surface protein. It was identified because it reacts with the monoclonal antibody K1 in cells, such as the ovarian carcinoma line OVCAR-3, also expressing the CAKI surface glycoprotein. The encoded protein has two enzymatic activities: catalysis of hydroquinone or NADH oxidation, and protein disulfide interchange. The two activities alternate with a period length of about 24 minutes. The encoded protein also displays prion-like properties. Two transcript variants encoding different isoforms have been found for this gene.^[5]

Gene Location

The human ENOX2 gene is located on the long (q) arm of the X chromosome in humans, at region 2 band 6 sub band 1, from base pair 130,622,330 to 130,903,317 (build GRCh38.p7) (map). The gene is conserved in chimpanzee, Rhesus monkey, dog, mouse, rat, chicken, and zebrafish.

Function

ENOX2 and related NOX proteins exhibit two distinct oscillating functions: the oxidation of NADH to NAD+ and a protein disulfide isomerase-like activity, unprecedented in the biochemical literature.^{[6] [7] [8]} Regarding NADH oxidation, the protein has a specific activity of 10-20μmol/min/mg of protein with a turnover number of 200-500.^{[9] [10]} The oscillations are independent of temperature, with a period of 24 minutes, completing 60 cycles in a 24-hour day. The period of oscillation changes to 22 and 26 minutes in the cancer related (tNOX) and age-related (arNOX) forms respectively. This regular oscillation is attributed to the maintenance of biological clock^[11]

Interactions

NADH activity of ENOX2 has been shown to be stimulated by various hormones and growth factors, including insulin, EGF, transferrin, lactoferrin, vasopressin and glucagon.^[12] This stimulation is not seen in protein samples recovered from cancer cells, suggesting the regular NADH oxidase activity of ENOX2 is decoupled in cancer. ENOX2 also has a number of protein-protein interactions, with ENOX1 and SOX2, among others.^[13]

Cell Growth

Numerous studies in the 1990s correlated NADH oxidase activity with cell growth. Conditions which stimulated cell growth also stimulated NADH oxidase activity and conditions that inhibited cell growth inhibited NADH oxidase activity. Further experimental evidence showed that the rate of cell enlargement oscillates within the 24 minute oscillation of ENOX function.^[14] Maximum cell growth rates correspond to the portion of the ENOX cycle involved in protein dulsulfide bridge formation.^[15] Theories suggest that ENOX is responsible for the breakup and formation of disulfide bonds in membrane proteins, thus maximum cell growth coincides with maximum protein disulfide interchange activity.

Role In Disease

Cancer

The cancer associated, drug responsive variant of ENOX, tNOX, arises as a splice variant and is found on the cell surface of human cancers.^[16] tNOX exhibits a periodicity of 22 minutes, compared to the native 24 minutes and can be inhibited by a number of anticancer drugs, without affecting the native ENOX. These properties of tNOX are being used to develop early detection and intervention mechanisms for human cancers.^[17]

See also

Ecto-nox disulfide-thiol exchanger 1

Further reading

• Tarasoutchi F, Grinberg M, de Figueiredo Neto JA . [Mitral valve aneurysm associated with mitral insufficiency in absence of aortic insufficiency] . Arq. Bras. Cardiol. . 56 . 3 . 231–4 . 1991 . 1888291 . etal.
• Dai S, Morré DJ, Geilen CC . Inhibition of plasma membrane NADH oxidase activity and growth of HeLa cells by natural and synthetic retinoids. . Mol. Cell. Biochem. . 166 . 1–2 . 101–9 . 1997 . 9046026 . 10.1023/A:1006866726050 . 25814254 . etal.
• Morré DJ, Chueh PJ, Lawler J, Morré DM . The sulfonylurea-inhibited NADH oxidase activity of HeLa cell plasma membranes has properties of a protein disulfide-thiol oxidoreductase with protein disulfide-thiol interchange activity. . J. Bioenerg. Biomembr. . 30 . 5 . 477–87 . 1999 . 9932650 . 10.1023/A:1020594214379 . 20415997 .
• Kishi T, Morré DM, Morré DJ . The plasma membrane NADH oxidase of HeLa cells has hydroquinone oxidase activity. . Biochim. Biophys. Acta . 1412 . 1 . 66–77 . 1999 . 10354495 . 10.1016/S0005-2728(99)00049-3 . free .
• Kelker M, Kim C, Chueh PJ . Cancer isoform of a tumor-associated cell surface NADH oxidase (tNOX) has properties of a prion. . Biochemistry . 40 . 25 . 7351–4 . 2001 . 11412089 . 10.1021/bi010596i . etal.
• Yantiri F, Morré DJ . Isolation and characterization of a tumor-associated NADH oxidase (tNOX) from the HeLa cell surface. . Arch. Biochem. Biophys. . 391 . 2 . 149–59 . 2001 . 11437345 . 10.1006/abbi.2001.2404 .
• Morré DJ, Sedlak D, Tang X . Surface NADH oxidase of HeLa cells lacks intrinsic membrane binding motifs. . Arch. Biochem. Biophys. . 392 . 2 . 251–6 . 2001 . 11488599 . 10.1006/abbi.2001.2436 . etal.
• Chueh PJ, Morré DM, Morré DJ . A site-directed mutagenesis analysis of tNOX functional domains. . Biochim. Biophys. Acta . 1594 . 1 . 74–83 . 2002 . 11825610 . 10.1016/s0167-4838(01)00286-2.
• Cho N, Chueh PJ, Kim C . Monoclonal antibody to a cancer-specific and drug-responsive hydroquinone (NADH) oxidase from the sera of cancer patients. . Cancer Immunol. Immunother. . 51 . 3 . 121–9 . 2002 . 11941450 . 10.1007/s00262-001-0262-2 . 11032947 . 22275635 . etal.
• Morré DJ, Chueh PJ, Pletcher J . Biochemical basis for the biological clock. . Biochemistry . 41 . 40 . 11941–5 . 2002 . 12356293 . 10.1021/bi020392h . etal.
• Strausberg RL, Feingold EA, Grouse LH . Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. . Proc. Natl. Acad. Sci. U.S.A. . 99 . 26 . 16899–903 . 2003 . 12477932 . 10.1073/pnas.242603899 . 139241 . 2002PNAS...9916899M . etal. free .
• Ota T, Suzuki Y, Nishikawa T . Complete sequencing and characterization of 21,243 full-length human cDNAs. . Nat. Genet. . 36 . 1 . 40–5 . 2004 . 14702039 . 10.1038/ng1285 . etal. free .
• Gerhard DS, Wagner L, Feingold EA . The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). . Genome Res. . 14 . 10B . 2121–7 . 2004 . 15489334 . 10.1101/gr.2596504 . 528928 . etal.
• Chueh PJ, Wu LY, Morré DM, Morré DJ . tNOX is both necessary and sufficient as a cellular target for the anticancer actions of capsaicin and the green tea catechin (-)-epigallocatechin-3-gallate. . BioFactors . 20 . 4 . 235–49 . 2005 . 15706060 .
• Ross MT, Grafham DV, Coffey AJ . The DNA sequence of the human X chromosome. . Nature . 434 . 7031 . 325–37 . 2005 . 15772651 . 10.1038/nature03440 . 2665286 . 2005Natur.434..325R . etal.
• Rual JF, Venkatesan K, Hao T . Towards a proteome-scale map of the human protein-protein interaction network. . Nature . 437 . 7062 . 1173–8 . 2005 . 16189514 . 10.1038/nature04209 . 2005Natur.437.1173R . 4427026 . etal.

Notes and References

1. Web site: ENOX2 ecto-NOX disulfide-thiol exchanger 2 [Homo sapiens (human) ]]. NCBI. 2016-10-16.
2. Chang K, Pastan I . Molecular cloning and expression of a cDNA encoding a protein detected by the K1 antibody from an ovarian carcinoma (OVCAR-3) cell line . Int J Cancer . 57 . 1 . 90–7 . May 1994 . 8150545 . 10.1002/ijc.2910570117 . 1970834 .
3. Chueh PJ, Kim C, Cho N, Morre DM, Morre DJ . Molecular cloning and characterization of a tumor-associated, growth-related, and time-keeping hydroquinone (NADH) oxidase (tNOX) of the HeLa cell surface . Biochemistry . 41 . 11 . 3732–41 . Mar 2002 . 11888291 . 10.1021/bi012041t .
4. Morré. D. James. Morré. Dorothy M.. 2003-08-01. Cell surface NADH oxidases (ECTO-NOX proteins) with roles in cancer, cellular time-keeping, growth, aging and neurodegenerative diseases. Free Radical Research. 37. 8. 795–808. 1071-5762. 14567438. 10.1080/1071576031000083107. 28452870.
5. Web site: Entrez Gene: COVA1 cytosolic ovarian carcinoma antigen 1.
6. Morré. D. James. Morré. Dorothy M.. 1998-11-01. NADH oxidase activity of soybean plasma membranes oscillates with a temperature compensated period of 24 min. The Plant Journal. en. 16. 3. 277–284. 10.1046/j.1365-313x.1998.00293.x. 1365-313X. free.
7. Morré. D. J.. Chueh. P. J.. Lawler. J.. Morré. D. M.. 1998-10-01. The sulfonylurea-inhibited NADH oxidase activity of HeLa cell plasma membranes has properties of a protein disulfide-thiol oxidoreductase with protein disulfide-thiol interchange activity. 9932650. Journal of Bioenergetics and Biomembranes. 30. 5. 477–487. 0145-479X. 10.1023/A:1020594214379. 20415997.
8. Sun. Peichuan. Morré. D. James. Morré. Dorothy M.. 2000-10-20. Periodic NADH oxidase activity associated with an endoplasmic reticulum fraction from pig liver. Response to micromolar concentrations of retinol. Biochimica et Biophysica Acta (BBA) - Molecular Cell Research. 1498. 1. 52–63. 10.1016/S0167-4889(00)00079-3. 11042350.
9. Yantiri. F.. Morré. D. J.. 2001-07-15. Isolation and characterization of a tumor-associated NADH oxidase (tNOX) from the HeLa cell surface. 11437345. Archives of Biochemistry and Biophysics. 391. 2. 149–159. 10.1006/abbi.2001.2404. 0003-9861.
10. del Castillo-Olivares. A.. Yantiri. F.. Chueh. P. J.. Wang. S.. Sweeting. M.. Sedlak. D.. Morré. D. M.. Burgess. J.. Morré. D. J.. 1998-10-01. A drug-responsive and protease-resistant peripheral NADH oxidase complex from the surface of HeLa S cells. 9750173. Archives of Biochemistry and Biophysics. 358. 1. 125–140. 10.1006/abbi.1998.0823. 0003-9861.
11. Morré. D. James. Chueh. Pin-Ju. Pletcher. Jake. Tang. Xiaoyu. Wu. Lian-Ying. Morré. Dorothy M.. 2002-10-08. Biochemical basis for the biological clock. 12356293. Biochemistry. 41. 40. 11941–11945. 0006-2960. 10.1021/bi020392h.
12. Bruno. M. Brightman. A O. Lawrence. J. Werderitsh. D. Morré. D M. Morre. D J. 1992-06-15. Stimulation of NADH oxidase activity from rat liver plasma membranes by growth factors and hormones is decreased or absent with hepatoma plasma membranes.. 1132580. Biochemical Journal. 284. Pt 3. 625–628. 0264-6021. 10.1042/bj2840625. 1622384.
13. Web site: ENOX2 (RP5-875H3.1) Result Summary BioGRID. Lab. Mike Tyers. thebiogrid.org. 2016-10-16.
14. Wang. S.. Pogue. R.. Morré. D. M.. Morré. D. J.. 2001-06-20. NADH oxidase activity (NOX) and enlargement of HeLa cells oscillate with two different temperature-compensated period lengths of 22 and 24 minutes corresponding to different NOX forms. Biochimica et Biophysica Acta (BBA) - Molecular Cell Research. 11420117. 1539. 3. 192–204. 0006-3002. 10.1016/s0167-4889(01)00107-0. free.
15. Morré. D. James. Pogue. Rhea. Morré. Dorothy M.. Soybean cell enlargement oscillates with a temperature-compensated period length of CA. 24 min. In Vitro Cellular & Developmental Biology - Plant. en. 37. 1. 19–23. 10.1007/s11627-001-0004-3. 1054-5476. 2001. 12026936. 1724211.
16. Monoclonal antibody to a cancer-specific and drug-responsive hydroquinone (NADH) oxidase from the sera of cancer patients. Cancer Immunol Immunother. 51.
17. Book: Early Detection: An Opportunity for Cancer Prevention Through Early Intervention. James. D.. M.. Dorothy. 2012-04-20. InTech. 9789535105473. en. 10.5772/32415.