TXN2

Thioredoxin, mitochondrial also known as thioredoxin-2 is a protein that in humans is encoded by the TXN2 gene on chromosome 22.[5][6][7] This nuclear gene encodes a mitochondrial member of the thioredoxin family, a group of small multifunctional redox-active proteins. The encoded protein may play important roles in the regulation of the mitochondrial membrane potential and in protection against oxidant-induced apoptosis.[5]

TXN2
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 1UVZ, 1W4V, 1W89
Identifiers
Aliases	TXN2, MT-TRX, MTRX, TRX2, COXPD29, thioredoxin 2, TXN
External IDs	OMIM: 609063 MGI: 1929468 HomoloGene: 40849 GeneCards: TXN2
Gene location (Human) Chr. Chromosome 22 (human)[1] Band 22q12.3 Start 36,467,046 bp[1] End 36,481,640 bp[1]
Gene location (Mouse) Chr. Chromosome 15 (mouse)[2] Band 15|15 E1 Start 77,915,047 bp[2] End 77,929,006 bp[2]
RNA expression pattern More reference expression data
Gene ontology Molecular function • peptide-methionine (S)-S-oxide reductase activity • peptide-methionine (R)-S-oxide reductase activity • GO:0001948 protein binding • protein disulfide oxidoreductase activity • GO:0032403 macromolecular complex binding Cellular component • nucleolus • mitochondrion • mitochondrial matrix • neuronal cell body • dendrite Biological process • response to hypoxia • response to hormone • cellular response to nutrient levels • response to organic cyclic compound • response to oxidative stress • glycerol ether metabolic process • response to axon injury • response to glucose • response to drug • cell redox homeostasis • oxidation-reduction process • sulfur amino acid catabolic process Sources:Amigo / QuickGO
Orthologs
Species	Human	Mouse
Entrez	25828	56551
Ensembl	ENSG00000100348	ENSMUSG00000005354
UniProt	Q99757	P97493
RefSeq (mRNA)	NM_012473	NM_019913
RefSeq (protein)	NP_036605	NP_064297
Location (UCSC)	Chr 22: 36.47 – 36.48 Mb	Chr 15: 77.92 – 77.93 Mb
PubMed search	[3]	[4]
Wikidata
View/Edit Human View/Edit Mouse

Structure

As a thioredoxin, TXN2 is a 12-kDa protein characterized by the redox active site Trp-Cys-Gly-Pro-Cys. In its oxidized (inactive) form, the two cysteines form a disulfide bond. This bond is then reduced by thioredoxin reductase and NADPH to a dithiol, which serves as a disulfide reductase. In contrast to TXN1, TXN2 contains a putative N-terminal mitochondrial targeting sequence, responsible for its mitochondria localization, and lacks structural cysteines.[8][9] Two mRNA transcripts of the TXN2 gene differ by ~330 bp in the length of the 3′-untranslated region, and both are believed to exist in vivo.[9]

Function

This nuclear gene encodes a mitochondrial member of the thioredoxin family, a group of small multifunctional redox-active proteins.[5] The encoded protein is ubiquitously expressed in all prokaryotic and eukaryotic organisms, but demonstrates especially high expression in tissues with heavy metabolic activity, including the stomach, testis, ovary, liver, heart, neurons, and adrenal gland.[8][9] It may play important roles in the regulation of the mitochondrial membrane potential and in protection against oxidant-induced apoptosis.[5][8] Specifically, the ability of TXN2 to reduce disulfide bonds enables the protein to regulate mitochondrial redox and, thus, the production of reactive oxygen species (ROS). By extension, downregulation of TXN2 can lead to increased ROS generation and cell death.[8] The antiapoptotic function of TXN2 is attributed to its involvement in GSH-dependent mechanisms to scavenge ROS, or its interaction with, and thus regulation of, thiols in the mitochondrial permeability transition pore component adenine nucleotide translocator (ANT).[9]

Overexpression of TXN2 was shown to have attenuated hypoxia-induced HIF-1alpha accumulation, which is in direct opposition of the cytosolic TXN1, which enhanced HIF-1alpha levels.[10] Moreover, although both TXN2 and TXN1 are able to reduce insulin, TXN2 does not depend on the oxidative status of the protein for this activity, a quality which may contribute to their difference in function.[8]

Clinical Significance

It has been demonstrated that genetic polymorphisms in the TXN2 gene may be associated with the risk of spina bifida.[11]

TXN2 is known to inhibit transforming growth factor (TGF)-β-stimulated ROS generation independent of Smad signaling. TGF-β is a pro-oncogenic cytokine that induces epithelial–mesenchymal transition (EMT), which is a crucial event in metastatic progression. In particular, TXN2 inhibits TGF-β-mediated induction of HMGA2, a central EMT mediator, and fibronectin, an EMT marker.[12]

Interactions

TXN2 is shown to interact with ANT.[9]

References

1. GRCh38: Ensembl release 89: ENSG00000100348 - Ensembl, May 2017
2. GRCm38: Ensembl release 89: ENSMUSG00000005354 - Ensembl, May 2017
3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
5. "Entrez Gene: TXN2 thioredoxin 2".
6. Spyrou G, Enmark E, Miranda-Vizuete A, Gustafsson J (Jan 1997). "Cloning and expression of a novel mammalian thioredoxin". The Journal of Biological Chemistry. 272 (5): 2936–41. doi:10.1074/jbc.272.5.2936. PMID 9006939.
7. Zhou J, Damdimopoulos AE, Spyrou G, Brüne B (Mar 2007). "Thioredoxin 1 and thioredoxin 2 have opposed regulatory functions on hypoxia-inducible factor-1alpha". The Journal of Biological Chemistry. 282 (10): 7482–90. doi:10.1074/jbc.M608289200. PMID 17220299.
8. Damdimopoulos AE, Miranda-Vizuete A, Pelto-Huikko M, Gustafsson JA, Spyrou G (Sep 2002). "Human mitochondrial thioredoxin. Involvement in mitochondrial membrane potential and cell death". The Journal of Biological Chemistry. 277 (36): 33249–57. doi:10.1074/jbc.M203036200. PMID 12080052.
9. Chen Y, Cai J, Murphy TJ, Jones DP (Sep 2002). "Overexpressed human mitochondrial thioredoxin confers resistance to oxidant-induced apoptosis in human osteosarcoma cells". The Journal of Biological Chemistry. 277 (36): 33242–8. doi:10.1074/jbc.M202026200. PMID 12032145.
10. Zhou J, Damdimopoulos AE, Spyrou G, Brüne B (Mar 2007). "Thioredoxin 1 and thioredoxin 2 have opposed regulatory functions on hypoxia-inducible factor-1alpha". The Journal of Biological Chemistry. 282 (10): 7482–90. doi:10.1074/jbc.M608289200. PMID 17220299.
11. Wen S, Lu W, Zhu H, Yang W, Shaw GM, Lammer EJ, Islam A, Finnell RH (Feb 2009). "Genetic polymorphisms in the thioredoxin 2 (TXN2) gene and risk for spina bifida". American Journal of Medical Genetics Part A. 149A (2): 155–160. doi:10.1002/ajmg.a.32589. PMC 2970524. PMID 19165900.
12. Ishikawa F, Kaneko E, Sugimoto T, Ishijima T, Wakamatsu M, Yuasa A, Sampei R, Mori K, Nose K, Shibanuma M (Jan 2014). "A mitochondrial thioredoxin-sensitive mechanism regulates TGF-β-mediated gene expression associated with epithelial-mesenchymal transition". Biochemical and Biophysical Research Communications. 443 (3): 821–7. doi:10.1016/j.bbrc.2013.12.050. PMID 24342608.

Further reading

• Wang Z, Zhang H, Li XF, Le XC (2007). "Study of interactions between arsenicals and thioredoxins (human and E. coli) using mass spectrometry". Rapid Communications in Mass Spectrometry. 21 (22): 3658–66. doi:10.1002/rcm.3263. PMID 17939155.
• Udler M, Maia AT, Cebrian A, Brown C, Greenberg D, Shah M, Caldas C, Dunning A, Easton D, Ponder B, Pharoah P (Jul 2007). "Common germline genetic variation in antioxidant defense genes and survival after diagnosis of breast cancer". Journal of Clinical Oncology. 25 (21): 3015–23. doi:10.1200/JCO.2006.10.0099. PMID 17634480.
• Zhang H, Go YM, Jones DP (Sep 2007). "Mitochondrial thioredoxin-2/peroxiredoxin-3 system functions in parallel with mitochondrial GSH system in protection against oxidative stress". Archives of Biochemistry and Biophysics. 465 (1): 119–26. doi:10.1016/j.abb.2007.05.001. PMID 17548047.
• Oestergaard MZ, Tyrer J, Cebrian A, Shah M, Dunning AM, Ponder BA, Easton DF, Pharoah PD (Aug 2006). "Interactions between genes involved in the antioxidant defence system and breast cancer risk". British Journal of Cancer. 95 (4): 525–31. doi:10.1038/sj.bjc.6603272. PMC 2360671. PMID 16868544.
• Cebrian A, Pharoah PD, Ahmed S, Smith PL, Luccarini C, Luben R, Redman K, Munday H, Easton DF, Dunning AM, Ponder BA (Jan 2006). "Tagging single-nucleotide polymorphisms in antioxidant defense enzymes and susceptibility to breast cancer". Cancer Research. 66 (2): 1225–33. doi:10.1158/0008-5472.CAN-05-1857. PMID 16424062.
• Collins JE, Wright CL, Edwards CA, Davis MP, Grinham JA, Cole CG, Goward ME, Aguado B, Mallya M, Mokrab Y, Huckle EJ, Beare DM, Dunham I (2005). "A genome annotation-driven approach to cloning the human ORFeome". Genome Biology. 5 (10): R84. doi:10.1186/gb-2004-5-10-r84. PMC 545604. PMID 15461802.
• Damdimopoulos AE, Miranda-Vizuete A, Pelto-Huikko M, Gustafsson JA, Spyrou G (Sep 2002). "Human mitochondrial thioredoxin. Involvement in mitochondrial membrane potential and cell death". The Journal of Biological Chemistry. 277 (36): 33249–57. doi:10.1074/jbc.M203036200. PMID 12080052.
• Chen Y, Cai J, Murphy TJ, Jones DP (Sep 2002). "Overexpressed human mitochondrial thioredoxin confers resistance to oxidant-induced apoptosis in human osteosarcoma cells". The Journal of Biological Chemistry. 277 (36): 33242–8. doi:10.1074/jbc.M202026200. PMID 12032145.