NK2 homeobox 1

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NK2 homeobox 1
Protein TITF1 PDB 1ftt.png
PDB rendering based on 1ftt.
Available structures
PDB Ortholog search: PDBe, RCSB
Symbols NKX2-1 ; BCH; BHC; NK-2; NKX2.1; NKX2A; T/EBP; TEBP; TITF1; TTF-1; TTF1
External IDs OMIM600635 MGI108067 HomoloGene2488 GeneCards: NKX2-1 Gene
RNA expression pattern
PBB GE TITF1 210673 x at tn.png
PBB GE TITF1 211024 s at tn.png
More reference expression data
Species Human Mouse
Entrez 7080 21869
Ensembl ENSG00000136352 ENSMUSG00000001496
UniProt P43699 P50220
RefSeq (mRNA) NM_001079668 NM_001146198
RefSeq (protein) NP_001073136 NP_001139670
Location (UCSC) Chr 14:
36.52 – 36.52 Mb
Chr 12:
56.53 – 56.54 Mb
PubMed search [1] [2]

NK2 homeobox 1 (NKX2-1), also known as thyroid transcription factor 1 (TTF-1), is a protein which in humans is encoded by the NKX2-1 gene.[1][2]


Thyroid transcription factor-1 (TTF-1) is a protein that regulates transcription of genes specific for the thyroid, lung, and diencephalon. It is also known as thyroid specific enhancer binding protein. It is used in anatomic pathology as a marker to determine if a tumor arises from the lung or thyroid. NKX2.1 can be induced by activin A via SMAD2 signaling in a human embryonic stem cell differentiation model.[3]

Clinical significance[edit]

Micrograph of a metastatic lung adenocarcinoma (found in the brain) that exhibits nuclear staining (brown) for TTF-1.

TTF-1 positive cells are found in the lung as type II pneumocytes and club cells. In the thyroid, follicular and parafollicular cells are also positive for TTF-1.

For lung cancers, adenocarcinomas are usually positive, while squamous cell carcinomas and large cell carcinomas are rarely positive. Small cell carcinomas (of any primary site) are usually positive. TTF1 is more than merely a clinical marker of lung adenocarcinoma. It plays an active role in sustaining lung cancer cells in view of the experimental observation that it is mutated in lung cancer.[4][5][6][7]

However others have found that TTF-1 staining is often positive in pulmonary adenocarcinomas, large cell carcinomas, small-cell lung carcinomas, neuroendocrine tumors other than small-cell lung carcinomas and extrapulmonary small-cell carcinomas.[8]

It is also positive in thyroid cancers and is used for monitoring for metastasis and recurrence.[9]


NK2 homeobox 1 has been shown to interact with Calreticulin[10] and PAX8.[11]


  1. ^ "Entrez Gene: NKX2-1". 
  2. ^ Guazzi S, Price M, De Felice M, Damante G, Mattei MG, Di Lauro R (November 1990). "Thyroid nuclear factor 1 (TTF-1) contains a homeodomain and displays a novel DNA binding specificity". EMBO J. 9 (11): 3631–9. PMC 552115. PMID 1976511. 
  3. ^ Li Y, Eggermont K, Vanslembrouck V, Verfaillie C (December 2012). "NKX2-1 activation by SMAD2 signaling after definitive endoderm differentiation in Human ESC". Stem Cells Dev. 22: 1433–1442. doi:10.1089/scd.2012.0620. PMID 23259454. 
  4. ^ Kendall J, Liu Q, Bakleh A, Krasnitz A, Nguyen KC, Lakshmi B, Gerald WL, Powers S, Mu D (October 2007). "Oncogenic cooperation and coamplification of developmental transcription factor genes in lung cancer". Proc. Natl. Acad. Sci. U.S.A. 104 (42): 16663–8. doi:10.1073/pnas.0708286104. PMC 2034240. PMID 17925434. 
  5. ^ Tanaka H, Yanagisawa K, Shinjo K, Taguchi A, Maeno K, Tomida S, Shimada Y, Osada H, Kosaka T, Matsubara H, Mitsudomi T, Sekido Y, Tanimoto M, Yatabe Y, Takahashi T. (July 2007). "Lineage-specific dependency of lung adenocarcinomas on the lung development regulator TTF-1". Cancer Research 67 (13): 6007–11. doi:10.1158/0008-5472.CAN-06-4774. PMID 17616654. 
  6. ^ Weir BA, Woo MS, Getz G, Perner S, Ding L, Beroukhim R, Lin WM, Province MA, Kraja A, Johnson LA; et al. (December 2007). "Characterizing the cancer genome in lung adenocarcinoma". Nature 450 (7171): 893–8. doi:10.1038/nature06358. PMC 2538683. PMID 17982442. 
  7. ^ Kwei KA, Kim YH, Girard L, Kao J, Pacyna-Gengelbach M, Salari K, Lee J, Choi YL, Sato M, Wang P, Hernandez-Boussard T, Gazdar AF, Petersen I, Minna JD, Pollack JR. (June 2008). "Genomic profiling identifies TITF1 as a lineage-specific oncogene amplified in lung cancer.". Oncogene 27 (25): 3635–40. doi:10.1038/sj.onc.1211012. PMC 2903002. PMID 18212743. 
  8. ^ Kalhor N, Zander DS, Liu J (August 2006). "TTF-1 and p63 for distinguishing pulmonary small-cell carcinoma from poorly differentiated squamous cell carcinoma in previously pap-stained cytologic material". Mod. Pathol. 19 (8): 1117–23. doi:10.1038/modpathol.3800629. PMID 16680154. 
  9. ^ Espinoza CR, Schmitt TL, Loos U (August 2001). "Thyroid transcription factor 1 and Pax8 synergistically activate the promoter of the human thyroglobulin gene". J. Mol. Endocrinol. 27 (1): 59–67. doi:10.1677/jme.0.0270059. PMID 11463576. 
  10. ^ Perrone L, Tell G, Di Lauro R (February 1999). "Calreticulin enhances the transcriptional activity of thyroid transcription factor-1 by binding to its homeodomain". J. Biol. Chem. 274 (8): 4640–5. doi:10.1074/jbc.274.8.4640. PMID 9988700. 
  11. ^ Di Palma T, Nitsch R, Mascia A, Nitsch L, Di Lauro R, Zannini M (January 2003). "The paired domain-containing factor Pax8 and the homeodomain-containing factor TTF-1 directly interact and synergistically activate transcription". J. Biol. Chem. 278 (5): 3395–402. doi:10.1074/jbc.M205977200. PMID 12441357. 

Further reading[edit]

External links[edit]

This article incorporates text from the United States National Library of Medicine, which is in the public domain.