NK2 homeobox 1

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

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

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

For is_associated_with::lung cancers, is_associated_with::adenocarcinomas are usually positive, while is_associated_with::squamous cell carcinomas and is_associated_with::large cell carcinomas are rarely positive. is_associated_with::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.

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.

It is also positive in is_associated_with::thyroid cancers and is used for monitoring for is_associated_with::metastasis and recurrence.

Interactions
NK2 homeobox 1 has been shown to interact with is_associated_with::Calreticulin and is_associated_with::PAX8.