Homeobox Transcription Factor NKX2-1 Promotes Cyclin D1 Transcription in Lung Adenocarcinomas

The known oncogene cyclin D1 (CCND1) participates in progression of the cell cycle from G₁ to S-phase. Expression of cyclin D1 is frequently promoted in multiple human cancers including non-small cell lung cancer (NSCLC). However, a relationship between cyclin D1 expression and the prognosis of NSCLC has not been confirmed. NKX2-1 is a homeobox transcription factor involved in pulmonary development as a differentiation-promoting factor. In NSCLC, it acts as a metastasis suppressor and correlates with a good prognosis. Here, NKX2-1-binding motifs were identified in the cyclin D1 promoter, but it has not been clarified whether NKX2-1 is involved in cyclin D1 expression in NSCLC. To shed light on this issue, endogenous NKX2-1 was depleted in NSCLC cell lines, which resulted in decreased cyclin D1 mRNA and protein. In contrast, forced overexpression of NKX2-1 increased cyclin D1 levels. Moreover, NKX2-1 directly bound to the cyclin D1 promoter and enhanced its activity. Finally, using human NSCLC clinical specimens, it was determined that both NKX2-1 protein and mRNA were significantly correlated with cyclin D1 expression status in adenocarcinomas. These results indicate that NKX2-1 directly and positively regulates transcription of cyclin D1 Finally, expression of NKX2-1, but not cyclin D1, was significantly associated with metastatic incidence as an independent good prognostic factor of adenocarcinoma.Implications: NKX2-1-expressing adenocarcinomas, whereas NKX2-1 promoted cyclin D1 expression, may show good prognosis features by the metastasis inhibition potency of NKX2-1 regardless cyclin D1 expression. Mol Cancer Res; 15(10); 1388-97. ©2017 AACR.