Paired-like homeodomain 2B contributes to tumour progression and anti-autophagy in human lung cancer.

ABSTRACT

Paired-like homeodomain transcription factor 2 (PITX2) is well known to play an essential role in normal embryonic development. Emerging evidence suggests that PITX2 may be involved in human tumorigenesis, but the role of PITX2 in tumour progression remains largely unclear. The expression levels of PITX2 in lung cancer cells were determined by qRT-PCR and Western blot analyses. Gain- and loss-of-function experiments were conducted to investigate the biological roles of PITX2 in the phenotype of lung cancer cells. Immunofluorescence staining and transmission electron microscopy were used to observe autophagy. The expression level and clinical significance of PITX2 were determined in a Taiwanese cohort and the Gene Expression Omnibus (GEO) database, respectively. Here, we show that PITX2B is the most abundant isoform of the bicoid homeodomain family in lung cancer cells. The enforced expression of PITX2B promoted lung cancer tumorigenesis and progression in vitro and in vivo. The mechanistic analysis revealed that the nuclear localization of PITX2B is correlated with its oncogenic functions and two important nuclear localization signals. In addition, PITX2B knockdown in lung cancer cells caused a marked increase in autophagy and apoptosis, suggesting that PITX2B plays an important role in lung cancer cell survival. Moreover, a high expression of PITX2B was associated with a poor overall survival (P<0.05) in both Taiwanese non-small-cell lung cancer patients and GEO lung cancer cohorts. These results provide new insight into the contribution of PITX2B to lung cancer progression, implicate PITX2B as an important component of cell survival signals and further establish PITX2B as a therapeutic target for lung cancer treatment.