NGX6 inhibits AP-1 and Ets-1 expression and down-regulates cyclin D1 in human colorectal cancer.

Colorectal cancer (CRC) is a common malignant tumor that is associated with an increased incidence of morbidity and mortality. Nasopharyngeal carcinoma-associated gene 6 (NGX6) is a novel candidate suppressor gene of tumor metastasis, which is down-regulated in CRC. In the present study, we constructed a colorectal tissue microarray to examine the expression profiles of NGX6, phospho-c-Jun N-terminal kinase (p-JNK), and phospho-extracellular signal-regulated kinase (p-ERK ) in CRC tissues. We found that the NGX6 expression was lower in CRC tissues and metastatic lymph nodes, whereas the expressions of p-JNK and p-ERK were higher in CRC tissues, than in normal intestinal mucosa. The expressions of NGX6, p-JNK, and p-ERK were associated with the clinical pathological features of colorectal tissues. NGX6 overexpression inhibited the activation and nuclear translocation of JNK1, which led to an accumulation of p-JNK in the cytoplasm, but did not inhibit the activation and nuclear translocation of ERK1/2. NGX6 also inhibited the expression of the transcription factors AP-1 (c-jun and c-fos) and Ets-1. In addition, NGX6 overexpression decreased the expression of cyclin D1 and dramatically suppressed the transcriptional efficiency of the cyclin D1 promoter. We propose that NGX6 expression is lost in the multistep process of human colorectal carcinogenesis. Its overexpression can inhibit the expression of transcription factors AP-1 and Ets-1, and down-regulate the transcriptional activity of the cyclin D1 promoter in human CRC.