Upregulation of circadian gene 'hClock' contribution to metastasis of colorectal cancer.

Recent studies have shown that disruption of the circadian rhythm was one of the endogenous factors contributing to tumorigenesis of various human malignancies, including colorectal cancer (CRC). However, the roles of circadian genes in the development of CRC are still unexplored. In this study, we investigated the expression pattern and the underlying mechanism of human Clock gene (hClock) in CRC progression. Multiple methods such as qRT-PCR, immunohistochemistry, and western blotting were performed to evaluate the expression pattern of the gene hClock, as well as to observe the changes of angiogenesis-related proteins and EMT-related proteins. Transwell cell migration assays and an animal tumor metastasis model were used to examine the impact of hClock on the metastatic ability of CRC cells in vitro and in vivo. Our results showed that the expression level of hClock significantly increased in human CRC tissues, which strongly associated with late TNM stage and positive lymph node metastasis. Moreover, a higher level of hClock expression was found in CRC cell lines with a higher metastatic potential. Furthermore, ectopic expression of hClock promoted the migration of SW480 CRC cells, while knockdown of hClock inhibited the tumor metastasis of SW620 CRC cells, and targeting hClock by shRNA effectively suppressed the metastatic ability of SW620 CRC cells in nude mice. Finally, we found that overexpression of hClock enhanced the expression of angiogenesis-related genes such as HIF-1α, ARNT and VEGF, and promoted epithelial-mesenchymal (-like) transition (EMT) in CRC cells, both of which are considered to be critical for tumor progression. These findings suggest that upregulation of the circadian gene hClock plays an important role in metastasis of colorectal cancer.