hClock gene expression in human colorectal carcinoma

In this study, we aimed to investigate changes in the expression of human Clock (hClock), a gene at the core of the circadian gene family, in colorectal carcinomas (CRCs) and to discuss the possible effects. Previous studies have revealed that the disruption of circadian rhythms is one of the endogenous factors that contribute to the initiation and development of CRCs. However, the underlying molecular changes to the circadian genes associated with CRCs have not been explored. Immunofluorescence and quantitative polymerase chain reaction (qPCR) analysis of the hCLOCK protein and gene expression were performed in 30 cases of CRC. The hCLOCK protein was expressed in all specimens obtained from 30 CRC patients. Higher levels of hCLOCK expression were observed in human CRC tissues compared with the paired non-cancerous tissues. hCLOCK expression was significantly higher in poorly differentiated, or late-stage, Dukes' grade tumors and in 64.3% of tumor cases with lymph node metastasis. The hClock gene was expressed in all specimens. A significantly higher expression of hClock was found in human CRC cases compared with paired non-cancerous tissues. There was a strong positive linear correlation between hClock gene expression and protein expression in human CRCs. A strong positive linear correlation was also found between hClock gene expression and ARNT, HIF-1 alpha and VEGF expression in human CRCs. There was no significant correlation between hClock and Bak, Bax, Bid, tumor necrosis factor receptor I (TNFR I) and TNFR II. The circadian gene hClock was stably expressed in human colorectal mucosa and was important in regulating the expression of downstream clock-controlled genes. hCLOCK may interact with HIF-1 alpha/ARNT and activate VEGF to stimulate tumor angiogenesis and metastasis.