hClock gene expression in human colorectal carcinoma

Abstract

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-1α 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-1α/ARNT and activate VEGF to stimulate tumor angiogenesis and metastasis.

The circadian clock and hypoxia in tumor cell de-differentiation and metastasis

“…Bmal1, Npas2 and Clock have been indicated as important for VEGF-production during the night [33,34]. In agreement with these findings, Clock is often up-regulated and Period2 downregulated in human colorectal cancer and the levels of tumor Clock expression exhibit a tight positive correlation with tumor VEGF-levels and metastatic dissemination in patients [35,36].…”

Circadian Clock, Cell Division, and Cancer: From Molecules to Organism

“…This pro-proliferative effect of certain clock genes was not specific to untransformed cells, since very similar properties were also attributed to cancer cell lines. For instance, human colorectal cancers often show higher expression of Clock or Bmal1 genes compared to healthy tissue [112,113,114]. In agreement with this, overexpression of CLOCK increases proliferation of colorectal carcinoma cells in vitro and in vivo [115].…”

Circadian angiogenesis

“…From a molecular point of view, and in agreement with the findings from pre-clinical models, CLOCK was reported to be significantly up-regulated and Per2 was down-regulated in human colorectal cancer tumors compared to adjacent healthy tissue and the levels of CLOCK from different patients strongly correlated with the level of VEGF detected in their tumor biopsies as well as degree of metastatic dissemination of tumor cells and poor prognosis (91,92). In addition, other angiogenic factors have been found to oscillate in a circadian fashion, including bFGF, EGF and IGFBP in breast cancer patients, where peak plasma levels are generally found during the day and low levels in the night (93).…”