BACKGROUND: Circadian disruption is a potential cancer risk factor in humans. However, the role of the clock gene, cryptochrome 2 (CRY2), in osteosarcoma (OS) is still not clear.

MATERIAL AND METHODS: To evaluate the potential role of CRY2 in HOS osteosarcoma cells, CRY2-silenced cell lines were established. Furthermore, we investigated the effect of CRY2 knockdown on HOS cells by CCK-8, colony formation, migration assay, and flow cytometry, in vitro.

RESULTS: CRY2 knockdown promoted HOS OS cell proliferation and migration. We used a cell cycle assay to show that CRY2 knockdown increased the S phase cell population and reduced the G1 phase cell population. Western blot analyses showed that CRY2 knockdown decreased P53 expression and increased expression of c-myc and cyclin D1. Simultaneously, CRY2 knockdown increased the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, but did not change the phosphorylation of c-Jun N terminal kinase (JNK) and P38. CRY2 knockdown also increased the expression of matrix metalloproteinase (MMP)-2 and β-catenin, and increased OS cell proliferation and migration by inducing cell cycle progression and promoting mitogen-activated protein kinase (MAPK) and Wnt/β-catenin signaling pathways. Although it has previously been unclear whether the expression of CRY2 affects the expression of other clock genes in the clock gene network, our results show that knockdown of CRY2 significantly increased the mRNA expression of CRY1, Period (PER) 1, PER2, BMAL1, and CLOCK.

CONCLUSIONS: Our results suggest that CRY2 may be an anti-oncogene in OS, whose functions involve both downstream genes and other circadian genes.

Keywords: Circadian clocks, Cryptochromes