Cucurbitacin B inhibits cell proliferation and induces cell apoptosis in colorectal cancer by modulating methylation status of BTG3

A previous report has revealed that cucurbitacin B (CuB) inhibits cancer cell proliferation and tumorigenesis in non-small cell lung cancer (NSCLC) through epigenetic modifications of several genes. However, whether CuB regulates cell proliferation and apoptosis by altering methylation status of BTG3 in colorectal cancer (CRC) remains unknown. In the present study, the results showed that BTG3 was downregulated in CRC tissues compared with adjacent normal tissues. CuB significantly increased BTG3 levels, induced promoter demethylation, and decreased the levels of DNA methyltransferases (DNMT1, DNMT3a and DNMT3b) in both CRC cell lines (SW480 and Caco-2), and the effects of CuB were comparable with those of 5-Aza-dC. We also found that CuB inhibited cell proliferation, accompanied with decreased expression of Ki67. Furthermore, CuB treatment induced cell cycle arrest at G1 phase in SW480 and Caco-2 cells, as well as decreased levels of Cyclin D1 and Cyclin E1. Incubation with CuB promoted cell apoptosis in both CRC cell lines in vitro, accompanied with elevation of cleaved caspase-3 and cleaved PARP. BTG3 knockdown abolished the effects of CuB in CRC cells. In summary, CuB-induced proliferation inhibition and cell apoptosis may be due to the reactivation of BTG3 by promoter demethylation. CuB may be a promising agent for CRC therapy.