Previous epidemiological studies have demonstrated that moderate coffee consumption is associated with a lower risk of certain types of cancer, particularly colon cancer. To elucidate the molecular basis for this protective action, the effect of coffee on Caco-2 human colon carcinoma cells was investigated. Low concentrations of coffee (<5%) inhibited proliferation of Caco-2 cells without affecting cell viability. Coffee also reduced KRAS proto-oncogene, GTPase (KRAS) gene expression in a dose-dependent manner; however, caffeine, caffeic acid and chlorogenic acid, three major constituents of coffee, did not exhibit this effect. Increasing the duration of coffee bean roasting increased the reduction in KRAS expression, suggesting that the active constituents responsible for this effect emerged during the roasting process. MicroRNA (miR) analysis revealed that coffee induced the expression of miR-30c and miR-96, both of which target the KRAS gene. The results of the present study suggested that daily coffee consumption may reduce KRAS activity, thereby preventing the malignant growth of colon carcinoma cells.
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