Caffeic acid suppresses cyclin D1 expression by directly binding to ribosomal protein S5 in colorectal cancer cells

Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide, and dietary components such as coffee have been epidemiologically associated with a reduced risk of CRC. However, the molecular mechanisms underlying this effect remain elusive. In this study, we found that caffeic acid, a hydrolysate of chlorogenic acid abundant in coffee, significantly suppressed colony formation in human CRC cells. Chemical pull-down assays using nano-magnetic beads combined with mass spectrometry identified ribosomal protein S5 (RPS5) as a direct binding target of caffeic acid. Molecular dynamics simulations further supported the stability of the interaction between caffeic acid and a specific binding pocket on RPS5. Mechanistically, RNA interference-mediated knockdown of RPS5 induced G1 cell cycle arrest and downregulated cyclin D1 expression at both mRNA and protein levels, without affecting its promoter activity, suggesting a post-transcriptional regulatory mechanism of cyclin D1 by RPS5. These findings reveal a previously unrecognized RPS5-cyclin D1 axis targeted by caffeic acid and provide novel mechanistic insights into the potential chemopreventive effects of coffee against CRC.