Caffeic acid phenethyl ester induces E2F‐1‐mediated growth inhibition and cell‐cycle arrest in human cervical cancer cells

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Abstract
Caffeic acid phenyl ester (CAPE) has been identified as an active component of propolis, a substance that confers diverse activities in cells of various origins. However, the molecular basis of CAPE‐mediated cellular activity remains to be clarified. Here, we show that CAPE preferentially induced S‐ and G2/M‐phase cell‐cycle arrests and initiated apoptosis in human cervical cancer lines. The effect was found to be associated with increased expression of E2F‐1, as there is no CAPE‐mediated induction of E2F‐1 in the pre‐cancerous cervical Z172 cells. CAPE also up‐regulated the E2F‐1 target genes cyclin A, cyclin E and apoptotic protease activating of factor 1 (Apaf‐1) but down‐regulated cyclin B and induced myeloid leukemia cell differentiation protein (Mcl‐1). These results suggest the involvement of E2F‐1 in CAPE‐mediated growth inhibition and cell‐cycle arrest. Transient transfection studies with luciferase reporters revealed that CAPE altered the transcriptional activity of the apaf‐1 and mcl‐1 promoters. Further studies using chromatin immunoprecipitation assays demonstrated that E2F‐1 binding to the apaf‐1 and cyclin B promoters was increased and decreased, respectively, in CAPE‐treated cells. Furthermore, E2F‐1 silencing abolished CAPE‐mediated effects on cell‐cycle arrest, apoptosis and related gene expression. Taken together, these results indicate a crucial role for E2F‐1 in CAPE‐mediated cellular activities in cervical cancer cells.

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