Caffeic Acid Phenethyl Ester Inhibits T-Cell Activation by Targeting Both Nuclear Factor of Activated T-Cells and NF- B Transcription Factors

Caffeic acid phenethyl ester (CAPE), which is derived from the propolis of honeybee hives, has been shown to reveal anti-inflammatory properties. Since T-cells play a key role in the onset of several inflammatory diseases, we have evaluated the immunosuppressive activity of CAPE in human T-cells, discovering that this phenolic compound is a potent inhibitor of early and late events in T-cell receptor-mediated T-cell activation. Moreover, we found that CAPE specifically inhibited both interleukin (IL)-2 gene transcription and IL-2 synthesis in stimulated T-cells. To further characterize the inhibitory mechanisms of CAPE at the transcriptional level, we examined the DNA binding and transcriptional activities of nuclear factor (NF)B, nuclear factor of activated cells (NFAT), and activator protein-1 (AP-1) transcription factors in Jurkat cells. We found that CAPE inhibited NFB-dependent transcriptional activity without affecting the degradation of the cytoplasmic NFB inhibitory protein, I B . However, both NFB binding to DNA and transcriptional activity of a Gal4-p65 hybrid protein were clearly prevented in CAPE-treated Jurkat cells. Moreover, CAPE inhibited both the DNA-binding and transcriptional activity of NFAT, a result that correlated with its ability to inhibit phorbol 12-myristate 13-acetate plus ionomycin-induced NFAT1 dephosphorylation. These findings provide new insights into the molecular mechanisms involved in the immunomodulatory and anti-inflammatory activities of this natural compound. Caffeic acid phenethyl ester (CAPE) is an active phenolic compound present in propolis, which is the generic name of a resinous product derived from the bark of conifer trees and carried by honeybees to their hives. The biological activities of propolis and CAPE have been extensively studied, and it has been shown that CAPE has antitumoral (Chiao et al., 1995; Huang et al., 1996) and anti-inflammatory properties (Mirzoeva and Calder, 1996; Michaluart et al., 1999; Fitzpatrick et al., 2001). However, CAPE inhibits the transcriptional activity of the COX-2 gene in epithelial cells (Michaluart et al., 1999), inducible nitric-oxide synthase gene expression, and nitric oxide production in macrophage cell lines (Song et al., 2002; Nagaoka et al., 2003). In addition, CAPE may suppress the eicosanoid synthesis (Mirzoeva and Calder, 1996) and the release of arachidonic acid from cell membranes (Michaluart et al., 1999). It has been recently shown that this phenolic compound is a potent inhibitor of mitogen-induced T-cell proliferation, lymphokine production (Ansorge et al., 2003), and NFB activation as well (Natarajan et al., 1996). However, the detailed inhibitory mechanisms at the molecular level of CAPE on T-cell activation are