Dihydroxyphenylethanol induces apoptosis by activating serine/threonine protein phosphatase PP2A and promotes the endoplasmic reticulum stress response in human colon carcinoma cells

The search for effective chemopreventive compounds is a major challenge facing research into preventing the progression of cancer cells. The naturally occurring polyphenol antioxidants look very promising, but their mechanism of action still remains poorly understood. Here, we show that 2-(3,4-dihydroxyphenyl)ethanol (DPE), a phenol antioxidant derived from olive oil, induces growth arrest and apoptosis in human colon carcinoma HT-29 cells. The mechanisms involve prolonged stress of the endoplasmic reticulum (ER) leading to the activation of the two main branches of the unfolded protein response (UPR), including the Ire1/XBP-1/GRP78/Bip and PERK/eIF2alpha arms. DPE treatment led to overexpression of the pro-apoptotic factor CHOP/GADD153 and persistent activation of the Jun-NH2-terminal kinase/activator protein-1 signaling pathway. DPE concomitantly modulated the extracellular signal-regulated kinase 1/2 and Akt/PKB pro-survival factors by altering their phosphorylation status as well as inhibiting tumor necrosis factor-alpha-induced nuclear factor-kappaB activation by inactivating the phosphorylation of nuclear factor inhibitor-kappaB kinase. These findings prompted us to investigate the possible involvement of phosphatases in DPE-mediated action. Using phosphatase inhibitors and RNA interference to silence the Ser/Thr phosphatase 2A (PP2A) prevented DPE-induced cell death. These findings demonstrate that DPE specifically activates PP2A, which plays a key initiating role in various pathways that lead to apoptosis in colon cancer cells.