Resveratrol activates adenylyl-cyclase in human breast cancer cells: a novel, estrogen receptor-independent cytostatic mechanism

Resveratrol (RSVL) is a well-established chemopreventive agent in human breast cancer models. The molecular basis of its action is far less characterized. We investigated the effects of RSVL on activity of adenylate- and guanylate-cyclase (AC, GC) enzymes; two known cytostatic cascades in MCF-7 breast cancer cells. RSVL increased cAMP levels in both time- and concentration-dependent manners (t(1/2), 6.2 min; EC50 0.8 muM). In contrast, it had no effect on cGMP levels. The stimulatory effects for RSVL on AC were not altered either by the protein synthesis inhibitor (actinomycin-D, 5 muM) or the estrogen-receptor (ER) blockers (tamoxifen and ICI182,780, 1 muM each). Likewise, cAMP formation by RSVL was insensitive to either the broad-spectrum phosphodiesterase (PDE) inhibitor (IBMX, 0.5 mM) or the cAMP-specific PDE inhibitor (rolipram, 10 muM). Instead, these PDE inhibitors significantly augmented maximal cAMP formation by RSVL. Parallel experiments showed that either RSVL or rolipram inhibited the proliferation of these cells in a concentration-responsive manner. Further, concurrent treatment with RSVL and rolipram significantly enhanced their individual cytotoxic responses. The antiproliferative effects were appreciably reversed by the kinase-A inhibitors, Rp-cAMPS (100-300 muM) or KT-5720 (10 muM). Pretreatment with the cPLA(2) inhibitor arachidonyl trifluoromethyl ketone (10 muM) markedly antagonized the cytotoxic effects of RSVL, but had no effect on that of rolipram. Altogether, the present study demonstrates, for the first time, that the chemotherapeutic agent RSVL is an agonist for the cAMP/kinase-A system, a documented pro-apoptic and cell-cycle suppressor in breast cancer cells.