Piceatannol induces Fas and FasL up-regulation in human leukemia U937 cells via Ca2+/p38α MAPK-mediated activation of c-Jun and ATF-2 pathways

To verify whether piceatannol-induced death of leukemia cells was associated with Fas-mediated death pathway, the present study was conducted. Piceatannol-induced apoptotic death of human leukemia U937 cells was characterized by increase in intracellular Ca2+ concentration ([Ca2+]i), ERK inactivation, p38 MPAK activation, degradation of procaspase-8 and production of t-Bid. Piceatannol treatment increased Fas and FasL protein expression, and up-regulated transcription of Fas and FasL mRNA. Down-regulation of FADD blocked piceatannol-induced procaspase-8 degradation and rescued viability of piceatannol-treated cells. Abolition of piceatannol-induced increase in [Ca2+]i abrogated p38 MAPK activation and up-regulation of Fas and FasL expression, but restored ERK activation and viability of piceatannol-treated cells. Suppression of p38α MAPK or transfection of constitutively active MEK1 abolished piceatannol-induced Fas and FasL up-regulation. Piceatannol treatment repressed ERK-mediated c-Fos phosphorylation but evoked p38α MAPK-mediated c-Jun and ATF-2 phosphorylation. Knockdown of c-Fos, c-Jun and ATF-2 by siRNA reflected that c-Fos attenuated the effect of c-Jun and ATF-2 on Fas/FasL up-regulation. Taken together, our data indicate that Fas/FasL up-regulation in piceatannol-treated U937 cells is elicited by Ca2+/p38α MAPK-mediated activation of c-Jun and ATF-2, and suggest that autocrine Fas-mediated apoptotic mechanism is involved in piceatannol-induced cell death.