Adaphostin promotes caffeine-evoked autocrine Fas-mediated death pathway activation in Bcr/Abl-positive leukaemia cells

Abstract

The present study was conducted to verify whether caffeine is beneficial for improving leukaemia therapy. Co-treatment with adaphostin (a Bcr/Abl inhibitor) was found to potentiate caffeine-induced Fas/FasL up-regulation. Although adaphostin did not elicit ASK1 (apoptosis signal-regulating kinase 1)-mediated phosphorylation of p38 MAPK (mitogen-activated protein kinase) and JNK (c-Jun N-terminal kinase), co-treatment with adaphostin notably increased p38 MAPK/JNK activation in caffeine-treated cells. Suppression of p38 MAPK and JNK abrogated Fas/FasL up-regulation in caffeine- and caffeine/adaphostin-treated cells. Compared with caffeine, adaphostin markedly suppressed Akt/ERK (extracellular-signal-regulated kinase)-mediated MKP-1 (MAPK phosphatase 1) protein expression in K562 cells. MKP-1 down-regulation eventually elucidated the enhanced effect of adaphostin on p38 MAPK/JNK activation and subsequent Fas/FasL up-regulation in caffeine-treated cells. Knockdown of p38α MAPK and JNK1, ATF-2 (activating transcription factor 2) and c-Jun by siRNA (small interfering RNA) proved that p38α MAPK/ATF-2 and JNK1/c-Jun pathways were responsible for caffeine-evoked Fas/FasL up-regulation. Moreover, Ca2+ and ROS (reactive oxygen species) were demonstrated to be responsible for ASK1 activation and Akt/ERK inactivation respectively in caffeine- and caffeine/adaphostin-treated cells. Likewise, adaphostin functionally enhanced caffeine-induced Fas/FasL up-regulation in leukaemia cells that expressed Bcr/Abl. Taken together, the results of the present study suggest a therapeutic strategy in improving the efficacy of adaphostin via Fas-mediated death pathway activation in Bcr/Abl-positive leukaemia.