Pharmacological inhibitors of the mitogen-activated protein kinase (MAPK) kinase/MAPK cascade interact synergistically with UCN-01 to induce mitochondrial dysfunction and apoptosis in human leukemia cells
Y. Dai et al., Pharmacological inhibitors of the mitogen-activated protein kinase (MAPK) kinase/MAPK cascade interact synergistically with UCN-01 to induce mitochondrial dysfunction and apoptosis in human leukemia cells, CANCER RES, 61(13), 2001, pp. 5106-5115
interactions between the checkpoint abrogator UCN-01 and several pharmacolo
gical inhibitors of the mitogen-activated protein kinase (MAPK) kinase (MEK
)/MAPK pathway have been examined in a variety of human leukemia cell lines
. Exposure of U937 monocytic leukemia cells to a marginally toxic concentra
tion of UCN-01 (e.g., 150 nM) for 18 h resulted in phosphorylation/activati
on of p42/44 MAPK. Coadministration of the MEK inhibitor PD184352 (10 muM)
blocked UCN-01-induced MAPK activation and was accompanied by marked mitoch
ondrial damage (e.g., cytochrome c release and loss of Delta Psi (m)), casp
ase activation, DNA fragmentation, and apoptosis. Similar interactions were
noted in the case of of her MEK; inhibitors (e.g., PD98059; U0136) as well
as in multiple other leukemia cell types (e.g., HL-60, Jurkat, CCRF-CEM, a
nd Raji). Coadministration of PD184352 and UCN-01 resulted in reduced bindi
ng of the cdc25C phosphatase to 14-3-3 proteins, enhanced dephosphorylation
/activation of p34(cdc2) and diminished phosphorylation of cyclic AMP-respo
nsive element binding protein. The ability of UCN-01, when combined with PD
184352, to antagonize cdc25C/14-3-3 protein binding, promote dephosphorylat
ion of p34(cdc2), and potentiate apoptosis was mimicked by the ataxia telan
gectasia mutation inhibitor caffeine. In contrast, cotreatment of cells wit
h UCN-01 and PD184352 did not substantially increase c-Jun-NH2-terminal kin
ase activation nor did if alter expression of Bcl-2, Bcl-x(L), Bar, or X-in
hibitor of apoptosis. However, coexposure of U937 cells to UCN-01 and PD184
352 induced a marked increase in p38 MAPK activation. Moreover, SB203580, w
hich inhibits multiple kinases including p38 MAPK, partially antagonized ce
ll death. Lastly, although UCN-01 c PD184352 did not induce p21(CIP1), stab
le expression of a p21(CIP1) antisense construct significantly increased su
sceptibility to this drug combination. Together, these findings indicate th
at exposure of leukemic cells to UCN-01 leads to activation of the MAPK; ca
scade and that interruption of this process by R MEK inhibition triggers pe
rturbations in several signaling and cell cycle regulatory pathways that cu
lminate in mitochondrial injury, caspase activation, and apoptosis. They al
so raise the possibility. that disrupting multiple signaling pathways, e.g.
, by combining UCN-01 with MEK inhibitors, may represent a novel antileukem
ic strategy.