B. Eymin et al., p27(Kip1) induces drug resistance by preventing apoptosis upstream of cytochrome c release and procaspase-3 activation in leukemic cells, ONCOGENE, 18(7), 1999, pp. 1411-1418
The cyclin-dependent kinase inhibitor p27(Kip1) has been implicated as a dr
ug resistance factor in tumor cells grown as spheroids or confluent monolay
ers. Here, we show that p27(Kip1) overexpression also induces resistance to
drug-induced apoptosis and cytotoxicity in human leukemic cells growing in
suspension, The anti-apoptotic effect of p27(Kip1) is not restricted to DN
A-damaging agents but extends to the tubulin poison vinblastin, agonistic a
nti-Fas antibodies and macromolecule synthesis inhibitors. To further ident
ify at which level this protein interferes with the cell death pathway, we
investigated its influence on caspase activation and mitochondrial changes.
Exposure df mock-transfected U937 cells to 50 mu M etoposide activates pro
caspase-3 and the long isoform of procaspase-2 and induces mitochondrial po
tential decrease and cytochrome c release from mitochondria to the cytosol,
All these events are prevented by p27(KiP1) overexpression. p27(Kip1) does
not modulate BcL-2, BcL-X-L, Mel-1 and Bar protein level in leukemic cells
but suppresses Mel-1 expression decrease observed in mock-transfected U937
cells undergoing etoposide-induced cell death. We conclude that p27(Kip1)
prevents cell death upstream of the final pathway common to many apoptotic
stimuli that involves cytochrome c release from mitochondria and activation
of downstream caspases.