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Molecular and Cellular Biology, June 2001, p. 3684-3691, Vol. 21, No. 11
Radiumhemmet's Research Laboratory, Cancer Center
Karolinska, Department of Oncology-Pathology, Karolinska Institute,
S-171 76 Stockholm,1 and Department of
Medical Biochemistry and Microbiology, BMC, Uppsala University,
S-751 23 Uppsala,2 Sweden, and Saitama
Cancer Center Research Institute, Kita-adachigun, Saitama
362-0806,3 and Tokyo Metropolitan
Hospital, Bunkyo-ku, Tokyo,4 Japan
Received 20 September 2000/Returned for modification 29 November
2000/Accepted 22 February 2001
In a panel of four human melanoma cell lines, equitoxic doses of
cisplatin induced the proapoptotic conformation of the Bcl-2 family
protein Bak prior to the execution phase of apoptosis. Because
cisplatin-induced modulation of the related Bax protein was seen in
only one cell line, a degree of specificity in the signal to Bak is
indicated. Little is known about upstream regulation of Bak activity.
In this study, we examined whether the apoptosis-specific pathway
mediated by a kinase fragment of MEKK1 (
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.11.3684-3691.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Cisplatin Induces the Proapoptotic Conformation of
Bak in a
MEKK1-Dependent Manner
MEKK1) is involved in the
observed Bak modulation. We report that expression of a kinase-inactive
fragment of MEKK1 (dominant negative MEKK [dnMEKK]) efficiently
blocked cisplatin-induced modulation of Bak and cytochrome c release and consequently also reduced DEVDase activation
and nuclear fragmentation. Accordingly, expression of a kinase-active MEKK1 fragment (dominant positive MEKK) was sufficient to induce modulation of Bak in three cell lines and to induce apoptosis in two of
these. dnMEKK did not block cisplatin-induced c-Jun N-terminal kinase
(JNK) activation, in agreement with a specifically proapoptotic role
for the
MEKK1 pathway. Finally, we show that reduction of Bak
expression by antisense Bak reduced cisplatin-induced loss of
mitochondrial integrity and caspase cleavage activity in breast cancer
cell lines. In summary, we have identified Bak as a cisplatin-regulated
component downstream in a proapoptotic, JNK-independent
MEKK1 pathway.
*
Corresponding author. Mailing address: Radiumhemmet's
Research Laboratory, Cancer Center Karolinska, Department of
Oncology-Pathology, Karolinska Institute, S-171 76 Stockholm, Sweden.
Phone: 46 8 51 77 54 60. Fax: 46 8 33 90 31. E-mail:
mimmi.shoshan{at}onkpat.ki.se.
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