Induction of oocyte maturation by jun-N-terminal kinase (JNK) on the oncogenic ras-p21 pathway is dependent on the raf-MEK signal transduction pathway.
OBJECTIVE
We have previously found that microinjection of activated MEK (mitogen activated kinase kinase) and ERK (mitogen-activated protein; MAP kinase) fails to induce oocyte maturation, but that maturation, induced by oncogenic ras-p21 and insulin-activated cell ras-p21, is blocked by peptides from the ras-binding domain of raf. We also found that jun kinase (JNK), on the stress-activated protein (SAP) pathway, which is critical to the oncogenic ras-p21 signal transduction pathway, is a strong inducer of oocyte maturation. Our purpose in this study was to determine the role of the raf-MEK-MAP kinase pathway in oocyte maturation and how it interacts with JNK from the SAP pathway.


METHODS
We microinjected raf dominant negative mutant mRNA (DN-raf) and the MEK-specific phosphatase, MKP-T4, either together with oncogenic p21 or c-raf mRNA, into oocytes or into oocytes incubated with insulin to determine the effects of these raf-MEK-MAP kinase pathway inhibitors.


RESULTS
We found that oocyte maturation induced by both oncogenic and activated normal p21 is inhibited by both DN-raf and by MKP-T4. The latter more strongly blocks the oncogenic pathway. Also an mRNA encoding a constitutively activated MEK strongly induces oocyte maturation that is not inhibited by DN-raf or by MKP-T4. Surprisingly, we found that oocyte maturation induced by JNK is blocked both by DN-raf and MKP-T4. Furthermore, we discovered that c-raf induces oocyte maturation that is inhibited by glutathione-S-transferase (GST), which we have found to be a potent and selective inhibitor of JNK.


CONCLUSIONS
We conclude that there is a strong reciprocal interaction between the SAP pathway involving JNK and the raf-MEK-MAP kinase pathway and that oncogenic ras-p21 can be preferentially inhibited by MEK inhibitors. The results imply that blockade of both MEK and JNK-oncogenic ras-p21 interactions may constitute selective synergistic combination chemotherapy against oncogenic ras-induced tumors.
Chie
L
L
Department of Biology, Long Island University, Brooklyn, NY 11201, USA.
Amar
S
S
Kung
H F
HF
Lin
M C
MC
Chen
H
H
Chung
D L
DL
Adler
V
V
Ronai
Z
Z
Friedman
F K
FK
Robinson
R C
RC
Kovac
C
C
Brandt-Rauf
P W
PW
Yamaizumi
Z
Z
Michl
J
J
Pincus
M R
MR
D000818:Animals; D005260:Female; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D009865:Oocytes / Q000254:growth & development*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*; D015398:Signal Transduction; D014982:Xenopus laevis
D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D016283:Proto-Oncogene Proteins p21(ras)