Functional Interactions of Raf and MEK with Jun-N-Terminal Kinase (JNK) Result in a Positive Feedback Loop on the Oncogenic Ras Signaling Pathway

In previous studies we have found that oncogenic (Val 12)-ras-p21 induces Xenopus laevis oocyte maturation that is selectively blocked by two ras-p21 peptides, 35−47, also called PNC-7, that blocks its interaction with raf, and 96−110, also called PNC-2, that blocks its interaction with jun-N-termin...

Full description

Saved in:
Bibliographic Details
Published in:Biochemistry (Easton) 2005-08, Vol.44 (32), p.10784-10795
Main Authors: Adler, Victor, Qu, Yongxia, Smith, Steven J, Izotova, Lara, Pestka, Sidney, Kung, Hsiang-Fu, Lin, Marie, Friedman, Fred K, Chie, Lyndon, Chung, Denise, Boutjdir, Mohamed, Pincus, Matthew R
Format: Article
Language:English
Subjects:
Animals
Butadienes - pharmacology
Cell Line, Tumor
Feedback, Physiological
Humans
JNK Mitogen-Activated Protein Kinases - metabolism
MAP Kinase Kinase 1 - antagonists & inhibitors
MAP Kinase Kinase 1 - metabolism
Multiprotein Complexes
Nitriles - pharmacology
Oocytes
Phosphorylation
Proto-Oncogene Proteins c-raf - metabolism
Proto-Oncogene Proteins p21(ras) - metabolism
Receptor Cross-Talk
Signal Transduction
Xenopus laevis
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:In previous studies we have found that oncogenic (Val 12)-ras-p21 induces Xenopus laevis oocyte maturation that is selectively blocked by two ras-p21 peptides, 35−47, also called PNC-7, that blocks its interaction with raf, and 96−110, also called PNC-2, that blocks its interaction with jun-N-terminal kinase (JNK). Each peptide blocks activation of both JNK and MAP kinase (MAPK or ERK) suggesting interaction between the raf−MEK−ERK and JNK−jun pathways. We further found that dominant negative raf blocks JNK induction of oocyte maturation, again suggesting cross-talk between pathways. In this study, we have undertaken to determine where these points of cross-talk occur. First, we have immunoprecipitated injected Val 12-Ha-ras-p21 from oocytes and found that a complex forms between ras-p21 raf, MEK, MAPK, and JNK. Co-injection of either peptide, but not a control peptide, causes diminished binding of ras-p21, raf, and JNK. Thus, one site of interaction is cooperative binding of Val 12-ras-p21 to raf and JNK. Second, we have injected JNK, c-raf, and MEK into oocytes alone and in the presence of raf and MEK inhibitors and found that JNK activation is independent of the raf−MEK−MAPK pathway but that activated JNK activates raf, allowing for activation of ERK. Furthermore, we have found that constitutively activated MEK activates JNK. We have corroborated these findings in studies with isolated protein components from a human astrocyte (U-251) cell line; that is, JNK phosphorylates raf but not the reverse; MEK phosphorylates JNK but not the reverse. We further have found that JNK does not phosphorylate MAPK and that MAPK does not phosphorylate JNK. The stress-inducing agent, anisomycin, causes activation of JNK, raf, MEK, and ERK in this cell line; activation of JNK is not inhibitable by the MEK inhibitor, U0126, while activation of raf, MEK, and ERK are blocked by this agent. These results suggest that activated JNK can, in turn, activate not only jun but also raf that, in turn, activates MEK that can then cross-activate JNK in a positive feedback loop.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi050619j