Functional analysis of CNK in RAS signaling.
Connector enhancer of KSR (CNK) is a multidomain protein required for RAS signaling. Its C-terminal portion (CNK(C-term)) directly binds to RAF. Herein, we show that the N-terminal portion of CNK (CNK(N-term)) strongly cooperates with RAS, whereas CNK(C-term) efficiently blocks RAS- and RAF-dependent signaling when overexpressed in the Drosophila eye. Two effector loop mutants of RAS(V12), S35 and C40, which selectively activate the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase pathways, respectively, do not cooperate with CNK. However, a strong cooperation is observed between CNK and RAS(V12G37), an effector loop mutant known in mammals to activate specifically the RAL pathway. We have identified two domains in CNK(N-term) that are critical for cooperation with RAS. Our results suggest that CNK functions in more than one pathway downstream of RAS. CNK(c-term) seems to regulate RAF, a component of the MAPK pathway, whereas CNK(N-term) seems to be involved in a MAPK-independent pathway.
Therrien
M
M
Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3200, USA.
Wong
A M
AM
Kwan
E
E
Rubin
G M
GM
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D004330:Drosophila; D029721:Drosophila Proteins; D005123:Eye / Q000201:enzymology / Q000378:metabolism / Q000648:ultrastructure; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008855:Microscopy, Electron, Scanning; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D014162:Transfection; D018631:ras Proteins / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C115753:CNK protein, Drosophila; D002352:Carrier Proteins; D029721:Drosophila Proteins; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins