Identification of a novel Ras-regulated proapoptotic pathway.
BACKGROUND
The Ras-GTPase controls cell fate decisions through the binding of an array of effector molecules, such as Raf and PI 3-kinase, in a GTP-dependent manner. NORE1, a noncatalytic polypeptide, binds specifically to Ras-GTP and to several other Ras-like GTPases. NORE is homologous to the putative tumor suppressor RASSF1 and to the Caenorhabditis elegans polypeptide T24F1.3.


RESULTS
We find that all three NORE-related polypeptides bind selectively to the proapoptotic protein kinase MST1, a member of the Group II GC kinases. Endogenous NORE and MST1 occur in a constitutive complex in vivo that associates with endogenous Ras after serum stimulation. Targeting recombinant MST1 to the membrane, either through NORE or myristoylation, augments the apoptotic efficacy of MST1. Overexpression of constitutively active Ki-RasG12V promotes apoptosis in a variety of cell lines; Ha-RasG12V is a much less potent proapoptotic agent; however, a Ha-RasG12V effector loop mutant (E37G) that binds NORE, but not Raf or PI 3-kinase, exhibits proapoptotic efficacy approaching that of Ki-RasG12V. The apoptotic action of both Ki-RasG12V and Ha-RasG12V, E37G is suppressed by overexpression of the MST1 carboxy-terminal noncatalytic segment or by the NORE segment that binds MST1.


CONCLUSIONS
MST1 is a phylogenetically conserved partner of the NORE/RASSF polypeptide family, and the NORE-MST1 complex is a novel Ras effector unit that mediates the apoptotic effect of Ki-RasG12V.
Khokhlatchev
Andrei
A
Diabetes Unit and Medical Services, Massachusetts General Hospital, Boston, MA 02114, USA.
Rabizadeh
Shahrooz
S
Xavier
Ramnik
R
Nedwidek
Maria
M
Chen
Tao
T
Zhang
Xian-feng
XF
Seed
Brian
B
Avruch
Joseph
J
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D019556:COS Cells; D017173:Caenorhabditis elegans; D002462:Cell Membrane / Q000378:metabolism; D016147:Genes, Tumor Suppressor; D015801:Helminth Proteins / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells; D046911:Macromolecular Substances; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins; D018631:ras Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000099317:Hippo Kinases
D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D015801:Helminth Proteins; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D020559:Monomeric GTP-Binding Proteins; D009363:Neoplasm Proteins; D010455:Peptides; D017346:Protein Serine-Threonine Kinases; D025521:Tumor Suppressor Proteins; D018631:ras Proteins; C411762:RASSF1 protein, human; C454042:RASSF5 protein, human; C490660:Stk4 protein, mouse; D000099317:Hippo Kinases; C095566:STK4 protein, human