Reversal of the Ras-induced transformed phenotype by HR12, a novel ras farnesylation inhibitor, is mediated by the Mek/Erk pathway.
We have used the selective farnesylation inhibitor HR12 [cysteine-N(methyl)valine-N(cyclohexyl) glycine-methionine-O-methyl-ester] to study the role of oncogenic Ras in cytoskeletal reorganization in Ha-ras(V12)-transformed Rat1 cells (Rat1/ras). Application of HR12 resulted in complete restoration of the cytoskeleton and associated cell adhesions disrupted by oncogenic Ras. This included an increase in the number and size of focal adhesions, accompanied by massive stress fiber formation and enhanced tyrosine phosphorylation. Furthermore, HR12 induced assembly of adherens junctions and dramatically elevated the level of the junctional components, cadherin and beta-catenin. HR12 was unable to restore the nontransformed phenotype in cells expressing farnesylation-independent, myristylated Ras. Examination of the main Ras-regulated signaling pathways revealed that HR12 induced a dose- and time-dependent decline in Erk1&2 activation (t(1/2) approximately 6 h), which correlated with the accumulation of nonfarnesylated oncogenic-Ras. Inhibition of the Mek/Erk pathway in Rat1/ras cells, using the Mek inhibitor, PD98059, resulted in complete cytoskeletal recovery, indistinguishable from that induced by HR12. Moreover, a constitutively active Mek mimicked the effect of ras transformation in Rat1 cells, and prevented HR12-induced cytoskeletal effects in Rat1/ras cells. No such effects were observed after treatment of Rat1/ras cells with the phosphatidylinositol 3-kinase inhibitor LY294002. These findings establish the Mek/Erk pathway as the dominant pathway involved in conferring the cytoskeletal and junctional manifestations of the Ras-induced transformed phenotype.
Reuveni
H
H
Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Geiger
T
T
Geiger
B
B
Levitzki
A
A
D016475:3T3 Cells; D022005:Adherens Junctions; D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors*; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002471:Cell Transformation, Neoplastic; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051231:Farnesyltranstransferase; D005419:Flavonoids / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D020935:MAP Kinase Signaling System; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects; D009842:Oligopeptides / Q000737:chemistry*; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects; D010766:Phosphorylation; D017368:Protein Prenylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins / Q000378:metabolism*
D019883:Alkyl and Aryl Transferases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D051231:Farnesyltranstransferase; D005419:Flavonoids; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D009842:Oligopeptides; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins; C418163:cysteine-N(methyl)valine-N(cyclohexyl)glycine-methionine-O-methyl-ester; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one