The Mos/MAP kinase pathway stabilizes c-Fos by phosphorylation and augments its transforming activity in NIH 3T3 cells.
The c-mos proto-oncogene product, Mos, is a serine/threonine kinase that can activate ERK1 and 2 mitogen-activated protein (MAP) kinases by direct phosphorylation of MAPK/ERK kinase (MEK). ERK activation is essential for oncogenic transformation of NIH 3T3 cells by Mos. In this study, we examined how mitogenic and oncogenic signalling from the Mos/MEK/ERK pathway reaches the nucleus to activate downstream target genes. We show that c-Fos (the c-fos protooncogene product), which is an intrinsically unstable nuclear protein, is metabolically highly stabilized, and greatly enhances the transforming efficiency of NIH 3T3 cells, by Mos. This stabilization of c-Fos required Mos-induced phosphorylation of its C-terminal region on Ser362 and Ser374, and double replacements of these serines with acidic (Asp) residues markedly increased the stability and transforming efficiency of c-Fos even in the absence of Mos. Moreover, activation of the ERK pathway was necessary and sufficient for the c-Fos phosphorylation and stabilization by Mos. These results indicate that c-Fos undergoes stabilization, and mediates at least partly the oncogenic signalling, by the Mos/MEK/ERK pathway. The present findings also suggest that, in general, the ERK pathway may regulate the cell fate and function by affecting the metabolic stability of c-Fos.
Okazaki
K
K
Division of Molecular Genetics, Institute of Life Science, Kurume University, Fukuoka, Japan.
Sagata
N
N
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002471:Cell Transformation, Neoplastic; D003001:Cloning, Molecular; D015151:Immunoblotting; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D017231:Proto-Oncogene Proteins c-mos / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection
D009419:Nerve Tissue Proteins; D016760:Proto-Oncogene Proteins c-fos; D011994:Recombinant Proteins; D012694:Serine; D017231:Proto-Oncogene Proteins c-mos; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases