Phosphorylation of c-Fos at the C-terminus enhances its transforming activity.
c-Fos is phosphorylated by MAP kinase and the 90 kDa-ribosomal S6 kinase (RSK) in vitro at serines 362 and 374 (rat) which we demonstrate are major in vivo phosphorylation sites in early G1. We have constructed c-Fos mutants with these serines changed to aspartic acid residues (FosD) to mimic phosphorylation or to alanine residues (FosA) to prevent phosphorylation. Cells expressing FosD exhibited a more extensive transformed phenotype than those expressing either FosA or wild type c-Fos (FosWT). We also observed that FosA has a reduced half-life in comparison with FosD in G1. Furthermore, we observed enhanced AP-1 transactivation activity in cells expressing FosD. These results indicate that phosphorylation of c-Fos at its extreme carboxyterminus, possibly by MAP kinase and RSK, supports the proliferative response by increasing c-Fos stability and/or by increasing its transactivation activity. Under conditions in which the MAP kinase pathway is constitutively activated, c-Fos phosphorylation probably contributes to cellular transformation. The highly conserved nature of these phosphorylation sites in other c-fos family members suggests that these may also be targets of MAP kinase and RSK.
Chen
R H
RH
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Juo
P C
PC
Curran
T
T
Blenis
J
J
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D002460:Cell Line; D002461:Cell Line, Transformed; D006207:Half-Life; D051379:Mice; D008934:Mitogens / Q000494:pharmacology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D019893:Ribosomal Protein S6 Kinases; D012694:Serine / Q000378:metabolism
D008934:Mitogens; D016760:Proto-Oncogene Proteins c-fos; D001224:Aspartic Acid; D012694:Serine; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases