Growth factors can activate ATF2 via a two-step mechanism: phosphorylation of Thr71 through the Ras-MEK-ERK pathway and of Thr69 through RalGDS-Src-p38.
Transcription factor ATF2 regulates gene expression in response to environmental changes. Upon exposure to cellular stresses, the mitogen-activated proteinkinase (MAPK) cascades including SAPK/JNK and p38 can enhance ATF2's transactivating function through phosphorylation of Thr69 and Thr71. How ever, the mechanism of ATF2 activation by growth factors that are poor activators of JNK and p38 is still elusive. Here, we show that in fibroblasts, insulin, epidermal growth factor (EGF) and serum activate ATF2 via a so far unknown two-step mechanism involving two distinct Ras effector pathways: the Raf-MEK-ERK pathway induces phosphorylation of ATF2 Thr71, whereas subsequent ATF2 Thr69 phosphorylation requires the Ral-RalGDS-Src-p38 pathway. Cooperation between ERK and p38 was found to be essential for ATF2 activation by these mitogens; the activity of p38 and JNK/SAPK in growth factor-stimulated fibroblasts is insufficient to phosphorylate ATF2 Thr71 or Thr69 + 71 significantly by themselves, while ERK cannot dual phosphorylate ATF2 Thr69 + 71 efficiently. These results reveal a so far unknown mechanism by which distinct MAPK pathways and Ras effector pathways cooperate to activate a transcription factor.
Department of Molecular Cell Biology, Section of Signal Transduction, Leiden University Medical Centre, Wassenaarseweg 72, 2333 AL Leiden, The Netherlands.
D Margriet
DM
Ouwens
Nancy D
ND
de Ruiter
Gerard C M
GC
van der Zon
Andrew P
AP
Carter
Jan
J
Schouten
Corina
C
van der Burgt
Klaas
K
Kooistra
Johannes L
JL
Bos
J Antonie
JA
Maassen
Hans
H
van Dam
D051698:Activating Transcription Factor 2; D001769:Blood; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000737:chemistry / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000502:physiology*; D006801:Humans; D007328:Insulin / Q000502:physiology*; D020935:MAP Kinase Signaling System; D010766:Phosphorylation; D013912:Threonine / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*
C497105:ATF2 protein, human; D051698:Activating Transcription Factor 2; D017362:Cyclic AMP Response Element-Binding Protein; D007328:Insulin; D014157:Transcription Factors; D013912:Threonine; D004815:Epidermal Growth Factor