Phosphorylation of the oncogenic transcription factor interferon regulatory factor 2 (IRF2) in vitro and in vivo.
IRF2 is a transcription factor, possessing oncogenic potential, responsible for both the repression of growth-inhibiting genes (interferon) and the activation of cell cycle-regulated genes (histone H4). Surprisingly little is known about the post-translational modification of this factor. In this study, we analyze the phosphorylation of IRF2 both in vivo and in vitro. Immunoprecipitation of HA-tagged IRF2 expressed in 32P-phosphate labelled COS-7 cells demonstrates that IRF2 is phosphorylated in vivo. Amino acid sequence analysis reveals that several potential phosphorylation sites exist for a variety of serine/threonine protein kinases, including those of the mitogen activated protein (MAP) kinase family. Using a battery of these protein kinases we show that recombinant IRF2 is a substrate for protein kinase A (PKA), protein kinase C (PKC), and casein kinase II (CK2) in vitro. However, other serine/threonine protein kinases, including the MAP kinases JNK1, p38, and ERK2, do not phosphorylate IRF2. Two-dimensional phosphopeptide mapping of the sites phosphorylated by PKA, PKC, and CKII in vitro demonstrates that these enzymes are capable of phosphorylating IRF2 at multiple distinct sites. Phosphoaminoacid analysis of HA-tagged IRF2 immunoprecipitated from an asynchronous population of proliferating, metabolically phosphate-labelled cells indicates that this protein is phosphorylated exclusively upon serine residues in vivo. These results suggest that the oncogenic protein IRF2 may be regulated via multiple pathways during cellular growth.
Birnbaum
M J
MJ
Department of Cell Biology, Cancer Center, University of Massachusetts Medical Center, Worcester 01655, USA.
van Zundert
B
B
Vaughan
P S
PS
Whitmarsh
A J
AJ
van Wijnen
A J
AJ
Davis
R J
RJ
Stein
G S
GS
Stein
J L
JL
D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D047390:Casein Kinase II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D050836:Interferon Regulatory Factor-2; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012097:Repressor Proteins; D012694:Serine / Q000378:metabolism; D014157:Transcription Factors
D004268:DNA-Binding Proteins; C494229:IRF2 protein, human; D050836:Interferon Regulatory Factor-2; D015513:Oncogene Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D012694:Serine; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C