An oncogenic mutation uncouples the v-Jun oncoprotein from positive regulation by the SAPK/JNK pathway in vivo.
Stimulation of c-Jun transcriptional activity via phosphorylation mediated by the stress-activated or c-Jun amino-terminal (SAPK/JNK) subgroup of mitogen-activated protein kinases (MAP kinases) is thought to depend on a kinase-docking site (the delta region) within the amino-terminal activation domain, which is deleted from the oncogenic derivative, v-Jun [1] [2] [3]. This mutation markedly enhances v-Jun oncogenicity [4] [5]; however, its transcriptional consequences have not been resolved. In part, this reflects uncertainty as to whether binding of SAPK/JNK inhibits c-Jun function directly [6] [7] or, alternatively, serves to facilitate and maintain the specificity of positive regulatory phosphorylation [8]. Using a two-hybrid approach, we show that SAPK/JNK stimulates c-Jun transactivation in yeast and that this depends on both catalytic activity and physical interaction between the kinase and its substrate. Furthermore, c-Jun is active when tethered to DNA via SAPK/JNK, demonstrating that kinase binding does not preclude transactivation. Taken together, these results suggest that SAPK/JNK acts primarily as a positive regulator of c-Jun transactivation in situ, and that loss of the docking site physically uncouples v-Jun from this control. This loss-of-function model accounts for the deficit of v-Jun regulatory phosphorylation and repression of TPA response element (TRE)-dependent transcription observed in v-Jun-transformed cells and predicts that an important property of the oncoprotein is to antagonise SAPK/JNK-dependent gene expression.
May
G H
GH
Beatson Institute for Cancer Research, Cancer Research Campaign Beatson Laboratories, Garscube Estate Switchback Road, Bearsden, Glasgow, G61 1BD, UK.
Funk
M
M
Black
E J
EJ
Clark
W
W
Hussain
S
S
Woodgett
J R
JR
Gillespie
D A
DA
D000818:Animals; D005786:Gene Expression Regulation; D006801:Humans; D048291:Mitogen-Activated Protein Kinase 12; D020928:Mitogen-Activated Protein Kinases; D009154:Mutation; D016759:Oncogene Protein p65(gag-jun) / Q000235:genetics / Q000378:metabolism*; D009857:Oncogenes; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins; D015398:Signal Transduction
D016759:Oncogene Protein p65(gag-jun); D011993:Recombinant Fusion Proteins; D011494:Protein Kinases; D048291:Mitogen-Activated Protein Kinase 12; D020928:Mitogen-Activated Protein Kinases