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. Author manuscript; available in PMC: 2008 Feb 12.

Published in final edited form as: Cancer Res. 2006 Jun 1;66(11):5729–5736. doi: 10.1158/0008-5472.CAN-05-4466

CSK-mediated c-Jun phosphorylation promotes c-Jun degradation. A, in vitro ubiquitination assay for GST wild type c-Jun or GST c-Jun double mutant (YY26, 170FF). B, the level of phosphorylated tyrosine was much higher in CSK^+/+ cells than in CSK^−/− cells and the total amount of c-Jun protein was also higher in CSK^−/− cells than in CSK^+/+ cells. Ubiquitination of c-Jun was stronger in CSK^+/+ cells than in CSK^−/− cells. C, stability of c-Jun was analyzed in CSK^+/+ cells or CSK^−/− cells at indicated time points by immunoblotting after addition of cycloheximide. D, stability of c-Jun in CSK^+/+ cells or CSK^−/− cells was analyzed by pulse-chase experiments. E, schematic illustration of the regulation of c-Jun ubiquitination. Under normal growth conditions, CSK phosphorylates c-Jun, which promotes ubiquitin-dependent degradation of c-Jun, resulting in a decrease in AP-1 activity. In contrast, with EGF stimulation, CSK is inhibited and c-Jun is activated by phosphorylation by MAP kinases, which inhibits ubiquitin-dependent degradation of c-Jun, resulting in an increased AP-1 activity.

CSK-mediated c-Jun phosphorylation promotes c-Jun degradation. A, in vitro ubiquitination assay for GST wild type c-Jun or GST c-Jun double mutant (YY26, 170FF). B, the level of phosphorylated tyrosine was much higher in CSK^+/+ cells than in CSK^−/− cells and the total amount of c-Jun protein was also higher in CSK^−/− cells than in CSK^+/+ cells. Ubiquitination of c-Jun was stronger in CSK^+/+ cells than in CSK^−/− cells. C, stability of c-Jun was analyzed in CSK^+/+ cells or CSK^−/− cells at indicated time points by immunoblotting after addition of cycloheximide. D, stability of c-Jun in CSK^+/+ cells or CSK^−/− cells was analyzed by pulse-chase experiments. E, schematic illustration of the regulation of c-Jun ubiquitination. Under normal growth conditions, CSK phosphorylates c-Jun, which promotes ubiquitin-dependent degradation of c-Jun, resulting in a decrease in AP-1 activity. In contrast, with EGF stimulation, CSK is inhibited and c-Jun is activated by phosphorylation by MAP kinases, which inhibits ubiquitin-dependent degradation of c-Jun, resulting in an increased AP-1 activity.