c-Jun phosphorylation in signal transduction and gene regulation

This study analyzed the post-translational regulation of the transcription factor AP-1 on the level of c-Jun phosphorylation. For this purpose a new assay system employing a histidine-tag method of transient expression and rapid purification of recombinant c-Jun, in conjunction with "southwestern" blotting and in situ phosphatase treatment, was developed. It is demonstrated that the specific DNA-binding potential of c-Jun which is dependent on dephosphorylation can be modulated both by extracellular and endogenous factors. Exposure of cells to phorbol esters as well as artificially increasing the intracellular concentration of AP-1 target sites can stimulate the DNA-binding function of c-Jun. These results indicate the existence of a novel cellular mechanism that serves to dynamically adjust the activity of c-Jun to the number of accessible responsive genes.