Phorbol esters stimulate the phosphorylation of c-Jun but not v-Jun: Regulation by the N-terminal δ domain

Victor Adler, Christopher C. Franklin, Andrew S. Kraft

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156 Scopus citations


c-Jun and its oncogenic counterpart v-Jun are completely conserved within the region from Ser-63 to Ser-73; these serines are sites for phorbol ester-inducible c-Jun phosphorylation. Using a U937 human leukemic cell line stably expressing v-Jun, we have demonstrated that phorbol esters stimulate the in vivo phosphorylation of c-Jun but not v-Jun. We developed an in vitro protein kinase assay to characterize the c-Jun protein kinase and to examine the determinants underlying this differential phosphorylation. Fusion proteins between glutathione S-transferase and the N terminus of c-Jun, v-Jun, or several c-Jun mutants were used as substrates. A c-Jun kinase activity was affinity-purified 5000-fold by using glutathione S-transferase - c-Jun-glutathione-Sepharose beads and was found to phosphorylate the N terminus of c-Jun but not v-Jun or c-Jun containing a 27-amino acid N-terminal deletion found in v-Jun. These effects were also observed in vivo as phorbol 12-myristate 13-acetate did not induce the phosphorylation of v-Jun or the c-Jun deletion mutant in U937 cell lines stably expressing these proteins. These findings indicate that the δ domain of c-Jun (amino acids 34-60), which is deleted in v-Jun, plays a critical role in regulating N-terminal c-Jun phosphorylation.

Original languageEnglish (US)
Pages (from-to)5341-5345
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number12
StatePublished - 1992

ASJC Scopus subject areas

  • General


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