TI  - Activation of <prot>protein kinase C</prot> decreases phosphorylation of <prot>c-Jun</prot> at sites
      that negatively regulate its DNA-binding activity.
PG  - 573-84
AB  - In resting human epithelial and fibroblastic cells,  <prot>c-Jun</prot>  is
      phosphorylated on serine and threonine at five sites, three of which are
      phosphorylated in vitro by  <prot>glycogen synthase kinase 3</prot> (<prot>GSK-3</prot>) . These three
      sites are nested within a single tryptic peptide located just upstream of
      the basic region of the <prot>c-Jun</prot> DNA-binding domain (residues 227-252).
      Activation of <prot>protein kinase C</prot> results in rapid, site-specific
      dephosphorylation of  <prot>c-Jun</prot>  at one or more of these three sites and is
      coincident with increased  <prot>AP-1</prot> -binding activity. Phosphorylation of
      recombinant human  <prot>c-Jun</prot>  proteins in vitro by  <prot>GSK-3</prot>  decreases their
      DNA-binding activity. Mutation of serine 243 to phenylalanine blocks
      phosphorylation of all three sites in vivo and increases the inherent
      trans-activation ability of <prot>c-Jun</prot> at least 10-fold. We propose that <prot>c-Jun</prot>
      is present in resting cells in a latent, phosphorylated form that can be
      activated by site-specific dephosphorylation in response to <prot>protein kinase
      C</prot> activation.
AD  - Molecular Biology and Virology Laboratory, Salk Institute, La Jolla,
