TI  - Phosphorylation of  <prot>c-jun</prot>  mediated by  MAP kinases .
PG  - 670-4
AB  - The proto-oncogene <prot>c-jun</prot> is a component of the <prot>AP-1</prot> transcription factor
      family involved in the mediation of nuclear events elicited by
      extracellular stimuli. The <prot>c-jun</prot> protein is negatively regulated by
      phosphorylation of residues near the carboxy terminus which are
      dephosphorylated in response to phorbol esters. Here we identify two
      serine residues in the amino terminal A1 transactivation domain which are
      phosphorylated in response to a variety of mitogens, phorbol esters and
      activated <prot>ras</prot>. We present evidence that  <prot>mitogen-activated protein-serine
      (MAP) kinases</prot>  (<prot>pp54</prot> and <prot>pp42</prot>/44) specifically phosphorylate these sites
      and that their phosphorylation positively regulates the transacting
      activity of  <prot>c-jun</prot> . The <prot>MAP kinase</prot> enzymes <prot>pp54</prot> and <prot>pp42</prot>/44 are regulated
      by tyrosine as well as serine/threonine phosphorylation.  <prot>MAP kinase</prot> 
      activation of  <prot>c-jun</prot>  may underlie the common stimulation of this
      transcription factor by mitogens, growth factors and oncogenes.
AD  - Ludwig Institute for Cancer Research, London, UK.
