DOMINANT-NEGATIVE MUTANTS OF CJUN INHIBIT AP-1 ACTIVITY THROUGH MULTIPLE MECHANISMS AND WITH DIFFERENT POTENCIES

We have previously described a dominant-negative mutant of cJun that l acks the transactivation domain (TAD) of cJun and prevents AP-1-mediat ed transcriptional activation by quenching endogenous Jun or Fos prote ins, We now report the development of a panel of cJun mutants that hav e inactivating mutations in the TAD, DNA-binding domain (DBD), or leuc ine zipper domain, These mutants are all unable to activate transcript ion, but only TAD and DBD mutants function in a dominant-negative fash ion by inhibiting both cJun-induced transcriptional activation and tra nsformation induced by the tumor promoter 12-O-tetradecanoylphorbol-13 -acetate in ras-transfected rat embryo cells, Although the TAD and DBD mutants both function as transdominant inhibitors, they work through different mechanisms and with different inhibitory potencies, The DBD mutants, which function by inhibiting DNA binding, are relatively weak inhibitors, whereas the TAD mutants inhibit by quenching and are much more potent, Dimerization assays demonstrate that mutations in the DB D decrease the dimerization affinity of these mutants with cJun, These results demonstrate that the most potent dominant-negative mutants of cJun are proteins that have intact DBDs and quench the activity of th e endogenous transcription factors.