Phorbol Ester Enhances KAI1 Transcription by Recruiting

Down-regulation of the KAI1 (CD82) metastasis suppressor is common in advanced human cancer, but underlying mechanism(s) regulating KAI1 expression are only now being elucidated. Recent data provide evidence that low levels of KAI1 mRNA in LNCaP cells are caused by binding of β-catenin/Reptin complexes to a specific motif in the proximal promoter, which prevents binding of Tip60/Pontin activator complexes to the same motif, thus inhibiting transcription. Here, we explored a pathway by which phorbol 12-myristate 13-acetate (PMA) up-regulates KAI1 tran- scriptionin LNCaPprostate cancercells. Pretreatment with specific inhibitors showedthat induction of KAI1by PMA uses classic isoforms of protein kinase C (cPKC), is independent of Ras and Raf, and requires activation of MEK1/2 and ERK1/2, but does not involve p38MAPK. Induction of KAI1 transcription by PMA was associated with enhanced overall acetylation of histones H3 and H4, but only acetylation of H3 was blocked by a PKC inhibitor. Chromatin im- munoprecipitation showed that PMA induces recruitment of Tip60/Pontin activator complexes to NFκB-p50 motifs in the proximal promoter, and this was blocked by a PKC inhibitor. These changes were not associated with differ- ences in overall levels of Tip60, Pontin, β-catenin, or Reptin protein expression but with PMA-induced nuclear trans- location of Tip60.