Acetylation of KLF5 alters the assembly of p15 transcription factors in transforming growth factor-beta-mediated induction in epithelial cells.

KLF5 plays important roles in a variety of cellular processes including proliferation and differentiation. Recently KLF5 was shown to reverse its function in proliferative and p15 regulation upon transforming growth factor-beta (TGFbeta)-mediated acetylation. To understand how KLF5 acetylation functions in TGFbeta-induced p15 transcription, we characterized the interactions of KLF5 with other transcription factors and promoter DNA elements in the context of TGFbeta. KLF5 interacted with Smad2-4 and Miz-1 in a TGFbeta-independent manner, but interacted with Myc only when TGFbeta was activated, and at least some of the interactions had an additive effect on TGFbeta-induced p15 transcription. Oligo pulldown assays showed that binding of Myc to the Inr element was KLF5-dependent, and TGFbeta could enhance the binding when more KLF5 was available. Furthermore, TGFbeta induced an interaction between KLF5 and the p300 acetylase, and acetylation of KLF5 was necessary for Smad4 to associate with p300. Failure in KLF5 acetylation not only prevented p300-assembled Smad4-KLF5 complex formation on p15 promoter but also affected the binding of Smad4 and FOXO3 on the p15 promoter in vivo. These findings suggest that without TGFbeta, some KLF5 associates with Smads in the nucleus and other KLF5 associates with Miz-1 on the p15 promoter to repress its transcription. Activation of TGFbeta recruits p300 to the KLF5-Smad complex to acetylate KLF5, and the complex with acetylated KLF5 binds to the Smad binding element and alters the binding of other factors to p15 promoter to induce its transcription.