Silencing of the Transforming Growth Factor-β (TGFβ) Receptor II by Kruppel-like Factor 14 Underscores the Importance of a Negative Feedback Mechanism in TGFβ Signaling

The role of non-Smad proteins in the regulation of transforming growth factor-beta (TGF beta) signaling is an emerging line of active investigation. Here, we characterize the role of KLF14, as a TGF beta-inducible, non-Smad protein that silences the TGF beta receptor II ( TGF beta RII) promoter. Together with endocytosis, transcriptional silencing is a critical mechanism for down-regulating TGF beta receptors at the cell surface. However, the mechanisms underlying transcriptional repression of these receptors remain poorly understood. KLF14 has been chosen from a comprehensive screen of 24 members of the Sp/KLF family due to its TGF beta inducibility, its ability to regulate the TGF beta RII promoter, and the fact that this protein had yet to be functionally characterized. We find that KLF14 represses the TGF beta RII, a function that is augmented by TGF beta treatment. Mapping of the TGF beta RII promoter, in combination with site-directed mutagenesis, electromobility shift, and chromatin immunoprecipitation assays, have identified distinct GC-rich sequences used by KLF14 to regulate this promoter. Mechanistically, KLF14 represses the TGF beta RII promoter via a co-repressor complex containing mSin3A and HDAC2. Furthermore, the TGF beta pathway activation leads to recruitment of a KLF14-mSin3A-HDAC2 repressor complex to the TGF beta RII promoter, as well as the remodeling of chromatin to increase histone marks that associate with transcriptional silencing. Thus, these results describe a novel negative-feedback mechanism by which TGF beta RII activation at the cell surface induces the expression of KLF14 to ultimately silence the TGF beta RII and further expand the network of non-Smad transcription factors that participate in the TGF beta pathway.