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

摘要

The role of non-Smad proteins in the regulation of transforming growth factor-β (TGFβ) signaling is an emerging line of active investigation. Here, we characterize the role of KLF14, as a TGFβ-inducible, non-Smad protein that silences the TGFβ receptor II (TGFβRII) promoter. Together with endocytosis, transcriptional silencing is a critical mechanism for down-regulating TGFβ 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 TGFβ inducibility, its ability to regulate the TGFβRII promoter, and the fact that this protein had yet to be functionally characterized. We find that KLF14 represses the TGFβRII, a function that is augmented by TGFβ treatment. Mapping of the TGFβRII 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 TGFβRII promoter via a co-repressor complex containing mSin3A and HDAC2. Furthermore, the TGFβ pathway activation leads to recruitment of a KLF14-mSin3A-HDAC2 repressor complex to the TGFβRII 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 TGFβRII activation at the cell surface induces the expression of KLF14 to ultimately silence the TGFβRII and further expand the network of non-Smad transcription factors that participate in the TGFβ pathway.