title: TGF-beta regulates the expression of transcription factor KLF6 and its splice variants and promotes co-operative transactivation of common target genes through a Smad3-Sp1-KLF6 interaction.
abstract: KLF6 (Krüppel-like factor 6) is a transcription factor and tumour suppressor with a growing range of biological activities and transcriptional targets. Among these, KLF6 suppresses growth through transactivation of TGF-beta1 (transforming growth factor-beta1). KLF6 can be alternatively spliced, generating lower-molecular-mass isoforms that antagonize the full-length WT (wild-type) protein and promote growth. A key target gene of full-length KLF6 is endoglin, which is induced in vascular injury. Endoglin, a homodimeric cell membrane glycoprotein and TGF-beta auxiliary receptor, has a pro-angiogenic role in endothelial cells and is also involved in malignant progression. The aim of the present work was to explore the effect of TGF-beta on KLF6 expression and splicing, and to define the contribution of TGF-beta on promoters regulated by co-operation between KLF6 and Sp1 (specificity protein 1). Using co-transfection, co-immunoprecipitation and fluorescence resonance energy transfer, our data demonstrate that KLF6 co-operates with Sp1 in transcriptionally regulating KLF6-responsive genes and that this co-operation is further enhanced by TGF-beta1 through at least two mechanisms. First, in specific cell types, TGF-beta1 may decrease KLF6 alternative splicing, resulting in a net increase in full-length, growth-suppressive KLF6 activity. Secondly, KLF6-Sp1 co-operation is further enhanced by the TGF-beta-Smad (similar to mothers against decapentaplegic) pathway via the likely formation of a tripartite KLF6-Sp1-Smad3 complex in which KLF6 interacts indirectly with Smad3 through Sp1, which may serve as a bridging molecule to co-ordinate this interaction. These findings unveil a finely tuned network of interactions between KLF6, Sp1 and TGF-beta to regulate target genes.
authors.affiliation: Centro de Investigaciones Biológicas, CSIC (Consejo Superior de Investigaciones Científicas), 28040 Madrid, Spain. cibluisa@cib.csic.es
authors.forename: Luisa M
authors.initials: LM
authors.lastname: Botella
authors.forename: Francisco
authors.initials: F
authors.lastname: Sanz-Rodriguez
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Komi
authors.forename: Africa
authors.initials: A
authors.lastname: Fernandez-L
authors.forename: Elisa
authors.initials: E
authors.lastname: Varela
authors.forename: Eva M
authors.initials: EM
authors.lastname: Garrido-Martin
authors.forename: Goutham
authors.initials: G
authors.lastname: Narla
authors.forename: Scott L
authors.initials: SL
authors.lastname: Friedman
authors.forename: Soichi
authors.initials: S
authors.lastname: Kojima
mesh_terms: D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D003094:Collagen / Q000378:metabolism; D005434:Flow Cytometry; D031541:Fluorescence Resonance Energy Transfer; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D000075723:Kruppel-Like Factor 6; D051741:Kruppel-Like Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism*; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism*; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: C105465:KLF6 protein, human; D000075723:Kruppel-Like Factor 6; D051741:Kruppel-Like Transcription Factors; D011518:Proto-Oncogene Proteins; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D016329:Sp1 Transcription Factor; D016212:Transforming Growth Factor beta; D003094:Collagen