The Sp1-like Protein BTEB3 Inhibits Transcription via the Basic Transcription Element Box by Interacting with mSin3A and HDAC-1 Co-repressors and Competing with Sp1

Abstract

Sp1-like proteins are characterized by three conserved C-terminal zinc finger motifs that bind GC-rich sequences found in promoters of numerous genes essential for mammalian cell homeostasis. These proteins behave as transcriptional activators or repressors. Although significant information has been reported on the molecular mechanisms by which Sp1-like activators function, relatively little is known about mechanisms for repressor proteins. Here we report the functional characterization of BTEB3, a ubiquitously expressed Sp1-like transcriptional repressor. GAL4 assays show that the N terminus of BTEB3 contains regions that can act as direct repressor domains. Immunoprecipitation assays reveal that BTEB3 interacts with the co-repressor mSin3A and the histone deacetylase protein HDAC-1. Gel shift assays demonstrate that BTEB3 specifically binds the BTE site, a well characterized GC-rich DNA element, with an affinity similar to that of Sp1. Reporter and gel shift assays in Chinese hamster ovary cells show that BTEB3 can also mediate repression by competing with Sp1 for BTE binding. Thus, the characterization of this protein expands the repertoire of BTEB-like members of the Sp1 family involved in transcriptional repression. Furthermore, our results suggest a mechanism of repression for BTEB3 involving direct repression by the N terminus via interaction with mSin3A and HDAC-1 and competition with Sp1 via the DNA-binding domain.Sp1-like proteins, defined by the presence of three highly homologous C-terminal zinc finger motifs and variant N-terminal domains, are emerging as important regulators of cell homeostasis. Promoters containing Sp1-like sites are essential for the expression of numerous genes necessary for cell cycle progression (1-3), DNA synthesis (4), and other cell processes (5-8), and studies have shown that certain Sp1-like proteins induce apoptosis (9), cell growth inhibition (10 -12), differentiation (13, 14), and carcinogenesis (15). In addition, the disruption of some Sp1-like genes in mice shows that these proteins are critical for normal development (12, 16 -18). Thus, understanding how Sp1-like proteins bind DNA and regulate transcription is important to uncover the molecular mechanisms underlying a large number of cellular events.The existence of at least 17 different Sp1-like proteins offers a significant challenge for understanding how individual members regulate gene expression in a tissue-, cell-, and promoterspecific manner. One mechanism leading to specificity among Sp1-like proteins is a differential pattern of expression. For instance, Sp1, TIEG2, and BTEB1 1 are ubiquitously expressed, whereas the KLF proteins are restricted to certain tissues. Specificity among Sp1-like proteins is also dictated by recognition of DNA. For example, the Sp proteins preferentially bind GC sites (19,20) whereas the KLF subgroup prefers the CA site (21-23). Interestingly, co-expressed Sp1-like proteins exhibiting similar binding specificity, such as Sp1 and Sp3, but often display opposite transcriptional reg...

Histone Deacetylases Augment Cytokine Induction of the iNOS Gene

“…Only a few transcription factors have been found to interact with HDAC without intermediate coregulatory molecules. Retinoblastoma protein interacts directly with HDAC1 (41), and SP1 also interacts with HDAC2 (42). YY1-induced transcriptional repression is the result of direct interaction with HDAC2 (43).…”

Transcriptional Activity of Sp1 Is Regulated by Molecular Interactions between the Zinc Finger DNA Binding Domain and the Inhibitory Domain with Corepressors, and This Interaction Is Modulated by MEK

“…Although different corepressors are involved, Sp1-like transcription repressors like the BTEB-family and TIEG1-2 have been demonstrated to interact with another corepressor molecule, the mammalian Sin3A (mSin3A), via the Sin3-interacting domain (SID) (39,44,45). This interaction is important in the repression of transcription.…”

The mammalian zinc finger transcription factor Krüppel‐like factor 3 (KLF3/BKLF)

“…CtBP is known to interact with several additional cofactors to mediate gene repression (15). Group 3 KLFs, typified by KLF11 and KLF13, interact with Sin3 proteins, which in turn recruit a wide variety of cofactors, including histone deacetylases, histone methyltransferases, and chromatin remodeling enzymes (16)(17)(18)(19). Although these complexes can facilitate both gene activation and repression, their association with group 3 KLFs is generally described in the context of repression (20).…”