Ligand-dependent corepressor contributes to transcriptional repression by C2H2 zinc-finger transcription factor ZBRK1 through association with KRAB-associated protein-1

Abstract

We identified a novel interaction between ligand-dependent corepressor (LCoR) and the corepressor KRAB-associated protein-1 (KAP-1). The two form a complex with C2H2 zinc-finger transcription factor ZBRK1 on an intronic binding site in the growth arrest and DNA-damage-inducible α (GADD45A) gene and a novel site in the fibroblast growth factor 2 (FGF2) gene. Chromatin at both sites is enriched for histone methyltransferase SETDB1 and histone 3 lysine 9 trimethylation, a repressive epigenetic mark. Depletion of ZBRK1, KAP-1 or LCoR led to elevated GADD45A and FGF2 expression in malignant and non-malignant breast epithelial cells, and caused apoptotic death. Loss of viability could be rescued by simultaneous knockdowns of FGF2 and transcriptional coregulators or by blocking FGF2 function. FGF2 was not concurrently expressed with any of the transcriptional coregulators in breast malignancies, suggesting an inverse correlation between their expression patterns. We propose that ZBRK1, KAP-1 and LCoR form a transcriptional complex that silences gene expression, in particular FGF2, which maintains breast cell viability. Given the broad expression patterns of both LCoR and KAP-1 during development and in the adult, this complex may have several regulatory functions that extend beyond cell survival, mediated by interactions with ZBRK1 or other C2H2 zinc-finger proteins.

Mblk-1 Transcription Factor Family: Its Roles in Various Animals and Regulation by NOL4 Splice Variants in Mammals

“…LCoR ablation in cultured cells by siRNA expression caused increased expression of some ERα-target genes such as IGFBP1, but it also caused decrease (e.g., CYP26B1) or had no effect (e.g., pS2) on several target genes [43]. These observations suggest that the role of LCoR on transcription activity is different from gene to gene.…”

Complex regulation of LCoR signaling in breast cancer cells

“… 5 LCoR corepressor functions are not specific to members of the nuclear receptor family because it also interacts with other transcription factors, such as Kruppel-like factor 6 7 and KRAB-associated protein 1. 8 Moreover, LCoR is a component of a CoREST-CtBP complex that contains the histone H3 demethylase LSD1. 9 LCoR also contributes to cell type-dependent and Kruppel-like factor 6-mediated transcriptional repression of the CDKN1A gene that encodes the cell cycle regulator p21 WAF1/CIP1 .…”

ZBRK1, a novel tumor suppressor, activates VHL gene transcription through formation of a complex with VHL and p300 in renal cancer

“…Western blot analysis on the endogenous expression of ZBRK1 and VHL also confirmed that VHL was decreased in the ZBRK1 knockdown cells (Figure 5D). Given that ZBRK1 generally functions as a transcriptional repressor through association with co-repressor proteins, including KAP1 and BRCA1 [11, 12, 20, 21], we sought to determine whether ZBRK1 regulates the expression of VHL dependent on KAP1 and BRCA1. Treatment of ACHN cells by lentiviral transfer of KAP1 -specific shRNA or BRCA1 -specific shRNA depleted endogenous KAP1 or BRCA1, respectively (Supplementary Figure S4A and B).…”

“…Of note, the KRAB and CTRD domains are transcriptional repression domains located in the N- and C-terminal of ZBRK1, respectively [11]. The KRAB domain silences gene expression via recruitment of transcriptional repressor including KAP-1/KRIP-1/TIFb co-repressor [15, 21] and CTRD domain has been shown to be responsible for recruiting both homotypic and heterotypic proteins on ZBRK1 DNA consensus motifs and thus facilitating ZBRK1-directed transcriptional regulation [25]. Besides its canonical function as E3-ubiquitin ligase, VHL also behaves as a cofactor of p53 by recruiting p300 [22].…”