A Novel Zinc Finger Transcription Factor with Two Isoforms That Are Differentially Repressed by Estrogen Receptor-α

Abstract

Estrogen receptor-␣ (ER␣) can induce the expression of genes in response to estrogen by binding to estrogen response elements in the promoters of target genes. There is growing evidence that ER␣ can alter patterns of gene expression in response to ligand by regulating the activity of other factors through a direct proteinprotein interaction. To identify other factors that are regulated by ER␣, a yeast two-hybrid screen was performed that identified a novel Cys 2 His 2 zinc finger protein named ZER6. The ZER6 protein contains a Kruppelassociated box domain and six Cys 2 His 2 zinc fingers. Transcripts from the ZER6 gene can have alternate 5 exons and encode either a p71 or p52 isoform. The p52-ZER6 protein interacts strongly with ER␣ in the presence of 17␤-estradiol, whereas the p71-ZER6 isoform has a HUB-1 amino-terminal domain that inhibits the interaction with ER␣. A consensus ZER6 binding element was defined using PCR-assisted binding site selection. In COS-1 cells, both the p52 and p71 isoforms can activate transcription through the ZER6 binding element; however, in the presence of ER␣, transactivation by the p52 isoform is specifically repressed. Overexpression of the p52 isoform was able to abrogate activation by p71-ZER6. Expression of ZER6 was largely restricted to the mammary gland with a lower level of expression in the kidney. We conclude that ZER6 is a novel zinc finger transcription factor in which regulation of transcription in hormone-responsive cells can be controlled by the relative level of expression of two distinct isoforms. Two human estrogen receptors (ERs)1 have been identified: ER␣ and ER␤ (1-4). These nuclear receptors are members of the steroid-thyroid-retinoic acid superfamily of transcription factors (5). In the classic model of transactivation by the receptor, ligand-activated ER␣ forms a homodimer, which is able to bind specific DNA regulatory sequences in the promoters of ER␣ target genes called estrogen response elements (6). This mechanism of transactivation by ER␣ induces the expression of a set of target genes in hormone-responsive tissues and tumors. Several ER␣ target genes have been described in hormoneresponsive breast tumors including progesterone receptor (7), pS2(8), transforming growth factor-␣ (9), cathepsin D (10), HSP27(11), and GREB1(12). The promoters of these genes are directly activated by ER␣, and induction of target gene expression is dependent upon the ability of ER␣ to bind to DNA.Over the past several years, data have been accumulating demonstrating that ER␣ can alter the expression of genes independent of direct DNA binding. One mechanism that has been proposed is through the ability of ER␣ to regulate the activity of other nuclear transcription factors by mechanisms involving direct protein-protein interactions. In many cases the interactions between ER␣ and other nuclear factors have been shown to be ligand-dependent. One example of this alternate mechanism of gene regulation is the effect of ER␣ on expression of genes regulated by AP1(13). ER␣ and ER␤ ha...

SUMOylation of ZFP282 potentiates its positive effect on estrogen signaling in breast tumorigenesis

“…Similarly, another Krüppel type zinc finger protein ZBP-89 has been shown to compete with Sp1 for DNA binding and oppose transcriptional activation by Sp1 but also has been shown to function as a modest activator in the absence of Sp1 14 . ZFP398, a paralog of ZFP282, was also shown to modestly activate U5RE-like element-driven reporter expression 15 . Thus, although on its own ZFP282 appears to be a weak activator, it has the capacity to exert quite substantial effects on U5RE-mediated transcriptional activation when it is SUMOylated and complexed with CoCoA (Figures S4 and S8).…”

Identification of the DNA Binding Element of the Human ZNF333 Protein

“…Most DNA-binding consensus sequences of zinc finger protein are GC-rich (Conroy et al, 2002;Peng et al, 2002;Tanaka et al, 2002;Chrisman et al, 2003), and the majority of housekeeping genes have high GC content, so the target genes of such zinc finger protein are also presumed to be housekeeping genes. In our study, the specific binding sequence of ZNF333 is not GC-rich, which means that the target genes of ZNF333 may be not housekeeping genes.…”

Deep Vertebrate Roots for Mammalian Zinc Finger Transcription Factor Subfamilies

“…Notably, the subset that is deeply conserved includes only three KRAB-ZNF genes, all of which map to a single familial cluster. These ancient genes share certain features that are unusual in mammalian genomes, including a noncanonical KRAB domain sequence that does not bind KAP1 and functions as a transcriptional activator (Okumura et al 1997; Conroy et al 2002). These and other findings suggest a history in which the KRAB-ZNF proteins expanded and diverged independently in every vertebrate lineage including amphibians, where they expanded without KAP1-interacting capabilities, very possibly as activating TFs.…”