WT1 Promoter Research Articles

Regulation of WT1 by phosphorylation: inhibition of DNA binding, alteration of transcriptional activity and cellular translocation.

Phosphorylation is one of the major post-translational mechanisms by which the activity of transcription factors is regulated. We have investigated the role of phosphorylation in the regulation of nucleic acid binding activity and the nuclear translocation of WT1. Two recombinant WT1 proteins containing the DNA binding domain with or without a three amino acid (KTS) insertion (WT1ZF + KTS and WT1ZF - KTS) were strongly phosphorylated by protein kinase A (PKA) and protein kinase C (PKC) in vitro. Both PKA and PKC phosphorylation inhibited the ability of WT1ZF + KTS or WT1ZF - KTS to bind to a sequence derived from the WT1 promoter region in gel mobility shift assays. The binding of WT1ZF - KTS to an EGR1 consensus binding site was also inhibited by prior PKA and PKC phosphorylation. We also demonstrate the RNA binding activity of WT1, but this was not altered by phosphorylation. PKA activation by dibutyryl cAMP in WT1-transfected cells resulted in the reversal of WT1 suppression of a reporter construct. Although WT1 protein is predominantly localized to the nucleus, this expression pattern is altered upon PKA activation, resulting in the cytoplasmic retention of WT1. Accordingly, phosphorylation may play a role in modulating the transcriptional regulatory activity of WT1 through interference with nuclear translocation, as well as by inhibition of WT1 DNA binding.

PAX8-mediated activation of the wt1 tumor suppressor gene.

The developing renal system has long been exploited to study the regulation of gene expression during mesenchymal-epithelial transitions. Several transcription factors, including WT1 and PAX8, are expressed early in nephrogenesis and play a key role in this process. The expression of PAX8 occurs in the induced mesenchyme of the developing kidney prior to the upregulation of WT1 levels in the same cells. In this report, we assessed whether the Pax-8 gene product resides upstream of wt1 in a common regulatory pathway. Transfection studies, as well as gel-shift assays, indicate that PAX8 transactivates wt1 through elements within a 38 bp conserved motif, present in human and murine promoters. Two PAX8 isoforms, generated by alternative splicing at the C-terminus and previously thought to lack transactivation potential, were found to be capable of activating wt1 expression. We also demonstrate that the endogenous wt1 promoter can be upregulated by exogenously supplied PAX8, suggesting that a function of PAX8 during mesenchymal--epithelial cell transition in renal development is to induce wt1 gene expression.

Differential Function of Wilms Tumor Gene WT1 Splice Isoforms in Transcriptional Regulation

The Wilms' tumor gene, WT1, encodes a zinc finger transcription factor that can repress transcription of a number of genes. WT1 mRNA undergoes alternative splicing at two locations, yielding four different mRNA species and protein products. One alternative splice alters the zinc finger region of WT1, resulting in the addition of three amino acids, Lys-Thr-Ser (KTS), between zinc fingers 3 and 4, altering the binding of WT1 to DNA. Here, we show that the WT1 protein with and without the KTS tripeptide can repress transcription from the human full-length WT1 promoter. Repression of transcription by WT1 has been shown to require two WT1 binding sites. We examined WT1 repression of the human minimal WT1 promoter, which contains two potential WT1 binding motifs. WT1 lacking the KTS tripeptide (WT1-KTS) was unable to repress transcription from a minimal WT1 promoter of 104 base pairs, whereas WT1 containing the KTS tripeptide (WT1+KTS) repressed transcription from the minimal promoter. The ability of WT1+KTS to repress transcription where WT1-KTS could not provided a functional assay to define differential WT1 binding motifs based on the presence or the absence of the KTS tripeptides. We present data defining the differential consensus DNA binding motifs for WT1-KTS and WT1+KTS. We demonstrate that WT1 zinc finger 1 plays a role in the differential DNA binding specificity of WT1-KTS and WT1+KTS.

Effects of Transfected Human and Mouse SRY/Sry Genes upon the Expression of Hypothetical SRY-Cascade Genes in Cultured Mouse Sertoli Cell Line, TM-4.

In mammals, the SRY (the sex determining region on the Y; Sry in the mouse) gene is responsible for the function of TDF (testis determining factor; Tdy in the mouse) locus, and plays a key role in the sex determination. In the mouse, the Sry open reading frame (ORF) is flanked at either end by a large inverted repeat, causing the formation of untranslatable circular transcripts; the linear transcripts have so far been known to be expressed only in the genital ridge between 10.5 and 12.5 d.p.c. In past attempts to examine the effects of expression of Sry exogenously introduced into cultured cells, the transfected Sry generated only the circular transcripts. In our experiments, cells from a cultured mouse Sertoli cell line, TM-4, which do not express endogenous Sry, were transfected with either human SRY or mouse Sry DNA where the inverted repeats responsible for the formation of circular transcripts were deleted. The expression of linear Sry transcripts was confirmed in the Sry-transfected TM-4 cell lines (TMHm series). Curiously, in TMHm cells, the gene coding for P450 aromatase (P450arom) was expressed, while P450arom was not expressed in the non-transfected TM-4 cells. No expression of P450arom was induced in the TM-4 cells transfected with the human SRY (hSRY) DNA. Although WT-1 promoter has been shown to possess a SRY binding motif, no evidence for the Sry- or hSRY-induced WT-1 expression was obtained in the transfected cell lines of either TMHm or TMHh series. MIS, another putative target gene of Sry, is expressed in non-transfected TM-4 cells, confirming the previous reports indicating that Sry expression is not a prerequisite for the MIS expression.

Transcriptional Silencer of the Wilms' Tumor Gene WT1 Contains an Alu Repeat

Expression of the Wilms' tumor gene WT1 is tightly regulated throughout development. In contrast, the WT1 promoter is promiscuous, functioning in all cell lines tested. We have cloned a transcriptional silencer that is involved in regulation of the WT1 gene. The transcriptional silencer is located in the third intron of the WT1 gene, approximately 12 kilobases from the promoter, and functions to repress transcription from the WT1 promoter in cell lines of non-renal origin. The 460-base pair silencer region is unusual in that it contains a full-length Alu repeat. We have also cloned an enhancer like-element located 1.3 kilobases upstream of the WT1 promoter.

Autoregulation of the human WT1 gene promoter

The human Wilms tumour suppressor gene, WT1, encodes a zinc-finger protein which can function as a transcriptional activator or suppressor. This study reports the analysis of the human WT1 gene promoter, and demonstrates that high levels of WT1 expression lead to autosuppression of the WT1 promoter. Deletion analyses of the promoter region implicate sequences 5′ and 3′ of the transcriptional start site as being crucial in WT1 autosuppression. Loss or alteration of this function of WT1 may be important in tumourigenesis.

Transcriptional regulation of the human Wilms' tumor gene (WT1). Cell type-specific enhancer and promiscuous promoter.

The Wilms' tumor gene, WT1, is expressed in few tissues, mainly the developing kidney, genitourinary system, and mesothelium, and in immature hematopoietic cells. To develop an understanding of the role of WT1 in development and tumorigenesis, we have identified transcriptional regulatory elements that function in transient reporter gene constructs transfected into kidney and hematopoietic cell lines. We found three transcription start sites of the WT1 gene and have identified an essential promoter region by deletion analysis. The WT1 promoter is a member of the GC-rich, TATA-less, and CCAAT-less class of polymerase II promoters. Whereas the WT1 promoter is similar to other tumor suppressor gene promoters, the WT1 expression pattern (unlike Rb and p53) is tissue-restricted. The WT1 GC-rich promoter is promiscuous, functioning in all cell lines tested, independent of WT1 expression. This finding suggests that the promoter is not tissue-specific, but that tissue-specific expression of WT1 is modulated by additional regulatory elements. Indeed, we have identified a transcriptional enhancer located 3' of the WT1 gene > 50 kilobases downstream from the promoter. This orientation-independent enhancer increases the basal transcription rate of the WT1 promoter in the human erythroleukemia cell line K562, but not in any of the other cell lines tested.

The Wilms' tumor suppressor gene WT1 is negatively autoregulated.

The Wilms' tumor suppressor gene WT1 encodes a zinc-finger DNA-binding protein that functions as a transcriptional repressor. WT1 is expressed in a dramatic spatial and temporal pattern during kidney development and is thought to be critical during mesenchymal-epithelial conversion. The WT1 protein bound multiple sites in the WT1 promoter and functioned as a powerful transcriptional repressor of its gene in vivo (> 50-fold). The WT1 protein carrying an NH2-terminal 17-amino acid insertion and a 3-amino acid insertion (KTS) between zinc fingers 3 and 4, arising from the most abundant of four alternatively spliced transcripts, was the most powerful repressor. Of importance, a subset of WT1-binding sites differs from the Egr-1 consensus sequence, which has been shown to bind one splice variant of the WT1 protein (WT1(-KTS)). We characterized two of these sites and show that they bind both -KTS and +KTS forms of the WT1 zinc-finger protein and can confer repression on a heterologous promoter construct. Our data demonstrate that WT1, in addition to its known effects on insulin-like growth factor II, platelet-derived growth factor A, and Pax-2 transcription, is a powerful repressor of its own gene. These observations emphasize its critical role as a transcriptional regulatory protein during normal kidney development.

Sequence of the WT1 Upstream Region Including the Wit-1 Gene

The Wilms tumor gene WT1 encodes a Cys2His2-type zinc finger protein that can bind DNA and function as a transcriptional regulator. The pathological spectrum of tumorigenesis and various developmental defects produced by different WT1 alterations suggests that WT1 controls a number of subsequent effector genes. To define the role of WT1 in these developmental processes it will be important to elucidate mechanisms that govern expression of WT1 itself. To facilitate mapping of the WT1 promoter region and 5′ control elements we have determined the sequence upstream of the WT1 transcription unit. This includes the Wit-1 gene that is transcribed in the opposite direction.