Regulation of ornithine decarboxylase gene expression by the Wilms' tumor suppressor WT1

Abstract

The importance of ornithine decarboxylase (ODC) to cell proliferation is underscored by the complex array of cell-specific mechanisms invoked to regulate its synthesis and activity. Misregulation of ODC has severe negative consequences on normal cell function, including the acquisition of tumorigenic growth properties by cells overexpressing ODC. We hypothesize that ODC gene expression is a candidate target for the anti-proliferative function of certain tumor suppressors. Here we show that the Wilms' tumor suppressor WT1 binds to multiple sites within the human ODC promoter, as determined by DNase I protection and methylation interference assays. The expression of WT1 in transfected HCT 116, NIH/3T3 and HepG2 cells represses activity of the ODC promoter controlling expression of a luciferase reporter gene. In contrast WT1 expression enhances ODC promoter activity in SV40-transfected HepG2 cells. Both the extent of modulation of ODC gene expression and the mediating WT1 binding elements are cell specific. Constructs expressing WT1 deletion mutants implicate two regions required for repressor function, as well as an intrinsic activation domain. Understanding the regulation of ODC gene expression by WT1 may provide valuable insights into the roles of both WT1 and ODC in development and tumorigenesis.

Wnt-4 regulation by the Wilms' tumour suppressor gene, WT1

“…The ornithine decarboxylase (ODC) gene was weakly expressed (ODC was only detectable on the WT array after extensive exposure, see Figure 2b) and downregulated in C2A on both arrays. This ®nding was essentially contrary to previous ®ndings from in vitro analyses suggesting repression of ODC by WT1 (Moshier et al, 1996;Li et al, 1999), but the change was less than twofold and in some instances WT1 can activate ODC (Moshier et al, 1996;Li et al, 1999). The sensitivity of the Wilms' tumour array should be questioned as murine WT1 failed to be detected in either the parental cell line or the C2A transfectant.…”

Assessment by Molecular Dynamics Simulations of the Structural Determinants of DNA-binding Specificity for Transcription Factor Sp1

“…78 Examination of the sequence of the four zinc fingers of this transcription factor (Figure 1) and consideration of their amino acid specificity according to the rules discussed above (Figure 6) suggest that WT1 can bind to the 5 0 -GCG TGG GCT GAG-3 0 sequence overlapping the EGR1 binding sequence in the mdr1 promoter (Figure 2) that is responsive to TPA, as well as the Sp1-binding site that is partly responsible for activation by UV-irradiation. 30 Overlapping EGR1/Sp1/WT1 or EGR1/Sp1 sites similar to those described here for the mdr1 promoter have been shown to be involved in the regulation of genes encoding, for example, adenosine deaminase (in which Sp1 acts as an activator and EGR1 acts as a repressor), 79 tyrosine hydroxylase, 80 human tumor necrosis factor, 81 tumor growth factor, 82 ornithine decarboxylase, 83 and platelet-derived growth factor A-chain (PDGF-A) 84 and B-chain (PDGF-B). 85 In this latter case, Sp1 has been shown to be bound to the promoter in unstimulated cells and to be displaced by EGR1 in a dose-dependent manner in response to vascular injury.…”

Anlaysis of complementary expression profiles following WT1 induction versus repression reveals the cholesterol/fatty acid synthetic pathways as a possible major target of WT1

“…Although c-myc has previously been shown to be repressed by WT1 (Hewitt et al, 1995), studies have shown that WT1 can either activate or repress GC-rich promoter reporters, depending on experimental conditions (Reddy et al, 1995a). In fact, WT1-A has been reported to activate or repress the ODC promoter depending on the cell line used (Moshier et al, 1996;Li et al, 1999). Amphiregulin and podocalyxin, both recently identified as WT1 target genes (Lee et al, 1999;Palmer et al, 2001), were not present on either the OCI or SRC arrays.…”