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Wilms’ tumor 1/Wilms’ tumor protein (Gene WT1) Homo sapiensThe WT1 gene (map locus 11p13) product, Wilms’ tumor-1/Wilms’ tumor protein, is a transcription factor that contains four EGR-family C2H2-type zinc-fingers at 323-347, 353-377, 383-405, and 414-438 and a 57 amino acid, proline-rich region (27-83), which recognizes and binds the DNA sequence 5'-CGCCCCCGC-3'. Wilms’ tumor protein exists as five isoforms which result from alternative splicing with Exon 5 (17AA coding) and Exon 9 (KTS coding), Haber DA, et al. (1991). Exon 5 and 9 splice variant mRNAs are expressed in fixed ratios during development, with +KTS being the dominant form, Haber DA, et al. (1991). Isoform 1 (17AA(+)/KTS(+); +/+) is 449 amino acids long (49.2 kDa). Isoform 2 (-/-), (429 AA) is missing two short sequences from 250-266 (-17AA) and 408-410 (-KTS). Isoform 3 (-/+) is missing the 250-266 (-17AA) sequence and isoform 4 (-KTS, +/-) (446AA) is missing the 408-410 (-KTS) sequence. Isoform 5 (497AA) contains an extended N-terminal sequence by the addition of 68 amino acids between the methionine and glycine of the N-terminal of isoform 2. The biological effects of WT1 depend upon sequence-specific features that are present or absent among the variant isoforms where the actual effect of WT1 in any tissue is dependent upon the ratio of the isoforms present. Broadly speaking, KTS exon 9 appears to modulate strength of DNA binding and interaction with mRNAs, factors involved with gene expression and translation; whereas, exon 5 is emerging as important for anti-apoptosis via the intrinsic (mitochondrial) pathway. The three amino acid sequence, KTS, exon 9, provides a spacer between the third and fourth zinc-fingers of WT1 that affects binding to the cognate site in the DNA major groove. Insertion of the KTS sequence reduces DNA binding stability, Laity JH, et al. (2000) but frees the fourth zinc-finger to interact with splice factors and RNA. Morrison AA, et al. (2006) demonstrated that WT1 (+KTS) could bind near the start codon of alpha-actinin 1 (ACTN1) mRNA. The expression of specific genes, both upregulated and down regulated by Wilms' tumor protein, has been linked to the exon 5 +/- ratio within Wilms’ tumor, Baudry D, et al. (2002). Wilms’ tumor is the most frequent kidney cancer in children. The WTI (-KTS) isoforms have been linked to genes and processes that promote tumor metastasis. WT1 (-KTS) variants are involved in regulation of p21(Waf1/Cip1) expression and suppression of lymph node metastasis in human lung squamous cell carcinoma, Moriya S, et al. (2008). WTI 17AA(-)/KTS(-) isoform induces morphological changes and promotes cell migration and invasion, in small-sized cell shape in TYK-nu.CP-r (TYK) ovarian cancer cells, Jomgeow T, et al. (2006). WT1 (-/-) isoform inhibits G1/S progression and accelerates G-CSF-mediated differentiation in 32D c13 cells, a murine myeloid progenitor cell line, Loeb, DM (2003). Burwell EA, et al. (2007) transfected the mammary epithelial line H16N-2, which normally does not express WT1, with WTI (-/-) and showed that this promoted the appearance of highly organized acinar cellular aggregates. Tranfection with WTI (+/+) induced an epithelial-mesenchymal transition (EMT) response. Presence of the 17AA region, exon 5 may confer anti-apoptotic feature on WT1. Wilms' tumor protein 1 (WT1) is essential for tumor cell proliferation and is highly expressed in various hematological and solid malignancies. The 17AA(+)(-KTS) WT1 (with exon 5) isoforms are emerging as anti-apoptotic, intrinsic (mitochondrial) pathway, mediators in various malignancies including gastric, lung, ovarian, TYKnuCPr cancers, fibrosarcoma and glioblastoma, Tatsumi N, et al. (2008). 17AA(+)(-KTS)WT1 isoform is anti-apoptotic in human primary leukemia and solid tumors; it decreases the expression of pro-apoptotic Bak upstream of the mitochondria intrinsic apoptosis pathway, Ito K, et al. (2006). Loss of 17AA(+)(-KTS)WT1 isoform in B16F10 murine melanoma increases intrinsic (mitochondrial) apoptosis, Zamora-Avila DE, et al. (2007). 17AA(+)KTS(+)WTI is expressed in melanoma, where it may induce expression of Nestin and Zyxin, Wagner N, et al. (2008). WT1 gene dysfunctions are the cause of renal and urogenital diseases including; Wilms’ tumor 1 (nephroblastomas), desmoplastic small round cell tumor (DSRCT), Hypospadias, Meacham syndrome, isolated diffuse mesangial sclerosis (IDMS), Denys-Drash syndrome (DDS), genitrourinary dysplasia component of WAGR syndrome and Frasier syndrome (FS). Wilms’ tumor is expressed in glomerular epithelium and related mesonephric glomeruli of kidney; gonadal ridge of developing gonad (gonadal morphogenesis) and fetal gonad; Sertoli cells; and epithelial and granulose cells of ovary; Pelletier J, et al. (1991); Pritchard-Jones K, et al. (1990). Wilms’ tumor protein is required for the development of the genital system. It has been identified along with SRY as responsible for gonadal development. While WT1 acts synergistically, in complex, with SRY, Matsuzawa-Watanabe Y, et al. (2003), it appears to be a downstream target of sex-determining region of the Y chromosome (SRY). Toyooka Y, et al. (1998) introduced an SRY gene construct, which codes for testis determining factor (Tdy) into an embryonic stem cell line, TMA-18 with XX karyotype (gene set required for testicular differentiation, but not spermatogenesis) Koopman et al. (1991), which lead to expression of WT1, but not MIS, SF1, P450arom or SoX9. Sigma offers antibodies, shRNAs and other products useful for the study of the Wilms’ tumor protein. References: Baudry D, Faussillon M, Cabanis MO, Rigolet M, Zucker JM, Patte C, Sarnacki S, Boccon-Gibod L, Junien C, Jeanpierre C. (2002) Changes in WT1 splicing are associated with a specific gene expression profile in Wilms' tumour. Oncogene. 21: 5566-5573. |
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