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→Gene Overview
==Gene Overview==
==Gene Overview==
===Structure and Function===
Wilms’ Tumor 1 (WT1) was originally cloned in 1990 as a tumour suppressor gene in Wilms’ tumor, a typically pediatric renal tumor (Call et al., 1990). A combination of alternative transcription and translation start sites, splicing, and RNA editing means that WT1 has many isoforms. Human WT1 spans up to 10 exons across multiple isoforms.
All WT1 isoforms contain four zinc finger regions at the C-terminus of the protein which are involved in DNA binding (Haber et al., 1991). The N-terminal region is comprised of proline-glutamine-rich sequences and is involved in RNA and protein interactions. A nine nucleotide (three amino acid – lysine, threonine, serine, or KTS) sequence exists at the 3’ end of exon 9. Alternative splicing leads to certain isoforms retaining or omitting the KTS sequence (Haber et al., 1991). Both +KTS and -KTS isoforms appear to have non-overlapping functions and are expressed in a specific ratio in normal cells (Haber et al., 1991; Hammes et al., 2001). Germline splice-site mutations resulting in reduced +KTS/-KTS ratios are responsible for Frasier syndrome (Barbaux et al., 1997). Alternative splicing of WT1 exon 5 also leads to some isoforms containing a 17 amino acid domain responsible for transcriptional activation through interaction with the prostate apoptosis response factor PAR4 (Richard et al., 2001).
WT1 is involved in cell growth and development. It has roles in, among others, the mesenchymal-to-epithelial transition during kidney and gonad development, the epithelial-to-mesenchymal transition during heart and diaphragm development, sensory neuron differentiation within the central nervous system, and adult tissue homeostasis (reviewed in (Hastie, 2017)). In the developing embryo it is expressed highly in the urogenital system, but in adults it can be found additionally in the central nervous system and in haematopoietic tissues (Menke et al., 1998). ''In vitro'' evidence suggests WT1 regulates ''BCL2'' and ''MYC'' expression, and interacts with TP53 (Hewitt et al., 1995; Maheswaran et al., 1993).
Other than the tumours for which the gene is named, germline mutations affecting ''WT1'' also variously cause WAGR syndrome (Wilms’ tumour, aniridia, genitourinary anomalies and retardation) (Riccardi et al., 1978), Denys-Drash syndrome (DDS) (Pelletier et al., 1991), the previously mentioned Frasier syndrome, and less clearly Meacham syndrome (Suri et al., 2007).
===Role in Cancer===
Due to the various and non-overlapping roles of WT1 depending on isoform, expression domain, and stage of development, mutations have diverse effects. ''WT1'' can function as a tumour suppressor (as in Wilms’ Tumour) or as an oncogene (reviewed in (Yang et al., 2007)). Overexpression of ''WT1'' is seen in a number of cancer contexts (Dohi et al., 2009; Hylander et al., 2006; Mikami et al., 2013; Rauscher et al., 2014; Ujj et al., 2016).
====Wilms' Tumor====
Accounting for 95% of pediatric renal tumors but rare in adults, Wilms’ tumour appears in both sporadic and hereditary forms. The tumor forms from undifferentiated cells and can be caused by multiple developmental errors. Mutations in ''WT1'' were the first to be described (Huff and Saunders, 1993), and occur in ~15% of sporadic Wilms’ tumours (Gessler et al., 1994). In this context ''WT1'' functions as a tumour suppressor. ''WT1'' mutations in Wilms’ tumour are often associated with activating mutations in β-Catenin (''CTNNB1'') (Breslow et al., 2006; Maiti et al., 2000). ''WTX'' (also known as ''AMER1'' or ''FAM123B'') is also frequently mutated in WT1-mutated Wilms’ tumour (Rivera et al., 2007).
====Acute Myeloid Leukemia====
''WT1'' mutations occur in approximately 10-20% of adult and paediatric cytogenetically normal acute myeloid leukaemia (CN-AML), and with lower frequency in most other cytogenetic subgroups (Gaidzik et al., 2009; Hollink et al., 2009; Sano et al., 2013; Virappane et al., 2008). Mutations are typically frameshifts in exon 7 which truncate the DNA-binding domain or substitutions within exon 9, although other mutations do occur. Association between ''WT1'' mutations and ''FLT3''-ITD, ''KIT'', and ''CEBPA'' biallelic mutations has been observed, but data varies by study (Gaidzik et al., 2009; Hollink et al., 2009; Krauth et al., 2015; Paschka et al., 2008; Sano et al., 2013; Virappane et al., 2008). ''WT1'' mutations appear to be rarer in ''DNMT3A'', ''ASXL1'', ''TET2'', ''IDH1'', or ''IDH2'' mutated AML (Krauth et al., 2015). WT1 and TET2 have been shown to interact, and ''WT1''-mutant AML has aberrant DNA methylation similar to ''TET2'' and ''IDH1/2'' mutants, suggesting overlapping pathways (Rampal et al., 2014).
Complex cytogenetic abnormalities also correlate with reduced ''WT1'' mutation frequency, but there is an increased frequency of WT1 mutations in individuals with t(15;17)/PML-RARA translocations (Krauth et al., 2015). ''WT1'' mutation frequency increases in individuals less than 60 years of age. Overall, ''WT1'' mutation appears to be associated with a poorer prognosis at least in CN-AML (Gaidzik et al., 2009; Hollink et al., 2009; Krauth et al., 2015; Paschka et al., 2008; Sano et al., 2013; Virappane et al., 2008). One report suggests that patients with ''WT1'' and ''FLT3''-ITD mutations may have poorer response to standard induction therapy than patients with ''FLT3''-ITD mutations alone (Summers et al., 2007). ''WT1'' mutations tend to be secondary rather than initiating events in leukemogenesis, and hence may only be present in subclones (Krauth et al., 2015). ''WT1'' vaccination is being investigated as a therapeutic method in haematological malignancies (Brayer et al., 2015; Di Stasi et al., 2015).
====Other Cancers====
''WT1'' overexpression enhances ovarian cancer cell proliferation in vitro (Liu et al., 2014). Higher expression of ''WT1'' is associated with higher stage in ovarian cancer and more aggressive clinical features, but evidence for the use of WT1 expression as a prognostic marker for overall survival is mixed (Köbel et al., 2008; Liu et al., 2014; Netinatsunthorn et al., 2006). A meta-analysis of solid cancers including breast cancer, endometrial cancer, colorectal cancer, and glioma among others found that ''WT1'' expression correlated with worse clinical outcomes such as overall and disease-free survival (Qi et al., 2015). ''WT1''-targeting therapies are being explored (Koido et al., 2014; Sawada et al., 2016; Shirakata et al., 2012).
==Common Alteration Types==
==Common Alteration Types==