WT1 – A Complex Life

By: Chen Zhu

WT1 – Outline Introduction Function Structure Role in development

In mice In humans

Role in cancer Wilm’s Tumor, related illnesses

Introduction Wilms’ Tumor 1 (WT1) is found on

human chromosome 11p13 WT1 is important for the development of

the genitourinary system and mesothelial tissues.

The inactivation of WT1 is responsible for ~10-15% of Wilms’ tumor

Function WT1 is a transcriptional and post-

transcriptional regulator It contains signals that allow it to localize

inside the nucleus It contains domains that can bind to

several DNA sequences

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Structure WT1 is a 50kb gene with ten exons,

together encoding a mRNA of ~3kb. The N-terminus of WT1 contains a proline

and glutamine-rich region that facilitates homodimerization

There are two alternatively spliced exons in WT1

Exon 5 Exon 5 encodes 17 amino acids between

the N-terminus and the first Zn finger domain

Encodes a protein-protein interaction domain

Exon 9 Encodes the sequence KTS between the

third and fourth zinc fingers of the protein WT1 (-KTS) variants have been shown to

act as transcriptional regulators1

WT1 (+KTS) may play a role in RNA processing.

Adapted from Figure 5 in Keith W. Brown and Karim T.A. Malik, “The molecular biology of Wilms’ Tumor,” Exp. Rev. Mol. Med. 14 May, http://www.expertreviews.org/01003027h.htm

Alternate Splicing 24 alternate isoforms of WT1 have been

described (+KTS)/(-KTS) is by far the most

important alternate splicing mechanism

Function Many target genes of WT1 have been

identified The role of WT1 in transcriptional

regulation, however, is not well understood

Function We do understand, however, that WH1 is

involved in many different pathways: The differentiation of leukemic cell lines The differentiation of pheochromocytoma cells Both the induction and prevention of apoptosis

WT1 Target Genes2

Role In Development WT1 is expressed during development in the

following systems: Urinogenital system Epicardium and subepicardial mesenchyme

(heart) Kidneys Spleen Parts of the brain Spinal chord Mesothelial organs Diaphram

Jordan A. Kreidberg, et al., “WT-1 is required for early liver development,” Cell 74: 679-691 (1993)

Knockout Mice WT1 (-/-) die from embryonic day 12 to the

end of gestation Many defects are evident in many of the

areas mentioned in the previous slide Mutant embryos lack kidneys and gonads

Heterozygous Mice WT1 (+/-) mice usually die after several

months due to renal insufficiency The severity of symptoms can be

correlated with WT1 levels Symptoms are similar to the human

Frasier Syndrome

Jordan A. Kreidberg, et al., “WT-1 is required for early liver development,” Cell 74: 679-691 (1993)

Kidney Development

Loose mesenchyme forms epithelial condenses around ureteric bud tips

S-shaped bodies develop and eventually elongate to attach to the collecting duct

Kidney Development -The role of WT1 Without WT1, the loose mesenchyme

becomes apoptotic WT1 may thus act as a survival factor for

populations of embryonic kidney cells during development

An antiapoptotic protein encoded by Bcl-2 may be an upstream mediator of WT1

Heart Development

WT1(-/-) mutants show smaller hearts and thinning of muscular walls

The epicarium, especially, requires WT1 WT1 is thought to play a role in the

transformation of epicardial to mesenchymal cells

Jordan A. Kreidberg, et al., “WT-1 is required for early liver development,” Cell 74: 679-691 (1993)

Role In Cancer WAGR: heterozygous deletions at

chromosome 11p13 Frasier Syndrome : heterozygous point

mutations in intron 9 Leukemia: heterozygous WT1 mutations

WAGR WAGR is a syndrome for affected children

predisposed to develop:Wilms’ tumorAniridiaGenitourinary anomaliesmental Retardation

http://bms.brown.edu/pedisurg/images/ImageBank/Abdomen/WilmsCT8yo.jpg

WAGR Aniridia Genitourinary Anomalies Mental Retardation

http://www.abdn.ac.uk/clsm/UserFiles/Image/collinson-eye-large.jpg

Wilms’ Tumor is a cancer of the kidney About 500 cases are diagnosed yearly Onset is early, with nearly everybody

diagnosed under the age of 25 Survival with therapy is very good: ~85% WAGR patients should undergo frequent

ultrasound testing

Wilm’s Tumor

Wilm’s Tumor Wilm’s tumor arises from mesenchyme

that fails to differentiate into the epithelial component of the nephron

Inactivation of WT1 produces foci of primitive renal cells called nephrogenic rests

Sometimes called tri-phasic type, consisting of undifferentiated mesenchyme, stromal and epiphelial cells

Leukemia WT1 is inappropriately expressed in many

Leukemia cell lines (~15%) WT1 is usually expressed in stem cells of

bone marrow, but not in normal mature blood cells, linking it to an immature state for leukemia cells

WT1 expression levels increase during the progression of acute myeloid leukemia

Patients with low WT1 mRNA had a better prognosis than those with high WT1 mRNA

Questions?

Bibliography1. Holger Scholz and Karin M. Kirschner, “A Role for the Wilms’

Tumor Protein WT1 in Organ Development,” Physiology 20: 54-59 (2005)

2. Volkher Scharnhorst, et al., “WT1 proteins: functions in growth and differentiation,” Gene 273: 141-161 (2001)

3. Kay-Dietrich Wagner, et al., “The complex life of WT1,” Journal of Cell Science 116: 1653-1658 (2003)

4. Jordan A. Kreidberg, et al., “WT-1 is required for early liver development,” Cell 74: 679-691 (1993)

5. National Cancer institute, “Wilms’ Tumor and Other Childhood Kidney Tumors,” November 27, 2006. <http://www.cancer.gov/cancertopics/pdq/treatment/wilms/Patient>

6. International WAGR Syndrome Association, “What is WAGR Syndrome?” Accessed April 27, 2007. <http://www.wagr.org/>

7. Monika L. Metzger, Jeffrey S. Dome., “Current Therapy for Wilms’ Tumor,” Oncologist 10: 815-826 (2005)