Expression of the wt1 Wilms' tumor gene by normal and malignant human melanocytes

Immunohistochemical Expression of Wilms’ Tumor 1 Protein in Human Tissues: From Ontogenesis to Neoplastic Tissues

The human Wilms’ tumor gene (WT1) was originally isolated in a Wilms’ tumor of the kidney as a tumor suppressor gene. Numerous isoforms of WT1, by combination of alternative translational start sites, alternative RNA splicing and RNA editing, have been well documented. During human ontogenesis, according to the antibodies used, anti-C or N-terminus WT1 protein, nuclear expression can be frequently obtained in numerous tissues, including metanephric and mesonephric glomeruli, and mesothelial and sub-mesothelial cells, while cytoplasmic staining is usually found in developing smooth and skeletal cells, myocardium, glial cells, neuroblasts, adrenal cortical cells and the endothelial cells of blood vessels. WT1 has been originally described as a tumor suppressor gene in renal Wilms’ tumor, but more recent studies emphasized its potential oncogenic role in several neoplasia with a variable immunostaining pattern that can be exclusively nuclear, cytoplasmic or both, according to the antibodies used (anti-C or N-terminus WT1 protein). With the present review we focus on the immunohistochemical expression of WT1 in some tumors, emphasizing its potential diagnostic role and usefulness in differential diagnosis. In addition, we analyze the WT1 protein expression profile in human embryonal/fetal tissues in order to suggest a possible role in the development of organs and tissues and to establish whether expression in some tumors replicates that observed during the development of tissues from which these tumors arise.

WT1 expression in endocrine mucin-producing sweat gland carcinoma: a study of 13 cases

BACKGROUND

Endocrine mucin-producing sweat gland carcinoma (EMPSGC), a low-grade sweat gland carcinoma with a predilection for the eyelids, often shows areas of benign eccrine cysts, atypical intracystic proliferation and associated mucinous carcinoma, suggesting tumor progression. Wilms tumor 1 (WT1) protein, a transcription factor, is overexpressed in many tumors and plays a role in oncogenesis.

METHODS

A computer-based search for tumors diagnosed between 1989 and 2009 was conducted. Clinical data were obtained from pathology reports and patient records. Biopsies were reviewed for histologic features. Immunostaining was performed for WT1, chromogranin, synaptophysin, estrogen receptor (ER), epithelial membrane antigen (EMA), polyclonal carcinoembryonic antigen (P-CEA), cytokeratin 7 (CK7), cytokeratin 20 (CK20) and MIB-1.

RESULTS

Eight women and five men (mean age: 61.2 years; range: 40-77 years) presented with slow-growing eyelid nodules. Cases of EMPSGC were characterized by the presence of dermal nodules with various growth patterns. Adjacent eccrine cysts were present in five patients, atypical epithelial proliferation within the cyst wall in four patients, and an associated mucinous carcinoma in one patient. All tumors were positive for WT1, CK7, ER, P-CEA and EMA and negative for CK20. Tumors were positive for synaptophysin in 12 cases and chromogranin in nine cases. The MIB-1 proliferation index was low in most cases. No WT1 staining was observed in the overlying epidermis, adnexal structures or areas of benign eccrine cyst. WT1 expression was observed in areas of atypical epithelial proliferation, and the neoplastic cells.

CONCLUSIONS

The present study shows WT1 expression in the neoplastic epithelial cells of EMPSGC, areas of atypical intraductal proliferations, and mucinous carcinoma. The absence of WT1 expression in areas of benign eccrine cyst and cutaneous sweat glands suggests WT1 upregulation plays a role in tumor cell proliferation and progression of EMPSGC.

Trial Watch: Peptide-based anticancer vaccines

Malignant cells express antigens that can be harnessed to elicit anticancer immune responses. One approach to achieve such goal consists in the administration of tumor-associated antigens (TAAs) or peptides thereof as recombinant proteins in the presence of adequate adjuvants. Throughout the past decade, peptide vaccines have been shown to mediate antineoplastic effects in various murine tumor models, especially when administered in the context of potent immunostimulatory regimens. In spite of multiple limitations, first of all the fact that anticancer vaccines are often employed as therapeutic (rather than prophylactic) agents, this immunotherapeutic paradigm has been intensively investigated in clinical scenarios, with promising results. Currently, both experimentalists and clinicians are focusing their efforts on the identification of so-called tumor rejection antigens, i.e., TAAs that can elicit an immune response leading to disease eradication, as well as to combinatorial immunostimulatory interventions with superior adjuvant activity in patients. Here, we summarize the latest advances in the development of peptide vaccines for cancer therapy.

Transcriptional regulation of the human thromboxane A2 receptor gene by Wilms' tumor (WT)1 and hypermethylated in cancer (HIC) 1 in prostate and breast cancers

The prostanoid thromboxane (TX) A(2) plays a central role in hemostasis and is increasingly implicated in neoplastic disease, including prostate and breast cancers. In humans, TXA(2) signals through the TPα and TPβ isoforms of the T prostanoid receptor, two structurally related receptors transcriptionally regulated by distinct promoters, Prm1 and Prm3, respectively, within the TP gene. Focusing on TPα, the current study investigated its expression and transcriptional regulation through Prm1 in prostate and breast cancers. Expression of TPα correlated with increasing prostate and breast tissue tumor grade while the TXA(2) mimetic U46619 promoted both proliferation and migration of the respective prostate (PC3) and breast (MCF-7 and MDA-MD-231) derived-carcinoma cell lines. Through 5' deletional and genetic reporter analyses, several functional upstream repressor regions (URRs) were identified within Prm1 in PC3, MCF-7 and MDA-MB-231 cells while site-directed mutagenesis identified the tumor suppressors Wilms' tumor (WT)1 and hypermethylated in cancer (HIC) 1 as the trans-acting factors regulating those repressor regions. Chromatin immunoprecipitation (ChIP) studies confirmed that WT1 binds in vivo to multiple GC-enriched WT1 cis-elements within the URRs of Prm1 in PC3, MCF-7 and MDA-MB-231 cells. Furthermore, ChIP analyses established that HIC1 binds in vivo to the HIC1((b))cis-element within Prm1 in PC3 and MCF-7 cells but not in the MDA-MB-231 carcinoma line. Collectively, these data establish that WT1 and HIC1, both tumor suppressors implicated in prostate and breast cancers, transcriptionally repress TPα expression and thereby provide a strong genetic basis for understanding the role of TXA2 in the progression of certain human cancers.

WT1 silencing by RNAi synergizes with chemotherapeutic agents and induces chemosensitization to doxorubicin and cisplatin in B16F10 murine melanoma cells

The Wilm's tumor gene (WT1), encoding a transcription factor that modulates the expression of certain genes that are involved in proliferation and apoptosis, is overexpressed in numerous solid tumors. WT1 is important for cell proliferation and in the diagnosis of melanoma. The objectives of this study were to investigate whether WT1 silencing is capable of synergizing with chemotherapeutic agents and whether this silencing is capable of sensitizing cancer cells to doxorubicin and cisplatin in the B16F10 murine melanoma cell line. In the present study, B16F10 cells were simultaneously treated with median lethal doses (LD50s) of WT1-1 or WT1-2 small hairpin RNAs (shRNAs) and chemotherapeutic agents. A total of 24 h post-transfection, a [3-(4,5-dimethylthiazol-2yl)-2,5- diphenyl tetrazolium bromide assay] MTT assay was performed. To determine whether shRNA interference (shRNAi) is capable of sensitizing B16F10 cells to chemotherapeutic agents, cells were transfected with an LD50 of each of the recombinant plasmids, treated with varying concentrations of doxorubicin or cisplatin 24 h post-transfection, and analyzed 48 h later for inhibition of cell proliferation using the MTT assay. We observed that WT1-RNAi and the two chemotherapeutic agents acted synergistically to inhibit B16F10 cell proliferation. The greatest inhibition of cell proliferation was observed with the WT1-2/cisplatin (91%) and WT1-1/cisplatin combinations (85%). WT1 silencing using shRNAi induced the chemosensitization of cells to doxorubicin and cisplatin, with the greatest inhibition (85%) of cell proliferation being observed in the cells treated with the WT1-2/cisplatin 6 ng/µl combination. Our results provide direct evidence that WT1 gene silencing has a synergistic effect with chemotherapeutic drugs and sensitizes B16F10 melanoma cells to doxorubicin and cisplatin. This suggests that these combination strategies are potentially utilized in melanoma therapy.

Wilms' tumor 1 silencing decreases the viability and chemoresistance of glioblastoma cells in vitro: a potential role for IGF-1R de-repression

Wilms' tumor 1 (WT1) is a transcription factor with a multitude of downstream targets that have wide-ranging effects in non-glioma cell lines. Though its expression in glioblastomas is now well-documented, the role of WT1 in these tumors remains poorly defined. We hypothesized that WT1 functions as an oncogene to enhance glioblastoma viability and chemoresistance. WT1's role was examined by studying the effect of WT1 silencing and overexpression on DNA damage, apoptosis and cell viability. Results indicated that WT1 silencing adversely affected glioblastoma viability, at times, in synergy with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and cisplatin. To investigate other mechanisms through which WT1 could affect viability, we measured cell cycle distribution, senescence, and autophagy. WT1 silencing had no effect on these processes. Lastly, we examined WT1 regulation of IGF-1R expression. Counterintuitively, upregulation of IGF-1R was evident after WT1 silencing. In conclusion, WT1 functions as a survival factor in glioblastomas, possibly through inhibition of IGF-1R expression.

WT-1 expression in a spectrum of melanocytic lesions: Implication for differential diagnosis

A previous in vitro study revealed that Wilms's tumor 1 (WT-1) transcripts were detectable in 7 of 9 melanoma cell lines, but not in any of 5-normal melanocyte strains tested. Our current study assessed the expression levels of WT-1 protein in clinical samples, to determine whether the expression levels of the WT-1 protein may be used as a novel marker to assist differential diagnosis. Paraffin-embedded tissue sections from 15 cases of malignant melanomas and 25 cases of benign nevi were subjected to immunohistochemistry with a monoclonal antibody against the human WT-1 protein. The expression levels of WT-1 protein among normal, benign, and malignant melanocytes were semi-quantitatively assessed. Strong and uniform WT-1 immunoreactivities were seen in all or nearly all tumor cells in both the junctional and dermal components of all malignant melanomas, and also in a vast majority of the tumor cells of Spitz's (n = 8), recurrent (n = 2), and junction (n = 2) nevi. Distinct WT-1 immunoreactivities were also seen in some isolated individual tumor cells or tumor cell clusters in the junctional component of compound nevus (9) and in intradermal nevus (2). It is interesting to note that some isolated normal appearing melanocytes or cell clusters, and all morphologically distinct endothelial cells were strongly positive to WT-1. However, all tumor cells within the dermal component of compound (n = 9) or deep penetrating nevi (n = 1), or capsular nevus inclusion of lymph node (1) were devoid of WT-1 expression. Our findings suggest that the expression level of the WT-1 protein has no significant value in distinguishing between Spitz's nevi and malignant melanoma, but it may be a useful marker in differentiating between benign and malignant melanocytes within the dermal component. Our findings also suggest that aberrant WT-1 expression may have oncogenic properties that promote the initiation and progression of melanocytic lesions.

WT1 marker is not sufficient for distinguishing between melanoma and melanocytic nevi

BACKGROUND

The heterogeneous histological features of melanoma may often overlap with melanocytic nevi. For this reason, pathologists have sought after immunohistochemistry to assist with difficult cases. Recently, Wilms' tumor 1 protein (WT1) has been suggested to differentiate between melanoma and melanocytic nevi.

OBJECTIVE

Our objective was to determine whether immunohistochemistry analysis of WT1 expression is a reliable tool in differentiating cutaneous melanoma from melanocytic nevi.

METHODS

Forty-five melanoma and 43 melanocytic nevi were immunostained with anti-WT1 monoclonal antibody (clone 6F-H2).

RESULTS

Forty of the 45 cutaneous melanoma (89%) and 22 of the 43 melanocytic nevi (51%) stained (> 10% cells) for WT1. The highest sensitivity for WT1 was expressed by nodular melanoma (19/20), superficial spreading melanoma (8/10) and Spitz nevi (9/11). At the threshold of above 75% WT1-stained cells, the specificity for melanoma was 95% but the sensitivity was only 31%. At the threshold of 10%, the sensitivity increased to 89% but the specificity decreased to only 49%. Finally, at the threshold of 25% and 50%, the sensitivity and specificity were 71%, 61% and 64%, 77%, respectively.

CONCLUSIONS

Our data suggest that melanoma is associated with increased WT1 expression. However, as a single immunostaining marker, WT1 is not sufficient for distinguishing melanoma from melanocytic nevi.

Induction of Wilms' tumor protein (WT1)-specific antitumor immunity using a truncated WT1-expressing adenovirus vaccine

PURPOSE

Wilms' tumor protein (WT1) is overexpressed in most leukemias and many solid tumors and is a promising target for tumor immunotherapy. WT1 peptide-based cancer vaccines have been reported but have limited application due to HLA restriction of the peptides. We sought to vaccinate using adenoviral (Ad) vectors encoding tumor-associated antigens such as WT1 that can stimulate tumor-associated antigen-specific immunity across a broad array of HLA types and multiple class I and class II epitopes.

EXPERIMENTAL DESIGN

We developed a novel Ad vector encoding a truncated version of WT1 (Ad-tWT1) lacking the highly conserved COOH terminus zinc finger domains and tested its ability to stimulate WT1-specific immune responses and antitumor immunity in two murine models of WT1-expressing tumors.

RESULTS

Despite encoding a transcription factor, we found that Ad-tWT1-transduced murine and human dendritic cells showed cytoplasmic expression of the truncated WT1 protein. In addition, vaccination of C57BL/6 mice with Ad-tWT1 generated WT1-specific cell-mediated and humoral immune responses and conferred protection against challenge with the leukemia cell line, mWT1-C1498. Moreover, in a tumor therapy model, Ad-tWT1 vaccination of TRAMP-C2 tumor-bearing mice significantly suppressed tumor growth.

CONCLUSIONS

This is the first report of a WT1-encoding Ad vector that is capable of inducing effective immunity against WT1-expressing malignancies. Based on these findings, Ad-tWT1 warrants investigation in human clinical trials to evaluate its applications as a vaccine for patients with WT1-expressing cancers.

No evidence for WT1 involvement in a beta-catenin-independent activation of the Wnt signaling pathway in pituitary adenomas

The overexpression of Wilms' tumor gene product WT1, which acts as a tumor suppressor or oncogene, has been reported in various malignancies. Recent studies have shown that the interaction partner Wnt-4 is upregulated in pituitary adenomas dependent on the Pit-1 lineage (somatotrophs, lactotrophs, and thyrotrophs). However, no data on WT1 expression in nontumorous pituitary tissue or pituitary adenomas is available to date. We investigated WT1 expression in 90 paraffin-embedded pituitary adenomas, including eight atypical adenomas, and in 28 nontumorous pituitary glands by immunohistochemistry. WT1 is absent in epithelial cells of all nontumorous pituitary glands and in 87 out of 90 pituitary adenomas. Only two GHomas (including one atypical adenoma) and one gonadotropin-producing adenoma expressed WT1 in the cytoplasm of single tumor cells without nuclear staining. There is no evidence that WT1 does regulate the Wnt-4/beta-catenin-independent pathway which is activated in the Pit-1-expressing subset of pituitary adenomas.

Diagnostic value of WT1 in neuroepithelial tumours

AIMS

Currently, clinical trials using WT1 (Wilms tumour gene) peptide vaccines are conducted in haematopoietic malignancies and solid cancers. Single reports showed that the Wilms tumour gene product WT1 is also expressed in astrocytic neoplasms. Our aim was to investigate WT1 expression in a large cohort of various neuroepithelial tumours of different World Health Organization (WHO) grades and in normal central nervous system (CNS) tissue specimens to test its potential value as a diagnostic marker.

METHODS

Specimens were assessed by RT-PCR, Western blotting and immunohistochemistry. The samples investigated in our study consisted of 334 human neuroepithelial tumours, among those 33 oligodendrogliomas, 219 astrocytomas (including 105 glioblastomas) and 47 ependymomas.

RESULTS

Our results showed a de novo WT1 expression in neuroepithelial tumours. In diffuse astrocytomas and ependymomas, WT1 expression increased significantly with the grade of malignancy. In contrast, no significant difference was seen between WHO grade-II and -III oligodendrogliomas. Controlling for WHO grade, the comparison of oligodendrogliomas with ependymal and astrocytic tumours showed higher expression values for the latter.

CONCLUSIONS

Our study shows that WT1 is expressed de novo in numerous neuroepithelial tumours and increases with the grade of malignancy. These results suggest an important role of WT1 in tumourigenesis and progression in human brain tumours.

Early growth response-1 mediates downregulation of telomerase in cervical cancer

Early growth response (Egr)-1 is a transcription factor that triggers transcription of downstream genes within 15-30 min of various stimulations. These genes are expressed rapidly through specific promoter activation and mediate cell growth and angiogenesis. Following the previous computational identification of a site that was thought to be an Egr-1 consensus binding site at -273 to -281 in the human telomerase reverse transcriptase (hTERT) promoter region, the present study was conducted to evaluate the role of Egr-1 in the regulation of hTERT and telomerase in uterine cervical cancer. First, the expression of Egr-1 and hTERT at the mRNA level was examined in cervical cancer tissues. Egr-1 and hTERT were expressed much higher in cervical cancer tissues than in the normal cervix. However, a negative correlation was noted in the expression between Egr-1 and hTERT. By luciferase assay using hTERT promoter constructs, hTERT transcriptional activation was shown to be inhibited when Egr-1 was overexpressed. Furthermore, Egr-1 overexpression decreased hTERT protein production as well as hTERT mRNA as observed by western blotting analysis and real-time reverse transcription-polymerase chain reaction, respectively. The present study suggests that Egr-1 plays an important regulatory role in the transcriptional activation of hTERT.

The Wilms' tumor suppressor WT1 is associated with melanoma proliferation

Expression of the Wilms' tumor suppressor WT1 has been demonstrated in a variety of tumors and tumor cell lines, e.g., in breast cancer and melanoma cell lines. Its role is controversial, with evidence for both tumor-promoting and tumor-suppressing activities. In this paper, we show that WT1 is expressed in malignant melanoma in >80% of the tumor cells, but not in normal skin or benign melanocytic nevi in vivo. We detected an unusual shift of WT1 isoforms towards WT1(+17AA/+KTS) in melanoma. WT1 shared an overlapping expression with proliferating nuclear cell antigen and with Nestin and Zyxin, which are involved in melanoma cell proliferation. To investigate whether WT1 is directly involved in melanoma cell proliferation, we made use of an RNAi approach in vitro. WT1 silencing significantly reduced the expression of Nestin and Zyxin and resulted in inhibition of melanoma cell proliferation as determined by a reduced BrdU incorporation. These findings suggest a direct role of WT1 in melanoma proliferation, which might be mediated via Nestin and Zyxin. Furthermore, expression of WT1 in vivo clearly discriminates between benign acquired nevi and malignant melanomas and appears to be correlated with melanocytic atypia and malignancy.

A tumor suppressor and oncogene: the WT1 story

The Wilms' tumor 1 (WT1) gene encodes a transcription factor important for normal cellular development and cell survival. The initial discovery of WT1 as the causative gene in an autosomal-recessive condition identified it as a tumor suppressor gene whose mutations are associated with urogenital disease and the development of kidney tumors. However, this view is not in keeping with the frequent finding of wild-type, full-length WT1 in human leukemia, breast cancer and several other cancers including the majority of Wilms' tumors. Rather, these observations suggest that in those conditions, WT1 has an oncogenic role in tumor formation. In this review, we explore the literature supporting both views of WT1 in human cancer and in particular human leukemias. To understand the mechanism by which WT1 can do this, we will also examine its functional activity as a transcription factor and the influence of protein partners on its dual behavior.

FGFR1 and WT1 are markers of human prostate cancer progression

BACKGROUND

Androgen-independent prostate adenocarcinomas are responsible for about 6% of overall cancer deaths in men.

METHODS

We used DNA microarrays to identify genes related to the transition between androgen-dependent and androgen-independent stages in the LuCaP 23.1 xenograft model of prostate adenocarcinoma. The expression of the proteins encoded by these genes was then assessed by immunohistochemistry on tissue microarrays (TMA) including human prostate carcinoma samples issued from 85 patients who had undergone radical prostatectomy.

RESULTS

FGFR1, TACC1 and WT1 gene expression levels were associated with the androgen-independent stage in xenografts and human prostate carcinoma samples. MART1 protein expression was correlated with pT2 tumor stages.

CONCLUSION

Our results suggest that each of these four genes may play a role, or at least reflect a stage of prostate carcinoma growth/development/progression.

hnRNP-U directly interacts with WT1 and modulates WT1 transcriptional activation

The Wilms' tumour suppressor gene, WT1, encodes a zinc-finger protein that is mutated in Wilms' tumours and highly expressed in a wide variety of other malignancies. WT1 is a transcription factor that is likely to have additional, post-transcriptional, regulatory roles, although the molecular mechanisms by which WT1 acts remain poorly understood. We have combined genetic and biochemical approaches to show, that endogenous WT1 binds to heterogeneous nuclear ribonuclear protein U (hnRNP-U), that this interaction does not require any other proteins or nucleic acids, involves the zinc-fingers of WT1 and the middle domain of hnRNP-U, and that hnRNP-U can modulate WT1 transcriptional activation of a bona fide WT1 target gene. These findings increase our knowledge of how WT1 exerts its transcriptional regulatory role and suggests that hnRNP-U may be a candidate Wilms' tumour gene at 1q44.

Correlation of minimal residual disease by assessing Wilms tumor gene expression and engraftment by variable number of tandem repeats in children with leukemia posthematopoietic stem cell transplantation

An important measure to ensure successful follow-up in patients with allogeneic stem cell transplant is to evaluate for engraftment. Recent studies have shown that detecting minimal residual disease is important in order to predict early clinical relapse. We followed 88 leukemic patients with pre- and posttransplant Wilms tumor gene (WT1) levels to predict relapse and variable number of tandem repeats (VNTR) for engraftment. We have found that high pretransplant WT1 levels correlated significantly with relapse in all patient groups, but more significantly in the acute nonlymphoblastic leukemia (ANLL) patients. Posttransplant WT1 level correlated with VNTR status such that low WT1 is associated invariably with VNTR of 100% donor origin, while high WT1 is associated with VNTR of 20%. The association is significant in all patients, specifically in ANLL patients. In this preliminary study, we demonstrate that patients harboring detectable levels of WT1 prior to stem cell transplant have a higher chance of relapse, and posttransplant WT1 and VNTR status appeared to be dependent parameters predicting relapse when present in the posttransplant period. By combining 2 highly sensitive molecular techniques, we have found that this combined technique provided us with a promising alternative for overcoming the limitations imposed by each separate procedure. More studies are necessary before we can come to any significant conclusions.

DNA sequences acting as binding sites for NM23/NDPK proteins in melanoma M14 cells

We isolated and analyzed by chromatin immunoprecipitation (ChIP) in viable M14 cells DNA sequences bound to the antimetastatic protein nucleoside diphosphate kinase (NM23/NDPK) to shed some light on the nuclear functions of this protein and on the mechanism by which it acts in development and cancer. We assessed the presence of selected sequences from promoters of platelet-derived growth factor A (PDGF-A), c-myc, myeloperoxidase (MPO), CD11b, p53, WT1, CCR5, ING1, and NM23-H1 genes in the cross-linked complexes. Quantitative PCR (Q-PCR) showed a substantial enrichment of the correlated oncosuppressor genes p53, WT1, ING1, and NM23-H1 in the immunoprecipitated (IP) DNA. This suggests that NM23/NDPK binding is involved in the transcription regulation of these genes. These results reveal new interactions that should help us to disclose the antimetastatic mechanism of NM23.

WT1 is a tumor-associated antigen in colon cancer that can be recognized by in vitro stimulated cytotoxic T cells

The Wilms' tumor suppressor gene (WT1) has been shown to be overexpressed in acute and chronic leukemias and in a variety of solid human malignancies, including cancers of the breast and lung. In our present study, we investigated the potential role of WT1 gene in human colon cancer. WT1 mRNA and protein expression was analyzed in a panel of human colon cancer cell lines and primary colon carcinomas by RT-PCR and Western blot analysis, respectively. A mutational screen of WT1' zinc-finger region was carried out by sequence analysis. Finally, using peptide-stimulated cytotoxic T cells it was investigated whether WT1-expressing colon tumor cells are a potential target for antigen-specific immunotherapy. Medium to high abundant levels of WT1 mRNA were detected by RT-PCR in 10 of 12 (83%) colon cell lines and by quantitative, real-time RT-PCR in 13 of 15 (87%) primary tumors, whereas only very low levels of expression were found in 2 primary tumors. Interestingly, however, low levels of WT1 mRNA were also detected in all samples derived from normal colon mucosa. When RT-PCR products were examined by sequence analysis, both +KTS and -KTS splice isoforms but no zinc-finger mutations were found, suggesting that the wild-type form of the WT1 gene is expressed. To determine whether the WT1 protein can serve as a target antigen for immunotherapy, 2 HLA-A2.1-restricted WT1 peptides (Db126 and WH187) were used for the in vitro induction of WT1-specific cytotoxic T lymphocytes (CTLs). The WH187-specific CTLs not only lysed target cells pulsed exogenously with cognate peptide but also WT1-expressing colon tumor cells in a HLA-restricted manner. These findings identify the WT1 protein as an attractive target for the development of antigen-specific immunotherapy in human colon cancer.

WT1 in acute leukemia, chronic myelogenous leukemia and myelodysplastic syndrome: therapeutic potential of WT1 targeted therapies

Among clinicians, initial awareness of the Wilms' tumor gene was limited mostly to pediatric oncologists. Almost a decade ago, overexpression of Wilms' tumor 1 (WT1) was observed in adult acute leukemia. Subsequent studies indicated that WT1 overexpression occurs in most cases of acute myelogenous leukemia, acute lymphoblastic leukemia, chronic myelogenous leukemia (CML), and myelodysplastic syndrome (MDS). Limited tissue expression of WT1 in adults suggests that WT1 can be a target for leukemia/MDS therapy. WT1 expression in stem/progenitor cells remains unsettled. However, lack of progenitor cell suppression by WT1 antisense or WT1-specific cytotoxic T cells provide some assurance that WT1 expression in progenitor cells is minimal or absent. Immunotherapy-based WT1 approaches are furthest along in preclinical development. WT1-specific cytotoxic lymphocytes can be generated from normals and leukemic patients. In mice, WT1 vaccines elicit specific immune responses without evidence of tissue damage. In this paper, we review studies validating the immunogenicity of WT1 and propose that leukemia and MDS may be a good clinical model to test the efficacy of a WT1 vaccine.

The lck promoter-driven expression of the Wilms tumor gene WT1 blocks intrathymic differentiation of T-lineage cells

In the thymi of WT1-transgenic (Tg) mice with the 17AA+/KTS- spliced form of the Wilms tumor gene WT1 driven by the lck promoter, the frequencies of CD4-CD8- double-negative (DN) thymocytes were significantly increased relative to those in normal littermates. Of the 4 subsets of CD4-CD8- DN thymocytes, the DN1 (CD44+CD25-) subset increased in both frequency and absolute cell number, whereas the DN2 (CD44+CD25+) and DN3 (CD44-CD25+) subsets decreased, indicating the blocking of thymocyte differentiation from the DN1 to the DN2 subsets. Furthermore, CD4-CD8+ T-cell receptor (TCR) -gammadelta T-cells increased in both frequency and absolute cell number in the spleen and peripheral blood of the WT1-Tg mice relative to those of normal littermates. The CD8 molecules of these CD4-CD8+ TCRgammadelta T-cells were CD8alphabeta, suggesting that they originated from the thymus. These results are the first direct evidence demonstrating that the WT1 gene is involved in the development and differentiation of T-lineage cells.

Wilms tumor gene (WT1) expression as a panleukemic marker

The Wilms tumor gene (WT1) is expressed in blasts of patients with acute leukemia, irrespective of lineage, and WT1 nuclear protein is detectable in the majority of such blasts. Only very few physiologic hematopoietic progenitors express WT1, but the WT1 expression level of these progenitors and that of leukemic blasts are comparable. Although not specific for acute hematologic malignant diseases, continuous WT1 expression in almost all leukemic blasts strikingly contrasts to its rather transient expression in very few physiologic hematopoietic progenitors. Quantitative and semiquantitative WT1 reverse transcriptase polymerase chain reaction (RT-PCR) protocols have limitations in discriminating physiologic from pathologic overall WT1 expression levels in mononuclear cell preparations. Because of these limitations, reports conflict on the usefulness of long-term monitoring of WT1 expression in patients with acute leukemia. Real-time quantitative WT1 RT-PCR protocols, however, have been developed and tested in small series of patients with acute leukemia. Such protocols hold promise to enable evaluation of the individual treatment response (short-term monitoring) and early diagnosis of imminent relapse through the detection and long-term monitoring of minimal residual disease in patients with acute leukemia. These protocols also should facilitate the notoriously difficult distinction between eosinophilic leukemia and hypereosinophilic syndromes. Data on WT1 expression in leukemic blasts and their physiologic counterparts are discussed in light of clinical relevance.

Cancer immunotherapy targeting WT1 protein

The Wilms tumor gene WT1 is expressed in leukemias and various kinds of solid tumors, including lung and breast cancer, and exerts an oncogenic function in these malignancies, suggesting that WT1 protein is a novel, overexpressed tumor antigen. The WT1 protein, in fact, is an attractive tumor rejection antigen in animal models. Stimulation in vitro of peripheral blood mononuclear cells with HLA-A*2402--and HLA-A*0201--restricted 9-mer WT1 peptides elicits WT1-specific cytotoxic T-lymphocytes (CTLs), and the CTLs kill endogenously WT1-expressing leukemia or solid tumor cells. Furthermore, WT1 immunoglobulin M (IgM) and IgG antibodies are detected in patients with hematopoietic malignancies such as acute myeloid leukemia, chronic myeloid leukemia, and myelodysplastic syndromes, indicating that WT1 protein overexpressed by leukemia cells is indeed immunogenic. Taken together, these results demonstrate that WT1 protein is a promising tumor antigen for cancer immunotherapy against leukemias and various kinds of solid tumors, including lung and breast cancer.

The role of WT1 in oncogenesis: tumor suppressor or oncogene?

Although originally identified as a tumor suppressor gene, WT1 is overexpressed in a variety of hematologic malignancies and solid tumors, including acute leukemia, breast cancer, malignant mesothelioma, renal cell carcinoma, and others. Overexpression of both wild-type and mutant WT1 has been reported. In some cases, this finding represents overexpression of a gene that should be expressed at lower levels, but in other cases, WT1 is expressed at high levels in a tissue type in which there is normally no expression at all. In this review, the mechanisms of altered WT1 expression are explored, including changes in promoter methylation. WT1 target genes that may be important for oncogenesis are discussed, as is the use of WT1 expression as a diagnostic tool. The prognostic implications of altered WT1 expression and the potential for immunotherapy aimed at WT1 are also discussed.

Humoral immune responses against Wilms tumor gene WT1 product in patients with hematopoietic malignancies

Wilms tumor gene WT1 is expressed at high levels in hematopoietic malignancies, such as leukemias and myelodysplastic syndromes (MDS), and in various kinds of solid tumors, including lung cancer, and it exerts an oncogenic function in these malignancies. IgM and IgG WT1 antibodies were measured by means of dot blot assay in 73 patients with hematopoietic malignancies (16 acute myeloid leukemia [AML], 11 acute lymphoid leukemia [ALL], 13 chronic myeloid leukemia [CML], and 33 MDS) and 43 healthy volunteers. Immunoglobulin IgM, IgG, and IgM+IgG WT1 antibodies were detected in 40 (54.8%), 40 (54.8%), and 24 (32.8%), respectively, of the 73 patients with hematopoietic malignancies, whereas 7 (16.2%), 2 (4.7%), and none of the 43 healthy volunteers had IgM, IgG, or IgM+IgG WT1 antibodies, respectively. Furthermore, immunoglobulin isotype class switching of WT1 antibodies from IgM to IgG occurred in conjunction with disease progression from refractory anemia (RA) to RA with excess of blasts (RAEB), and further to RAEB in transformation (RAEB-t) in MDS patients. These results showed that humoral immune responses against the WT1 protein could be elicited in patients with WT1-expressing hematopoietic malignancies, and they suggested that the helper T-cell responses needed to induce humoral immune responses and immunoglobulin isotype class switching from IgM to IgG were also generated in these patients. Our findings may provide new insight into the rationale for elicitation of cytotoxic T-cell responses against the WT1 protein in cancer immunotherapy using the WT1 vaccine.

Utility of WT1 as a reliable tool for the detection of minimal residual disease in children with leukemia

WT1 encodes a transcription factor involved in the pathogenesis of Wilms' tumor. A high level of expression has been reported in blasts from patients with various hematological malignancies. The study was performed to evaluate the utility of monitoring WT1 expression in children with leukemia at diagnosis, during therapy, and following bone marrow transplant. We tested a total of 204 samples prospectively. These included samples from patients with the following diagnoses: acute lymphoblastic leukemia (ALL) at diagnosis (n = 45), at relapse (n = 14), and in remission (n = 45); acute non-lymphoblastic leukemia (ANLL) at diagnosis (n = 14), at relapse (n = 5), and in remission (n = 12); and chronic myelogenous leukemia (CML) in blast crisis (n = 1) and in chronic phase (n = 1). A total of 33 of these patients were transplanted: 19 ALL, 12 ANLL, and 2 CML. In addition, samples from 5 patients with aplastic anemia and 28 controls were obtained from peripheral blood (n = 17), cord blood (n = 3), and bone marrow (n = 8). Primer pairs were designed to locate specific nucleotide sequences for mRNA of WT1. RT-PCR was performed in all samples and compared with K562 cells from ATCC (defined as 1.0) as positive control. A positive test was arbitrarily defined as WT1/K562 > 0.5. Samples at diagnosis and relapse, including 56 out of 59 ALL (95%), 26 ANLL (100%), and 1 CML in blast crisis, demonstrated high levels of WT1 expression. In contrast, only 5 of 90 samples obtained in remission or post-transplant showed high levels of WT1 expression ( P < 0.0001; 95% CI = 0.66-0.94). The five patients with high WT1 expression during follow-up relapsed within 2 to 6 months. In conclusion, we have found that WT1 is consistently elevated in children with leukemia. Significant differences in the level of WT1 expression were noted between these patients during diagnosis and at relapse, and those during remission. More importantly, following bone marrow transplant, a significant high level of WT1 expression preceded clinical relapse by 2 to 6 months. Therefore, WT1 is a reliable marker for monitoring minimal residual disease during therapy as well as in the post-transplant period.

Biology of kidney cells: ontogeny-recapitulating phylogeny

Biology of kidney cells can be used as a model for further understanding of ontogeny-recapitulating phylogeny. The common and species-specific structural and functional relationship between blood capillaries and the environment via a filtration barrier of nephrons is a biological phenomenon resulting from renal cell memory acquired through evolution. Genetically programmed development, a subsequent series of gene expression, and inductive interactions played a key role in differentiation and maintenance of specific activities of kidneys in birds and mammals. Various environmental factors may alter kidney development and specific activities at the levels of gene expression, repression, or derepression, and defensive mechanisms involved in reaction to risk factors are developed. Autoimmunity and cancerogenesis are closely dependent on a variety of environmental agents, such as antigens originating from infections with some viruses and toxins, or irradiation, advanced industrialization, and progress of civilization. As a result of gene mutation, delation, rearrangement, and/or susceptibility to different agents, renal cell memory is altered. Instead of cell-specific activities, the abilities for regeneration, and other genetically programmed activities, the genesis of kidney diseases are common. Balkan endemic nephropathy, as regional disease, is an important example of the role, of environmental agents, at the level of genes. Research programs on molecular genetics will contribute to our efforts both to prevent infections and to elucidate the genesis, diagnosis, prognosis, prevention, and therapy of kidney diseases.

Wilms' tumor gene WT1: its oncogenic function and clinical application

The Wilms' tumor gene WT1 is a gene responsible for the childhood renal tumor. Wilms' tumor, and is defined as a tumor suppressor gene. However, the wild-type WT1 gene is highly expressed in leukemic blast cells of myeloid and lymphoid origin, and thus, WT1 messenger RNA provides a novel tumor marker for detection of minimal residual disease of leukemias and for monitoring disease progression of myelodysplastic syndromes. The WT1 gene exerts an oncogenic function rather than a tumor-suppressor gene function in solid tumors as well as leukemias, and the WT1 gene product is an attractive tumor antigen capable of eliciting cytotoxic T lymphocytes against WT1-expressing tumors.

Immunohistochemical distinction of endometrial stromal sarcoma and cellular leiomyoma

Distinguishing low grade endometrial stromal sarcoma (ESS) from benign smooth muscle proliferations like cellular leiomyoma (CL) can be problematic; because of differing treatments and prognosis, this distinction is important. The authors tested the hypothesis that low grade ESS could be distinguished from CL by immunohistochemistry using a panel of antibodies that have not previously been used in this setting. Antibodies to calponin, smooth muscle myosin heavy chain (SMM-HC), the Wilms tumor gene product (WT-1), and CD10 were applied to 14 cases of ESS (10 low grade, 4 high grade) and 9 CL. Among low grade ESS, 3 of 10, 3 of 10, 9 of 10, and 10 of 10 were positive for expression of calponin, SMM-HC, WT-1, and CD10, respectively. Of CL, all 9 were positive for calponin, SMM-HC, and WT-1, whereas 3 of 9 marked with antibodies to CD10. Overall, SMM-HC and calponin were expressed strongly in CL but weakly expressed in ESS; the converse was true for CD10. Expression of WT-1 and the reticulin-staining pattern do not discriminate between these two tumors. Antibodies to SMM-HC, CD10, and calponin can reliably distinguish ESS from CL.

Immunity to WT1 in the animal model and in patients with acute myeloid leukemia

The Wilms' tumor (WT1) gene participates in leukemogenesis and is overexpressed in most types of leukemia in humans. WT1 is also detectable in many types of lung, thyroid, breast, testicular, and ovarian cancers and melanoma in humans. Initial studies evaluated whether immune responses to murine WT1 can be elicited in mice. Murine and human WT1 are similar. Thus, mouse models might lead to resolution of many of the critical issues for developing WT1 vaccines. C57/BL6 (B6) mice were injected with synthetic peptides from the natural sequence of WT1 containing motifs for binding to major histocompatibility (MHC) class II molecules. Immunization induced helper T-cell responses specific for the immunizing WT1 peptides and antibody responses specific for WT1 protein. Screening of multiple murine cancer cell lines identified 2 murine cancers, TRAMP-C and BLKSV40, that “naturally” overexpress WT1. Immunization with MHC class I binding peptides induced WT1 peptide-specific cytotoxic T-lymphocyte (CTL) that specifically lysed TRAMP-C and BLKSV40. WT1 specificity of lysis was confirmed by cold target inhibition. No toxicity was noted by histopathologic evaluation in the WT1 peptide-immunized animals. WT1 peptide immunization did not show any effect on TRAMP-C tumor growth in vivo. Immunization of B6 mice to syngeneic TRAMP-C elicited WT1-specific antibody, demonstrating that WT1 can be immunogenic in the context of cancer cells. To evaluate whether WT1 might be similarly immunogenic in humans, serum from patients with leukemia was evaluated for pre-existing antibody responses. Western blot analyses showed WT1-specific antibodies directed against the N-terminus portion of the WT1 protein in the sera of 3 of 18 patients with acute myeloid leukemia (AML).

Immunity to WT1 in the animal model and in patients with acute myeloid leukemia

The Wilms' tumor (WT1) gene participates in leukemogenesis and is overexpressed in most types of leukemia in humans. WT1 is also detectable in many types of lung, thyroid, breast, testicular, and ovarian cancers and melanoma in humans. Initial studies evaluated whether immune responses to murine WT1 can be elicited in mice. Murine and human WT1 are similar. Thus, mouse models might lead to resolution of many of the critical issues for developing WT1 vaccines. C57/BL6 (B6) mice were injected with synthetic peptides from the natural sequence of WT1 containing motifs for binding to major histocompatibility (MHC) class II molecules. Immunization induced helper T-cell responses specific for the immunizing WT1 peptides and antibody responses specific for WT1 protein. Screening of multiple murine cancer cell lines identified 2 murine cancers, TRAMP-C and BLKSV40, that “naturally” overexpress WT1. Immunization with MHC class I binding peptides induced WT1 peptide-specific cytotoxic T-lymphocyte (CTL) that specifically lysed TRAMP-C and BLKSV40. WT1 specificity of lysis was confirmed by cold target inhibition. No toxicity was noted by histopathologic evaluation in the WT1 peptide-immunized animals. WT1 peptide immunization did not show any effect on TRAMP-C tumor growth in vivo. Immunization of B6 mice to syngeneic TRAMP-C elicited WT1-specific antibody, demonstrating that WT1 can be immunogenic in the context of cancer cells. To evaluate whether WT1 might be similarly immunogenic in humans, serum from patients with leukemia was evaluated for pre-existing antibody responses. Western blot analyses showed WT1-specific antibodies directed against the N-terminus portion of the WT1 protein in the sera of 3 of 18 patients with acute myeloid leukemia (AML).

Wilms' tumor gene expression by normal and malignant human B lymphocytes

Very little is known about Wilms' tumor gene (WT1) expression in B cells and its importance for growth regulation and differentiation. We have investigated WT1 expression in fresh B lymphocytes and in a panel of B-cell lines of normal and malignant origin, including both Epstein-Barr virus (EBV) genome negative and EBV carrying cell lines. WT1 is constitutively activated in all lymphoblastoid cell lines (LCL) derived from EBV immortalization of lymphocytes from normal donors in vitro. These cell lines are distinguished for the presence of activated B-cell markers and an unrestricted expression of viral latent genes. In contrast, WT1 expression is abrogated in normal B lymphocytes and in all Burkitt tumor derived cell lines, irrespective of the EBV genome carrying status and their phenotype pattern. A single step RT-PCR for simultaneous detection of the four spliced transcript isoforms has been applied to confirm their expression. Analysis of variant relative proportions suggested the maintenance of a balanced expression of the isoforms in LCL, as reported in non tumorous tissues. These data, together with the evidence that the replication in vitro of lymphoblastoid cells is not affected by WT1 activation following viral immortalization, support the hypothesis that gene inactivation, in addition to disrupted alternate splicing, may play a role in growth control derangements.

A clinical overview of WT1 gene mutations

Mutations in the WT1 gene were anticipated to explain the genetic basis of the childhood kidney cancer, Wilms tumour (WT). Six years on, we review 100 reports of intragenic WT1 mutations and examine the accompanying clinical phenotypes. While only 5% of sporadic Wilms' tumours have intragenic WT1 mutations, > 90% of patients with the Denys-Drash syndrome (renal nephropathy, gonadal anomaly, predisposition to WT) carry constitutional intragenic WT1 mutations. WT1 mutations have also been reported in juvenile granulosa cell tumour, non-asbestos related mesothelioma, desmoplastic small round cell tumour and, most recently, acute myeloid leukemia.

Immunohistochemical expression of WT1 by desmoplastic small round cell tumor: a comparative study with other small round cell tumors

Desmoplastic small round cell tumors (DSRCTs) present a reciprocal chromosomal translocation, t(11;22)(p13;q12), that results in fusion of Ewing's sarcoma and Wilms' tumor (WT1) genes. The authors evaluated 15 DSRCTs and 71 other tumors often considered in the differential diagnosis for immunoreactivity using a polyclonal antibody directed against the WT1 part of the chimeric protein resulting from this translocation. WT1 immunostaining was performed on paraffin material using the WT(C-19) antibody after heat-antigen retrieval. All the DSRCTs (15 of 15, 100%) demonstrated strong WT1 nuclear immunoreactivity. Ten of 14 nephroblastomas (71%) disclosed WT1-positive nuclei in accordance with the staining reported by others, and rare and focal nuclear positivity was detected in two of 17 rhabdomyosarcomas. WT1 immunoreactivity was not observed in Ewing's sarcoma/primitive neuroectodermal tumors (zero of 21, 0%), neuroblastomas (zero of 17, 0%), or rhabdoid tumors of the kidney (zero of two, 0%). In nephroblastoma, differential diagnosis with DSRCT was not difficult: Clinical and morphologic data are not similar for these two entities. The current study validates WT1 immunoreactivity as a useful marker to separate DSRCT from other small round cell tumors.

Selective elimination of leukemic CD34+ progenitor cells by cytotoxic T lymphocytes specific for WT1

Hematologic malignancies such as acute and chronic myeloid leukemia are characterized by the malignant transformation of immature CD34+ progenitor cells. Transformation is associated with elevated expression of the Wilm's tumor gene encoded transcription factor (WT1). Here we demonstrate that WT1 can serve as a target for cytotoxic T lymphocytes (CTL) with exquisite specificity for leukemic progenitor cells. HLA-A0201– restricted CTL specific for WT1 kill leukemia cell lines and inhibit colony formation by transformed CD34+ progenitor cells isolated from patients with chronic myeloid leukemia (CML), whereas colony formation by normal CD34+ progenitor cells is unaffected. Thus, the tissue-specific transcription factor WT1 is an ideal target for CTL-mediated purging of leukemic progenitor cells in vitro and for antigen-specific therapy of leukemia and other WT1-expressing malignancies in vivo.

Selective elimination of leukemic CD34+ progenitor cells by cytotoxic T lymphocytes specific for WT1

Hematologic malignancies such as acute and chronic myeloid leukemia are characterized by the malignant transformation of immature CD34+ progenitor cells. Transformation is associated with elevated expression of the Wilm's tumor gene encoded transcription factor (WT1). Here we demonstrate that WT1 can serve as a target for cytotoxic T lymphocytes (CTL) with exquisite specificity for leukemic progenitor cells. HLA-A0201– restricted CTL specific for WT1 kill leukemia cell lines and inhibit colony formation by transformed CD34+ progenitor cells isolated from patients with chronic myeloid leukemia (CML), whereas colony formation by normal CD34+ progenitor cells is unaffected. Thus, the tissue-specific transcription factor WT1 is an ideal target for CTL-mediated purging of leukemic progenitor cells in vitro and for antigen-specific therapy of leukemia and other WT1-expressing malignancies in vivo.

Analysis of Wilms tumor gene (WT1) expression in acute leukemia patients with special reference to the differential diagnosis between eosinophilic leukemia and idiopathic hypereosinophilic syndromes

Continuous Wilms' tumor gene (WT1) expression is a typical feature of leukemic blasts in AML, ALL, and blast crisis CML patients. It is easily detectable by a variety of RT-PCR protocols, which differ mainly in their sensitivity. The nuclear WT1 protein can be found in blasts of approximately 50-60% of acute leukemia patients at diagnosis. Conversely, WT1 is only transiently expressed in normal hemopoiesis. Early CD34+ hemopoietic progenitors express WT1, whereas no WT1 mRNA transcripts can be found in mature blood cells and differentiation-induced committed CD34- progenitors. As a powerful complementary diagnostic tool, testing for WT1 expression can be helpful to discriminate between eosinophilic leukemia (EoL) patients and patients with idiopathic hypereosinophilic syndromes. Conflicting data about the usefulness of testing for WT1 expression to monitor minimal residual disease (MRD) in treated leukemia patients will be discussed. Finally, research strategies to circumvent shortcomings in detecting leukemia-associated WT1 expression will be outlined.

Wilms' tumour gene (wt1) expression at diagnosis has no prognostic relevance in childhood acute lymphoblastic leukaemia treated by an intensive chemotherapy protocol

Expression of the Wilms' tumour gene (wt1) has been demonstrated in a large proportion of human acute leukaemias and is thought to play a role in leukaemogenesis. Recent observations in adult patients with acute leukaemia suggest that wt1 gene expression is a poor prognostic factor. In childhood acute leukaemia, the clinical role of wt1 gene expression has not been established. We have therefore investigated bone marrow samples from 50 children with acute lymphocytic leukaemia at the time of diagnosis for the presence of wt1 transcripts to determine whether wt1 gene expression is associated with specific characteristics of leukaemic cells and whether it is predictive of response to treatment. All patients were treated according to the ALL-BFM 90 protocol. The median observation time was 30 months. Wt1 transcripts were detected by RT-PCR in 60% of the diagnostic samples. Wt1 PCR positive patients showed a higher median leukocyte and peripheral blast cell count than wt1 negative patients. High and intermediate risk patients more frequently displayed wt1 transcripts than low risk patients. No correlation between wtl gene expression and FAB type, immunophenotype, co-expression of myeloid antigens or karyotype has been observed. Furthermore, there was no correlation between wt1 gene expression at diagnosis and achievement of complete remission (CR) and no difference in disease-free survival (DFS) or overall survival (OS) between wt1 positive and negative patients (p > 0.1). These data indicate that (1) wt1 gene expression at diagnosis is detected more frequently in patients with high leukocyte and peripheral blast cell counts, but is not associated with specific characteristics of leukaemic cells, (2) wt1 gene expression is not an independent prognostic factor for CR, DFS or OS in childhood ALL treated by an intensive therapy protocol.

Hypermethylation of the Wilms' tumor suppressor gene CpG island in human breast carcinomas

CpG island hypermethylation is known to be associated with transcriptional silencing of tumor suppressor genes in neoplasia. We have previously detected aberrantly methylated sites in the first intron of the Wilms' tumor suppressor (WT1) gene in breast cancer. In the present study, we extended the investigation to a CpG island located in the promoter and first exon regions of WT1. Methylation of this CpG island was found to be extensive in MCF-7 and MDA-MB-231 breast cancer cells, as well as in 25% (five of 20 patients) of primary breast tumors. While levels of the known 3.0-kb WT1 mRNAs were decreased or not detected in these cell lines, the expression could be partially restored following treatment with a demethylation agent, 5-aza-2'-deoxycytidine. Surprisingly, a novel 2.5-kb WT1 transcript was expressed at high levels in both untreated and treated MDA-MB-231 cells. This novel transcript was likely a WT1 variant missing the first exon, and therefore escaped the methylation control present in the normal transcript. Our study implicates the future need to investigate the significance of this aberrant transcript as well as the role of WT1 CpG island hypermethylation in breast neoplasia.

Downregulation of Wilms' tumor gene (WT1) is not a prerequisite for erythroid or megakaryocytic differentiation of the leukemic cell line K562

The Wilms' tumor gene (WT1) encodes a transcription factor of the zinc finger type. A high expression of WT1 has been detected in a range of acute leukemias, and WT1 is downregulated during induced differentiation of some leukemic cell lines. Overexpression of WT1 in some myeloid cell lines confers resistance to differentiation induction. These observations suggest that a high WT1 expression in hematopoietic cells is incompatible with differentiation. In this study, each of the four different isoforms of WT1 was constitutively overexpressed in the leukemic cell line K562. K562 cells express endogenous WT1, which is downregulated as a response to induced differentiation along the erythroid and megakaryocytic pathways. We now demonstrate that a forced exogenous expression of the four different isoforms of WT1 in K562 does not affect the differentiation response, as judged by accumulation of hemoglobin in response to hemin or the expression of megakaryocytic cell surface markers in response to 12-O-tetradecanoylphorbol-13-acetate (TPA). We conclude that downregulation of WT1 during induced differentiation of K562 cells is not a prerequisite for erythroid or megakaryocytic differentiation of these cells.

The Wilms' tumor gene product represses the transcription of thrombospondin 1 in response to overexpression of c-Jun

Thrombospondin 1 (TSP1) is known for its significant anti-angiogenic properties. In a previous study, we have shown that transient or stable overexpression of the transcription factor c-Jun, in rat fibroblasts, leads to repression of TSP1. We now demonstrate that the c-Jun-induced repression of TSP1 does not occur directly and does not require binding of c-Jun to the TSP1 promoter. Instead, repression involves a factor secreted by c-Jun-overexpressing cells. This secreted factor triggers a signal transduction pathway from the membrane to the nucleus, and these signals lead to the binding of the product of the Wilms' tumor suppressor gene, WT1, to the -210 region of the TSP1 promoter. This region binds WT1 and SP1, but not EGR1, although its sequence fits the consensus binding site for this transcription factor. WT1 overexpression in transfected cells inhibits endogenous TSP1 gene expression and TSP1 transcription in experiments using TSP1 promoter-reporter constructs. The WT1 - KTS isoform is more active in repressing TSP1 transcription than WT1 + KTS, while EGR1 is inactive. Enhancement of WT1 binding to DNA in response to c-Jun does not require de novo protein synthesis. The above mechanism for TSP1 repression could apply to other genes, thus coordinating their regulation in the vicinity of a c-Jun-overexpressing cell. We conclude that WT1, which was discovered as a result of its tumor suppressor properties, may also possess oncogenic characteristics in the c-Jun transformation process, and thus repress the anti-angiogenic protein, TSP1.

Expression of Wilms tumor gene (WT1) in children with acute leukemia

Wilms tumor gene (WT1) expression occurs in various malignancies including adult leukemia. WT1 expression was studied in children with acute leukemia according to morphological types and immunophenotypes. RT-PCR was used to examine relative level of WT1 transcripts from the peripheral blood of 15 children diagnosed with acute leukemia: 12 acute lymphoblastic leukemias (ALLs) and 3 acute myelogenous leukemias (AMLs); 8 ALLs newly diagnosed, 2 ALLs in first marrow relapse, 2 ALLs in remission over 2 years, 2 AMLs newly diagnosed, and 1 AML in second marrow relapse. Six healthy adult volunteers were studied for controls. WT1 was detectable in 7 out of 10 ALLs and all 3 AMLs, but not in 2 ALLs in remission and the controls. The expression levels were higher for AMLs than for ALLs. According to the types of ALL, WT1 was detectable in 2 out of 2 non-T group II, 4 out of 6 non-T group III, but not in one CD20+ non-T group IV, while one T-ALL showed a relatively high level. WT1 expression was detectable more frequently in ALL-L2 than in ALL-L1 and with higher levels for ALL-L2. WT1 expression was frequently noted in children with acute leukemia. The results suggest that WT1 transcripts may prove to be a significant tumor marker, possibly as an MRD monitor in evaluating remission status and early relapse, and may also prove to be useful in predicting outcomes in acute leukemia in children.

Regulation of the Wilms' tumour suppressor (WT1) gene by an antisense RNA: a link with genomic imprinting?

Antisense transcripts are typically associated with the down-regulation of gene expression. In this issue, Moorwood et al. present evidence that an antisense RNA can enhance expression of the Wilms' tumour suppressor locus WT1. We suggest that the unusual function of the WT1 antisense RNA might relate to the recent discovery of an antisense transcript that is involved in regulating imprinted expression of the murine Igf2r gene, particularly since there is some evidence that the WT1 gene is regulated by genomic imprinting in humans.