Loss of alleles at loci on human chromosome 11 during genesis of Wilms' tumour

[Research on Analysis of Final Diagnosis and Prognostic Factors, and Development of New Therapeutic Drugs for Malignant Tumors (Especially Malignant Pediatric Tumors)]

Outcomes of treatment for malignant pediatric tumors including leukemia are improving by conventional multimodal treatment with strong chemotherapy, surgical resection, radiotherapy, and bone marrow transplantation. However, patients with advanced neuroblastoma, metastatic Ewing's sarcoma family of tumor (ESFT), and metastatic osteosarcoma continue to have an extremely poor prognosis. Therefore novel therapeutic strategies are urgently needed to improve their survival. Apoptotic cell death is a key mechanism for normal cellular homeostasis. Intact apoptotic mechanisms are pivotal for embryonic development, tissue remodeling, immune regulation, and tumor regression. Genetic aberrations disrupting programmed cell death often underpin tumorigenesis and drug resistance. Moreover, it has been suggested that apoptosis or cell differentiation proceeds to spontaneous regression in early stage neuroblastoma. Therefore apoptosis or cell differentiation is a critical event in this cancer. We extracted many compounds from natural plants (Angelica keiskei, Alpinia officiarum, Lycaria puchury-major, Brassica rapa) or synthesized cyclophane pyridine, indirubin derivatives, vitamin K3 derivatives, burchellin derivatives, and GANT61, and examined their effects on apoptosis, cell differentiation, and cell cycle in neuroblastoma and ESFT cell lines compared with normal cells. Some compounds were very effective against these tumor cells. These results suggest that they may be applicable as an efficacious and safe drug for the treatment of malignant pediatric tumors.

11p13 Deletion and Reduced RBC Catalase in a Patient with Aniridia, Glaucoma and Bilateral Wilms’ Tumor

A rare case of a one-year-old child with Wilms’ tumor, aniridia and glaucoma is described, in whom bone marrow chromosome analysis showed the presence of an interstitial micro-deletion on the short arm of chromosome 11, presumably involving the pl3 band. Research of the enzyme activity of RBC catalase showed a 40% reduction. This finding is compatible with the loss of the 11p13 band which contains the gene coding this enzyme. 11p13 deletion in Wilms’ tumor and 13q interstitial deletion in retinoblastoma provide a rare case of pre-zygotic chromosome abnormality, which may be considered to have a determinant role in the tumor etiopathogenesis.

IGF2-derived miR-483 mediated oncofunction by suppressing DLC-1 and associated with colorectal cancer

Emerging evidence indicates that IGF2 plays an important role in various human malignancies, including colorectal cancer (CRC). Hsa-miR-483 is located within intron 7 of the IGF2 locus. However, the mechanism by which increased IGF2 induces carcinogenesis remains largely elusive. DLC-1 has been identified as a candidate tumor suppressor. In this study, we aimed at investigating whether miR-483 transcription is IGF2-dependent, identifying the functional target of miR-483, and evaluating whether tissue and serum miR-483-3p or miR-483-5p levels are associated with CRC. Our results showed that sequences upstream miR-483 had undetectable promoter activity and levels of IGF2, miR-483-3p, and miR-483-5p were synchronously increased in CRC tissues. Positive correlations between IGF2 and miR-483-3p (r=0.4984, ***p<0.0001), and between IGF2 and miR-483-5p (r=0.6659, ***p<0.0001) expression were found. In addition, patients with CRC had a significantly higher serum miR-483-5p level (*p<0.05) compared to normal controls. DLC-1 expression was decreased in colorectal cancer tissues and diminished through transient transfection with miR-483-3p. Our results suggest that IGF2 may exert its oncofunction, at least partly, through its parasitic miR-483 which suppressed DLC-1 in CRC cells. Thus, miR-483 might serve as a new target for therapy and a potential biomarker for the detection of colorectal cancer.

Clonality and evolutionary history of rhabdomyosarcoma

To infer the subclonality of rhabdomyosarcoma (RMS) and predict the temporal order of genetic events for the tumorigenic process, and to identify novel drivers, we applied a systematic method that takes into account germline and somatic alterations in 44 tumor-normal RMS pairs using deep whole-genome sequencing. Intriguingly, we find that loss of heterozygosity of 11p15.5 and mutations in RAS pathway genes occur early in the evolutionary history of the PAX-fusion-negative-RMS (PFN-RMS) subtype. We discover several early mutations in non-RAS mutated samples and predict them to be drivers in PFN-RMS including recurrent mutation of PKN1. In contrast, we find that PAX-fusion-positive (PFP) subtype tumors have undergone whole-genome duplication in the late stage of cancer evolutionary history and have acquired fewer mutations and subclones than PFN-RMS. Moreover we predict that the PAX3-FOXO1 fusion event occurs earlier than the whole genome duplication. Our findings provide information critical to the understanding of tumorigenesis of RMS.

Oncogenic role of miR-483-3p at the IGF2/483 locus

hsa-mir-483 is located within intron 2 of the IGF2 locus. We found that the mature microRNA (miRNA) miR-483-3p is overexpressed in 100% of Wilms' tumors. In addition, colon, breast, and liver cancers exhibit high or even extremely high levels of miR-483-3p in approximately 30% of the cases. A coregulation with IGF2 mRNA was detected, although some tumors exhibited high expression of miR-483-3p without a concomitant increase of IGF2. These findings suggested that miR-483-3p could cooperate with IGF2 or act as an autonomous oncogene. Indeed, here we prove that an anti-miRNA oligonucleotide against miR-483-3p could inhibit the miRNAs without affecting IGF2 mRNA and it could suppress tumorigenicity of HepG2 cells, a cell line that overexpresses miR-483-3p and IGF2. Conversely, no antitumor effect was elicited by inhibition of IGF2. The oncogenic mechanism of miR-483-3p was at least partially clarified by the finding that it could modulate the proapoptotic protein BBC3/PUMA and miR-483-3p enforced expression could protect cells from apoptosis. Our results indicate that miR-483-3p could function as an antiapoptotic oncogene in various human cancers and reveal a new, potentially important target for anticancer therapy.

DNA fingerprints of dogs and cats

Human minisatellite probes consisting of tandem repeats of the 'core' sequence, a putative recombination signal in human DNA, cross-hybridize to multiple polymorphic fragments in dog and cat DNA to produce individual-specific DNA 'fingerprints'. Pedigree analysis shows that most of the DNA fragments detected in an individual are heterozygous, and that these fragments are derived from multiple dispersed autosomal loci. DNA fingerprints of cats and dogs should prove suitable for individual identification and for establishing family relationships. They are also suitable for rapid marker generation in large pedigrees and could be applied to linkage analysis in these animals.

A genetic basis for tumour suppression

The technique of somatic cell hybridization has established the phenomenon of tumour suppression and provided evidence for a genetic basis for suppression. Further refinements aimed at eventually identifying 'tumour suppressor' genes include the use of monochromosome transfer via microcell hybridization. The application of this technique to the study of tumour suppression in tumorigenic HeLa cell x fibroblast hybrids, Wilms' tumour, retinoblastoma and osteosarcoma cells is described. The issue of whether tumour suppression involves a direct effect on expression of activated oncogenes is discussed. Transformation of normal human cells in culture by activated cellular oncogenes is an extremely rare event. This may be due to a relatively greater genomic stability of human cells compared to rodent cells. We describe the use of a spontaneously immortalized human keratinocyte cell line, HaCaT, for studies of the effects of introduction of activated c-Ha-ras oncogene into these cells, with particular reference to tumorigenic conversion.

Epidemiology of genetically determined cancer

Dominantly heritable susceptibility is known for virtually every cancer. Susceptibility is typically restricted to one or a few tumours. For some tumours there appear to be at least two different predisposing conditions. Some mutant gene carriers survive to old age without developing the expected tumour(s). Some cases are new germline mutations. None of the conditions is very common, because of natural selection against gene carriers. Two questions arise: What is inherited? What is the relationship between the hereditary and non-hereditary forms of the same tumour? Retinoblastoma is a prototypic tumour. Penetrance in humans is nearly complete by the age of five years in the heritable form, which usually affects both eyes. Rare cases in which there is a constitutional deletion of chromosomal band 13q14 permitted localization of the responsible gene. Tumour formation is clearly a rare event at the cellular level, suggesting the necessity of a second, somatic, event. The difference in ages at diagnosis between unilateral and bilateral cases also suggests that two somatic events occur in non-hereditary cases. One explanation is that the gene is recessive and the second event involves loss of the remaining normal allele by mutation, non-disjunction, deletion or somatic recombination. The normal allele may be regarded as anti-oncogenic.

Loss of genetic information in cancer

The determination and comparison of genotypic combinations at genomic loci in normal and tumour tissues from patients with various types of cancer have defined the chromosomal locations of loci at which recessive mutations play a role in disease. The predisposing nature of some of these mutant alleles is exemplified in studies of retinoblastoma and osteogenic sarcoma. These two clinically associated diseases share a pathogenetically causal predisposition that maps to chromosome position 13q14. A similar mechanism at 11p15.5 is involved in the development of the embryonal variant of rhabdomyo-sarcoma, Wilms' tumour and hepatoblastoma. Finally, genomic alteration of chromosome 10 is apparent in glioblastomas and mixed tumours of glioblastoma/astrocytoma grade III but not in homogenous astrocytoma grades II or III, suggesting the definition of a locus involved in tumour progression and, perhaps, an approach to molecular genetic staging of tumours.

[Wilms tumor]

Wilms tumor is the most frequent malignancy of the urogenital tract in children. Its treatment gives an excellent example of the efficacy of multimodal therapeutic strategies in oncological diseases. In particular, the performance of international, randomized multicenter studies has led to a continuous increase in disease-free survival among the affected patients in recent decades, thanks to increasingly detailed stratification of individual elements of the therapy. The pediatric urologist has a definite place in interdisciplinary teams treating Wilms tumor, being needed for the operative component of the treatment. For further improvement of the prognosis in this disease and to reduce the comorbidity caused by the treatment, the major challenge for pediatric urologists in coming years will be to make the surgery less traumatic and thus also to reduce the incidence and severity of perioperative complications.

Frequency and heritability of WT1 mutations in nonsyndromic Wilms' tumor patients: a UK Children's Cancer Study Group Study

PURPOSE

Constitutional WT1 mutations in patients with Wilms' tumor (WT) have specifically been associated with genitourinary abnormalities, such as cryptorchidism and hypospadias. We sought to ascertain the frequency and heritability of constitutional WT1 mutations in nonsyndromic WT patients.

PATIENTS AND METHODS

Constitutional DNA from 282 patients treated at seven United Kingdom Children's Cancer Study Group centers was screened for WT1 mutations using heteroduplex analysis. Bidirectional sequencing was used to confirm the mutation and to analyze the corresponding parental DNA samples.

RESULTS

Five different constitutional WT1 mutations were identified in six children. Mutations in four patients were confirmed to be de novo, and all five mutations are predicted to produce truncated protein. The WT1 mutation group had a young median age at diagnosis of 13.8 months, compared with 34.9 months in the group in whom no WT1 mutations were found; four were female and two were male; and all tumors were of favorable histology. The three tumors with known histologic subtype were stromal-predominant. Contrary to expectation, four of six mutations occurred in children with unilateral tumors without any associated genitourinary abnormality.

CONCLUSION

Constitutional WT1 mutations occur with a low frequency (2.1%; 95% CI, 0.8% to 4.6%) in nonsyndromic WT patients. Most mutations occurred in children with unilateral WT without associated genitourinary abnormalities, creating difficulties in identifying individuals with germline mutations on phenotype alone. Two factors that may indicate that an individual is carrying a germline WT1 mutation are an early age of onset and stromal-predominant histology of the WT.

A novel t(2;20)(q35;p12) in embryonal rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood, accounting for 5%-8% of all pediatric malignancies. RMS can be categorized into several subtypes, including embryonal RMS (ERMS), the botryoid and spindle cell variants of ERMS, and alveolar RMS (ARMS). The t(2;13)(q35;q14) and the variant t(1;13)(p36;q14) are seen in a majority of ARMS cases. In contrast, the embryonal subtype of rhabdomyosarcoma has not been associated with a recurring chromosomal translocation. We describe here a novel chromosomal t(2;20)(q35;p12) occurring in a case of childhood RMS with embryonal histology. It is notable that this translocation harbors breakpoints at or near the locus of the PAX3 gene, which is involved in the most common recurring translocation associated with ARMS.

Usefulness of quantitative assessment of Wilms tumor suppressor gene expression in chronic myeloid leukemia patients undergoing imatinib therapy

The Wilms tumor suppressor gene (WT1) is overexpressed in a number of human hematological malignancies, including chronic myeloid leukemia (CML). Although at present, the biological significance of WT1 expression in CML in still unclear, this marker could represent a useful tool for molecular monitoring of CML patients prior to and post imatinib therapy. In fact, the use of real-time polymerase chaine reaction (PCR) to quantitatively measure the WT1 transcript amount may be a predictor of patient response to imatinib therapy.

Molecular analysis of region t(5;6)(q21;q21) in Wilms tumor

We have previously described the physical localization of a constitutional t(5;6)(q21;q21) in a patient (tumor cell sample designated as MA214) with bilateral Wilms tumor (WT). We have now physically refined the breakpoints and identified putative gene targets within this region. The translocation breakpoints are contained within a 2.5-Mbp region on 5q21 containing four candidate genes and a 1.3-Mbp region on 6q21 that contains three candidate genes. To explore the role of this region in WT genesis, we have performed loss of heterozygosity (LOH) analysis with markers flanking the translocation breakpoints in tumor from MA214 and a panel of sporadic WT. Alleles were retained for all informative markers used in the MA214 tumor. In sporadic tumors LOH was found in 6 of 63 (9.5%) and 5 of 62 (8%) informative cases for flanking markers D6S301 and D6S1592 on 6q21. LOH was found in 3 of 58 (5.2%) and 2 of 54 (3.6%) for flanking markers D5S495 and D5S409 on 5q21. These preliminary data suggest LOH at the t(5;6)(q21;q21) region is unlikely to be a mechanism for tumor development in MA214, but may be important for a subgroup of sporadic WT.

C/EBP-beta, C/EBP-delta, PU.1, AML1 genes: mutational analysis in 381 samples of hematopoietic and solid malignancies

Mutations of transcription factors are associated with the pathogenesis of cancer. Genomic DNA from 381 cancers and cell lines representing leukemias, lymphomas and a variety of solid tumors were examined for mutations of genes coding for the C/EBP-beta, C/EBP-alpha, PU.1, and AML1 transcription factors using single strand conformation polymorphism (SSCP) and direct DNA sequencing. Mutation of C/EBP-beta (a chronic myelogenous leukemia cell line, Kcl22) and C/EBP-delta (a Burkitt's lymphoma cell line, Raji) were found. Interestingly, the sample with a C/EBP-beta alterations had two missense (P236L and G252A) and two silent mutations in a highly conserved region of the gene. The C/EBP-delta alteration in Raji was a missense mutation (A177G). These findings suggest that mutations of the C/EBP-beta, C/EBP-delta, PU.1, and AML1 rarely contribute to the development of hematopoietic or solid cancers.

Wilms tumor and the WT1 gene

Wilms tumor or nephroblastoma is a pediatric kidney cancer arising from pluripotent embryonic renal precursors. Multiple genetic loci have been linked to Wilms tumorigenesis; positional cloning strategies have led to the identification of the WT1 tumor suppressor gene at chromosome 11p13. WT1 encodes a zinc finger transcription factor that is inactivated in the germline of children with genetic predisposition to Wilms tumor and in a subset of sporadic cancers. When present in the germline, specific heterozygous dominant-negative mutations are associated with severe abnormalities of renal and sexual differentiation, pointing to the essential role of WT1 for normal genitourinary development. The role of this tumor suppressor in normal organ-specific differentiation is also supported by the highly restricted temporal and spatial expression of WT1 in glomerular precursors of the developing kidney and by the failure of kidney development in wt1-null mice. Of two major alternative splicing products encoded by WT1, the (-KTS) isoform appears to mediate transcriptional activation of genes implicated in cellular differentiation, possibly also repressing proliferation-associated genes. The (+KTS) isoform, whose DNA-binding domain is disrupted by the insertion of three amino acids, may be involved in some aspect of mRNA processing. In addition to its function in genitourinary development, a role for WT1 in hematopoiesis is suggested by its aberrant expression and/or mutation in a subset of acute human leukemias. WT1 is also expressed in mesothelial cells; a specific oncogenic chromosomal translocation fusing the N-terminal domain of the Ewing sarcoma gene EWS to the three C-terminal zinc fingers of WT1 underlies desmoplastic small round cell tumor, an abdominal tumor thought to arise from the peritoneal lining. Understanding the distinct functional properties of WT1 isoforms and tumor-associated variants will provide unique insight into the link between normal organ-specific differentiation and malignancy.

Progress in the diagnosis and treatment of rhabdomyosarcoma and related soft tissue sarcomas

Advances in the diagnosis and treatment of rhabdomyosarcoma and related soft tissue sarcomas continue in the Intergroup Rhabdomyosarcoma Study Group (IRSG) and European cooperative groups. The use of molecular biology techniques in soft tissue sarcomas are redefining the classic pathology of these small blue cell tumors. Improvements in imaging, radiotherapy, and surgery, in part, deserve credit for the better survival seen in all cooperative trials. These advances confound the interpretation of consecutively run chemotherapy trials using historical comparisons. The IRSG has reported improvement in the prognosis of both nonmetastatic and metastatic embryonal rhabdomyosarcoma as attributable to three, three-drug regimens that use cyclophosphamide at 2.2 g/m2 in either maintenance or induction and maintenance therapy. Patients of any age with metastatic, nonembryonal, and those over 10 years of age with metastatic embryonal rhabdomyosarcoma continue to have a poor prognosis, which even megatherapy has failed to change. The doublet of ifosfamide and etoposide in combination with vincristine, actinomycin D, and cyclophosphamide at 2.2 g/m2 achieved a remarkable 3-year survival of 58% in patients with metastatic rhabdomyosarcoma and undifferentiated soft tissue sarcoma. The topoisomerase I inhibitor, topotecan, has recently been found by the IRSG to have a 57% overall response rate in patients with metastatic alveolar rhabdomyosarcoma. Topotecan has completed testing with cyclophosphamide in a phase II window study in newly diagnosed patients with metastatic disease and has been incorporated into a randomized trial in intermediate risk patients in IRSG-V. Molecular studies in IRSG-V will be applied in the detection of occult bone marrow metastases and the evaluation of resection margins at initial and second-look surgery. Long-term follow-up will be required in patients with gross residual sarcoma randomized to conventional and hyperfractionated radiotherapy in IRSG-IV to assess late effects. Although older patients with unfavorable histology and metastatic disease continue to have a poor prognosis, the overall 5-year survival of children and adolescents with nonmetastatic and metastatic rhabdomyosarcoma is approaching 80%. As molecular discoveries advance the diagnosis and detection of rhabdomyosarcoma, it is hoped that the futuristic molecular based treatment strategies in development and early testing will further improve survival in high-risk patients with metastatic soft tissue sarcoma.

Pathogenesis of adrenocortical incidentalomas and genetic syndromes associated with adrenocortical neoplasms

The study of genetic syndromes associated with adrenocortical tumors (Beckwith-Wiedemann, Li-Fraumeni, McCune-Albright, Carney, and multiple endocrine neoplasia type 1) has shed light on the molecular basis of tumorigenesis. Abnormalities at the 11p15 locus appear as crucial and frequent events found specifically in malignant, sporadic tumors, leading to overexpression of a growth-promoting factor and loss of expression of tumor suppressor genes. In benign tumors, the cAMP pathway can be exacerbated in an ACTH-independent manner when various membrane receptors of the seven transmembrane superfamily are "illegitimately" expressed.

Dissociation of p53-mediated suppression of homologous recombination from G1/S cell cycle checkpoint control

The tumor suppressor p53 is considered as the guardian of the genome which is activated following genotoxic stress. In many cell types, p53 mediates G1 cell cycle arrest as the predominant cellular response. Inactivation of wild-type p53 leads to loss of G1/S checkpoint control and to genomic instability, including increased spontaneous homologous recombination (HR). To determine whether regulation of the G1/S checkpoint is required for suppression of HR, we assessed recombination events using a plasmid substrate that stably integrated into the genome of p53-null mouse fibroblasts. Exogenous expression of a temperature-sensitive p53 protein (Ala135 to Val), which had lost trans-activation function and could not regulate G1/S transition when in mutant conformation, reduced HR rates to the same extent as wild-type p53. Furthermore, a p53 construct with an alternatively-spliced carboxy terminus also retained this ability in the absence of both activities, G1/S control and non-sequence specific DNA binding as mediated by the carboxy terminus. Our data dissociate regulation of HR by p53 from its role as a cell cycle checkpoint protein. The results support a model which extends p53's role as a guardian of the genome to include transactivation-independent regulatory functions in DNA repair, replication and recombination.

Molecular genetic studies of chromosome 11 and chromosome 22q DNA sequences in pediatric medulloblastomas

Medulloblastomas are primitive neuroectodermal tumors (PNETs) of the cerebellum with poorly understood pathogenesis. Previous molecular studies suggested a role for loci on chromosome 11 in the development of medulloblastomas-PNETs. In order to identify the frequency of loss and eventually the extent of allelic loss on chromosome 11, we have examined 23 pediatric medulloblastomas for loss of heterozygosity (LOH) with 16 polymorphic microsatellites. Our data reveal that LOH on 11p or 11q occurs rarely (13%) suggesting the unlikely involvement of chromosome 11 in most cases of medulloblastomas. The same frequency of LOH in medulloblastomas was detected using 8 microsatellites on 22q. Alterations of microsatellite length were found in only 4/594 PCR analyses using 28 markers located on chromosomes 2, 9, 11, 18, and 22, demonstrating that genomic instability is uncommon in medulloblastomas.

Molecular biology for the pediatric surgeon

Molecular biology is leading a revolution in our understanding, diagnosis, and treatment of disease and will continue to do so. Medicine in the future will require a greater understanding of this field and its methods by medical practitioners. This report reviews the basic aspects of the field including recombinant DNA methods. Of particular importance is how molecular biology will impact pediatric surgeons. Accordingly, the final section of this report briefly reviews the molecular biology of three diseases commonly treated by pediatric surgeons.

Hemihypertrophy and a poorly differentiated embryonal rhabdomyosarcoma of the pelvis

BACKGROUND

Asymmetry of the limbs (conventionally known as hemihypertrophy) is one of the overgrowth syndromes occurring sporadically in the general population at a frequency of approximately 1:86,000. Hemihypertrophy is also reported as part of the Beckwith-Wiedemann syndrome which has as its cardinal features omphalocele, macroglossia and gigantism with hypoglycemia, organomegaly, renal anomalies, hemihypertrophy, and embryonal tumors occurring less frequently. Various neoplasms are also associated with isolated hemihypertrophy. Wilms tumor, adrenocortical carcinoma, and hepatoblastoma are the most frequent. Rhabdomyosarcoma, neuroblastoma, phaeochromocytoma, and undifferentiated sarcoma of the lung are encountered only rarely. Loss of heterozygosity (LOH) of chromosome 11p15.5 is strongly associated with childhood embryonal tumors, particularly Wilms tumor, hepatoblastoma, and rhabdomyosarcoma.

PROCEDURE AND RESULTS

In this article, we describe an adolescent male with congenital asymmetry of the lower limbs who presented with a large poorly differentiated pelvic sarcoma. Conventional histologic, immunohistochemical, and ultrastructural studies of this tumor were insufficient for accurate subclassfication. However, positive staining for MyoD1 (a recently identified embryonically expressed marker of muscle differentiation) and LOH at the tyrosine hydroxylase locus of chromosome 11p15.5 by molecular analysis favored the diagnosis of embryonal rhabdomyosarcoma over an undifferentiated sarcoma.

CONCLUSIONS

This case stresses the importance of pursuing clinical findings when they occur in conditions with an increased risk of developing cancer, which in this case was asymmetry of a limb. Also illustrated by this patient is the need for early consideration of molecular diagnostic tests where available, to refine an uncertain pathologic diagnosis that may ultimately have an impact on treatment and prognosis.

Cytogenetically unrelated clones in therapy-related myelodysplasia and acute myeloid leukemia: experience from the Copenhagen series updated to 180 consecutive cases

During the period from 1995 to 1997, we studied 19 new cases of therapy-related myelodysplasia (t-MDS) and acute myeloid leukemia (t-AML), extending our series to 180 consecutive cases: 123 patients with t-MDS and 57 patients with t-AML. Cytogenetically unrelated clones were observed in 13 patients: 11 patients with two unrelated clones, one patient with three unrelated clones, and one patient with four unrelated clones. Twelve cases of unrelated clones presented as t-MDS, whereas only one case presented as overt t-AML. Partial or complete deletions of the long arms or monosomy for chromosome 5 or chromosome 7, which are characteristic of t-MDS and t-AML, were observed in both unrelated clones in four patients and in one unrelated clone only in six patients, whereas three patients showed aberrations in both clones that were uncharacteristic of t-MDS or t-AML. Three different interpretations of the origin and significance of cytogenetically unrelated clones in t-MDS and t-AML are presented, although the disease is still considered to be monoclonal. First, patients with different defects of the long arm of chromosome 5 or chromosome 7 in two unrelated clones often seem to have acquired these aberrations as independent events. For this reason, it is possible that they may play an important role in leukemic transformation, for instance, by activating or potentiating the effect of a genetic change that is present in all cells but not disclosed as a visible chromosome abnormality. In cases with involvement of other chromosomes, unrelated clones sometimes develop by cytogenetic change in only a subclone of cells, indicating that they play a role only in tumor progression. Finally, unrelated clones in t-MDS and t-AML may represent two different monoclonal diseases: the primary tumor and t-MDS. This view is supported by the significant excess of unrelated clones observed in t-MDS following multiple myeloma (4 in 13 cases) compared with other diseases (9 in 167 cases; P = 0.02), and by results from a case with a balanced translocation that is highly characteristic of non-Hodgkin's lymphoma in one clone and a t-MDS-associated deletion of the long arm of chromosome 5 in another.

Wilms tumor genetics

Wilms tumor (WT), a sporadic and familial childhood kidney tumor, is genetically heterogeneous. One WT gene, WT1 at 11p13, has been cloned, but only a minority of WTs carry detectable mutations at that locus. WT1 can also be excluded as the predisposition gene in most WT families, implying the existence of other WT genes. Studies of WT families have demonstrated that familial predisposition is also heterogeneous and involves at least two other loci besides WT1. In addition to WT1 and the familial predisposition genes, a role for other genes in the development of WTs is implied by the somatic occurrence of genetic and epigenetic alterations such as loss of heterozygosity and loss of imprinting in tumors and, rarely, the observation of nonchromosome-11 constitutional aberrations in WT patients. Determining the pattern of presence or absence of these various genetic alterations in tumors and elucidating the function of the genes involved will provide a better understanding of the cellular processes that are critical for normal cell growth and differentiation, but are abrogated in the course of tumorigenesis.

Increased somatic recombination in methylation tolerant human cells with defective DNA mismatch repair

We have studied whether spontaneous intrachromosomal recombination is altered in methylation tolerant human cells with a defect in mismatch repair. Somatic recombination was analysed in HeLaMR cells containing the vector pTPSN, which carries two copies of the gene for hygromycin resistance. The hygromycin genes are both inactivated by an inserted HindIII linker but hygromycin-resistant clones can arise by recombination. The spontaneous rate of recombination in a clone of HeLaMR cells containing a single integrated copy of pTPSN (HeLaG1) was 3.1x10(-6)/cell per generation. Two methylation tolerant variants from HeLaG1 cells (clone 12 and clone 15) were isolated by exposure to MNNG. Clone 12 cells exhibited a 16-fold increase in spontaneous mutation rate at the HPRT gene and extensive microsatellite instability at both mono- and dinucleotide repeats. Microsatellite instability limited to mononucleotide repeats was found in clone 15, whereas the mutation rate at HPRT was not significantly affected. A mismatch binding defect in extracts of clone 15 could be complemented by exogenous GTBP but not by purified hMSH2 protein. These data suggest that clone 15 is defective in GTBP. Extracts of clone 12 were unable to correct a single C:T mispair and complementation by extracts of human colorectal carcinoma cells with known deficiencies in mismatch repair indicated a defect in hMutLalpha. Western blotting with antibodies against different human mismatch repair proteins showed that clone 12 cells did not express hPMS2 protein, but expression of hMLH1, hMSH2 and GTBP appeared normal. The spontaneous recombination rate of clone 12 was 19-fold higher than the parental HeLaG1 cells, whereas no increase was observed in clone 15. Analysis of individual recombinants showed that hygromycin resistance arose exclusively by gene conversion. Our data indicate that mismatch correction regulates somatic recombination in human cells.

Molecular cytogenetic studies of pediatric ependymomas

Cytogenetic and molecular studies of ependymomas have previously demonstrated deletions of chromosomes 17 and 22 as frequent abnormalities, implicating inactivation of tumor suppressor genes in the pathogenesis of these tumors. In the present study, we analyzed 22 childhood ependymomas by standard cytogenetic analysis, fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR)-based microsatellite analysis of chromosomes 17 and 22. Microsatellite analysis of chromosome 6 was performed to identify submicroscopic deletions implicated by the cytogenetic studies. Among the 22 cases, we demonstrated loss of chromosome 22 in 2 patients, deletion of chromosome 17 in 2 patients, and rearrangements or deletions of chromosome 6 in 5 patients. These data do not suggest that loss of a gene on chromosome 17p plays a primary role in the initiation of pediatric ependymomas. This is in contrast to what has been reported for pediatric CNS primitive neuroectodermal tumors and malignant astrocytomas, in which deletion of 17p is regarded as a primary event. Furthermore, loss of chromosome 22 may define a subset of ependymomas more commonly seen in adults. Cytogenetic studies in this series, however, suggest that a region on the long arm of chromosome may be involved in the development and/or progression of ependymomas in children.

The molecular pathology of urological malignancies

Urological malignancies kill over 16,000 people annually in England and Wales. There have been exciting recent developments in our understanding of the molecular pathogenesis of these diseases, although many questions remain unanswered. Three separate genes (WT1, WT2, and WT3) have been implicated in Wilms' tumour development. Patients with von Hippel-Lindau (VHL) syndrome develop renal cell carcinoma and it has been shown that VHL protein inhibits elongin, a cellular transcription factor which controls RNA elongation. Use of molecular markers to identify superficial bladder tumours likely to progress to muscle invasive disease has met with some success. Increased epidermal growth factor receptor (EGFR) and p53 expression, and decreased E-cadherin expression all correlate with tumour progression. Tumours in patients with carcinoma in situ have distinct molecular features. Androgen ablation delays disease progression in men with prostate cancer, but relapse is inevitable. Research has been directed towards elucidating the mechanisms by which prostate cancer 'escapes' hormonal control. Mutations in the androgen receptor have been identified. It is apparent that locally produced growth factors mediate androgen-dependent processes and these too have been implicated in prostate carcinogenesis.

Identical genetic changes in different histologic components of Wilms' tumors

BACKGROUND

In young children and infants, Wilms' tumor is the most common cancer of the kidney. Wilms' tumor exhibits heterogeneous histopathologic features, consisting of rapidly proliferating blastemal and epithelial cells and a stromal component that has heterologous elements (e.g., cartilage, bone, and striated muscle). It is unclear whether the stromal and heterologous components of sporadic Wilms' tumor are neoplastic or should be considered non-neoplastic.

PURPOSE

Our purpose was twofold: 1) to selectively analyze the different histologic tissue components of sporadic Wilms' tumors, including blastemal, epithelial, stromal, and heterologous elements, for loss of heterozygosity (LOH) of the WT1 gene and for expression of the WT1 gene and 2) to determine the role of WT1 gene expression in the development of these tissues.

METHODS

By use of tissue microdissection techniques, various histologic elements (blastema, stroma, epithelium, and striated muscle) of sporadic Wilms' tumor were obtained from specimens taken from 18 patients. DNA was extracted from the dissected tissue fragments, and DNA solutions were amplified by use of the polymerase chain reaction and the polymorphic genomic markers D11S1392 and D11S904 to detect LOH at the WT1 gene locus (11p13). Three selected specimens with heterologous elements and LOH at 11p13 were analyzed for expression of the WT1 gene by means of the in situ reverse transcription-polymerase chain reaction.

RESULTS

Nine (50%) of the 18 specimens showed LOH at the WT1 locus. Although identical WT1 gene deletion was consistently observed in all of the various histologic components of these nine specimens, WT1 gene expression was high in the blastemal and epithelial elements and low in the stromal and heterologous elements.

CONCLUSIONS AND IMPLICATIONS

Identical allelic deletion at 11p13 in all components of the sporadic Wilms' tumors examined suggests that the stromal tissue components are neoplastic rather than non-neoplastic. In conjunction with variable WT1 gene expression in the different histologic components, the results raise the possibility that undifferentiated blastemal cells are the precursors of the stromal and heterologous elements. Morphologically benign stromal and heterologous elements may therefore be derived from neoplastic cells. The developmental state of the various tissue components of Wilms' tumor may be attributed to an altered residual WT1 gene that is required for the maturation of blastemal and epithelial cells but that is not required for the maturation of stromal and heterologous elements.

Genetic predisposition to cancer and familial cancer syndromes

Approximately 10% to 15% of childhood cancers are hereditary or familial in nature. For several genetic disorders, the development of cancer is a secondary manifestation of the clinical phenotype, whereas cancer predisposition syndromes are generally recognized by the manifestation of characteristic malignancies. The study of pediatric cancer and rare hereditary cancer syndromes and associations has led to the identification of numerous cancer genes that are known to play critical roles in both normal and abnormal cellular growth, differentiation, and proliferation. The potential to identify such genetic markers of cancer predisposition poses difficult social, legal, and ethical questions in their application to clinical practice.

Chromosome 11 abnormalities in Bowen disease of the vulva

Chromosomal cytogenetic abnormalities are common in tumor cells and are often the basis for more detailed chromosomal mapping of tumor suppressor and oncogenes. Chromosome 11 abnormalities are frequently recognized in various neoplasms. We report a case of Bowen disease (squamous cell carcinoma in situ) of the vulva with an isolated 11p cytogenetic abnormality. A chromosome 11 paint confirmed two copies of chromosome 11 in all analyzed metaphases. An 11p subtelomeric probe confirmed an abnormality of 11p15-->pter indicative of a deletion. Previous studies of invasive vulvar cancers also frequently show 11p cytogenetic abnormalities, but never as an isolated finding. The patient suffered from other diseases that may also be related to this locus. Breakage and p53 studies were normal. It is possible that an 11p abnormality in Bowen's disease is a precursor in the evolution of invasive vulva cancer.

Comparative cytogenetic studies of benign, borderline, and malignant epithelial ovarian tumors

Comparative cytogenetic studies were performed in 40 cases of untreated epithelial ovarian tumors. Of these 40 tumors, 13 were classified as benign, 3 as borderline, and 24 as malignant, according to the WHO classification for ovarian tumors. Of 13 benign ovarian tumors, 4 (30.8%) showed chromosomal abnormalities. Of 4 ovarian tumors, 3 (75%) had single chromosomal abnormalities, and the remaining tumor (25%) retained multiple chromosomal abnormalities. Of 3 borderline-malignant ovarian tumors, 2 (66.7%) showed chromosomal abnormalities. Of 2 ovarian tumors, 1 (50%) indicated single chromosomal abnormalities, and the remaining tumor (50%) revealed multiple chromosomal abnormalities. Of 24 malignant ovarian tumors, 20 (83.3%) showed chromosomal abnormalities. Of these 20 ovarian tumors, 3 (15%) had single chromosomal abnormalities, and the other 17 (85%) exhibited multiple chromosomal abnormalities. These data indicate that the rate of chromosomal abnormalities, especially multiple abnormalities, increases following the progression of malignancy in epithelial ovarian tumors.

Numerical aberrations of chromosomes 11 and 17 in colorectal adenocarcinomas

Fluorescence in situ hybridization (FISH) is an easy and efficient means of measuring numerical chromosome aberrations in the interphase nuclei of solid tumors; however, the correlation between numerical chromosome aberrations and the clinical stage of solid tumors remains unknown. Thus, in the present study, we investigated the relationship between numerical chromosome aberrations and clinicopathologic features in colorectal adenocarcinomas. FISH was applied to surgically resected colorectal cancer samples from 45 patients to evaluate the numerical aberrations of chromosomes 11 and 17. The mean age of the patients was 65.1 years, and they comprised 13 women and 32 men. According to Dukes' classification, 5 patients were categorized as stage A, 21 as stage B, 10 as stage C, and 9 as stage D. Histologically, 18 of the samples were lymph node metastasis-positive. FISH revealed numerical aberrations of chromosome 11 in 27 out of the 45 patients (60%), and those with a lower chromosome 11 number had a significantly lower incidence of lymph node metastasis (P < 0.05). Chromosome 17 proved to have numerical abnormalities in 33 of the 45 patients (73%), and those with a higher chromosome 17 number had more DNA aneuploidy (P < 0.005). This is the first report to reveal the relationship between monosomy 11 and lymph node metastasis in colorectal adenocarcinomas.

Role of genomic imprinting in Wilms' tumour and overgrowth disorders

Activation of the silent maternal IGF2 allele has recently been found in approximately half of Wilms' tumour (WTs) examined. This process of imprint relaxation leads to biallelic expression of IGF2 and it has been suggested that this is a key event in the onset of some WTs. Although it has previously been proposed that the 11p15 chromosome region contains a growth-promoting gene and a tumour suppressor gene, the simplest explanation is that increased expression of the IGF2 gene is responsible for somatic overgrowth in the BWS and predisposition to tumours. This model explains overgrowth in BWS cases with unbalanced translocations with paternal dup(11p), and cases with balanced maternal translocations which are physically close to the IGF2 gene. Maternal translocations are envisaged to disrupt the maternal IGF2 imprint by a mechanism similar to the position-effect variegation mechanism in Drosophila. Relaxation of IGF2 imprinting has also been detected in several patients with the BWS syndrome and a patient with gigantism and Wilms' tumour. Recent gene disruption experiments have shown that inactivation of the mouse h19 gene leads to biallelic lgf2 expression and extensive proportional overgrowth. This mouse model has parallels with the BWS and WT where it has been found that biallelic IGF2 expression is accompanied by an epigenetic modification of the H19 gene. From these data it is possible to speculate that an epigenetic modification of the H19 gene may be the primary event leading to the relaxation of IGF2 imprinting.

Hereditary cancer: two hits revisited

According to a "two-hit" model, dominantly inherited predisposition to cancer entails a germline mutation, while tumorigenesis requires a second, somatic, mutation. Non-hereditary cancer of the same type requires the same two hits, but both are somatic. The original tumor used in this model, retinoblastoma, involves mutation or loss of both are somatic. The original tumor used in this model, retinoblastoma, involves mutation or loss of both copies of the RB1 tumor-suppressor gene in both hereditary and non-hereditary forms. In fact, most dominantly inherited cancers show this relationship. New dominantly inherited cancers show this relationship. New questions have arisen, however. When a tumor-suppressor gene is ubiquitously expressed, why is there any specificity of tumor predilection? In some instances, it is clear that two hits produce only a benign precursor lesion and that other genetic events are necessary. As the number of necessary events increase, the impact of the germline mutation diminishes. The number of events is least for embryonal tumors, and relatively small for certain sarcomas. Stem-cell proliferation evidently plays a key role early in carcinogenesis. In some tissues it is physiological, as in embryonic development and in certain tissues in adolescence. In adult renewal tissues, the sites of the common carcinomas, mutation may be necessary to impair the control of switching between renewal and replicative cell divisions; the APC gene may be the target of such a mutation.

A common region of loss of heterozygosity in Wilms' tumor and embryonal rhabdomyosarcoma distal to the D11S988 locus on chromosome 11p15.5

The development of Wilms' tumor has been associated with two genetic loci on chromosome 11: WT1 in 11p13 and WT2 in 11p15.5. Here, we have used loss of heterozygosity (LOH) in Wilms' tumors to narrow the WT2 locus distal to the D11S988 locus. A similar region was apparent for the clinically associated tumor, embryonal rhabdomyosarcoma. We have also demonstrated that a constitutional chromosome translocation breakpoint associated with Beckwith-Wiedemann syndrome and an acquired somatic chromosome translocation breakpoint in a rhabdoid tumor each occur in the same chromosomal interval as the smallest region of LOH in Wilms' tumors and embryonal rhabdomyosarcoma. Finally, we report the first Wilms' tumor without a cytogenetic deletion that shows targeted LOH for 11p15 and 11p13 while maintaining germline status for 11p14.

Localization of a tumor suppressor gene in 11p15.5 using the G401 Wilms' tumor assay

Multiple studies have underscored the importance of loss of tumor suppressor genes in the development of human cancer. To identify these genes, we used somatic cell hybrids in a functional assay for tumor suppression in vivo. A tumor suppressor gene in 11p15.5 was detected by transferring single human chromosomes into the G401 Wilms' tumor cell line. In order to better map this gene, we created a series of radiation-reduced t(X;11) chromosomes and characterized them at 24 loci between H-RAS and beta-globin. Interestingly, three of the chromosomes were indistinguishable as determined by genomic and cytogenetic analyses. Each contains an interstitial deletion with one breakpoint in 11p14.1 and the other breakpoint between the D11S601 and D11S648 loci in 11p15.5. PFGE analysis localized the 11p15.5 breakpoints to a 175 kb MluI fragment that hybridized to D11S601 and D11S648 probes. Genomic fragments from this 175 kb region were hybridized to DNA from mouse hybrid lines containing the delta t(X;11) chromosomes. This analysis detected the identical 11p15.5 breakpoint which disrupts a 7.8 kb EcoRI fragment in all three of the delta t(X;11) chromosomes, suggesting they are subclones of the same parent colony. Upon transfer into G401 cells, one of the chromosomes suppressed tumor formation in nude mice, while the other two chromosomes lacked this ability. Thus, our mapping data indicate that the gene in 11p15.5 which suppresses tumor formation in G401 cells must lie telomeric to the D11S601 locus. Koi et al. (Science 260: 361-364, 1993) have used a similar functional assay to localize a growth suppressor gene for the RD cell line centromeric to the D11S724 locus. The combination of functional studies by our lab and theirs significantly narrows the location of the tumor suppressor gene in 11p15.5 to the approximately 500 kb region between D11S601 and D11S724.

High affinity binding sites for the Wilms' tumour suppressor protein WT1

The Wilms' tumour suppressor protein (WT1) is a putative transcriptional regulatory protein with four zinc fingers, the last three of which have extensive sequence homology to the early growth response-1 (EGR-1) protein. Although a peptide encoding the zinc finger domain of WT1[-KTS] can bind to a consensus 9 bp EGR-1 binding site, current knowledge about the mechanisms of zinc finger-DNA interactions would predict a more extended recognition site for WT1. Using a WT1[-KTS] zinc finger peptide (WT1-ZFP) and the template oligonucleotide GCG-TGG-GCG-NNNNN in a binding site selection assay, we have determined that the highest affinity binding sites for WT1[-KTS] consist of a 12 bp sequence GCG-TGG-GCG-(T/G)(G/A/T)(T/G). The binding of WT1-ZFP to a number of the selected sequences was measured by a quantitative nitrocellulose filter binding assay, and the results demonstrated that these sequences have a 4-fold higher affinity for the protein than the nonselected sequence GCG-TGG-GCG-CCC. The full length WT1 protein regulates transcription of reporter genes linked to these high affinity sequences. A peptide lacking the first zinc finger of WT1[-KTS], but containing the three zinc fingers homologous to EGR-1 failed to select any specific sequences downstream of the GCG-TGG-GCG consensus sequence in the binding site selection assay. DNA sequences in the fetal promoter of the insulin-like growth factor II gene that confer WT1 responsiveness in a transient transfection assay bind to the WT1-ZFP with affinities that vary according to the number of consensus bases each sequence possesses in the finger 1 subsite.