Renal tumors induced transplacentally in the rat by n-ethylnitrosourea

Intrarenal Pelvic Nephroblastoma in a Meerkat (Suricata Suricatta)

Nephroblastoma is the most common primary renal tumor in children and has also been reported in domestic and nondomestic animal species. Intrapelvic renal nephroblastoma is a rare variant of this tumor type in human patients. Postmortem examination of a captive meerkat ( Suricata suricatta), which was found dead, revealed enlargement of the pelvis of the left kidney by a tumor mass. Gross, histological, and immunohistochemical findings were consistent with a diagnosis of triphasic intrapelvic renal nephroblastoma. This is the first reported spontaneous case of intrapelvic renal nephroblastoma in a nonhuman species.

Age dependence of radiation-induced renal cell carcinomas in an Eker rat model

Exposure to carcinogens early in life may contribute to cancer development later in life. The amount of radiation exposure children experience during medical procedures has been increasing, so it is important to evaluate the radiation risk of cancer in developing organs. Toward this goal, we assessed the risk of developing renal cell carcinoma using Eker rats as a kidney tumor model. F1 hybrids of male Eker (Tsc2 mutant) and female F344 rats were irradiated with 0.5 or 2 Gy gamma radiation on gestation days 15 and 19, and on postnatal days 5, 20, and 49. At 27 weeks of age, kidneys were examined for proliferative lesions. Preneoplastic lesions such as phenotypically altered tubules increased after postnatal irradiation as a function of age-at-irradiation, and hyperplasia were greatly increased after perinatal and postnatal irradiation. In contrast, development of adenoma and adenocarcinoma were evident in animals irradiated at perinatal ages, being maximal at gestational day 19. The frequency of LOH at the Tsc2 locus was unexpectedly low - 0% (0 of 4) for the unirradiated control, and 17% (6 of 35) for the irradiated group. Irrespective of LOH, the mTOR (mammalian target of rapamycin) pathway, which is negatively regulated by the Tsc1/2 complex, was activated in both benign and malignant lesions, as evidenced by phosphorylation of S6 ribosomal protein and 4E-BP1. This suggests that the wild-type Tsc2 allele may be functionally inactivated. In conclusion, actively growing kidneys in perinatal-aged (F344 x Eker) F1 rats (Tsc2(+/-)) are at risk for radiation-induced malignant transformation of the renal epithelium associated with mTOR activation.

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.

Renal transplacental carcinogenicity of 3,3-dimethyl-1-phenyltriazene in rats: relationship of renal mesenchymal tumor to congenital mesoblastic nephroma and intralobar nephrogenic rests

Exposure of rat embryos to 3,3-dimethyl-1-phenyltriazene (DMPT) results in numerous malformations, but the urogenital system is not affected. In contrast, exposure of rat fetuses to DMPT has been reported to result in renal neoplasms, which were not further classified. To better understand this discrepancy in organotropism of the teratogenic and transplacental carcinogenic processes, the present study was undertaken to characterize the neoplasms induced in rat fetuses exposed to DMPT in utero. Renal neoplasms and persistent mesenchyme were observed in 19.2 and 11.5%, respectively, of the offspring of rats treated with 1 mg DMPT/kg body weight intraperitoneally on gestation days 16, 18, and 20. The majority of these renal lesions were observed in females. The renal neoplasms were mixtures of various types of mesenchymal tissue derivatives including smooth muscle and fibrous connective tissue. These neoplasms would be classified as renal mesenchymal tumors in rats. Brain neoplasms (numerous types), compound odontomas, and micrognathism were observed predominantly in male offspring from the same group. This treatment also resulted in decreased body weights, increased incidence of sudden loss of body weight, tremors and ataxia, and hypoplastic testes. Exposure to single intraperitoneal doses of DMPT on gestation day 20 did not produce a classic dose-response pattern: Minimal effects were observed with 10 mg DMPT/kg (occasional renal mesenchymal tumors and brain neoplasms), marked effects were observed with 30 mg DMPT/kg (lower incidence rate of most of the alterations observed with 1 mg/kg on gestation days 16, 18, and 20), and no effects were observed with 60 mg DMPT/kg. DMPT administered intraperitoneally at 1 mg/kg body weight on gestation days 16, 18, and 20 is an animal model of transplacental chemically induced renal neoplasms, which provide lesions with similarities to both intralobar nephrogenic rests and congenital mesoblastic nephroma of humans. Why the kidney is a carcinogenic target and not a teratogenic target remains unknown.

Isolation of subclones with different tumorigenicity and metastatic ability from rat nephroblastoma cell line, ENUT

Seven subclones derived from a chemically induced rat nephroblastoma cell line, ENUT, were isolated and their cytological characteristics were examined in order to investigate the biological nature of the parent tumor. The subclones were divisible into two types based on morphological and biological features: polygonal cells with well developed junctional complexes and less developed cell surface microvilli, showing a doubling time of 13.0 to 14.0 h and tumorigenicity in nude mice of 42-100%, and spindle-shaped cells with poorly developed junctional complexes and well developed microvilli, showing a doubling time of 9.7 to 12.2 h and 100% tumorigenicity. Potential for both spontaneous and experimental metastasis to the lungs was apparently higher in the spindle-shaped clones than in the polygonal clones. In spite of their differing characteristics, the cytochemical phenotypes of the two clonal types were almost identical to those of immature renal tubules of the developing fetal kidney. The present findings suggest that these subclones possess characteristics of early nephrogenic epithelial cells, and we speculate that the biological differences observed among the subclones may be explained by differences in malignant progression. In addition, these clones appear to be a useful model for the study of tumorigenicity and metastasis.

Induction of tubules in rat metanephrogenic mesenchyme in the absence of an inductive tissue

Differentiation of metanephrogenic mesenchyme to renal tubular epithelium requires induction by the ureteric bud in vivo or any of several embryonic tissues in vitro. In an effort to eliminate the tissue requirement in embryonic induction, extracellular matrices and soluble factors were analyzed individually or in combination for their ability to stimulate tubulogenesis in uninduced metanephrogenic mesenchyme from 13-gestation-day rat embryos. These evaluations have established that pituitary extract and epidermal growth factor (EGF) in concert with a matrix can promote morphogenesis of mesenchymal rudiments in culture. While type I collagen, laminin, or fibronectin matrices all promoted tubulogenesis in the presence of pituitary extract and EGF, type IV collagen proved the most effective. Under these conditions, tubules were induced in 23/24 mesenchymal rudiments by 9 days in culture. Mesenchyme was not induced prior to explanation since it formed no tubules when cultured in a medium that allowed tubulogenesis in intact embryonic kidneys. Preliminary characterization of the undefined factor in pituitary extract was consistent with a protein of molecular weight greater than 100,000 but less than 300,000. When uninduced metanephrogenic mesenchyme from mouse was used instead of rat tissue, a similar pattern of morphogenesis was not observed, suggesting that the described medium is inappropriate for promoting differentiation in mouse or, less likely, that different mechanisms mediate differentiation in rat and mouse. These studies show that embryonic induction can occur in explanted rat renal mesenchyme in an appropriate environment and does not require the presence of an inductive tissue.

A mouse model of the aniridia-Wilms tumor deletion syndrome

Deletion of chromosome 11p13 in humans produces the WAGR syndrome, consisting of aniridia (an absence or malformation of the iris), Wilms tumor (nephroblastoma), genitourinary malformations, and mental retardation. An interspecies backcross between Mus musculus/domesticus and Mus spretus was made in order to map the homologous chromosomal region in the mouse genome and to define an animal model of this syndrome. Nine evolutionarily conserved DNA clones from proximal human 11p were localized on mouse chromosome 2 near Small-eyes (Sey), a semidominant mutation that is phenotypically similar to aniridia. Analysis of Dickie's Small-eye (SeyDey), a poorly viable allele that has pleiotropic effects, revealed the deletion of three clones, f3, f8, and k13, which encompass the aniridia (AN2) and Wilms tumor susceptibility genes in man. Unlike their human counterparts, SeyDey/+ mice do not develop nephroblastomas. These findings suggest that the Small-eye defect is genetically equivalent to human aniridia, but that loss of the murine homolog of the Wilms tumor gene is not sufficient for tumor initiation. A comparison among Sey alleles suggests that the AN2 gene product is required for induction of the lens and nasal placodes.

Establishment and characterization of an immature epithelial cell line (ENU-T-1) derived from a rat nephroblastoma

A new cell line designated ENU-T-1 has been established from a xenotransplanted experimental rat nephroblastoma. The cultured cells are spindle-shaped or polygonal and are arranged in a wavy fashion morphologically similar to cultured embryonal renal epithelial cells. The cells exhibit a number of epithelial characteristics. Enzyme histochemistry gives positive reactions for gamma-glutamyltranspeptidase and alkaline phosphatase, both of which are present in renal tubular epithelial cells. Immunofluorescence studies show positive reactions for vimentin and cytokeratin. When inoculated into athymic nude mice, the cultured cells form tumors composed of sheets of epithelial cells with focal tubular formation. This cell line may be of value in studying differentiation of nephroblastoma, and possibly normal nephrogenesis.