The Wilms tumor suppressor gene WT1 encodes a developmentally regulated transcription factor that is mutated in a subset of embryonal tumors. To test its functional properties, we developed osteosarcoma cell lines expressing WT1 under an inducible tetracycline‐regulated promoter. Induction of WT1 resulted in programmed cell death. This effect, which was differentially mediated by the alternative splicing variants of WT1, was independent of p53. WT1‐mediated apoptosis was associated with reduced synthesis of the epidermal growth factor receptor (EGFR), but not of other postulated WT1‐target genes, and it was abrogated by constitutive expression of EGFR. WT1 repressed transcription from the EGFR promoter, binding to two TC‐rich repeat sequences. In the developing kidney, EGFR expression in renal precursor cells declined with the onset of WT1 expression. Repression of EGFR and induction of apoptosis by mechanism that may contribute to its critical role in normal kidney development and to the immortalization of tumor cells with inactivated WT1 alleles.

The in vitro culture of human kidney epithelial cells of defined nephronal origin would prove valuable in a variety of studies defining the factors and mechanisms responsible for diseases and disorders of the kidney. In this study we have tested the hypothesis that employing a serum-free growth medium allows the selective cultivation of human kidney epithelial cells. It is demonstrated that human kidney cortex, explanted into serum-free hormonally defined growth medium gives rise to a primary culture of kidney epithelial cells of homogeneous morphology capable of hemicyst formation. While these cells were able to proliferate to confluency as an explant culture, they were unable to undergo stable subculture. Subsequent manipulation of the culture vessel surface (an initial coat of bovine type I collagen followed by the absorption of macromolecules from fetal calf serum) yielded cultures able to be subcultured with growth to at least 30 cell generations. These cells were identified to be of proximal tubule origin by employment of enzyme histochemistry, immunohistochemistry, and ultrastructural examination.

The unbalanced translocation, der(17)t(X;17)(p11.2;q25), is characteristic of alveolar soft part sarcoma (ASPS). We have recently shown that this translocation fuses the TFE3 transcription factor gene at Xp11.2 to ASPL, a novel gene at 17q25. We describe herein eight morphologically distinctive renal tumors occurring in young people that bear the identical ASPL-TFE3 fusion transcript as ASPS, with the distinction that the t(X;17) translocation is cytogenetically balanced in these renal tumors. A relationship between these renal tumors and ASPS was initially suggested by the cytogenetic finding of a balanced t(X;17)(p11.2;q25) in two of the cases, and the ASPL-TFE3 fusion transcripts were then confirmed by reverse transcriptase-polymerase chain reaction. The morphology of these eight ASPL-TFE3 fusion-positive renal tumors, although overlapping in some aspects that of classic ASPS, more closely resembles renal cell carcinoma (RCC), which was the a priori diagnosis in all cases. These tumors demonstrate nested and pseudopapillary patterns of growth, psammomatous calcifications, and epithelioid cells with abundant clear cytoplasm and well-defined cell borders. By immunohistochemistry, four tumors were negative for all epithelial markers tested, whereas four were focally positive for cytokeratin and two were reactive for epithelial membrane antigen (EMA) (one diffusely, one focally). Electron microscopy of six tumors demonstrated a combination of ASPS-like features (dense granules in four cases, rhomboid crystals in two cases) and epithelial features (cell junctions in six cases, microvilli and true glandular lumens in three cases). Overall, although seven of eight tumors demonstrated at least focal epithelial features by electron microscopy or immunohistochemistry, the degree and extent of epithelial differentiation was notably less than expected for typical RCC. We confirmed the balanced nature of the t(X;17) translocation by fluorescence in situ hybridization in all seven renal tumors thus analyzed, which contrasts sharply with the unbalanced nature of the translocation in ASPS. In summary, a subset of tumors previously considered to be RCC in young people are in fact genetically related to ASPS, although their distinctive morphological and genetic features justify their classification as a distinctive neoplastic entity. Finally, the finding of distinctive tumors being associated with balanced and unbalanced forms of the same translocation is to our knowledge, unprecedented.

Wilms tumor is a pediatric neoplasm that arises from the metanephric blastema.