Human sarcomatous Wilms' tumor lines: evidence for epithelial differentiation in clear cell sarcoma of the kidney

The biological nature of human sarcomatous Wilms' tumor (SWT) was studied by analyzing newly established SWT lines, both heterotransplantable in nude mice and cultured in vitro. Five lines in nude mice include two from clear cell sarcoma of the kidney (CCSK), two from malignant rhabdoid tumor of the kidney (MRTK), and one from unclassified sarcoma. Five in vitro lines include three from CCSK, one from MRTK, and one from unclassified sarcoma. All of these in vitro cell lines produced tumors when innoculated in nude mice. Most of lines, especially of MRTK and unclassified sarcoma, well maintained their original morphological characteristics. However, CCSK lines, both heterotransplantable and in vitro, often showed unique morphological changes such as the increase of cells with eosinophilic cytoplasms and the production of mucin. Ultrastructurally, clusters of intermediate filaments, twisted sheaves of filaments resembling tonofilaments, intermediate junctions, and intracellular canaliculi were found in these cells. These findings suggested that CCSK had the latent epithelial nature which became obvious in the cell lines. This was confirmed by immunohistochemical and immunoblotting analyses with anticytokeratin antibodies. The result proved that CCSK expressed cytokeratin 8 (Mr 52,000) and 19 (Mr 40,000) as well as nephroblastic Wilms' tumor and strongly indicated that there was a close relationship between CCSK and nephroblastic Wilms' tumor.