Development of High‐grade Renal Cell Carcinomas in Rats Independently of Somatic Mutations in the Tsc2 and VHL Tumor Suppressor Genes

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Abstract
Ferric nitrilotriacetate (Fe‐NTA) induces renal proximal tubular damage that ultimately leads to a high incidence of renal cell carcinoma (RCC) in rats. The RCCs are characterized by 1) high incidence of pulmonary metastasis and peritoneal invasion, 2) high incidence of tumor‐associated mortality and 3) possible involvement of reactive oxygen species in carcinogenesis. The present study investigated the possible role of Tsc2 and VHL tumor suppressor genes in this model. Thirty‐four Fe‐NTA‐induced primary RCCs and 20 other primary or metastatic tumors of rats were searched for genetic alteration in all the coding exons of both genes by polymerase chain reaction‐single‐strand‐conformation polymorphism analysis and sequencing in conjunction with morphological evaluation. In the Fe‐NTA‐induced RCCs, frequency of metastasis or invasion was proportionally associated with the nuclear grade of the tumor (grades 1–3). Only one Fe‐NTA‐induced RCC of grade 1 revealed missense mutations with loss of heterozygosity in exon 10 of the Tsc2 gene (codons 334, GTG (Val) to GCG (Ala), and 336, TAT (Tyr) to CAT (His)). No mutation was found in the VHL gene. The results suggest that 1) high‐grade RCCs can develop in the absence of mutations in the Tsc2 and VHL genes in rats, and that 2) Tsc2 gene somatic mutation can nonetheless be one of the causes of non‐Eker rat RCCs.

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