Urinary bladder transitional cell carcinogenesis is associated with down-regulation of NF1 tumor suppressor gene in vivo and in vitro

The NF1 gene product (neurofibromin) is known to act as a tumor suppressor protein by inactivating ms. The best documented factors involved in urinary bladder transitional cell carcinoma (TCC) are ras proto-oncogene activatio n and p53 suppressor gene mutations. This Is the first study reporting alte rations In NF1 gene expression in TCC. We examined NF1 gene expression in a total of 29 surgical urinary bladder TCC specimens representing grades 1 t o 3 and in three cell lines, RT4, 5637, and T24 (representing grades 1 to 3 , respectively). Decreased NF1 gene expression was observed in 23 of 29 (83 %) TCC specimens as estimated by immunohistochemistry the decrease being mo re pronounced in high-grade tumors. NF1 mRNA levels were markedly lower in TCC tissue compared with adjacent non-neoplastic urothelium, as studied by in situ hybridization for grade 3 TCC. Immunohistochemistry and Western blo tting demonstrated that TCC cell lines expressed NF1 protein at different l evels, expression being almost undetectable in T24 (grade 3) cells. Norther n blotting for cell lines demonstrated reduced NF1 mRNA levels in grade 3 T CC cells. Reverse transcription polymerase chain reaction for cell lines an d selected grade 2 and grade 3 tissue samples demonstrated NF1 type II mRNA isoform predominance in all samples studied. Our results show that both NF 1 mRNA and protein levels are decreased in high-grade TCC, suggesting that alterations of NF1 gem expression may be involved In. bladder TCC carcinoge nesis.