engleski

DEFINING MOLECULAR PATHWAYS IN ENDEMIC NEPHROPATHY -ASSOCIATED UPPER TRACT UROTHELIAL CARCINOMA

Mutations of p53 have been found in nearly all tumor types and are estimated to contribute to more than 50% of all cancers. Inactivation of the p53 gene is predominantly due to missense mutations (90% of cases) in the central effector domain of the protein. Mutations lead to the synthesis of highly stable, inactive proteins that accumulate in the nucleus of cancer cells. Among 393 codons of the human p53 gene, 222 are targets of 698 different types of mutations. Alterations of codons 175, 248, 273 and 282 correspond to 19% of all mutations and are considered general hot spot mutations. The vast majority of urothelial cancers are transitional cell carcinomas of the bladder that arise from urothelium, the epithelial lining of the urinary tract. Currently 93 mutations of the p53 gene are recorded for urothelial carcinomas (IARC p53 database). The mutational spectrum shows hotspots in codons 175, 220, 248, 280 and 282. Codon 220 is relatively specific for urothelial carcinomas and is the only mutational hotspot in urothelial tumors associated with an adenine change. Of note, A:T-->T:A mutations are very rare in sporadic bladder cancers. The major causative agent in the development of urothelial carcinoma in patients with Chinese herb nephropathy is thought to be aristolochic acid (AA). Aristolochic acid preferentially binds to purines in p53 gene and is associated with the predicted A-->T mutations, generating a carcinogen fingerprint. Aristolochic acid also causes A:T-->T:A mutations in codon 61 of the c-H-ras gene in rats. Importantly, Endemic (Balkan) Nephropathy (EN) is associated with a 100-200 fold higher risk (compared to non-endemic near-by towns) of urothelial carcinoma, albeit of an unusual high location (proximal ureter or renal pelvis), supporting exogenous carcinogen(s). These carcinomas overexpress mutant p53. To gain insight into the causative agent of EN-associated carcinoma, it is important to determine the mutational spectrum of urothelial tumors of EN patients and compare it with that from sporadic urothelial tumors of the general population. We have initiated mutational analysis of the p53 gene in DNA obtained from confirmed upper urothelial cancers removed from patients residing in endemic villages in Croatia. Mutational analysis was performed on tumor samples that stain strongly with antibody directed against p53. The new Roche p53 sequencing AmpliChip powered by Affymetrix was used to sequence exons 2-11. Mutations at A:T pairs account for > 50% of mutations sequenced to date, supporting the hypothesis that exposure to aristolochic acid is responsible for the urothelial cancer associated with EN.

p53 mutation; endemic nephropathy; aristolochic acid; urothelial carcinoma

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