TP53 mutations in p53-negative dysplastic urothelial cells from Belgian AAN patients: New evidence for aristolochic acid-induced molecular pathogenesis and carcinogenesis.

The Aristolochic Acid (AA)-specific mutational pattern was recently characterized in urothelial carcinoma (UC) from Belgian AA Nephropathy (AAN) patients (n=5). Besides the A>T transversion hallmark, a specific AA-mutational pattern was found in the TP53 hotspot region in p53-positive immunohistochemistry (IHC) areas and consisted of poly- or multiclonal TP53 alterations and an unusual high prevalence of G>T transversion. In the current study, these data were complemented using the same validated methodology for assessing the complete coding sequence of the TP53 gene in tumor areas stratified according to the percentage of p53-stained cells (i.e., [+], ≥60%; [+/-], 1-59%, [-], no staining). Results were compared to existing data (i.e., other series of AA-associated UC and IARC TP53 database). Aside of the TP53 hotspot region (exons 5-8), multiple mutations were also found in exons 4 and 10. A unique TP53 mutational pattern was characterized by a large spectrum of mutations among which A>T and C>T have the highest prevalence. Most A>T mutations were characterized by the 5'Py-A-Pu sequence. Interestingly, the majority of p53-negative areas were dysplastic (low grade intra-urothelial neoplasia) and disclosed TP53 mutations among which a majority of A>T transversions. Beside nonsense p53-negative mutations, several missense mutations are also known to affect p53 DNA- or zinc-binding domains, hence probably impairing the antigen binding site and/or masking the antigenic epitope. These uncommon histologic, immunopathologic and genetic features in Belgian AAN patients probably result from the unique pattern of duration and extent of AA exposure which led to a cumulative toxic dose ingested over a short period of time. Consequenlty, current results bring additional and valuable evidence unravelling the molecular pathogenesis of AA-induced carcinogenesis and the origin of related high-grade UCs.