VHL/HIF1α pathway in early renal cell carcinoma

Objectives: Von Hipple Lindau gene (VHL) inactivation represents the most frequent abnormality in clear cell renal carcinoma (ccRCC). Hypoxia-inducible factor1α (HIF1α) is a transcription factor activating genes involved in hypoxia which expression is regulated by O2 level. In normal O2 conditions pVHL binds HIF1α and it allows HIF1α proteasomal degradation. The study analyzes VHL/HIF1α proteins and their molecular status in early-stage ccRCC, correlating genetic alterations, protein expression and subcellular localization with prognosis. Materials and Methods: Two anti-pVHL (clones Ig32 and Ig33) and 1 anti-HIFα were used on tissue microarrays from 136 intracapsular ccRCCs. Then we performed mutational analysis for the whole VHL gene and for HIF1α SNP (Pro582Ser), promoter methylation of VHL gene and loss of heterozygosity (LOH) at (3p25) locus. The data obtained were correlated with VHL and HIF1α protein expression and with survival (TSS). Results: A strong cytoplasmic positivity was found for all Abs in the largest part of cases, associated to a strong nuclear localization in the case of HIF1α. All pVHL-negative cases were associated with high HIF1α expression. pVHL negativity and HIF1α nuclear positivity significantly correlated with shorter TSS. VHL mutations, methylation and LOH were detected in 51%, 11% and 12% cases. The SNP, Pro582Ser, located in exon 12 of HIF1α was analyzed in 117 cases. We found C/T genotype in 30 samples (30/117, 26%), and T/T genotype in 5 samples (5/117, 4%). Instead the wild type genotype C/C was found in 82 samples (82/117, 70%). We found an association between the wild type genotype C/C and the presence of HIF1α protein in the nucleus, associated also with a worse TSS. Our results showed again a worse TSS in the patients presenting a biallelic alteration together with the absence of VHL protein. Conclusions: We confirmed the knowledge about pVHL and HIF1α subcellular localizations and about their pathway. Furthermore, we detected the involvement of Pro582Ser SNP of HIF1α gene in ccRCC progression. Our results confirmed the typical VHL/HIF1α pathway known so far, as the samples without a biallelic VHL molecular alteration and with the presence of the pVHL protein have a better prognosis than the samples presenting a biallelic mutation and without pVHL.