Biallelic VHL Gene Alterations Promote Cancer Progression in Early-Stage Clear Cell Renal Carcinoma through Nuclear Localization of Hypoxia-Inducible Factor-1
C Di Cristofano, A Minervini, M Leopizzi, F Lessi, M Menicagli, G Salinitri, G Bertacca, G Pefanis, L Masieri, P Collecchi, V Petrozza, C Della Rocca, R Minervini, M Carini, A Cavazzana, G Bevilacqua. Sapienza University of Rome, Rome, Italy; University of Florence, Florence, Italy; University of Pisa, Pisa, Italy
Background: Von Hipple-Lindau gene (VHL) inactivation represents the most frequent abnormality in clear cell renal carcinoma (cRCC). VHL encods two different proteins: VHL30 and VHL19 arising as a result of an alternative translation initiation. Hypoxia-inducible factor-1 (HIF-1) is a heterodimer composed of a and subunit. HIF-1 is constitutively expressed, while HIF-1 expression is regulated by O2 level. In normal O2 conditions VHL binds HIF-1, after hydroxylation in ODD (oxygen-dependent degradation domain) and it allows HIF-1 proteasomal degradation. In this domain a SNP at codon 582 is located. In hypoxia, VHL/HIF-1 interaction is abolished and HIF-1 activates target genes in the nucleus. The study analyzes the VHL and codon 582 of HIF-1 gene (HIF-1) status in cRCC, correlating genetic alterations, protein expression and subcellular localization with prognosis.
Design: Tissues microarray fom 136 intracapsular cRCC cases (8ys FU) were constructed and two anti-pVHL Ab (Ig32 and Ig33) and a polyclonal anti-HIF-1 Ab were used for IHC analysis. It was performed mutational analysis for the whole VHL and for HIF-1 SNP (C1772T), promoter methylation of VHL and LOH (3p25). The results were correlated with survival (TSS).
Results: VHL gene alteration was found in 57% of cases. VHL mutations, methylation and LOH were detected in 51%, 11% and 17% cases. Patients with biallelic VHL alteration had a short TSS (p=0.01). We found a statistical association between biallelic VHL alteration and no pVHL expression (p=0.004) and nuclear localization of HIF-1 (p=0,04). The SNP was associated with a only cytoplasmic localization of HIF-1 (p=0.007). pVHL negativity and HIF-1 nuclear positivity were correlated with a short TSS.
Conclusions: VHL and HIF-1 alterations influence their protein expression and localization. Biallelic VHL gene alterations with loss of pVHL expression are associated to nuclear localization of HIF1-a and poor prognosis in early-stage cRCC. Alteration of pVHL/HIF-1 pathway is an early event in cRCC carcinogenesis and it's involved in cancer progression through nuclear localizzation of HIF-1.
Category: Genitourinary (including renal tumors)
Wednesday, March 11, 2009 1:00 PM
Poster Session VI # 113, Wednesday Afternoon