Abstract
Mutations of the von Hippel-Lindau (VHL) tumor suppressor gene occur in the majority of sporadic renal-cell carcinomas (RCC). Loss of VHL function is associated with stabilization of hypoxia-inducible factor α (HIFα). We and others demonstrated that there is a two-way interaction between the aryl hydrocarbon receptor, which is an important mediator in the metabolic activation and detoxification of carcinogens, and the HIF1-pathway leading to an increased genetic instability when both pathways are simultaneously activated. The aim of this study was to investigate how environmental carcinogens, such as benzo[a]pyrene (BaP), which can be metabolically activated to BaP-7,8-diOH-9,10-epoxide (BPDE) play a role in the etiology of RCC. We exposed VHL-deficient RCC4 cells, in which HIFα is stabilized regardless of oxygen tension, to 0.1 μM BaP for 18 h. The mutagenic BPDE-DNA adduct levels were increased in HIFα stabilized cells. Using qRT-PCR, we demonstrated that absence of VHL significantly induced the mRNA levels of AhR downstream target CYP1A1. Furthermore, HPLC analysis indicated that loss of VHL increased the concentration of BaP-7,8-dihydroxydiol, the pre-cursor metabolite of BPDE. Interestingly, the capacity to repair BPDE-DNA adducts in the HIFα stabilized RCC4 cells, was markedly reduced. Taken together, these data indicate that loss of VHL affects BaP-mediated genotoxic responses in RCC and decreases repair capacity.
Highlights
Renal-cell carcinoma (RCC) is the most common type of kidney cancer in adults and accounts for 4% of all cancers [1]
We demonstrated that the kinetics of BaP metabolism is altered under hypoxia resulting in a prolonged time of exposure and a higher amount of BPDE-DNA adducts being formed (Schults et al manuscript submitted for publication)
BPDE-DNA ADDUCT LEVELS ARE HIGHER IN CELLS DEFICIENT IN von Hippel-Lindau (VHL) To examine the influence of VHL deletion on BaP-mediated genotoxic responses, we quantified the amount of BPDE-DNA adducts in VHL-deficient RCC4 cells and compared it with the genetically wild type RCC4-VHL cells and normalized it to the total amount of DNA (Figure 1)
Summary
Renal-cell carcinoma (RCC) is the most common type of kidney cancer in adults and accounts for 4% of all cancers [1]. The most frequently observed genetic alteration in RCC is the somatic mutation of the von Hippel-Lindau (VHL) tumor suppressor gene [2, 3]. The VHL protein (pVHL) is a crucial regulator of the oxygen sensing pathway, which involves the transcription factor hypoxiainducible factor alpha (HIFα) [2, 4]. In the presence of oxygen, HIFα is hydroxylated by an oxygen-dependent prolyl hydroxylase (HIF-PH) [5]. An E3 ubiquitin ligase complex containing the pVHL recognizes the hydroxylated HIFα, and targets it for ubiquitination [6] and subsequently proteasomal degradation [7]. HIFα is not prolyl-hydroxylated and unrecognized by pVHL
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