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Epidemiological studies have linked exposure to trichloroethylene (TCE), an organic solvent classified as a group 1 carcinogen and recognized contaminant in groundwater, with increased incidences of clear cell renal cell carcinoma (ccRCC). A tumor-specific somatic C454T missense mutation in the von Hippel-Lindau tumor suppressor gene (VHL) has been linked with TCE-associated ccRCC cases (1,2). This mutation results in a single amino acid change from proline to serine at codon 81 of the VHL protein (P81S) and is observed in more than 39% of TCE-exposed individuals who developed ccRCC (1). The VHL tumor suppressor functions as a redox sensor, controlling stability of the hypoxia-inducible transcription factor family (HIFs). VHL forms a complex with Elongin B (TCEB2), Elongin C (TCEB1), Ringbox1 (RBX1), and Cullin2 (CUL2) to form an E3 ubiquitin ligase complex (VBC complex) (3). Under normal oxygen conditions, oxygen-dependent prolyl-hydroxylase (PHD) enzymes hydroxylate HIF proteins at two specific proline residues that are recognized by VHL, and the VBC complex then polyubiquitinates HIF for degradation by the 26S proteasome (4). Cancer-associated missense mutations in VHL disrupt its function in the E3 ubiquitin ligase complex, resulting in variable deregulation of HIF factors (5,6). Structural models of molecular interactions between VHL and TCEB1 showed codons 81 and 82 of VHL are direct TCEB1 binding sites, suggesting that the P81S mutation associated with TCE exposure could destabilize the VBC complex and result in HIF-mediated transcriptional activation of hypoxia response targets (7). The HIF family members (HIF1A and HIF2A) play a central role in metabolic reprogramming observed in human renal tumors, which is thought to provide a selective survival advantage in changing microenvironments by modifying energy use during periods of hypoxic and glycolytic stress (8). This diversification of energy sources through increased glycolysis (the Warburg Effect) (9), fatty acid oxidation (10,11), and glutaminolysis (12–14) can promote cell proliferation and, in some cases, resistance to chemotherapeutic-induced apoptosis (15). HIF activation and metabolic changes have also been implicated as a result of Ataxia Telangiectasia Mutated (ATM) activation, a protein kinase involved in the response to DNA damage (16,17). Although HIF activation suggests a possible link between ATM-mediated DNA damage response and VHL, this has not been previously detected. In this study, the TCE-associated P81S VHL mutation was modeled and its activity compared with cells expressing normal VHL and the hotspot R167Q VHL mutant that was previously shown to dysregulate both HIF factors in graded fashion (5,6,18). The results show that the unique TCE-associated VHL mutation has pleiotropic effects that selectively influence the tumor behavior in a mutation-specific manner, providing a selective growth advantage through metabolic diversification, apoptosis suppression, and alteration of the DNA damage response.

Trichloroethylene (TCE) is a widely used industrial chemical and a common environmental contaminant. It is a well-known carcinogen in rodents and a probable carcinogen in humans. Studies utilizing panels of mouse inbred strains afford a unique opportunity to understand both metabolic and genetic basis for differences in responses to TCE. We tested the hypothesis that strain- and liver-specific toxic effects of TCE are genetically controlled and that the mechanisms of toxicity and susceptibility can be uncovered by exploring responses to TCE using a diverse panel of inbred mouse strains. TCE (2100 mg/kg) or corn oil vehicle was administered by gavage to 6- to 8-week-old male mice of 15 mouse strains. Serum and liver were collected at 2, 8, and 24 h postdosing and were analyzed for TCE metabolites, hepatocellular injury, and gene expression of liver. TCE metabolism, as evident from the levels of individual oxidative and conjugative metabolites, varied considerably between strains. TCE treatment-specific effect on the liver transcriptome was strongly dependent on genetic background. Peroxisome proliferator‐ activated receptor‐mediated molecular networks, consisting of the metabolism genes known to be induced by TCE, represent some of the most pronounced molecular effects of TCE treatment in mouse liver that are dependent on genetic background. Conversely, cell death, liver necrosis, and immune-mediated response pathways, which are altered by TCE treatment in liver, are largely genetic background independent. These studies provide better understanding of the mechanisms of TCE-induced toxicity anchored on metabolism and genotype-phenotype correlations that may define susceptibility or resistance.

The transcription factor Kruppel-like factor 4 (KLF4) is an important regulator of cell-fate decision, including cell-cycle regulation, apoptosis, and stem cell renewal, and plays an ambivalent role in tumorigenesis as a tissue-specific tumor suppressor or oncogene. Here, we report that the Von Hippel-Lindau gene product, pVHL, physically interacts with KLF4 and regulates its rapid turnover observed in both differentiated and stem cells. We provide mechanistic insights into KLF4 degradation and show that pVHL depletion in colorectal cancer cells leads to cell-cycle arrest concomitant with increased transcription of the KLF4-dependent p21 gene. Finally, immunohistochemical staining revealed elevated pVHL and reduced KLF4 levels in colon cancer tissues. We therefore propose that unexpectedly pVHL, via the degradation of KLF4, is a facilitating factor in colorectal tumorigenesis.