rs8192780 — CYP2E1

CYP2E1 rs8192780 — A Regulatory Tag Variant and Smoking Interaction

CYP2E1 is the liver and lung enzyme that metabolizes ethanol, acetaminophen, and a wide spectrum of environmental carcinogens including tobacco-specific nitrosamines (NNK), polycyclic aromatic hydrocarbons, benzene, and chlorinated solvents. rs8192780 sits approximately 1.5 kilobases downstream of the CYP2E1 gene in a 3' flanking regulatory region. Unlike the well-studied upstream *5B variant (rs2031920), this SNP has limited direct functional characterization, but one moderately-sized genetic association study links it to nasopharyngeal carcinoma (NPC) risk — particularly among young smokers of Cantonese ancestry.

The Mechanism

The variant is located in the 3' flanking region of CYP2E1 ¹¹ The 3' flanking region contains regulatory elements including polyadenylation signals and enhancers that can influence mRNA stability and transcription termination. It falls within the CYP2E1 RefSeqGene locus (NG_008383.1) and is located on the plus strand. No protein-coding change is produced. The mechanistic hypothesis is that the T allele alters a cis-regulatory element²² cis-regulatory element
DNA sequences near a gene that control its expression in the same cell affecting CYP2E1 mRNA stability or transcriptional read-through, potentially modulating basal enzyme expression in tissues relevant to NPC — particularly the nasopharyngeal epithelium and liver. However, no in vitro or luciferase reporter studies have directly confirmed altered transcriptional activity for this specific SNP. Its significance may also arise in part because it tags a broader CYP2E1 haplotype block shared with functionally characterized upstream variants.

The Evidence

The primary evidence comes from a case-control and family-based study in Cantonese individuals³³ case-control and family-based study in Cantonese individuals
Jia WH et al. A case-control and family-based association study revealing an association between CYP2E1 polymorphisms and nasopharyngeal carcinoma risk in Cantonese. Carcinogenesis, 2009. The study examined 546 nuclear families (2,499 individuals) and 755 cases with 755 controls. Among the eight CYP2E1 SNPs genotyped, rs8192780 emerged as significantly associated with NPC in the family-based analysis. In a case-control analysis restricted to smokers under age 46, odds ratios for rs8192780 ranged from 1.88 to 2.99. Haplotype analysis identified two high-risk haplotypes (h2: OR=1.65, P=0.026; h5: OR=2.58, P=0.007), with false-positive report probabilities below 0.015, supporting the robustness of the findings. NPC is highly prevalent in Cantonese and other Southern Chinese populations, where Epstein-Barr virus (EBV) infection interacts with tobacco carcinogens and genetic susceptibility. CYP2E1 activates the tobacco-derived nitrosamine NNK⁴⁴ nitrosamine NNK
4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, the major lung carcinogen in tobacco to DNA-reactive species.

For the canonical upstream CYP2E1 c2 haplotype (most commonly defined by rs2031920), large meta-analyses present a complex picture. The c2 allele appears protective against hepatocellular carcinoma in East Asians (OR 0.75, 95% CI 0.59–0.95 in a 12-study meta-analysis of 1,552 HCC cases⁵⁵ (OR 0.75, 95% CI 0.59–0.95 in a 12-study meta-analysis of 1,552 HCC cases
Tian Z et al. CYP2E1 RsaI/PstI polymorphism and liver cancer risk among east Asians. Asian Pac J Cancer Prev, 2012) and also protective against lung cancer in Asians (OR 0.734 in homozygotes across 21 studies⁶⁶ (OR 0.734 in homozygotes across 21 studies
Zhan P et al. CYP2E1 Rsa I/Pst I polymorphism is associated with lung cancer risk among Asians. Lung Cancer, 2010), yet associated with increased oral cancer risk in Asians (c1/c2 OR 1.30, 95% CI 1.04–1.62 in 12 studies⁷⁷ (c1/c2 OR 1.30, 95% CI 1.04–1.62 in 12 studies
Niu Y et al. CYP2E1 Rsa I/Pst I polymorphism contributes to oral cancer susceptibility. Mol Biol Rep, 2012). These discordant findings across cancer types illustrate that CYP2E1 variant effects are tissue-specific and exposure-dependent, making extrapolation from the canonical variants to rs8192780 uncertain.

Practical Actions

The most direct implication of rs8192780 is for smokers, particularly those of East Asian or African ancestry where the T allele is substantially more common. The combination of CYP2E1 variant status and tobacco smoke exposure is the documented risk context. Reducing or eliminating tobacco exposure directly attacks the CYP2E1-mediated carcinogen activation pathway. No specific drug dosing guidance exists for this variant given the absence of clinical guidelines.

Interactions

rs8192780 lies within the CYP2E1 gene region and likely captures some of the same haplotype signal as the upstream *5B variant (rs2031920) and other CYP2E1 regulatory polymorphisms. The Jia et al. study analyzed rs8192780 alongside rs9418990, rs915908, rs3813865, rs915906, and rs2249695, finding that the rs8192780 signal was among the strongest. No direct studies assess interaction between rs8192780 and other pharmacogenomic loci such as NQO1 rs1800566 or GSTP1 rs1695, though pathway logic suggests these detoxification variants would modulate downstream consequences of CYP2E1 carcinogen activation.