<i>HORMAD1</i> Polymorphisms Influence Susceptibility to Esophageal Squamous Cell Carcinoma Through Gene–Smoking Interaction

Tobacco smoke is a major risk factor for esophageal squamous cell carcinoma (ESCC), yet only a subset of smokers develop this disease, implicating gene-smoking interactions in modulating individual susceptibility. Through integrative transcriptomic analyses of normal and tumor samples from smokers and nonsmokers, we identify four smoke-responsive genes (CXCL14, HORMAD1, WFDC5, and MPZ) as potential contributors to ESCC carcinogenesis. Among these, HORMAD1 is markedly upregulated in ESCC cells upon exposure to cigarette smoke condensate (10 µg/mL), benzo[a]pyrene (3 µM), or 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (10 µM), correlating with activation of error-prone nonhomologous end joining (NHEJ) in response to DNA damage. Notably, smokers with higher HORMAD1 expression levels exhibit enhanced NHEJ but impaired homologous recombination (HR), leading to increased genomic instability. Through a two-stage case-control study involving 5151 ESCC cases and 5963 controls, we identify two regulatory variants of HORMAD1, rs11204679 and rs33924488, significantly associated with ESCC risk through a gene-smoking interaction (p_interaction = 0.0027). Both variants confer a protective effect among smokers (OR = 0.80, 95% CI: 0.74-0.87, p = 9.58 × 10^- ⁸) but not in nonsmokers (OR = 0.98, 95% CI: 0.90-1.06, p = 0.5950). Mechanistically, the rs11204679 G > C and rs33924488 GA > G- variants attenuate HOXA6 and SOX15 binding at a distal enhancer, respectively, suppressing HORMAD1 expression via long-range chromatin interactions. These findings establish HORMAD1 as a critical mediator of tobacco-related DNA repair dysregulation and a potential biomarker for ESCC risk stratification and precision prevention.