Defect of MLH1 expression sensitized esophageal squamous cell carcinoma cells to Polθ inhibitor.

BACKGROUND

A large scale detection of MLH1 methylation is lacking in esophageal cancer. MLH1 is a well-known mismatch repair gene. The mechanism of MLH1 in DNA double strand break (DSB) repair remains unclear.

METHODS

Esophageal cancer cell lines and 1018 cases of primary cancer samples were employed. Methylation specific PCR, Western Blot, and CRISPR/Cas9 knockout technique were utilized.

RESULTS

Methylation of MLH1 was detected in 3.93%. MLH1 methylation was significantly associated with tumor differentiation, male gender, smoking, and tumor size (all p < 0.05). The median overall survival (OS) was 24.7 months (95% CI 13.4-36.0) and 51.5 months (95% CI 40.4-62.5) in MLH1 methylated and unmethylated groups, respectively. OS was shorter in MLH1 methylated compared to unmethylated group patients (p < 0.01). Multivariate factor analysis indicated that MLH1 methylation is an independent poor prognosis marker (p < 0.05). MLH1 promotes ataxia telangiectasia mutated (ATM), ataxia telangiectasia and RAD3-related (ATR), and non-homologous end-joining repair (NHEJ), while inhibiting microhomology-mediated end joining (MMEJ) repair signaling pathways. Deletion of MLH1 sensitized esophageal cancer cells to novobiocin.

CONCLUSIONS

MLH1 plays important roles in DSB repair and deletion of MLH1 sensitizes ESCC cells to Polθ inhibitor.