DNA polymerase iota promotes EMT and metastasis of esophageal squamous cell carcinoma by interacting with USP7 to stabilize HIF-1α

Esophageal squamous cell carcinoma (ESCC) is one of the most lethal cancer types, with a low 5-year survival rate of similar to 20%. Our prior research has suggested that DNA Polymerase iota (Pol iota), a member of Y-family DNA polymerase, plays a crucial role in the invasion and metastasis of ESCC. However, the underlying mechanism is not well understood. In this study, we utilized ChIP-PCR and luciferase reporter assays to investigate the binding of HIF-1 alpha to the promoter of the Pol iota gene. Transwell, wound healing, and mouse models were employed to assess the impact of Pol iota and HIF-1 alpha on the motility of ESCC cells. Co-immunoprecipitation and Western blot were carried out to explore the interaction between Pol iota and HIF-1 alpha, while qRT-PCR and Western blot were conducted to confirm the regulation of Pol iota and HIF-1 alpha on their downstream targets. Our results demonstrate that HIF-1 alpha activates the transcription of the Pol iota gene in ESCC cells under hypoxic conditions. Furthermore, the knockdown of Pol iota impeded HIF-1 alpha-induced invasion and metastasis. Additionally, we found that Pol iota regulates the expression of genes involved in epithelial-mesenchymal transition (EMT) and initiates EMT through the stabilization of HIF-1 alpha. Mechanistically, Pol iota maintains the protein stability of HIF-1 alpha by recruiting USP7 to mediate the deubiquitination of HIF-1 alpha, with the residues 446-578 of Pol being crucial for the interaction between Pol iota and USP7. Collectively, our findings unveil a novel feedforward molecular axis of HIF-1 alpha- Pol iota -USP7 in ESCC that contributes to ESCC metastasis. Hence, our results present an attractive target for intervention in ESCC.