NER-factor DDB2 regulates HIF1α and hypoxia-response genes in HNSCC

Area of Science:

• Oncology
• Molecular Biology
• Cancer Research

Background:

• Head and neck squamous cell carcinoma (HNSCC) is aggressive, characterized by recurrence and metastasis.
• Tumor hypoxia and activation of hypoxia-inducible factors (HIFs) are key features of aggressive HNSCC.

Purpose of the Study:

• To investigate the role of DDB2 (damaged DNA binding protein 2) in regulating hypoxia and HIF1α in HNSCC.
• To elucidate the mechanism by which DDB2 affects HIF1α expression and tumor growth.

Main Methods:

• Investigated DDB2 upregulation by hypoxia in HNSCC cells.
• Assessed DDB2's effect on HIF1α mRNA and protein levels under normoxia and hypoxia.
• Utilized a xenograft model to evaluate the impact of DDB2 knockdown on tumor growth and angiogenic markers.
• Performed chromatin immunoprecipitation assays to determine DDB2's binding to the HIF1A gene promoter and its effect on histone modifications (H3K9 trimethylation) via Suv39h1 recruitment.

Main Results:

• DDB2 is upregulated by hypoxia in HNSCC and inhibits HIF1α expression by reducing its mRNA levels.
• DDB2 knockdown leads to increased expression of angiogenic markers and enhanced tumor growth in vivo.
• DDB2 directly binds to the HIF1A gene promoter, recruiting Suv39h1 to promote H3K9 trimethylation, thereby suppressing HIF1α transcription.
• DDB2 suppresses the expression of endogenous hypoxia markers, which are prognostic indicators in HNSCC.

Conclusions:

• DDB2 acts as a novel negative regulator of HIF1α in HNSCC.
• This mechanism involves direct transcriptional repression of HIF1α via histone modification.
• DDB2's suppressive role on HIF1α and hypoxia-response genes suggests a potential therapeutic target for aggressive HNSCC.