Functional profiling of nucleotide Excision repair in breast cancer

Area of Science:

• Oncology
• Molecular Biology
• DNA Repair Mechanisms

Background:

• Homologous recombination deficiency (BRCA1/2 alterations) is common in breast cancer, conferring sensitivity to platinum chemotherapy and PARP inhibitors.
• Nucleotide excision repair (NER) activity influences sensitivity to DNA damaging agents, but its role in breast cancer remains understudied.

Purpose of the Study:

• To characterize NER activity in breast cancer models using a novel cellular assay.
• To identify novel mechanisms of DNA repair deficiency in breast cancer.
• To evaluate NER deficiency as a potential biomarker for platinum sensitivity.

Main Methods:

• Application of a novel immunofluorescence-based cellular NER assay.
• Screening of a large panel of breast epithelial and cancer cell lines.
• Analysis of ERCC4 gene methylation and XPF protein expression in cell lines and primary tumors.

Main Results:

• Identified a breast cancer cell line with profound NER deficiency.
• NER deficiency was attributed to epigenetic silencing of the ERCC4 gene, resulting in reduced XPF nuclease expression.
• ERCC4 methylation correlated with ERCC4 mRNA and XPF protein levels in primary breast tumors.
• Restoring XPF expression rescued NER deficiency and cisplatin sensitivity, but not PARP inhibitor sensitivity.

Conclusions:

• Functional assays can uncover novel DNA repair deficiencies.
• NER deficiency is a potential biomarker for platinum sensitivity in breast cancer.
• Epigenetic silencing of ERCC4 is a mechanism for NER deficiency in breast cancer.