SMARCA4 Loss Increases RNA Polymerase II Pausing and Elevates R-Loops to Inhibit BRCA1-Mediated Repair in Ovarian...

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) is a rare, aggressive ovarian cancer.
• SCCOHT is characterized by inactivating mutations in the SMARCA4 gene, a crucial component of the SWI/SNF chromatin remodeling complex.

Purpose of the Study:

• To identify druggable vulnerabilities in SCCOHT.
• To investigate the functional consequences of SMARCA4 loss in SCCOHT pathogenesis and identify potential therapeutic targets.

Main Methods:

• Compound screening to identify drug sensitivities.
• Proximity-dependent biotin identification to study protein interactions.
• Analysis of RNA polymerase II (Pol II) elongation and R-loop formation.
• Assessment of BRCA1 activity and DNA damage repair.

Main Results:

• SCCOHT cells and tumors are sensitive to PARP inhibitors.
• SMARCA4 loss leads to increased Pol II pausing, elevated R-loops, and BRCA1 sequestration, impairing DNA repair.
• Wild-type SMARCA4 promotes Pol II elongation via the PAF1 complex.
• Combined inhibition of PARP and CDK9 shows synergistic efficacy in SCCOHT and other SMARCA4-deficient ovarian cancers.

Conclusions:

• SMARCA4 loss in SCCOHT disrupts Pol II elongation and compromises BRCA1-mediated DNA repair.
• Dual targeting of PARP and CDK9 represents a promising therapeutic strategy for SCCOHT and related SWI/SNF-deficient ovarian cancers.