Nuclear localized Raf1 isoform alters DNA-dependent protein kinase activity and the DNA damage response

Area of Science:

• Molecular Biology
• Cancer Research
• Cell Signaling

Background:

• Raf1/c-Raf is a key kinase in the Ras-MAPK/ERK pathway.
• Protein truncation can alter protein function and localization.
• The DNA damage response is critical for maintaining genomic stability.

Purpose of the Study:

• To identify and characterize novel splice isoforms of human Raf1.
• To investigate the role of a novel truncated Raf1 isoform (Raf1-tr) in DNA damage response.
• To explore the therapeutic potential of targeting Raf1-tr in cancer.

Main Methods:

• Identification of a novel Raf1 splice isoform (Raf1-tr) with a truncated kinase domain.
• Assessment of Raf1-tr nuclear localization and binding interactions using cellular and biochemical assays.
• Evaluation of Raf1-tr's impact on DNA damage response in cancer cell lines (HCT-116, breast cancer) using irradiation and bleomycin treatments.

Main Results:

• Raf1-tr exhibits increased nuclear localization due to reduced binding to FK506 binding protein 5.
• Raf1-tr binds to DNA-dependent protein kinase (DNA-PK), inhibiting its function and amplifying DNA damage.
• Reduced Raf1-tr expression in colorectal cancer cells (HCT-116) and differential expression in breast cancer cells were observed.
• Reintroduction of Raf1-tr sensitized cancer cells to bleomycin-induced apoptosis.

Conclusions:

• A novel human Raf1 isoform (Raf1-tr) plays a noncanonical role in the DNA damage response.
• Raf1-tr modulates DNA-PK activity, impacting the cellular response to DNA damage.
• Raf1-tr expression levels correlate with sensitivity to genotoxic agents, suggesting its potential as a therapeutic target in cancer.