Loss of BCL-3 expression increases sensitivity to irradiation induced DNA damage in colorectal cancer cells


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Christopher Parker1,Adam Chambers1,Ann Williams1
1University of Bristol, Bristol, UK

Abstract

Background

In locally advanced rectal cancer, pre-operative long-course chemoradiotherapy (LCCRT) is an important addition to surgical resection, however up to 40% of patients do not respond. The proto-oncogene BCL-3 is upregulated in a subset of colorectal cancer patients and expression is associated with poorer patient outcome. We aimed to investigate whether BCL-3 expression confers resistance to DNA damaging agents used in LCCRT to determine whether BCL-3 is a useful marker for predicting patient response or as a target in therapy.

Method

BCL-3 expression in colorectal cancer cell lines was knocked down by siRNA (2D) and knocked out by CRISPR-Cas9 D10A based genome editing (3D). Cells were irradiated with a Caesium-137 source and responses were measured by crystal violet staining, γ-H2AX foci imaging, Western blotting and DNA damage repair reporter assays.

Results

Suppression of BCL-3 expression increases irradiation induced cell death in colorectal cancer cells. This is accompanied by an increased number of double strand breaks as shown by γ-H2AX foci and upregulation of double strand break dependent signalling (ATM and Chk2 phosphorylation). Reporter assays demonstrate that the increase in irradiation induced double strand breaks on loss of BCL-3 expression is due to a significant reduction in the rate of homologous recombination.

Conclusion

This study demonstrates a novel role for BCL-3 in promoting resistance to DNA damaging agents in colorectal cancer. The results indicate that increased BCL-3 expression seen in some colorectal cancer could aid homologous recombination allowing more efficient repair of DNA after damage, enhancing tumour survival. This suggests that targeting BCL-3 during rectal cancer treatment could enhance response to LCCRT.