Investigating the effects of biomarkers CHRDL2 and POLD3 on colorectal cancer risk

Abstract

Colorectal cancer (CRC) is one of the leading causes of cancer globally. Genome-wide association studies (GWAS) have identified several loci with single nucleotide polymorphisms that may increase CRC risk, including adjacent regions near the POLD3 and CHRDL2 genes. This thesis investigates the functional role these genes and their encoded proteins play in CRC development. Our research utilized cancer cell lines grown as 2D cultures engineered to overexpress CHRDL2 and knockdown POLD3 expression, alongside 3D organoid models treated with CHRDL2, supplemented by RNA sequencing. Chordin-like-2 (CHRDL2) is a secreted BMP antagonist with overexpression linked to poor CRC prognosis. However, its functional role remains unclear. BMP signalling promotes differentiation and counters WNT signalling, which sustains stem-cell maintenance in the intestinal epithelium. Reduced BMP and elevated WNT signalling leads to an increased stem-cell phenotype, a hallmark of CRC. We have found that CHRDL2 overexpression reduces BMP signalling and elevates WNT signalling, enhancing cancer cell survival during chemotherapy and irradiation by activation of DNA damage response pathways. Treated cells showed increased stem-cell markers and reduced differentiation, suggesting CHRDL2's potential to intensify the cancer stem-cell phenotype and influence therapy response. The second gene investigated, POLD3, is the third subunit of Pol δ and plays a critical role in DNA synthesis and repair, which are vital for cancer cells. Knock-down of POLD3 in CRC cells reduced their proliferative ability, causing cell cycle arrest in S phase, leading to apoptosis and cell death. Furthermore, POLD3 was shown to be essential for ALT telomere maintenance, with knockdown of POLD3 reducing telomere length, a key factor affecting cancer cell longevity. Additionally, POLD3 knockdown induced DNA damage and instability, and increased sensitivity to chemotherapy and irradiation. This research highlights the roles of POLD3 and CHRDL2 dysregulation in CRC, offering new insights into their potential as therapeutic targets and CRC biomarkers.