# Simultaneous Study of Circular RNAs and Messenger RNAs in Colorectal Cancer: The Unbalanced Fate of a Couple?

## TL;DR

This study explores how circular RNAs and messenger RNAs interact in colorectal cancer patients, finding an imbalance that may contribute to cancer development.

## Contribution

The study introduces the SEALigHTS technique to analyze circRNA-mRNA interactions and identifies novel circRNA junctions in colorectal cancer.

## Key findings

- Patients with colorectal cancer had a circRNA/mRNA ratio twice that of healthy controls.
- The POLD1 gene produced a circRNA with potential cancer-promoting effects.
- The imbalance between circRNAs and mRNAs in CRC is not due to competition between the two.

## Abstract

Circular RNAs (circRNAs) can compete with messenger RNAs (mRNAs) from their host gene, which can lead to the downregulation of mRNA. We investigated this potential mechanism of downregulation in colorectal cancer (CRC) predisposition in a large cohort of 712 patients suspected of having hereditary CRC and 249 healthy controls, with a focus on 23 genes associated with CRC. Using the novel SEALigHTS technique (Splice and Expression Analyses by Exon Ligation and High-Throughput Sequencing), we identified 220 circular RNA junctions, including 47 new ones. Patients exhibited a circRNA/mRNA ratio approximately twice that of controls, particularly for the POLD1 gene, which produces a circRNA with potential cancer-promoting effects. The findings imply that the balance between circRNAs and mRNAs is disturbed in CRC, though not due to competition between the two. They also suggest that specific circRNAs play a role in CRC development, either as a cause or a consequence.

Background/Objectives: Circular RNAs (circRNAs) are emerging players in human diseases, with functions as part of competing endogenous networks. Given the importance of messenger RNA (mRNA) regulation in human diseases and the potential of circRNAs in this regulation, we studied the circRNA–mRNA couple in blood within a cohort of 712 patients suspected of having hereditary colorectal cancer (CRC) and 249 matched controls. Methods: The circRNA–mRNA couple was studied by SEALigHTS (Splice and Expression Analyses by exon Ligation and High-Throughput Sequencing) with a panel of 23 genes involved in CRC predisposition, comprising 788 probes designed at exon ends, enabling the exploration of all exon–exon junctions. Following reverse transcription and probe hybridization on cDNA, nearby probes were ligated, and the number of ligations was quantified using unique molecular identifiers and sequencing. Results: We identified 220 circular junctions, including 47 novel ones. The circRNA/mRNA ratio was 2.42-fold higher in patients compared to controls (p < 10−16), irrespective of age at cancer onset. This increase was mainly driven by POLD1 (fold change 3.84) and a single circPOLD1(3,2) with oncogenic potential Conclusions: This study supports the existence of a physiological balance between circRNA and mRNA that can be disrupted under pathological conditions. It rules out a competitive mechanism between circular and linear transcripts in CRC predisposition and raises questions about the role of specific circRNAs in the development of CRC, either as a cause or a consequence.