Johns Hopkins Researchers Identify Receptor for Gut Bacterium Toxin Linked to Colon Cancer

Researchers at Johns Hopkins have identified a crucial missing link between a common gut bacterium and colorectal cancer, resolving a scientific question that has persisted for nearly two decades. The bacterium, Bacteroides fragilis, produces a toxin that damages the protective lining of the colon, triggers chronic inflammation, and promotes tumour formation.

While scientists have known for years that the bacterium produces a harmful toxin, the exact mechanism by which the toxin first attaches to intestinal cells remained unknown. Now, a research team led by scientists at the Johns Hopkins Kimmel Cancer Center, the Bloomberg-Kimmel Institute for Cancer Immunotherapy, and the Johns Hopkins University School of Medicine has identified the missing step.

The findings, published in Nature, reveal that a protein known as claudin-4 serves as the essential docking point for the bacterial toxin, referred to as BFT. The discovery emerged from a genome-wide CRISPR screening effort led by M.D./Ph.D. candidate Maxwell White in Cynthia Sears’ laboratory, in collaboration with Matthew Waldor’s laboratory at Harvard Medical School. By systematically switching off genes in colon epithelial cells, the team found that disabling the gene responsible for claudin-4 prevented BFT from binding to the cells.

The identity of the receptor surprised the researchers, who had initially expected the toxin to interact with a signalling protein such as a G protein-coupled receptor. Instead, claudin-4 functions to maintain tight junctions and physical connections between neighbouring cells. Furthermore, structural biologists at the Molecular Biology Institute of Barcelona confirmed that BFT and claudin-4 form a tightly bound complex in laboratory experiments, with each toxin molecule pairing with one receptor molecule.

Building on this discovery, the researchers developed a molecular decoy designed to intercept the toxin before it reaches the colon's protective lining. Working with Min Dong’s laboratory at Harvard Medical School, the team tested the decoy in mice. The experiments showed that instead of binding to claudin-4 receptors on colon cells, the toxin attached to the decoy proteins, successfully protecting the mice from damage.

Despite these promising laboratory results, important questions remain. Researchers have not yet captured the exact three-dimensional structure of how the two molecules fit together, and further experiments will be required to determine whether the decoy approach can safely and effectively prevent toxin-related diseases in humans.

"This fundamental scientific breakthrough highlights the critical importance of early-stage research in identifying specific biological targets. While the application is currently in the experimental stage, discoveries of this nature lay the groundwork for future biotechnology innovations and targeted therapeutics. For entrepreneurs and investors in the healthtech and life sciences sectors, understanding foundational research mechanisms is essential for evaluating long-term commercial potential in diagnostics and drug development." — Dr. Shishir Gupta, Founder & CEO, StartupLanes