Genetic variants of the intestinal carrier SLC22A4 shape the intratumor microbiota in favor of a pro-carcinogenic pathobiont by dampening innate immunity and increasing the tolerance of cancerous cells to bacterial invasion.
Key Findings
Results
F. nucleatum was similarly present in both colorectal cancer tissues and adjacent normal mucosa, but the F. nucleatum/E. coli ratio was significantly higher in tumors.
Study quantified F. nucleatum and E. coli in 99 cases of archival colorectal cancer and adjacent normal mucosa.
The F. nucleatum/E. coli ratio was 303.82 in tumors versus 30.86 in adjacent normal mucosa (p = 0.0396).
E. coli was used as a commensal reference organism to normalize F. nucleatum abundance.
Absolute F. nucleatum levels were similarly present in both tissue types, making the ratio comparison the key discriminating metric.
Results
The F. nucleatum/E. coli ratio in colorectal cancer tissues increased steadily with the number of mutant SLC22A4 503F (T) alleles.
The F. nucleatum/E. coli ratio was 23.48 for 0 T alleles, 159.56 for 1 T allele, and 211.03 for 2 T alleles (p = 0.0215).
Tissues were genotyped for the 503F variant of the Organic Cation Transporter OCTN1/SLC22A4.
The relationship followed an allele-dose-dependent pattern, suggesting a co-dominant or additive genetic effect.
This association was observed across the 99 archival colorectal cancer cases.
Results
Colon cancer spheroids overexpressing the 503F variant displayed attenuated inflammatory response to F. nucleatum infection compared to wild-type.
Colorectal cancer stem cells were engineered to express either the 503F variant or the wild-type SLC22A4 allele.
Spheroids overexpressing the 503F variant showed dampened innate immune/inflammatory response upon F. nucleatum infection.
The attenuated response was not observed in spheroids expressing the wild-type allele.
This in vitro experiment mechanistically linked SLC22A4 function to intratumoral F. nucleatum abundance.
Results
Colon cancer spheroids overexpressing the 503F variant showed impaired bacterial clearance compared to wild-type-expressing spheroids.
F. nucleatum clearance was specifically impaired in spheroids carrying the 503F variant but not the wild-type allele.
Impaired clearance was observed in an in vitro infection model using colorectal cancer stem cell-derived spheroids.
The finding provides a mechanistic explanation for the higher intratumoral F. nucleatum abundance observed in patients carrying the T allele.
Together with attenuated inflammation, impaired clearance indicates increased tolerance of cancerous cells to bacterial invasion.
Discussion
The SLC22A4 503F genetic variant mechanistically links host genetic profile to intratumoral microbiota composition in colorectal cancer.
SLC22A4/OCTN1 is an organic cation transporter expressed in the intestine.
The study combined population-level genotyping of archival tumor tissues with functional in vitro experiments to establish mechanistic linkage.
The findings suggest that host genetic variants can shape the intratumor microbiota in favor of pro-carcinogenic pathobionts.
The proposed mechanism involves dampening of innate immunity rather than direct effects on bacterial growth.
Background
The interaction between host genetics (SLC22A4 503F) and the microbiota represents a poorly understood axis in colorectal cancer tumorigenesis.
The study addresses the gap in understanding how the intestinal microbiota interacts with the host's genetic profile during tumorigenesis.
F. nucleatum is characterized as a CRC-associated pathobiont, and E. coli as a commensal control organism.
The study used archival (formalin-fixed or similar preserved) colorectal cancer tissue samples from 99 cases.
Results suggest that genetic susceptibility loci may partly act by modulating microbial tolerance rather than directly affecting tumor cell biology.
What This Means
This research suggests that a specific genetic variant in a protein called SLC22A4 (which helps transport molecules across the gut lining) influences how much of a harmful bacterium called Fusobacterium nucleatum accumulates inside colorectal tumors. The researchers analyzed tumor tissue and nearby normal tissue from 99 colorectal cancer patients and found that while the bacterium was present in both tissue types, it was relatively much more abundant in tumors compared to a harmless reference bacterium. Crucially, patients who carried one or two copies of the variant version of the SLC22A4 gene had progressively higher levels of this harmful bacterium in their tumors — a clear dose-dependent relationship.
To understand why this happens, the researchers conducted laboratory experiments using colorectal cancer stem cells engineered to carry either the variant or normal version of SLC22A4. They found that cells with the variant version were less able to mount an immune/inflammatory response against Fusobacterium nucleatum and were also less able to clear the bacteria once infected. This suggests the genetic variant essentially makes cancer cells more tolerant to bacterial invasion, allowing the harmful bacterium to persist and potentially worsen the tumor environment.
This research suggests that a person's genetic makeup can influence which bacteria thrive inside their tumors, and that this may be one way genetic risk factors contribute to colorectal cancer progression. The findings open a new avenue of investigation into how host genetics and the tumor microbiome interact, potentially pointing toward future strategies that target this relationship for prevention or treatment purposes.
Chouaibi S, Fertitta V, Porreca S, Njim L, Carcagnì A, Toietta G, et al.. (2026). Genetic variants of the transporter SLC22A4 affect the abundance and survival of Fusobacterium nucleatum in colorectal cancer.. Gut microbes. https://doi.org/10.1080/19490976.2026.2681818