Colorectal cancer remains one of the most common and lethal malignancies worldwide, and while immune checkpoint inhibitors have transformed the treatment landscape for many tumors, a large fraction of colorectal tumors stubbornly resist immunotherapy. A new study published in Medical Oncology by Yanyan Hu, Shengying Li, Minjing Zhu, Xuedan Lin, Chaoju Gong, Zejun Fang and colleagues points to an unexpected culprit behind this immune resistance: a nuclear RNA methyltransferase called METTL16, which appears to rewire the metabolic chemistry of tumor cells in a way that simultaneously accelerates cancer growth and disarms the very immune cells meant to destroy them.
The research focuses on N6-methyladenosine, or m6A, the most abundant internal chemical modification found on messenger RNA in eukaryotic cells. Rather than altering the genetic code itself, m6A marks act like adjustable dimmer switches, influencing how efficiently a given transcript is processed, exported, translated, or degraded. METTL16 is one of the key writer enzymes of this system, and previous work had already implicated it in a range of cancers, from gastric and pancreatic tumors to bladder carcinoma, where it can either promote or suppress malignancy depending on the tissue context. The new study set out to determine what METTL16 does in colorectal cancer, and the answer turned out to involve a surprising metabolic detour.
The team began by measuring METTL16 levels in clinical colorectal cancer samples and in colorectal cancer cell models, using immunohistochemistry, quantitative PCR and western blotting. Across these analyses, METTL16 was consistently elevated in tumor tissue compared with healthy references. That observation raised an obvious question: was the enzyme simply a passenger, or was it actively driving the disease? To find out, the researchers used short hairpin RNA to knock down METTL16 in colorectal cancer cells and then ran a battery of functional assays, including CCK-8 viability tests, EdU proliferation assays, wound healing experiments and transwell migration and invasion chambers.
The results were striking. When METTL16 was depleted, the malignant behavior of the cancer cells collapsed on multiple fronts: they proliferated more slowly, migrated less aggressively and invaded less effectively. But the most intriguing finding emerged when the team introduced a co-culture system in which colorectal cancer cells were grown alongside CD8-positive T cells, the cytotoxic soldiers of the adaptive immune system. In the presence of METTL16-depleted tumor cells, the T cells proliferated more vigorously and secreted higher levels of three critical effector molecules: interferon-gamma, interleukin-2 and granzyme B. In other words, silencing METTL16 in the tumor made the immune cells surrounding it measurably more lethal.
This suggested that METTL16 was not merely a growth promoter inside the tumor cell but also an architect of immune evasion, helping the cancer hide from cytotoxic T lymphocytes. The next challenge was to identify the molecular bridge connecting an RNA modification enzyme to tumor metabolism and T cell function. The researchers’ attention turned to branched-chain amino acid transaminase 1, or BCAT1, an enzyme that catalyzes the first step in the breakdown of the branched-chain amino acids leucine, isoleucine and valine. BCAT1 had previously been flagged as a risk factor in multiple cancers through pan-cancer analyses, and accumulating evidence indicates that branched-chain amino acid availability can reprogram glucose metabolism in CD8-positive T cells in ways that enhance their anti-tumor effector function.
Using a trio of molecular techniques, the team dissected how METTL16 controls BCAT1. RNA immunoprecipitation showed a physical association between METTL16 and the BCAT1 transcript. Methylated RNA immunoprecipitation, or MeRIP, revealed that METTL16 deposits m6A marks on BCAT1 mRNA. And mRNA stability assays demonstrated the functional consequence: the m6A modification stabilized the BCAT1 message, extending its lifespan inside the cell and thereby boosting BCAT1 protein production. Liquid chromatography tandem mass spectrometry metabolomics then confirmed that this increase in BCAT1 drove enhanced catabolism of branched-chain amino acids within the tumor cells.
To prove that BCAT1 was the critical downstream mediator rather than an incidental bystander, the researchers performed rescue experiments. When they forced overexpression of BCAT1 in METTL16-depleted colorectal cancer cells, the suppressive effects of the knockdown were largely reversed: the cells regained their malignant characteristics, and the CD8-positive T cells in the co-culture system lost their enhanced proliferative and cytotoxic responses. This gain-of-function experiment established BCAT1 as the linchpin connecting METTL16’s RNA modification activity to both tumor progression and immune suppression, effectively closing the mechanistic loop.
The story then moved from the dish to the living organism. In a xenograft mouse model, depletion of METTL16 significantly inhibited tumor growth and reduced Ki-67, a well-established marker of cellular proliferation, within the tumors. Critically, the METTL16-deficient tumors also showed enhanced infiltration by CD8-positive T cells and elevated levels of T cell effector molecules, mirroring the in vitro findings and confirming that the enzyme’s influence on anti-tumor immunity operates within the complex microenvironment of a living tumor. The convergence of cell culture, molecular biology, metabolomics and animal data gives the study an unusually complete chain of evidence for a single mechanistic axis.
The implications reach well beyond colorectal cancer. The work adds to a growing body of literature showing that RNA modifications, once considered little more than molecular noise, are master regulators of cancer metabolism and tumor immunology. Other m6A machinery components, such as the methyltransferase METTL3 and the reader protein YTHDF1, have been shown to modulate immune evasion in colorectal tumors, and METTL16 itself has previously been linked to PD-L1-mediated immune escape. What makes the new findings particularly compelling is the metabolic dimension: by consuming branched-chain amino acids through BCAT1, high-METTL16 tumors may starve infiltrating T cells of nutrients they need to sustain their attack, a form of metabolic competition that complements classical immune checkpoint mechanisms.
For patients, the study suggests several potential avenues. METTL16 or BCAT1 could serve as biomarkers to identify colorectal tumors that are particularly adept at suppressing T cell immunity, helping clinicians select candidates for immunotherapy combinations. More ambitiously, pharmacological inhibitors of METTL16 or BCAT1, or dietary and metabolic strategies that manipulate branched-chain amino acid availability, could in principle be combined with checkpoint blockade to re-energize exhausted T cells. Such applications remain distant, and the study’s findings will need validation in larger cohorts and independent models before they influence clinical practice. But the core message is clear and provocative: a single RNA-tagging enzyme can simultaneously build a faster-growing tumor and a blunter immune response, and undoing that dual sabotage may one day become a genuine therapeutic strategy against one of the world’s deadliest cancers.
Subject of Research: METTL16-mediated m6A modification of BCAT1 and branched-chain amino acid metabolism in colorectal cancer progression and CD8+ T cell immunity
Article Title: METTL16 promotes colorectal cancer progression and CD8+ T cell function through BCAT1-dependent branched-chain amino acid metabolism
Article References: Hu, Y., Li, S., Zhu, M., Lin, X., Gong, C., & Fang, Z. (2026). METTL16 promotes colorectal cancer progression and CD8+ T cell function through BCAT1-dependent branched-chain amino acid metabolism. Medical Oncology, 43(11), Article 295. https://doi.org/10.1007/s12032-026-03410-7
Image Credits: AI Generated
DOI: 10.1007/s12032-026-03410-7
Keywords: colorectal cancer, METTL16, BCAT1, m6A modification, branched-chain amino acids, CD8+ T cells, immune evasion, tumor metabolism, RNA methyltransferase, immunotherapy resistance, xenograft model, cancer epigenetics
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Nathaniel Bowman. (October 1, 2026). RNA Tagging Enzyme METTL16 Fuels Colorectal Cancer by Hijacking Amino Acid Metabolism and Silencing Immune Cells. Scienmag. https://scienmag.com/rna-tagging-enzyme-mettl16-fuels-colorectal-cancer-by-hijacking-amino-acid-metabolism-and-silencing-immune-cells/
Nathaniel Bowman. “RNA Tagging Enzyme METTL16 Fuels Colorectal Cancer by Hijacking Amino Acid Metabolism and Silencing Immune Cells.” Scienmag, 1 October 2026, https://scienmag.com/rna-tagging-enzyme-mettl16-fuels-colorectal-cancer-by-hijacking-amino-acid-metabolism-and-silencing-immune-cells/. Accessed 1 October 2026.
Nathaniel Bowman. “RNA Tagging Enzyme METTL16 Fuels Colorectal Cancer by Hijacking Amino Acid Metabolism and Silencing Immune Cells.” Scienmag. October 1, 2026. https://scienmag.com/rna-tagging-enzyme-mettl16-fuels-colorectal-cancer-by-hijacking-amino-acid-metabolism-and-silencing-immune-cells/
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Tags: amino acid metabolism reprogrammingBCAT1branched-chain amino acidscancer epigeneticsCancer Immunotherapy ResistanceCD8+ T cellsColorectal cancercolorectal tumor growthimmune cell suppressionimmune evasionImmune Evasion MechanismsImmunotherapy Resistancem6A modificationm6A RNA modificationmetabolic reprogramming in cancerMETTL16RNA methylation in cancerRNA methyltransferaseRNA methyltransferase METTL16RNA tagging enzymetumor immune resistancetumor metabolismxenograft model
