The research, led by Yinghuan Liu, Xianying Li, Tong Zhou, Jianhua Xie and colleagues under the supervision of Yongjun Wang, Dong Han and Lifu Li, focuses on N-acetyltransferase 10, or NAT10, the only known mammalian enzyme that installs N4-acetylcytidine, abbreviated ac4C, onto cytidine residues within mRNA. This chemical acetylation is a member of the expanding family of epitranscriptomic marks, modifications that do not change the genetic sequence itself but alter how RNA molecules behave, influencing their stability, localization, translation efficiency and fidelity. By stabilizing particular transcripts, ac4C can effectively turn up the volume of specific genes without the cell ever touching its DNA.

The team began by asking whether NAT10 is present in diseased valves. Analyzing tissue from 50 patients with calcific aortic valves and 50 non-calcified controls, they found that NAT10 mRNA and protein were both significantly elevated in the diseased tissue. A parallel increase appeared in a mouse model, in which apolipoprotein E-deficient mice fed a high-cholesterol diet for 24 weeks develop aortic valve calcification that mirrors the human condition. Dot blot assays measuring total RNA acetylation revealed that global ac4C levels rose alongside NAT10 in both human and mouse calcified valves, suggesting that the enzyme’s catalytic output, not merely its abundance, tracks with disease.

Cellular studies sharpened the picture. The chief cellular culprit in valve calcification is the human valvular interstitial cell, or hVIC, which under pathological stress abandons its usual quiescent state and transforms into an osteoblast-like cell that lays down mineral. When the researchers isolated hVICs and valve endothelial cells from patients, NAT10 was substantially higher in the interstitial cells, identifying them as the primary source of the enzyme in diseased valves. When hVICs were bathed in osteogenic medium, NAT10 expression climbed in a time-dependent manner together with the osteogenic marker osterix. Silencing NAT10 blunted the appearance of osteogenic markers, calcified nodule formation and calcium deposition, while forcing NAT10 overexpression intensified all of these features, effects that held true in cells from both diseased and healthy donors.

Correlation analyses in a second, independent validation cohort of 50 patients linked NAT10 to disease severity in a clinically meaningful way. NAT10 expression rose in step with the osteogenic markers osterix and osteopontin, and higher NAT10 levels were associated with a smaller aortic valve area and greater mean and peak transvalvular pressure gradients on echocardiography. In other words, the more NAT10 a patient’s valve expressed, the worse the valve functioned, positioning the enzyme as both a potential biomarker and a therapeutic target.

To find what NAT10 was actually doing downstream, the investigators performed a rigorous three-way screen. They intersected genes downregulated when NAT10 was knocked down in hVICs, established NAT10 perturbation targets from the RM2Target database, and aortic valve calcification genes curated in the Open Targets Platform. The overlap narrowed to just seven candidates: COL1A1, PCSK9, SCG2, UBE2C, FN1, THBS2 and SERPINE1. Rescue experiments then delivered a decisive verdict. Knocking down PCSK9, but none of the other six genes, almost completely abolished the pro-calcific phenotype driven by NAT10 overexpression, establishing PCSK9 as the dominant functional effector of the pathway.

PCSK9 is best known as a cholesterol regulator, famous for degrading low-density lipoprotein receptors in the liver and for the blockbuster antibody drugs that block it. But recent genetic and experimental work has implicated PCSK9 directly in valve calcification as well. The new study shows that NAT10 regulates PCSK9 post-transcriptionally. RNA decay assays using actinomycin D to halt transcription demonstrated that NAT10 knockdown shortened the half-life of PCSK9 mRNA, while NAT10 overexpression prolonged it, with corresponding changes in PCSK9 protein production and secretion. In human calcific valves, NAT10 and PCSK9 expression correlated positively, tying the molecular mechanism to clinical tissue.

The mechanistic proof that ac4C is the responsible mark came from a series of elegant experiments. RNA immunoprecipitation showed that PCSK9 mRNA is bound by both NAT10 and anti-ac4C antibodies, and that NAT10 depletion reduces the ac4C signal on the transcript. A predicted acetylation motif within positions 1886 to 1900 of the PCSK9 coding sequence was tested with luciferase reporters: mutating the cytosines in that motif to thymines made the reporter insensitive to NAT10 knockdown, whereas the wild-type reporter responded strongly. The researchers also deployed a catalytically dead NAT10 mutant, G641E, which retains expression but cannot acetylate RNA. Only the wild-type enzyme, not the mutant, boosted PCSK9 stability and production, proving that the acetyltransferase activity itself is essential. Control experiments confirmed that knockdown of NAT10 did not perturb other components of the ac4C machinery, including the cofactor THUMPD1, the reader NOP58 and the putative eraser SIRT7, underscoring the specificity of the effect.

The most clinically compelling results came from the mouse experiments. Apolipoprotein E-deficient mice on a high-cholesterol diet were treated either with remodelin, a small-molecule NAT10 inhibitor, or with NP1192, a first-in-class PROTAC degrader that selectively drags NAT10 into the cellular destruction machinery. Because remodelin is known to interact with multiple cellular targets, the PROTAC served as an orthogonal check on specificity. Both compounds partially reversed the echocardiographic hallmarks of aortic stenosis, reduced valve leaflet thickness and calcium deposition on histology, suppressed the osteogenic markers osterix and osteopontin, and lowered NAT10 protein and global ac4C levels in valve tissue. Crucially, blood glucose, total cholesterol, LDL, triglycerides and circulating PCSK9 were unchanged by treatment, indicating that the benefit arose from local action within the valve rather than from systemic lipid lowering, and that the anti-calcific effect was on-target rather than a metabolic side effect.

The study is not without caveats, which the authors acknowledge candidly. Calcific valve disease involves endothelial cells and macrophages in addition to interstitial cells, and NAT10’s role in those compartments was not explored; cell-type-specific knockout models will be needed to disentangle the contributions. Transcriptome-wide mapping of ac4C targets was not performed, so other NAT10-regulated transcripts may contribute to the phenotype. The upstream signals that raise NAT10 expression in the diseased valve, whether mechanical stress, lipid retention, oxidative stress or inflammatory cytokines, remain unidentified. Even so, the work delivers something the field has lacked: a concrete, druggable epitranscriptomic axis, NAT10-ac4C-PCSK9, that connects RNA chemistry to the bone-like transformation of the aortic valve. If future clinical studies confirm that NAT10 degraders such as NP1192 can slow or stop valve calcification in patients, the humble acetyl group on a single cytidine may turn out to be the handle medicine has been searching for on one of cardiology’s hardest diseases.

Subject of Research: The role of NAT10-mediated mRNA N4-acetylcytidine modification of PCSK9 in calcific aortic valve disease

Article Title: NAT10 exacerbates aortic valve calcification via PCSK9 mRNA ac4C acetylation

Article References: Liu, Y., Li, X., Zhou, T., Xie, J., Jiang, H., Zheng, B., Peng, J., Li, L., Han, D., & Wang, Y. (2026). NAT10 exacerbates aortic valve calcification via PCSK9 mRNA ac4C acetylation. iScience, 29(11), Article 117812. https://doi.org/10.1016/j.isci.2026.117812

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117812

Keywords: NAT10, ac4C, PCSK9, aortic valve calcification, calcific aortic valve disease, epitranscriptomics, valvular interstitial cells, RNA modification, PROTAC, NP1192, osteogenic differentiation, mRNA stability

The chemical tag in question is N4-acetylcytidine, abbreviated ac4C, a modification installed on messenger RNA mainly by the enzyme NAT10. Of the more than 170 known RNA modifications, ac4C is the only acetylation event known to occur on eukaryotic messenger RNA. Previous work has shown that ac4C enhances mRNA stability and translational efficiency, thereby governing cell cycle dynamics, metabolic reprogramming, and oncogenic behavior. What remained conspicuously missing, the researchers note, was a systematic map of the global ac4C landscape in colorectal cancer and an understanding of how it shapes the tumor microenvironment, particularly the cancer-associated fibroblasts that act as its primary architects.

To fill that gap, the team quantified ac4C modification patterns across multiple independent cohorts drawn from the Gene Expression Omnibus and The Cancer Genome Atlas, using single-sample Gene Set Enrichment Analysis to compute a continuous ac4C score for each patient. Rather than relying on consensus clustering, this approach assigned every tumor an absolute enrichment value for the ac4C signature. Stratifying patients at the median score revealed two molecularly distinct subgroups, and principal component analysis and t-distributed stochastic neighbor embedding confirmed clear transcriptional separation between them. Crucially, the classification held up across four independent validation datasets, suggesting that ac4C-based subtyping is not an artifact of any single platform or population.

The clinical implications of this stratification were striking. Patients in the high-ac4C group were significantly enriched for aggressive features, including advanced nodal stage and distant metastasis, and the proportion of high-ac4C tumors rose steadily as pathological stage advanced. Pathway analysis showed that high ac4C scores correlated strongly with epithelial-mesenchymal transition and TGF-beta signaling, the canonical engines of invasion and spread, whereas low scores aligned with cell cycle regulation, fatty acid metabolism, and microsatellite-stable biology. Survival analysis reinforced the picture: the high-ac4C subgroup exhibited markedly worse overall survival, a finding reproduced in both training and external validation cohorts.

Profiling of the tumor microenvironment added a crucial dimension. Using CIBERSORT for immune cell deconvolution and the ESTIMATE algorithm to compute stromal and immune scores, the researchers found that high-ac4C tumors harbored dense, stroma-rich microenvironments. These tumors showed upregulated expression of key immune checkpoint and inhibitory molecules, including LAG3, CD14, LILRB2, SIRPA, and CD8A, alongside a correlation with innate immune components such as NK cells, monocytes, and macrophages. The authors interpret this combination as evidence that ac4C overactivity fosters an immune-excluded, fibrotic niche, one in which physical barriers of extracellular matrix impede immune infiltration while inhibitory signals exhaust the cytotoxic cells that do arrive.

To convert these population-level patterns into a clinically usable tool, the team intersected differentially expressed genes between the ac4C subgroups with core ac4C regulators and applied LASSO-Cox regression to derive a prognostic gene signature. The resulting ac4C score predicted poor overall survival with high area-under-the-curve values at one, three, and five years, and a nomogram integrating the score with standard clinicopathological features outperformed traditional TNM staging alone. Pharmacogenomic predictions added a therapeutic twist: high-ac4C tumors were predicted to resist conventional agents such as cisplatin, gemcitabine, and doxorubicin, yet to show heightened sensitivity to targeted kinase inhibitors including pazopanib and gefitinib. The authors caution that these are algorithmic, hypothesis-generating inferences rather than validated treatment guidelines.

The study’s most consequential discovery emerged from single-cell RNA sequencing. Mining the scCancer Explorer database, the researchers identified CERCAM, or Cerebral Endothelial Cell Adhesion Molecule, as the gene carrying the highest coefficient weight in their prognostic model. Single-cell mapping showed that CERCAM was expressed almost exclusively within the cancer-associated fibroblast cluster, with virtually no expression in epithelial tumor cells, T cells, or B cells. High-resolution subclustering restricted to 10X Genomics datasets to eliminate batch effects revealed further specificity: CERCAM was enriched in matrix-remodeling, myofibroblastic CAFs, the subpopulation responsible for collagen deposition and extracellular matrix crosslinking, while remaining low in inflammatory CAFs and resting normal fibroblasts.

Epigenetic and clinical evidence converged on the same target. DNA methylation analysis showed that CERCAM promoter methylation was highest in metastatic cells, intermediate in primary tumor cells, and lowest in normal cells, hinting at a coordinated dual layer of regulation involving both RNA modification and DNA methylation during tumor spread. In a cohort of 70 paired fresh tumor and adjacent normal tissue samples, 60 patients showed higher CERCAM expression in tumor tissue than in matched normal tissue. Quantitative PCR across cell lines confirmed that CERCAM expression in cancer-associated fibroblasts dramatically exceeded levels in normal fibroblasts and all epithelial or tumor cell lines tested.

Functional experiments then tested whether fibroblast-derived CERCAM actually drives tumor behavior. The researchers knocked down or overexpressed CERCAM in CAFs and co-cultured the modified fibroblasts with RKO and HCT116 colorectal cancer cells in Transwell systems that permit paracrine signaling without direct contact. When CERCAM was depleted from the fibroblasts, co-cultured tumor cells showed significantly impaired proliferation in CCK-8 assays, along with reduced migration in wound-healing assays and diminished invasion through Matrigel-coated inserts. The result demonstrates that the ac4C network does not merely act within cancer cells; it also reprograms stromal cells to emit paracrine signals and remodel the extracellular matrix in ways that push tumors toward metastasis.

The authors are careful to delineate the limits of their evidence. Direct acetylation of CERCAM messenger RNA by NAT10 has not yet been experimentally validated, and the mechanistic link between ac4C modification and the observed CERCAM DNA methylation remains hypothetical, pending techniques such as ac4C-RIP sequencing. Discrepancies between single-cell and qPCR sensitivity, an uneven clinical validation split of 60 high versus 10 low expressors, and the inherent limitations of bulk-transcriptome drug prediction algorithms all warrant caution. Even so, the study establishes a compelling new taxonomy for colorectal cancer, one in which an RNA chemical mark predicts prognosis, sculpts a fibrotic and immune-excluded microenvironment, and points to CAF-derived CERCAM as a promising target for dismantling the immunosuppressive stroma that shields these tumors from both drugs and immune attack.

Subject of Research: ac4C RNA modification profiling and CERCAM-expressing cancer-associated fibroblasts in colorectal cancer prognosis and tumor microenvironment regulation

Article Title: Comprehensive Profiling of ac4C RNA Modification Identifies CERCAM in Cancer‐Associated Fibroblasts as a Key Prognostic and Microenvironmental Regulator in Colorectal Cancer

Article References: Xia, Y., Dai, J., Zhou, X., & Zhang, R. (2026). Comprehensive Profiling of ac4C RNA Modification Identifies CERCAM in Cancer‐Associated Fibroblasts as a Key Prognostic and Microenvironmental Regulator in Colorectal Cancer. Cancer Reports, 9(9), Article e70677. https://doi.org/10.1002/cnr2.70677

Image Credits: AI Generated

DOI: 10.1002/cnr2.70677

Keywords: colorectal cancer, ac4C, RNA modification, epitranscriptomics, NAT10, CERCAM, cancer-associated fibroblasts, tumor microenvironment, prognostic signature, single-cell RNA sequencing, immune exclusion, drug sensitivity