RNA Modification-Mediated Translational Control In Immune Cells

By Hua-Bing Li, Ph.D., principal investigator, Hua-Bing Li lab, Shanghai Institute of Immunology, Shanghai Jiao Tong University School of Medicine

RNA modifications have emerged as one of the most influential layers of post-transcriptional gene regulation in modern molecular biology. Among these modifications, N6-methyladenosine (m6A) has gained particular attention because of its abundance in eukaryotic messenger RNA and its extensive influence on RNA metabolism. Over the last decade, researchers have increasingly recognized that RNA modifications do far more than simply “decorate” transcripts. Instead, they function as dynamic molecular signals capable of regulating RNA stability, localization, splicing, decay, and translation. In immune cells, these regulatory systems are especially important because the immune response requires rapid and tightly controlled protein synthesis in response to constantly changing environmental signals.

Translational regulation allows immune cells to respond immediately to infection, inflammation, and tissue damage without waiting for new transcriptional programs to occur. T cells, dendritic cells, macrophages, and other immune populations rely on rapid shifts in protein production to control activation, differentiation, cytokine secretion, and metabolic adaptation. RNA modifications provide a mechanism through which these rapid changes can occur. By altering how efficiently specific transcripts are translated into proteins, RNA modifications help determine immune cell identity and function.

Among the many known RNA modifications, m6A methylation has become the most extensively studied in the context of immune regulation. Although earlier work focused heavily on its role in mRNA degradation and splicing, newer studies increasingly suggest that m6A also exerts substantial control over translation. However, the mechanisms behind this translational regulation remain controversial and incompletely understood. Some evidence suggests that m6A directly enhances translation through specialized reader proteins, while other findings imply that many observed effects may be indirect or context dependent. These unresolved questions have made the study of m6A-mediated translational control one of the most rapidly evolving areas in RNA biology.

The m6A regulatory system consists of three major classes of proteins: writers, erasers, and readers. Writers are methyltransferases that install the methyl group onto RNA molecules. The best-characterized methyltransferase complex includes METTL3, METTL14, and WTAP. METTL3 acts as the catalytic core, while METTL14 primarily stabilizes RNA recognition and WTAP functions as a scaffold that recruits the complex to nuclear speckles. Additional regulatory proteins such as ZC3H13, Virilizer, and Hakai further contribute to the localization and activity of the methyltransferase machinery.

Importantly, m6A modification is not restricted to messenger RNA. Other RNA species, including ribosomal RNA, transfer RNA, long non-coding RNA, circular RNA, and small nuclear RNA, can also contain m6A marks. Specialized methyltransferases such as METTL5, ZCCHC4, and METTL16 regulate these modifications in distinct RNA classes. This broad distribution suggests that m6A participates in nearly every stage of RNA biology.

The reversibility of m6A methylation is equally significant. The first identified RNA demethylase, FTO, demonstrated that RNA methylation is a dynamic and reversible process rather than a static modification. FTO removes m6A marks from RNA, while ALKBH5 serves as another major demethylase controlling mRNA stability and splicing. Because these enzymes can rapidly erase methylation marks in response to cellular conditions, they allow immune cells to adapt quickly to stress, infection, or environmental changes.

The biological outcome of m6A modification depends heavily on reader proteins that recognize methylated transcripts. These readers interpret m6A signals and determine the fate of modified RNAs. Among the best studied are the YTH domain-containing family proteins, particularly YTHDF1, YTHDF2, and YTHDF3. Earlier studies proposed that each protein performed distinct functions. YTHDF1 was thought to enhance translation efficiency, YTHDF2 to promote mRNA degradation, and YTHDF3 to coordinate interactions between the two. Although this model has since been debated, it remains influential in understanding translational regulation.

YTHDF1 has received particular attention in immune biology because of its role in promoting translation of m6A-modified transcripts. In dendritic cells, METTL3-mediated m6A modification enhances the translation of transcripts involved in Toll-like receptor signaling, including Tirap, CD40, and CD80. These molecules are essential for antigen presentation and T cell activation. Loss of METTL3 reduces the translation efficiency of these transcripts despite relatively stable mRNA levels, demonstrating that m6A can regulate protein production independently of transcript abundance. YTHDF1 mediates this process by recruiting translation initiation machinery to methylated RNAs.

The immunological consequences of YTHDF1 activity extend into cancer biology. Studies have shown that YTHDF1 regulates translation of lysosomal proteases in dendritic cells, reducing antigen cross-presentation and limiting activation of cytotoxic CD8+ T cells. Mice lacking YTHDF1 exhibit enhanced antitumor immunity and respond more effectively to PD-L1 checkpoint blockade therapy. These findings suggest that targeting m6A-dependent translation pathways could improve cancer immunotherapy by strengthening antigen presentation and T cell priming.

YTHDF1 also appears to influence immune suppression within tumors. In colorectal cancer, YTHDF1 promotes translation of immune checkpoint molecules such as PD-L1 and VISTA without significantly altering their mRNA levels. This translational regulation contributes to immune evasion and suppresses T cell function within the tumor microenvironment. Similar findings have emerged in tumor-associated macrophages and tumor-infiltrating myeloid cells, where METTL3 and YTHDF1 cooperate to regulate translation of signaling molecules involved in inflammation and immunosuppression.

Despite strong evidence supporting YTHDF1-mediated translational control, disagreement persists regarding the precise functions of YTH family proteins. Some researchers argue that YTHDF proteins mainly regulate RNA decay rather than translation. Others contend that earlier studies overestimated translation effects because they analyzed large transcript populations instead of focusing specifically on direct YTHDF1 targets. More recent transcriptome-wide approaches suggest that only a relatively small subset of methylated RNAs are directly bound by YTHDF1. This has led to a more refined understanding in which YTHDF-mediated translation may occur in highly selective and context-dependent ways.

Beyond YTH proteins, the IGF2BP family has emerged as another important class of m6A readers involved in translational control. IGF2BP proteins stabilize methylated transcripts and enhance their translation through interactions with translation initiation factors. These proteins have been linked to inflammatory signaling pathways, particularly the IL-17 and TNFα axis. In epithelial and fibroblast cells, IGF2BP2 enhances translation of inflammatory transcription factors such as C/EBPβ and C/EBPδ, thereby amplifying cytokine responses.

IGF2BP proteins may also regulate immune metabolism. Studies in leukemia have shown that IGF2BP2 promotes translation of genes involved in glutamine metabolism, including MYC and SLC1A5. Because glutamine metabolism profoundly influences macrophage activation and immune cell differentiation, this suggests that m6A-mediated translational control may integrate metabolic and inflammatory signaling pathways.

Researchers have also begun identifying additional noncanonical m6A readers. One example is ATXN2, which enhances translation of TNFR1 signaling components in esophageal squamous cell carcinoma. Another is FMRP, traditionally associated with fragile X syndrome, which can bind m6A-containing transcripts and regulate translation repression. These discoveries suggest that the landscape of m6A reader proteins is far broader than previously appreciated.

Interestingly, methyltransferases themselves may directly regulate translation independently of m6A deposition. METTL3 has been shown to associate with ribosomes and translation initiation complexes in the cytoplasm. When tethered near stop codons, METTL3 enhances translation efficiency through interactions with eIF3h. This indicates that METTL3 can function not only as a nuclear writer but also as a cytoplasmic translation regulator.

The subcellular localization of METTL3 appears highly dynamic and environmentally responsive. In tumors, lactate accumulation promotes METTL3 upregulation and alters its function through lactylation modifications. During antiviral responses, innate immune signaling phosphorylates METTL3 and enhances its ability to support antiviral protein synthesis. These findings highlight how immune and metabolic environments influence RNA modification machinery.

Non-coding RNAs also participate extensively in m6A-mediated translational regulation. Circular RNAs containing m6A sites can undergo cap-independent translation. This process requires YTHDF3 and translation initiation factors such as eIF4G2. Environmental stressors like heat shock can enhance circRNA translation through m6A-dependent pathways.

Long non-coding RNAs are similarly affected. Certain lncRNAs regulated by m6A influence assembly of translation initiation complexes and thereby control translation of protein-coding genes. Ribosomal RNAs are also modified by m6A, and these modifications influence ribosome assembly and translational efficiency. Because immune cells rely heavily on rapid protein synthesis, alterations in non-coding RNA modification could profoundly affect immune responses.

Another major emerging theme is crosstalk between different RNA modifications. m6A does not operate in isolation. Other modifications such as m1A, m5C, m7G, pseudouridine, and m6Am also regulate RNA metabolism and translation. Some regulatory proteins participate in multiple modification pathways simultaneously. FTO, for example, demethylates both m6A and m1A-containing RNAs.

This overlap becomes particularly important in immune cells. Recent work demonstrated that m1A-modified tRNAs enhance translation of key proteins required for T cell activation, including MYC. Because FTO regulates m1A demethylation, it may indirectly influence T cell function through multiple RNA modification pathways at once. Similarly, YTHDF proteins can recognize both m6A and m1A modifications, suggesting coordinated regulation between different epitranscriptomic systems.

RNA secondary structure further complicates this regulatory network. m6A modifications often occur in regions with stable secondary structures. Reader proteins such as YTHDC2 possess RNA helicase activity capable of resolving these structures and facilitating ribosome movement along transcripts. In this way, m6A may promote translation not only through recruitment of translation factors but also by physically altering RNA accessibility.

Despite rapid progress, many critical questions remain unresolved. One major challenge is distinguishing direct translational effects from indirect consequences of altered RNA stability or cellular signaling. Many studies infer translational regulation based on discrepancies between mRNA and protein levels, but such differences can arise through multiple mechanisms. Advanced methods such as ribosome profiling, PAR-CLIP, and single-nucleotide m6A mapping are helping refine our understanding, yet mechanistic clarity remains incomplete.

Another important issue is cell-type specificity. m6A modifications occur only on subsets of transcripts, and different immune cells express distinct repertoires of reader proteins and RNA-binding factors. Consequently, the same modification may produce entirely different outcomes in dendritic cells, macrophages, T cells, or tumor cells. Understanding these context-dependent regulatory networks will be essential for translating RNA modification biology into therapeutic strategies.

The therapeutic potential of targeting m6A pathways is enormous. Manipulating RNA modification machinery could enhance antiviral immunity, improve vaccine responses, suppress autoimmune inflammation, or overcome tumor immune evasion. Inhibitors of FTO and ALKBH5 are already being explored in cancer models, while modulation of YTHDF proteins could potentially reshape immune responses within the tumor microenvironment.

Ultimately, RNA modification-mediated translational control represents a sophisticated regulatory layer that enables immune cells to rapidly adapt to changing conditions. m6A modification acts as both a sensor and an effector, integrating environmental signals with translational machinery to fine-tune protein synthesis. As research continues, it is becoming increasingly clear that epitranscriptomic regulation is fundamental to immune cell biology.

Future studies will need to clarify how different RNA modifications interact, how reader proteins coordinate their functions, and how environmental signals reshape RNA modification landscapes. Equally important will be determining how these pathways operate in physiological versus pathological conditions. A deeper understanding of these mechanisms could open entirely new therapeutic avenues for autoimmune diseases, infectious diseases, and cancer.

The study of RNA modification-mediated translational control is still in its early stages, yet it has already transformed our understanding of immune regulation. What was once considered a simple chemical decoration on RNA is now recognized as a dynamic and highly influential signaling system that controls immune cell fate, activation, and function at the level of protein synthesis itself.

About The Author:

Hua-Bing Li, Ph.D., earned both his bachelor’s and master’s degrees from Nankai University, then obtained his doctorate in biochemistry in 2011 in Vincenzo Pirrotta lab at Rutgers, The State University of New Jersey, working on polycomb mediated long-distance chromatin interactions in Drosophila. Since 2012, Li has continued his postdoc training with Richard Flavell, Ph.D., at the Yale University School of Medicine, working on regulatory RNAs and RNA epigenetic switches of the immune system.

Li established his independent lab at Shanghai Jiao Tong University School of Medicine in 2017. The lab is especially interested in the physiological functions and molecular mechanisms of RNA epigenetic modifications and related RNA binding proteins in immune cells and related immune disease with mouse disease models. Combined with state-of-the-art technologies and international collaboration, the lab aims to reveal novel functions and mechanisms of inflammation and autoimmune disease, which will contribute to the identification of potential targets for anti-autoimmune and anti-tumor drug development.