The instructions for a human cell are written in a script punctuated by chemical marks that modify RNA, the molecule responsible for carrying DNA’s instructions. These modifications, known as the epitranscriptome, add a layer of control over how genetic information is used. One such chemical tag is N4-acetylcytidine (ac4C).
N4-acetylcytidine is an acetyl group placed onto a cytidine nucleoside, a fundamental component of RNA. This alteration occurs after the RNA molecule has been transcribed from its DNA template. This modification has significant consequences, influencing an RNA molecule’s stability and how efficiently it can be used to produce proteins.
The Role of N4-acetylcytidine in RNA Function
The primary function of N4-acetylcytidine is to enhance the stability of RNA molecules. The addition of the acetyl group to cytidine strengthens the base-pairing interaction between cytidine and its partner, guanosine. This chemical reinforcement makes the RNA strand more resistant to degradation by cellular enzymes called nucleases, extending its functional lifespan within the cell.
This increased stability has direct implications for translation, the process where the ribosome reads an mRNA molecule to synthesize a protein. A more stable mRNA transcript can endure for longer, allowing it to be read multiple times. This leads to a more efficient production of the protein it encodes. The presence of ac4C also ensures that the genetic message is accurate.
The responsibility for adding this mark falls to a single enzyme known as N-acetyltransferase 10 (NAT10). NAT10 is the “writer” enzyme that recognizes specific cytidine bases within various types of RNA, including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). It then catalyzes the attachment of the acetyl group. Without this enzyme, the ac4C modification cannot be made, impacting the stability of numerous RNAs.
The precision of NAT10’s activity is important for normal cellular operations. For instance, in ribosomal RNA, ac4C is important for the correct assembly of ribosomes, the machinery that carries out protein synthesis. In transfer RNA, the modification helps ensure the correct reading of the genetic code during translation. This demonstrates that ac4C is a targeted mechanism for fine-tuning gene expression.
N4-acetylcytidine’s Connection to Human Health and Disease
The regulatory network governed by ac4C is delicately balanced, and its disruption is linked to human diseases, particularly cancer. Many cancer types exhibit elevated levels of both ac4C and the NAT10 enzyme. This overexpression appears to be a strategy that cancer cells exploit to promote their own survival and proliferation.
In various cancers, including bladder, cervical, and gastric cancers, increased NAT10 activity leads to the stabilization of mRNAs that code for proteins promoting cell growth, invasion, and metastasis. For example, NAT10 stabilizes the mRNA of genes involved in epithelial-mesenchymal transition (EMT), a process where stationary cancer cells become mobile. It also stabilizes genes that help cancer cells resist programmed cell death.
The influence of ac4C extends to the metabolic processes that fuel tumors. Cancer cells often rewire their metabolism to support rapid growth, and NAT10 is implicated in this process by stabilizing the mRNAs of genes involved in fatty acid metabolism. This provides the cancer cells with the necessary energy to sustain their uncontrolled division.
While the connection to oncology is the most studied, research suggests ac4C’s role in other conditions. For instance, the modification plays a part in the life cycle of viruses like influenza A and HIV by stabilizing viral RNA and enhancing its translation. There is also evidence linking NAT10 and ac4C to autoimmune disorders and developmental processes.
N4-acetylcytidine as a Diagnostic Biomarker and Therapeutic Target
The consistent overexpression of NAT10 in tumor cells presents an opportunity for clinical applications. This has led researchers to investigate it as a potential biomarker—a measurable indicator that can signal the presence or state of a disease. By measuring NAT10 levels in a patient’s tissue or blood samples, doctors might diagnose cancer earlier or predict its behavior.
Higher levels of NAT10 have been correlated with a poorer prognosis in several types of cancer, including cervical and gastric cancer. This suggests its utility for determining the aggressiveness of a tumor and helping to guide treatment decisions. Monitoring these levels could also provide a way to track how well a patient is responding to therapy.
Beyond diagnostics, the role of the NAT10 enzyme makes it a therapeutic target. Since NAT10 is the sole writer of the ac4C mark, developing drugs that inhibit its function could destabilize the mRNAs that cancer cells rely on for growth and survival. This represents a targeted strategy to halt the disease.
Scientists are developing and testing small-molecule inhibitors that can block the enzymatic activity of NAT10. One such inhibitor, Remodelin, has shown promise in preclinical studies by impairing cancer cell proliferation. This approach offers a promising new avenue for cancer therapy with potentially fewer side effects than traditional chemotherapies.