Background

Epithelial-mesenchymal transition (EMT) is a prominent characteristic observed during cancer cell metastasis. EMT refers to a flexible cell-state program where epithelial cells lose their characteristics and transform into highly motile mesenchymal cells. Previously, EMT was understood as a simple On/Off switch where cancer cells completely transitioned from an epithelial to a mesenchymal state. However, recent research suggests that cancer cells undergo intermediate or partial EMT (partial EMT) stages between these two states. These intermediate cells maintain cell-cell adhesion while simultaneously acquiring motility and stress resistance. These intermediate states are major factors that make cancer treatment difficult, as they exhibit tumor invasion, distant metastasis, immune evasion, and drug resistance.

Until now, the scientific community has attempted to understand EMT by focusing on transcription factors. However, controlling EMT solely at the transcription factor level is insufficient to fully explain the rapid and flexible state changes in cancer cells. Another regulatory layer is needed that allows cells to sensitively respond to environmental changes and rapidly fine-tune protein production. A recently emerging area is RNA chemical modifications, also known as epitranscriptomics. This involves chemical modifications to RNA molecules, which alter gene translation efficiency or stability. This study systematically analyzed how RNA chemical modifications serve as a key post-transcriptional regulatory mechanism determining cancer cell plasticity.

Key Findings

The researchers discovered that cancer cells activate RNA modification systems in response to signals from the tumor microenvironment, such as hypoxia, transforming growth factor-beta (TGF-β) signaling, and therapeutic stress. The analysis revealed that various RNA chemical modifications, including N6-methyladenosine (m6A), 5-methylcytosine (m5C), and N4-acetylcytidine (ac4C), act as key molecular switches that regulate cancer cell plasticity. The roles of these modifications vary depending on their type.

The most extensively studied m6A modification functions as a 'Writer-Reader-Eraser' protein module, regulating EMT transcription factors and key signaling pathways. m6A alters the RNA stability of key signaling genes involved in tumor metastasis, such as TGF-β/SMAD, Wnt/β-catenin, and Notch. In particular, by shortening or lengthening the lifespan of mRNA, it helps cancer cells rapidly transition to a mesenchymal state.

In contrast, m5C and ac4C function by abnormally stabilizing transcripts and increasing the rate of gene translation. These two modifications ensure that cancer cells can continuously synthesize proteins necessary for survival even in harsh microenvironments. N7-methylguanosine (m7G) modification induces translational reprogramming, promoting biased protein synthesis towards specific codons, thereby selectively increasing the expression of EMT-related genes.

Furthermore, A-to-I RNA editing exhibits a highly dualistic nature. Depending on the direction of editing, it can either promote immune evasion and increase cell plasticity, or conversely, generate inhibitory gene isoforms that prevent metastasis. The mechanisms related to pseudouridine (Ψ) are still in the early stages of research, but it is known to contribute to the ability of cancer cells to adapt to external stress and invade surrounding tissues.

Significance and Prospects

This analysis demonstrates that the core mechanism of cell-state transition relies on subtle chemical modifications at the RNA level rather than the genome's genetic information. Therapeutic strategies can be developed to normalize epitranscriptome modification patterns, thereby fundamentally blocking the metastatic potential and drug resistance of cancer cells.

However, there are many challenges to overcome before clinical application. Most previous studies used bulk analysis techniques, which analyze large populations of cells rather than individual cells. This means that they cannot capture the diversity of cells within tumor tissues in detail. Furthermore, the technology for accurately verifying chemical modifications that occur at specific RNA base sequences is still lacking, and the causal evidence showing that modification changes directly induce EMT needs to be supplemented.

Therefore, the integration of single-cell analysis techniques and spatial epitranscriptomics has emerged as an essential task. Confirming the RNA modification status of individual cancer cells based on their location is necessary to lead to personalized treatments for actual patients. Future research that refines functional RNA editing tools and links them to large-scale clinical cohort data will determine the success of this field.