Alternative Polyadenylation Altering Cancer Cell Transcriptome Ends Emerges as New Drug Target and Diagnostic Biomarker
Background
In the process of converting genetic information into proteins, the three-dimensional structure of messenger RNA (mRNA) determines translation efficiency and lifespan. Post-transcriptional regulation is considered a key axis of gene expression control, and recently, alternative polyadenylation (APA) has been drawing attention in oncology as an oncogenic factor. Tumor cells establish protein expression profiles advantageous to themselves by selecting different mRNA termination sites compared to normal cells.
Previously, researchers interpreted APA simply as a uniform shortening phenomenon where the 3' Untranslated Region (3'UTR), the non-coding region at the back of mRNA, becomes shorter. This was due to the difficulty of precisely separating and quantifying various isoforms of the 3' end using existing sequencing technologies and analysis methods. Complex phenomena, such as premature cleavage within introns, or heterogeneous events that modify the protein amino acid sequence itself, remained unidentified due to these analytical limitations. As mutation-centered targeted therapies frequently encounter drug resistance, there is an urgent need for a new perspective to comprehensively reveal structural variations occurring during the transcriptome processing.
Key Findings
Recent studies have characterized APA as a complex regulatory mechanism that induces aberrant transcriptome termination, extending beyond simple 3'UTR shortening. Researchers clearly distinguished upstream APA events, including tandem 3'UTR APA and intronic polyadenylation (IPA), from downstream APA events. Analysis results indicate that tandem 3'UTR alternative polyadenylation (APA) functions by removing microRNA (miRNA) binding sites or RNA-binding protein (RBP) inhibitory sequences, thereby explosively amplifying oncogene expression.
Intronic polyadenylation leads to even more dramatic molecular alterations. When premature polyadenylation occurs at intronic sites during the intermediate stage of transcription, protein translation is abnormally terminated prematurely. This results in the production of truncated proteins that have lost normal function or the secretion of soluble isoforms that disrupt receptor signaling. The mechanism where atypical peptide sequences are expressed due to early termination, forming tumor-specific neoantigens, was also confirmed.
The mechanism of action of intracellular regulatory complexes has also been elucidated in detail. Not only the interaction between core 3' end processing factors and regulatory RBPs, but also the mutual binding between the splicing machinery and the polyadenylation machinery precisely regulate the frequency of IPA occurrence. Direct molecular communication between the promoter and the transcription termination site also affects transcription speed, disrupting 3' end selection. Aberrant APA induced in this process promotes tumor cell proliferation, invasion, and metabolic reprogramming, and remodels the tumor microenvironment into an immunosuppressive state to induce immune evasion.
Significance and Outlook
This framework expands the horizon of cancer transcriptome research from identifying gene mutations to elucidating abnormalities in post-transcriptional regulation. Cancer-specific 3'UTR signatures and IPA products can be utilized as highly sensitive biomarkers to increase the diagnostic accuracy of existing tissue biopsies. Integration with liquid biopsy technology, which detects atypical polyadenylation products in circulating transcripts within patient blood, is also anticipated.
In terms of treatment, small-molecule compounds that control the 3' end processing complex and antisense oligonucleotide (ASO)-based RNA therapeutics have emerged as new alternatives. CRISPR base editing techniques that mask abnormal premature termination sites in specific genes are also on the development track. However, since many core processing factors are also involved in the basic life-sustaining functions of normal cells, a prerequisite is to establish a targeted delivery system that precisely selects and targets only cancer-specific APA events while minimizing toxicity to normal tissues.
Alternative polyadenylation (APA) is a pervasive post-transcriptional regulatory mechanism that generates transcript isoforms with distinct 3' untranslated regions, terminal exons, or coding potential, thereby influencing mRNA stability, translation, localization, and protein output. Rather than representing a uniform 3'UTR-shortening process, APA comprises heterogeneous 3'-end regulatory events, including tandem 3'UTR APA and upstream APA events such as intronic polyadenylation (IPA), which differ in mechanisms, detection strategies, functional consequences, and clinical interpretation. Dysregulated APA is increasingly recognized as an important contributor to cancer initiation and progression. Tandem 3'UTR APA can remove miRNA- or RNA-binding protein-mediated repression and enhance oncogenic transcript output, whereas upstream APA events, including IPA, can generate prematurely terminated RNAs, truncated proteins, soluble isoforms, or neoantigenic products. In this review, we summarize the classification and biological consequences of major APA events, as well as experimental and computational approaches for APA analysis. We then discuss regulatory mechanisms involving core 3'-end processing factors, RNA-binding proteins, splicing-polyadenylation coupling in upstream APA/IPA, transcription-associated regulation, and promoter-terminator communication. Functionally, aberrant APA contributes to proliferation, invasion and metastasis, metabolic reprogramming, tumor microenvironment remodeling, antitumor immunity, and immune escape. Finally, we highlight APA events, APA regulators, 3'UTR-based signatures, and upstream APA/IPA-derived products as emerging biomarkers and discuss small-molecule, RNA-based, and CRISPR-based strategies for targeting APA or 3'-end processing in cancer.
This research provides a practical turning point for the design of early cancer diagnosis panels and customized anticancer strategies. In clinical settings, APA diagnostic markers can be used to identify patient groups with abnormally high expression levels of oncogenes, even in the absence of mutations in the oncogene nucleotide sequence. It becomes possible to perform precision classification, such as predicting responsiveness to immune checkpoint inhibitors by measuring the frequency of tandem 3'UTR shortening, or pre-identifying patients unresponsive to targeted anticancer drugs based on levels of IPA-derived soluble receptors.
In the field of therapeutic development, the pipeline for producing patient-specific mRNA cancer vaccines using neoantigens generated by IPA is promising. The construction of RNA drug pipelines, such as using splice-switching oligonucleotides (SSO) to block abnormal polyadenylation signals located in the introns of tumor suppressor genes to restore full-length protein expression, is also within sight.