The occurrence and progression of cancer are closely related to the expression of oncogenes, and the regulation of oncogene expression is a complex process. Among these mechanisms, the role of translation control in oncogene expression has gradually gained attention. MYC is a key oncogene that is overexpressed in various cancers, particularly in pancreatic ductal adenocarcinoma (PDAC), where its high expression is closely associated with tumor aggressiveness and poor prognosis. However, the translational regulation of MYC remains unclear. To uncover this mechanism, researchers conducted this study, aiming to identify key factors regulating MYC translation through functional genomic screening and to explore their role in PDAC tumorigenesis.

Source of the Paper

This paper was completed by a research team led by Joanna R. Kovalski, Goksu Sarioglu, Vishvak Subramanyam from the University of California San Francisco, and published in the journal Nature Cell Biology in March 2025, titled Functional screen identifies RBM42 as a mediator of oncogenic mRNA translation specificity.

Research Process

1. Functional Genomic Screening

The researchers first designed a genome-wide screening method based on CRISPR interference (CRISPRi) to identify factors regulating MYC translation. They constructed a fluorescent reporter system in PDAC cells, where the MYC 5’ untranslated region (5’ UTR) drives the expression of an unstable green fluorescent protein (GFP), while a minimized 5’ UTR drives the expression of an unstable red fluorescent protein (mCherry). Using fluorescence-activated cell sorting (FACS), the researchers screened for genes that specifically regulate MYC translation.

2. Validation of Candidate Genes

The screening results revealed that the RNA-binding protein RBM42 is a key factor regulating MYC translation. By transiently knocking down RBM42, the researchers observed a significant decrease in MYC protein levels, while MYC mRNA levels remained largely unchanged, indicating that RBM42 affects MYC expression through translational regulation. Further sucrose gradient centrifugation (polysome profiling) analysis showed that after RBM42 knockdown, MYC mRNA shifted from the polysome fraction to the untranslated fraction, confirming RBM42’s role in MYC translation regulation.

3. Functional Studies of RBM42

To further investigate the function of RBM42, the researchers performed gene set enrichment analysis (GSEA) and found that the expression of MYC target genes was significantly downregulated after RBM42 knockdown. Additionally, the researchers discovered that RBM42 is highly expressed in PDAC and is associated with poor patient prognosis. Through immunohistochemistry (IHC) analysis, they observed increased cytoplasmic localization of RBM42 in PDAC tissues, highlighting its important role in translational regulation.

4. Molecular Mechanisms of RBM42

To elucidate the molecular mechanisms by which RBM42 regulates MYC translation, the researchers conducted crosslinking immunoprecipitation sequencing (CLIP-seq) and found that RBM42 directly binds to the 5’ UTR of MYC mRNA. Through RNA structure analysis using dimethyl sulfate (DMS) treatment, they discovered that RBM42 binding remodels the MYC 5’ UTR structure, forming a more open loop structure that facilitates the formation of the translation initiation complex (PIC). Furthermore, the researchers found that RBM42 directly interacts with the 40S ribosomal subunit and the translation initiation factor eIF2β, further supporting its role in translation initiation.

5. In Vivo Experimental Validation

To validate the role of RBM42 in PDAC tumorigenesis, the researchers conducted xenograft experiments in mouse models. The results showed that knocking down RBM42 significantly inhibited PDAC tumor growth, while forced expression of MYC partially restored tumor growth, indicating that RBM42 plays a crucial role in PDAC tumorigenesis by regulating MYC translation.

Key Findings

1. RBM42 is a key regulator of MYC translation: Through CRISPRi screening, the researchers identified RBM42 as a key factor regulating MYC translation and validated its regulatory role through various experiments.
2. RBM42 promotes translation by remodeling the MYC 5’ UTR structure: CLIP-seq and DMS-seq analyses revealed that RBM42 binding remodels the MYC 5’ UTR structure, facilitating the formation of the translation initiation complex.
3. RBM42 interacts with ribosomes and translation initiation factors: Immunoprecipitation and mass spectrometry analyses showed that RBM42 directly interacts with the 40S ribosomal subunit and eIF2β, further supporting its role in translation initiation.
4. RBM42 plays a critical role in PDAC tumorigenesis: In vivo experiments demonstrated that knocking down RBM42 significantly inhibits PDAC tumor growth, while forced expression of MYC partially restores tumor growth.

Conclusion

This study reveals the critical role of RBM42 in regulating MYC translation and elucidates its molecular mechanism of promoting translation initiation by remodeling the MYC 5’ UTR structure. Additionally, the research demonstrates the important role of RBM42 in PDAC tumorigenesis, providing new insights for targeting RBM42 in PDAC treatment.

Research Highlights

1. Novel screening method: The researchers developed a functional genomic screening method based on CRISPRi, successfully identifying key factors regulating MYC translation.
2. Mechanism of RBM42 in translation regulation: The study is the first to reveal the molecular mechanism by which RBM42 promotes translation initiation by remodeling the MYC 5’ UTR structure.
3. Clinical significance of RBM42: The study shows that RBM42 is highly expressed in PDAC and is associated with poor patient prognosis, providing a new therapeutic target for PDAC.

Research Value

This study not only deepens our understanding of the translational regulation mechanisms of oncogenes but also provides new targets for PDAC treatment. By revealing the critical role of RBM42 in regulating MYC translation, the researchers lay the foundation for developing RBM42-targeted PDAC treatment strategies. Furthermore, the novel screening methods and molecular mechanism studies used in this research also provide references for translational regulation studies of other oncogenes.