Ribosomal RNA transcription governs splicing through ribosomal protein RPL22

Area of Science:

• Molecular Biology
• Cancer Biology
• Genetics

Background:

• Ribosome biosynthesis is a critical process often exploited in cancer.
• Targeting RNA polymerase I (Pol I) transcription is a strategy to inhibit ribosome production and combat cancer.
• Understanding the molecular drivers of sensitivity to Pol I inhibitors is crucial for developing effective cancer therapies.

Purpose of the Study:

• To identify genetic drivers of sensitivity to Pol I inhibitors.
• To elucidate the molecular mechanisms linking ribosome synthesis to cancer cell vulnerabilities.
• To explore the interplay between RNA polymerase I activity and mRNA splicing.

Main Methods:

• Integration of multi-omics data and drug sensitivity profiles from a large cancer cell panel.
• Development and application of specific Pol I inhibitors.
• Investigation of protein-RNA interactions and splicing regulation.
• Genetic and chemical inhibition of rRNA synthesis.

Main Results:

• A frameshift mutation in ribosomal protein RPL22 was identified as a key driver of Pol I inhibitor sensitivity in microsatellite instable cancers.
• RPL22 was found to directly interact with 28S rRNA and mRNA splice junctions, acting as a splicing regulator.
• RPL22 deficiency, exacerbated by rRNA sequestration, promoted splicing of RPL22L1 and MDM4.
• Inhibition of rRNA synthesis broadly altered mRNA splicing, affecting hundreds of targets.
• RPL22-dependent alternative splicing changes were reversed by Pol I inhibition, indicating a tumor-suppressive pathway.

Conclusions:

• Ribosome biosynthesis is a cancer vulnerability linked to mRNA splicing regulation.
• RPL22 plays a critical role in coordinating rRNA synthesis and mRNA splicing.
• Pol I inhibition activates a ribotoxic stress response that impacts splicing and tumor suppression.