Molecular Mechanisms and Therapeutic Targeting of Ribosome Assembly

Abstract

Protein synthesis is a tightly regulated cellular process regulated by major intracellular signaling pathways. In cancer, including acute myeloid leukemia (AML), these pathways are frequently dysregulated. Despite this, the role of protein synthesis control in AML remains incompletely understood. Ribosome assembly, where ribosomal subunits form a functional ribosome, is essential for protein synthesis. Disruption of this process causes Shwachman-Diamond Syndrome (SDS), a developmental disorder affecting multiple organs, underscoring the critical need for precise protein synthesis regulation. Here we show that immature fractions of leukemia cells have increased protein synthesis and ribosome biogenesis. Disrupting ribosome assembly in AML cells using a transgenic mouse model sharply reduced leukemia burden and prolonged survival. Single-cell RNA sequencing (scRNA-seq) revealed that leukemia cells adapt by upregulating ribosome biogenesis and downregulating myeloid transcription factors. Building on this, we set out to assess the effect of the clinically relevant protein synthesis inhibitor homoharringtonine. Transplantation assays showed improved survival without affecting normal hematopoietic stem cells counts. scRNA-seq revealed increased ribosome biogenesis, cell cycle activity, and upregulation of Myc and its targets in treatment-resistant leukemia cells. We examined ribosome assembly in the context of SDS using RNA and polysome-sequencing as well as subcellular fractionation, revealing a novel layer of spatial regulation. Dysregulation of key ribosome assembly players SBDS and eIF6 leads to a relative increase in translation of endoplasmic reticulum-targeted mRNAs. This shift is accompanied by a transcriptional adaptation characterized by increased ribosome biogenesis and downregulation of NMNAT2. This work validates protein synthesis and ribosome assembly as relevant therapeutic targets in AML. Additionally, by exploring the role of ribosome assembly in an SDS-like context, we add to the understanding of the cell’s response to insults to the translational machinery. Together, these findings highlight strategies to manipulate ribosomal machinery, either by correcting defects or exploiting them.