Ribosomes are a complex ensemble of rRNA and ribosomal proteins that function as mRNA translation machines. Ribosome biogenesis is a multistep process that begins in the nucleolus and concludes in the cytoplasm. The process is tightly controlled by multiple checkpoint and surveillance pathways. Perturbations in these checkpoints and pathways can lead to hyperactivation of ribosome biogenesis. Emerging evidence suggests that cancer cells harbor a specialized class of ribosomes (onco-ribosomes) that facilitates the oncogenic translation program, modulates cellular functions, and promotes metabolic rewiring. Mutations in ribosomal proteins, rRNA processing, and ribosome assembly factors result in ribosomopathies that are associated with an increased risk of developing malignancies. Recent studies have linked mutations in ribosomal proteins and aberrant ribosomes with poor prognosis, highlighting ribosome-targeted therapy as a promising approach for treating patients with cancer. Here, we summarize various aspects of dysregulation of ribosome biogenesis and the impact of resultant onco-ribosomes on malignant tumor behavior, therapeutic resistance, and clinical outcome. Ribosome biogenesis is a promising therapeutic target, and understanding the important determinants of this process will allow for improved and perhaps selective therapeutic strategies to target ribosome biosynthesis.

The tumor immune microenvironment dynamically evolves to support tumor growth and progression. Immunosuppressive regulatory T cells (Treg) promote tumor growth and metastatic seeding in patients with breast cancer. Deregulation of plasticity between Treg and Th17 cells creates an immune regulatory framework that enables tumor progression. Here, we discovered a functional role for Hedgehog (Hh) signaling in promoting Treg differentiation and immunosuppressive activity, and when Hh activity was inhibited, Tregs adopted a Th17-like phenotype complemented by an enhanced inflammatory profile. Mechanistically, Hh signaling promoted O-GlcNAc modifications of critical Treg and Th17 transcription factors, Foxp3 and STAT3, respectively, that orchestrated this transition. Blocking Hh reprogramed Tregs metabolically, dampened their immunosuppressive activity, and supported their transdifferentiation into inflammatory Th17 cells that enhanced the recruitment of cytotoxic CD8+ T cells into tumors. Our results demonstrate a previously unknown role for Hh signaling in the regulation of Treg differentiation and activity and the switch between Tregs and Th17 cells in the tumor microenvironment.

Macrophages are important cellular components of the innate immune system, serving as the first line of immune defense. They are also among the first immune cells to be reprogrammed by the evolving tumor milieu into tumor-supportive macrophages that facilitate tumor progression and promote therapeutic evasion. In this study, we uncovered that macrophages from preneoplastic breast lesions were enriched for ribosome biosynthesis genes, indicating that this is an early event that is maintained in the tumor tissue. Furthermore, following treatment with irradiation or chemotherapy, breast tumors featured an abundance of tumor-supporting macrophages that displayed an enrichment of signatures of rRNA expression and ribosome biosynthesis. Consistently, rRNA synthesis was increased in tumor-supportive macrophages. In preclinical models of mammary cancer, a low dose of the RNA biogenesis inhibitor BMH-21 converted protumor macrophages to tumor-suppressive macrophages and supported an inflammatory tumor microenvironment. Inhibition of rRNA transcription stimulated a nucleolar stress response that activated the p53 and NF-κB pathways, which orchestrated impaired ribosome biogenesis checkpoint signaling that induced an inflammatory program in macrophages. Finally, inhibiting ribosome biogenesis augmented the effectiveness of neoadjuvant therapy. Together, these findings provide evidence that ribosome biogenesis is a targetable dependency to reprogram the tumor immune microenvironment. Significance: Increased ribosome biogenesis is an integral attribute of protumor macrophages that occurs early during breast tumorigenesis and represents a therapeutically actionable process to reactivate the tumor-suppressive functions of macrophages.

Intratumoral low oxygen tension promotes cancer cell invasion and metastasis. Hypoxia-Inducible Factor 1-alpha (HIF1α) is the principal transcription factor orchestrating cellular responses to hypoxic stress, mediating the regulation of genes implicated in adapting to perturbations in oxygen homeostasis. Here, we describe our findings that functionally demonstrate a nucleolar localization domain in HIF1ɑ that enables HIF1ɑ to translocate to the nucleolus. Nucleolar HIF1ɑ binds the ribosomal DNA promoter and upregulates RNA Polymerase I activity leading to dysregulated ribosomal RNA transcription and consequently enhanced ribosome biogenesis. Ribosome biogenesis is important in supporting cellular metabolic processes and invasion and metastasis. Our findings are recapitulated in breast tumors wherein upregulated HIF1ɑ and rRNA biogenesis are associated with poor prognosis. Finally, our studies demonstrate that inhibition of RNA Polymerase I impedes aggressive traits of hypoxia-driven cancer progression, highlighting the potential of this approach as a therapeutic strategy in breast cancer. Cumulatively our work unravels an unprecedented role of HIF1ɑ in regulating rRNA biogenesis in breast cancer.

Ribosomal RNA Modifying Proteins (RRMPs) are integral to ribosome biogenesis, executing post-transcriptional modifications that influence translation fidelity and efficiency. Dysregulation of RRMPs has been increasingly implicated in cancer progression, yet their collective role across malignancies remains largely unexplored. Here, we performed a multi-omics analysis of 22 RRMPs across diverse cancer types using The Cancer Genome Atlas, the Molecular Taxonomy of Breast Cancer International Consortium, and additional high-throughput datasets. Our analysis revealed widespread genomic alterations and transcriptional dysregulation of RRMPs across malignancies, with distinct expression patterns in breast cancer subtypes. Notably, Triple-Negative Breast Cancer (TNBC) exhibited the highest RRMPs enrichment, which correlated with increased genomic instability including elevated tumor mutational burden and aneuploidy scores, and poor survival outcomes. Among the RRMPs, tRNA methyltransferase activator subunit 11-2 (TRMT112) emerged as a key regulator of tumor progression. Functional assays demonstrated that TRMT112 knockdown in TNBC cells significantly reduced proliferation, migration, invasion, and metastatic potential, whereas its overexpression enhanced these tumorigenic properties. Polysome profiling and RNA sequencing of actively translated transcripts revealed that TRMT112 reprograms the translational landscape by promoting pro-metastatic and stromal remodeling pathways while suppressing immune-related processes. In vivo studies using an orthotopic breast cancer model further confirmed that TRMT112 depletion impairs tumor growth and reduces metastatic burden. Collectively, our findings establish RRMPs as critical modulators of cancer progression and identify TRMT112 as a key driver of aggressive phenotypes in TNBC. The dysregulation of TRMT112 across breast cancer subtypes highlights its potential as both a prognostic biomarker and a therapeutic target. These insights provide a mechanistic foundation for future interventions aimed at targeting TRMT112-driven translational programs in aggressive breast cancer.

Metastasis is the leading cause of poor clinical outcomes in solid tumors; yet despite recent advances many of the driving factors of metastasis remain poorly understood. Tumor cells that successfully metastasize are subject to numerous stress points from intrinsic and extrinsic factors that the cell must overcome to survive and colonize a secondary site. The nucleolus, the site of ribosome biogenesis, serves as a central hub for sensing and responding to cellular stress and plays a crucial role in this process; furthermore, emerging evidence highlights the potential role of ribosome biogenesis in driving metastasis. To further elucidate the interplay between nucleolar function and metastasis, we performed a comprehensive analysis of nucleolar proteomes from primary and metastatic breast cancer cell lines and identified proteins differentially enriched in the nucleoli of metastatic cells, of which 48 showed statistically significant enrichment. Among these, S100A16 was the most significantly enriched nucleolar protein. Notably, chromatin immunoprecipitation mass spectrometry (ChIP-MS) revealed that S100A16 was associated at rDNA loci with RPA194, the catalytic subunit of RNA Polymerase I, indicating a role in rRNA biosynthesis. Functionally, loss of S100A16 disrupted RNA Polymerase I activation and subsequent rRNA synthesis, reversed epithelial-to-mesenchymal transition, inhibited invasion, and reduced metastatic incidence in animal models of breast cancer. Clinically, elevated S100A16 expression correlated with enrichment of ribosome biogenesis pathways and reduced relapse-free survival in metastatic breast cancer patients. In summary, we identified a critical role for S100A16 as a molecular modulator in the nucleolus that impinges upon breast cancer metastasis.