Browsing by Subject "Ribosome biogenesis"

Now showing 1 - 4 of 4
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    Bmi1 promotes erythroid development through regulating ribosome biogenesis
    (Wiley, 2015-03) Gao, Rui; Chen, Sisi; Kobayashi, Michihiro; Yu, Hao; Zhang, Yingchi; Wan, Yang; Young, Sara K.; Soltis, Anthony; Yu, Ming; Vemula, Sasidhar; Fraenkel, Ernest; Cantor, Alan; Antipin, Yevgeniy; Xu, Yang; Yoder, Mervin C.; Wek, Ronald C.; Ellis, Steven R.; Kapur, Reuben; Zhu, Xiaofan; Liu, Yan; Department of Pediatrics, Indiana University School of Medicine
    While Polycomb group protein Bmi1 is important for stem cell maintenance, its role in lineage commitment is largely unknown. We have identified Bmi1 as a novel regulator of erythroid development. Bmi1 is highly expressed in mouse erythroid progenitor cells and its deficiency impairs erythroid differentiation. BMI1 is also important for human erythroid development. Furthermore, we discovered that loss of Bmi1 in erythroid progenitor cells results in decreased transcription of multiple ribosomal protein genes and impaired ribosome biogenesis. Bmi1 deficiency stabilizes p53 protein, leading to upregulation of p21 expression and subsequent G0/G1 cell cycle arrest. Genetic inhibition of p53 activity rescues the erythroid defects seen in the Bmi1 null mice, demonstrating that a p53-dependent mechanism underlies the pathophysiology of the anemia. Mechanistically, Bmi1 is associated with multiple ribosomal protein genes and may positively regulate their expression in erythroid progenitor cells. Thus, Bmi1 promotes erythroid development, at least in part through regulating ribosome biogenesis. Ribosomopathies are human disorders of ribosome dysfunction, including Diamond-Blackfan anemia (DBA) and 5q- syndrome, in which genetic abnormalities cause impaired ribosome biogenesis, resulting in specific clinical phenotypes. We observed that BMI1 expression in human hematopoietic stem and progenitor cells from patients with DBA is correlated with the expression of some ribosomal protein genes, suggesting that BMI1 deficiency may play a pathological role in DBA and other ribosomopathies.
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    GCN2 eIF2 Kinase Promotes Prostate Cancer by Maintaining Amino Acid Homeostasis
    (2024-04) Cordova E., Ricardo A.; Wek, Ronald C.; Staschke, Kirk A.; Pili, Roberto; Mosley, Amber L.; Elmendorf, Jeffrey S.; Zhang, Ji
    Activation of the integrated stress response (ISR) contributes to the progression of many cancers, including prostate cancer (PCa). The ISR features a family of protein kinases that phosphorylate the eukaryotic translation initiation factor 2 (eIF2) during different stress conditions, repressing global protein synthesis. In parallel, eIF2 phosphorylation also enhances the translation of select gene transcripts, such as ATF4, which directs the transcription of ISR-target genes critical for stress adaptation. We reported that the eIF2 kinase GCN2 is a critical driver of the ISR in PCa and is crucial to maintaining amino acid (AA) homeostasis. GCN2 is activated in PCa due to AA limitation, resulting in increased expression of key AA transporters which providing nutrient import to fuel protein synthesis and metabolism that drive prostate tumor cell proliferation. Inhibition of GCN2 results in lowered expression of AA transporters, leading to severe depletion of intracellular AA and reduced proliferation in PCa. We identified purine biosynthesis as a key metabolic pathway dependent on GCN2. Inhibition of GCN2 and the accompanying depletion of AAs decreases purine levels in PCa cells, ultimately resulting in reduced ribosome biogenesis leading to the activation of a p53-dependent cell cycle checkpoint, termed the Impaired Ribosome Biogenesis Checkpoint (IRBC). Interestingly, induction of p53 promotes survival of PCa following GCN2 inhibition by halting cell cycle progression and reprogramming metabolism to restore metabolic homeostasis. We found that reductions in select AAs that impact nucleotide pools activate GCN2 and p53 in parallel, and that cooperation of these stress pathways is critical for maintaining AA and purine pools. Of importance, deletion of p53 sensitizes PCa cells to GCN2 inhibition suggesting that loss of p53 creates a dependency for GCN2. Of importance, we demonstrate that a small molecule inhibitor of GCN2 showed robust in vivo efficacy in androgen-sensitive and castrationresistant mouse models of PCa, supporting its therapeutic potential for the treatment of PCa.
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    Reduced rDNA transcription diminishes skeletal muscle ribosomal capacity and protein synthesis in cancer cachexia
    (Wiley, 2021) Kim, Hyo-Gun; Huot, Joshua R.; Pin, Fabrizio; Guo, Bin; Bonetto, Andrea; Nader, Gustavo A.; Surgery, School of Medicine
    Muscle wasting in cancer is associated with deficits in protein synthesis, yet, the mechanisms underlying this anabolic impairment remain poorly understood. The capacity for protein synthesis is mainly determined by the abundance of muscle ribosomes, which is in turn regulated by transcription of the ribosomal (r)RNA genes (rDNA). In this study, we investigated whether muscle loss in a preclinical model of ovarian cancer is associated with a reduction in ribosomal capacity and was a consequence of impaired rDNA transcription. Tumor bearing resulted in a significant loss in gastrocnemius muscle weight and protein synthesis capacity, and was consistent with a significant reduction in rDNA transcription and ribosomal capacity. Despite the induction of the ribophagy receptor NUFIP1 mRNA and the loss of NUFIP1 protein, in vitro studies revealed that while inhibition of autophagy rescued NUFIP1, it did not prevent the loss of rRNA. Electrophoretic analysis of rRNA fragmentation from both in vivo and in vitro models showed no evidence of endonucleolytic cleavage, suggesting that rRNA degradation may not play a major role in modulating muscle ribosome abundance. Our results indicate that in this model of ovarian cancer-induced cachexia, the ability of skeletal muscle to synthesize protein is compromised by a reduction in rDNA transcription and consequently a lower ribosomal capacity. Thus, impaired ribosomal production appears to play a key role in the anabolic deficits associated with muscle wasting in cancer cachexia.
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    Signaling to p53: ribosomal proteins find their way
    (Elsevier B.V., 2009-11-03) Zhang, Yanping; Lu, Hua; Department of Biochemistry & Molecular Biology, IU School of Medicine
    Inherently disparate cell growth and division, which are intimately coupled through a delicate network of intracellular and extracellular signaling, require ribosomal biogenesis. A number of events imparting instability to ribosomal biogenesis can cause nucleolar stress. In response to this stress, several ribosomal proteins bind to MDM2 and block MDM2-mediated p53 ubiquitination and degradation, resulting in p53-dependent cell cycle arrest. By doing so, the ribosomal proteins play a crucial role in connecting deregulated cell growth with inhibition of cell division. The ribosomal protein-MDM2-p53 signaling pathway provides a molecular switch that may constitute a surveillance network monitoring the integrity of ribosomal biogenesis.