Project description:Somatic ribosomal protein defects have recently been described in cancer, yet their impact on cellular transcription and translation remain poorly understood. Here we integrated mRNA sequencing, ribosome footprinting, polysomal RNA seq and quantitative mass spectrometry datasets obtained from an isogenic mouse lymphoid cell model in order to study the T-cell acute lymphoblastic leukemia (T-ALL) associated R98S mutation in ribosomal protein L10 (RPL10 R98S). RPL10 R98S induced changes in protein levels were to a much larger extent caused by transcriptional then translational changes and RPL10 R98S cells showed a gene signature corresponding to deregulation of hematopoietic transcription factors. Phosphoserine phosphatase (PSPH), a key enzyme in serine biosynthesis, displayed elevated transcription and translation and was one of the proteins showing the strongest upregulation in RPL10 R98S cells. Increased Psph protein levels were confirmed in RPL10 R98S engineered JURKAT cells and in hematopoietic cell cultures derived from Rpl10 R98S knock-in mice. Moreover, elevated serine and glycine biosynthesis in RPL10 R98S cells was supported by metabolic flux analyses. Analysis of PSPH expression levels in T-ALL patient samples revealed that PSPH upregulation is a generalized phenomenon in this disease, associated with elevated circulating serine and glycine levels. Addition of serine and glycine enhanced survival of stromal and myeloid cells, suggesting supportive effects on the hematopoietic niche. Finally, reduction of PSPH expression levels in T-ALL cell lines suppressed their in vitro proliferation and their capacity to expand in T-ALL xenograft models. In conclusion, transcriptome, translatome and proteome analysis of the RPL10 R98S mutation identified RPL10 R98S driven induction of cellular serine biosynthesis. Whereas serine metabolism has been implicated in cancer via PHGDH amplification, this is the first report supporting dependence of ALL cells on the serine biosynthesis enzyme PSPH.

Project description:Disruption of protein folding in the endoplasmic reticulum triggers the Unfolded Protein Response (UPR), a transcriptional and translational control network designed to restore protein homeostasis. Central to the UPR is PERK phosphorylation of the alpha subunit of eIF2 (eIF2~P), which represses global translation coincident with preferential translation of mRNAs, such as ATF4 and CHOP, that serve to implement the UPR transcriptional regulation. In this study, we used sucrose gradient ultracentrifugation and a genome-wide microarray approach to measure changes in mRNA translation during ER stress. Our analysis suggests that translational efficiencies vary across a broad range during ER stress, with the majority of transcripts being either repressed or resistant to eIF2~P, while a notable cohort of key regulators are subject to preferential translation. From this latter group, we identify IBTKa as being subject to both translation and transcriptional induction during eIF2~P in both cell lines and a mouse model of ER stress. Translational regulation of IBTKalpha mRNA involves the stress-induced relief of two inhibitory uORFs in the 5'-leader of the transcript. Depletion of IBTKalpha by shRNA reduced viability of cultured cells coincident with increased caspase 3/7 cleavage, suggesting that IBTKalpha is a key regulator in determining cell fate during the UPR. We used a genome-wide microarray approach to determine how individual mRNAs were differentially translated during endoplasmic reticulum stress. A microarray analysis from our laboratory identified gene transcripts suggested to be under translation control in mouse embryonic fibroblast (MEF) cells following a 6 hour treatment with thapsigargin, a potent inducer of ER stress, or no stress. The mRNAs were separated by sucrose gradient analyses to yield three fractions, those transcripts associated with large polysomes (?4 ribosomes per mRNA), those associated with monosome, disomes, or trisomes, and those fractionated at the top of the gradient with free ribosomes. RNA was extracted from sucrose gradients corresponding to these fractions and hybridized on Affymetrix microarrays. In parallel, we also measured total levels for each gene transcript in the presence or absence of thapsigargin treatment to address transcription regulation coincident with translational control. Please note that the treatment plus fractionation based on association with different numbers of ribosomes did yield different populations of mRNAs, which resulted in considerable variation in normalized data across the samples.

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The immune NIK1/RPL10/LIMYB signaling module regulates photosynthesis and translation under biotic and abiotic stresses

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