Control of mRNA translation during transition from one stage to another ? such as one adapted for stress conditions ? is vital to understanding of regulation of gene regulation in human cells including cancer cells, yet is not fully understood. Cellular signaling controls translation by modulating mRNA recruitment though cis regulatory elements or utilizing delayed re-initiation mechanisms involving upstream ORFs (uORF). Typically, the regulated mRNAs encode transcription factors, thereby allowing genome-wide transcriptional responses. Amino acid starvation activates Gcn2 eIF2? kinases. eIF2? phosphorylation causes slow growth partly through inhibition of protein synthesis, and yet facilitates translation of hundreds of specific mRNA species. Expression of resistance to a metabolic stress like this one is crucial for cancer cells to establish themselves during their migration and metastasis. Using fission yeast Schizosaccharomyces pombe as a model organism, the polysomal microarray hybridization experiments revealed hundreds of candidate genes whose translation is stimulated by amino acid starvation in Gcn2-dependent manner. Their functions include mitochondrial translation, mRNA splicing, tRNA production, and mRNA transcription including histone acetyltransferases and methyltransferases. Of particular interest is that the gene list contains many histone acetyltransferase genes including Gcn5, which is known to promote starvation response in this yeast. These and other listed genes possess multiple uORFs reminiscent of regulation by delayed re-initiation. Moreover, certain RNA motifs are enriched in translationally controlled genes. They include overlapping motifs that commonly contain a UGA(C/A)G sequence, reminiscent of the GAC motif characterized as N_6 adenosine methylation (m6A) site for the adenine residue in the middle. Thus, one aim of this proposal is to reveal distinct mechanisms of translational regulation, i. e. through cis regulatory elements, paired uORFs and potentially yet new mechanisms involving uORFs. If the UGA(C/A)G motif is proven important, involvement of mRNA m6A methylation will be tested.
A second aim i s to investigate the functional role of regulated genes, specifically in transcription of tRNA and mRNA, and those coding for histone acetyl- and methyl-transferases. Overall, the grant aims to test the hypothesis that the starvation-induced translational program utilizes a set of mRNA-specific mechanisms to re-configure metabolites specific to each stage and chemical modification of chromosomes in favor of gene expression specific for each stage of cell growth.
/ Medical Relevance: The results of this study will contribute to fundamental understanding of control of mRNA translation during metabolic stress response, which is vital to understanding of normal and cancer cell regulation.
| Murakami, Ryo; Singh, Chingakham Ranjit; Morris, Jacob et al. (2018) The Interaction between the Ribosomal Stalk Proteins and Translation Initiation Factor 5B Promotes Translation Initiation. Mol Cell Biol 38: |
