Specialised ribosomes facilitating cellular responses to oxidative stress

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We study how cells control the conversion of nutrients (or food) into the new proteins that are required for life and how cells moderate these processes in response to environmental cues. Termed 'protein synthesis' this process occurs within relatively large and complex molecular machines called ribosomes that decode instructions relayed from the genome within intermediary molecules called messenger RNAs (mRNAs). Human cells each contain over a million ribosomes. mRNA decoding by ribosomes is made possible by the concerted action of 'helpers': protein synthesis factors and transfer RNAs (tRNAs). In concert they bring the necessary amino acids together with the instructions to ensure the correct proteins are made at the right time. Making the right proteins at the right time is critical when organisms have to respond to changing environments, especially those containing toxins or other harmful agents. How cells sense the changes and control their responses is critical to many areas of biology. Until relatively recently it was assumed that ribosomes simply translated all mRNAs equally and that mRNA levels were a good proxy for the expression of genes. However increasingly accurate measurements of mRNA and protein levels in cells show that there can be a wide discrepancy between mRNA and protein levels. Translational control is the term used to describe a major contributor to these differences. Translational controls also allow changes in protein levels to be generated very rapidly in response to different signals. One stress we are studying here is the cellular responses to oxidative damage inducing agents which causes widespread repression of protein synthesis, but specifically allows translation of a subset of mRNAs, including antioxidant enzymes needed to overcome the stress imposed. At present how mRNAs overcome the general stress induced repression of protein synthesis and remain actively translated is not clear, but our previous work has provided strong clues and this is the focus of our proposal.Ribosomes interact with many accessory proteins, which are present in lower amounts and can moderate ribosome activity. In this way ribosome interacting proteins may act to generate specialised ribosomes, for example ribosomes instructed to translate particular mRNAs. We have identified one family of these proteins for study in this proposal. These proteins are called La Related proteins or LARPs. As their name suggests, they are related to a protein called La, which was identified in the study of autoimmune disease. La and LARP proteins are RNA binding proteins that contain a conserved RNA binding domain called the La motif or LaM. The LARPs we are studying also bind active ribosomes. We will study two LARPs that our preliminary studies suggest function to give different translation outcomes. One is a potential activator of protein synthesis that allows targeted mRNAs to escape translational repression in response to oxidative stress. In this proposal we wish to uncover how it interacts with both ribosomes and mRNAs and how these interactions lead to enhanced protein synthesis of targets and their continued translation during oxidative stress. As such this proposal is primarily a basic science proposal. However the outcomes of the work may also be of interest to companies that produce specific proteins as drug therapeutics or commercial products. Improved understanding of protein synthesis mechanisms will assist in the design of optimized commercial protein expression or fermentation systems that are used to make advanced products and medicines.