Regulation of translation after exposure to stress

Proteins are the "workhorses" of the cell, carrying out all the functions necessary for life. The instructions for how to make a certain protein are contained in the genes, and the proteins are made after this recipe in a series of complex processes. It is estimated that the human body can generate hundreds of thousands of different types of proteins, but not all are produced in all cells at all times. The functionality and viability of cells are absolutely dependent upon producing the right proteins at the right time. When encountering environmental stress such as UV-radiation or damaging chemicals, all types of cells change their protein repertoire so that they produce proteins that help them to better respond to the stress. All the processes leading from gene to protein are carefully regulated to achieve this. We are interested in the regulation of translation, the process when the proteins are manufactured in the cells. The importance of translation regulation is underlined by the findings that expression or activity of proteins regulating translation is altered in a number of cancers. In addition, there are numerous reports that defective regulation of translation results in neurological problems in humans. Therefore understanding the molecular details of how and when proteins are made is highly relevant for knowledge-based therapy of these diseases. In this project we wish to investigate fundamental aspects of the regulation of translation. We have demonstrated the existence of a novel mechanism regulating translation after stress in three organisms including human cells. The aim of the current project was to understand the molecular details of the novel mechanism. We know that the unknown mechanism impinges on translation very quickly after stress and this suggests that the mechanism involves a change in protein levels or modifications. We have performed mass spectrometry analysis of the proteome to identify changes upon stress. We have identified dramatic and quick changes in proteins regulating the cytoskeleton. Furthermore, the downregulation of translation could be prevented by interfering with the reorganization of the cytoskeleton, suggesting a close regulatory link between translation regulation and cytoskeleton after stress.

Our findings will have a deep impact both on the translation field and on the cytoskeleton field in the academic community. An intact cytoskeleton has been known to be important for translation, supported by a number of studies showing that depolymerizing the actin cytoskeleton diminishes translation in several model systems. However, it was thought that the cytoskeleton simply serves as a scaffold. Our results strongly suggest that reorganization of the actin cytoskeleton is at least part of the mechanism that downregulates translation in response to stress. Several drugs that are affecting the cytoskeleton are in clinical use today without any knowledge and consideration of how they may affect translation. Our findings highlight the importance of the link between translation and cytoskeleton, and might lead to better treatment strategies in the long run.

The functionality and viability of cells are absolutely dependent upon their gene expression pattern. Gene expression involves a series of complex processes, culminating in translation. When encountering environmental stress all types of cells respond by alterations in the gene expression pattern, partly at the levels of transcription, but mostly at the translational level, which leads to rapid changes in the repertoire of proteins produced. Expression or activity of translation factors is altered in a number of cancers. In addition, there are numerous reports that defective regulation of translation results in neurological problems in humans. Therefore understanding the molecular details of the novel mechanism is highly relevant for knowledge-based therapy of these diseases. In this project we wish to investigate fundamental aspects of the regulation of translation. We have shown that after exposure to ultraviolet light or oxidative stress a novel mechanism dramatically reduces general translation levels. We have demonstrated the existence of this mechanism in fission and budding yeasts as well as in human cells, suggesting that it is was conserved during evolution. The aim of the current project is to understand the molecular details of the novel mechanism. We shall first investigate which stage of translation is regulated by the novel mechanism. This will give us clues as to the mechanism. The translational response to stress is very rapid, leading us to speculate that it involves protein modifications. We shall employ a broad approach to identify all molecular changes that occur in the cell shortly after UV-irradiation. This will most likely reveal the signature molecular changes and modifications involved in the novel mechanism, in addition to a number of other changes. Finally, we shall investigate the consequences of the novel mechanism on cell-cycle progression and survival employing appropriate fission yeast mutants.