The background in our current research direction derives from an interest in the regulation of the cell cycle, particularly the G1/S transition, in response to cellular stress. Cell-cycle progression through G1 phase is of particular importance because this is the stage where the decision is made to embark on another cell cycle and the preparation for DNA replication begins. A majority of cancer cells are defective in the regulation of the G1/S transition 1, 2, arguing that this transition is of particular relevance to cancer development. We discovered a novel G1/S checkpoint in fission yeast 3-5. The checkpoint delays entry into S phase by delaying formation of the pre-replicative complex (pre-RC), an obligatory step for initiation of DNA replication. Surprisingly, we found that this delay is absolutely dependent on the Gcn2 kinase.
GCN2 was first described in budding yeast as a regulator of translation in response to nutrient starvation, when it phosphorylates the translation initiation factor eIF2α. Later work showed that this function has been conserved through evolution all the way to human cells. Human GCN2 is important in the response to nutritional changes such as shortage of amino acids and glucose starvation 6, 7. GCN2 is also known to be activated in human cells in response to UV irradiation 8.
The finding that GCN2 can regulate the cell cycle is novel 9. Furthermore, the feature that GCN2 links growth control and cell-cycle progression alone is likely to make GCN2 important for tumor development. Cancer cells often suffer under poor growth conditions, the very situation where the function of GCN2 is extremely important. Indeed, a number or recent studies support the general view in the field that GCN2 is a potential target in cancer therapy, because a strategy based on GCN2 inhibition would target tumour cells, particularly aggressively growing and/or metastasizing cells, with high specificity.
In addition to its relevance to cancer, an increasing amount of data point to the importance of GCN2 and eIF2α phosphorylation in neurodegenerative diseases. In this context, GCN2 is important for long-term memory, and, most interestingly, suppressing GCN2 could alleviate synaptic plasticity and memory deficits in Alzheimer's disease model mice 10.
Our findings suggest that GCN2 has important, novel functions related to cell-cycle and checkpoint regulation. Detailed knowledge of the molecular mechanisms involved in these processes is crucial for knowledge-based therapy. We are studying the roles of GCN2 in cell-cycle control and translation regulation in fission yeast and mammalian cells. During this work we have established methods to study translation in vivo and found a novel mechanism that regulates translation in response to UV irradiation and oxidative stress 11. We are investigating the molecular mechanism of this novel pathway.
Translational regulation can, in many instances, have a much stronger impact on gene expression than transcriptional regulation. However, translation has been given less attention than, for example, transcription or epigenetic regulation, mainly for technical reasons. It is intuitive that fast-growing cells have to translate more than non-dividing cells, and consistently, cancer cells often overexpress translation factors. Furthermore, deregulation of selective translation can drive cancer development. Regulation of translation leads to rapid changes in the protein repertoire and the preferential synthesis of proteins required in a given setting will make the cells more able to cope with and to adapt to stressful situations. Thus, aberrant regulation of translation of selected mRNAs can lead to carcinogenesis. Such alterations in translational regulation in human cancers may present opportunities for therapeutic interventions. A deeper understanding of the regulation of translation will allow the development of targeted approaches for therapy. With this in mind, we wish to study the regulation of translation under stress in the long term.
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10. Ma T, Trinh MA, Wexler AJ, Bourbon C, Gatti E, Pierre P, Cavener DR, Klann E. Suppression of eIF2alpha kinases alleviates Alzheimer's disease-related plasticity and memory deficits. Nature neuroscience 2013; 16:1299-305.
11. Knutsen JHJ, Rødland GE, Bøe CA, Håland TW, Sunnerhagen P, Grallert B, Boye E. Stress-induced inhibition of translation independently of eIF2α phosphorylation. Journal of Cell Science 2015; 128:4420-7.