DYRK protein kinases regulate p62/SQSTM1 to orchestrate cellular responses to oxidative stress, protein misfolding and nutrient starvation

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The cells in our body are constantly exposed to chemical and physical 'stress' and accumulate a lifetime of damage to proteins, DNA and various key sub-cellular structures (organelles). It is vital that cells are able to respond appropriately to this damage; failure to do so progressively undermines cellular 'fitness' contributing to age-related declines in cell and tissue function that underpin the normal ageing process and can contribute to age-related diseases such as cancer and dementia.One way that cells respond to stress is to increase the abundance of enzymes that detoxify the cell by removing potentially harmful chemicals. When a cell receives a stress signal the genes that code for detoxifying enzymes are 'read' by 'transcription factors', discrete proteins that bind to DNA and transcribe the DNA information into RNA molecules, which are in turn 'translated' into the relevant proteins. One such transcription factor, called NRF2, coordinates cellular responses to oxidative stress.Another way in which cells deal with cellular damage is through a process called 'autophagy' (self eating) in which damaged proteins are targeted to cellular recycling centres (called autophagosomes), where they are broken down to their raw materials, which can then be re-used. This process of autophagy requires 'cargo receptors', which bind to damaged proteins and transport them to the recycling centre for autophagy.These complex processes are orchestrated by signalling pathways within cells that involve cascades of enzymes called protein kinases. These enzymes 'tag' other proteins with a phosphate group (a process called phosphorylation) and this changes the activity, abundance or localisation of the protein. The tagged protein is referred to as the 'substrate' of the protein kinase enzyme.This project concerns two protein kinases, called DYRK1B and DYRK2, and a specific 'cargo receptor' called p62 or sequestosome-1; here we'll call it p62. Our new results point to a link between the DYRKs and p62 in coordinating how cells respond to stress and damage:- 1. p62 acts as a scaffold to coordinate the activation of the NRF2 transcription factor. We have now discovered that DYRK1B controls the expression of detoxifying enzymes that are known to be targets of NRF2 suggesting that DYRK1B may control activation of NRF2.2. p62 acts as a cargo receptor for damaged proteins, transporting them to recycling centres for autophagy. It has also been shown that p62 can shuttle in and out of the cell nucleus to collect damaged nuclear proteins for autophagy. This nuclear shuttling requires phosphorylation of p62 but the kinase responsible for this has remained a mystery. We have now discovered for the first time that p62 is phosphorylated by DYRK1B and DYRK2; we propose that this sends p62 into the nucleus to help collect damaged nuclear proteins.3. p62 coordinates activation of a protein kinase enzyme called mTOR when cells are starved of nutrients. Indeed, mTOR is a critical regulator of lifelong health and controls the lifespan of organisms such as worms, flies, mice and possibly man. Regulation of mTOR by nutrients takes place at specific organelles called lysosomes. However, the phosphorylation of p62 may take it away from lysosomes to the nucleus. Indeed, we find that DYRK2 and p62 co-locate in cells at aggresomes - sites of damaged proteins, consistent with the cargo function of p62. It is not known what effect this re-location of p62 has on nutrient signalling via mTOR at lysosomes.In this study we will define how the DYRKs regulate p62 to coordinate cellular responses to stress and damage. This work is critical to understanding how stress contributes to normal ageing but may also have implications for diseases of old age (dementia, cancer); thus, our results may have wider impacts and we will work with scientists in these areas to progress this.