The role of RNA in the response to cellular stress
Programme Leader: Martin Bushell
Summary of Research Interests
DNA, RNA and proteins are the macromolecules that lie at the core of every lifeform. Cellular stress through toxic insult affects all three types of molecules. However, uniquely out of the three, RNA molecules have the capacity to function both as catalysts in enzymatic reactions and as information storage molecules. This gives them the ability to function as an adaptive molecule in a plethora of cellular contexts. Critical from the toxicological point of view is the fast acting nature of RNA molecules in their ability to respond to cellular stress to allow resolution of the toxic insult. While it is clear that RNA is central to life, its role in the response to toxic insult and cellular stress has only just started to be explored. Importantly, currently a great deal of effort is being invested into the development of RNA-based medical therapies and a better understanding of the toxicological issues related to these new therapeutic approaches is required for their safe application.
Our laboratory is currently engaged in investigating the role of different classes of RNA molecules in response to cellular insult from a range of toxic compounds, determining the fundamental mechanisms by which they function and identifying mechanisms for modulating these activities to influence cellular outcomes.
- The role of small RNA molecules in the response to DNA damage.
It is now clear that microRNAs (miRNAs; a group of small non-coding RNA molecules) play important roles in the response to DNA damage and have been identified as new components of the p53 pathway. Recently, we have shown that the master regulator of the cell cycle – c-myc – is a target of miRNAs, and demonstrated that following DNA damage and subsequent p53 activation, miRNAs mediate repression of c-myc mRNA translation. Due to the pivotal role of the miR-34 family in the p53 pathway it is now essential to evaluate the role of c-myc repression following p53 activation and its effects on tumourigenesis
We are now examining the full influence of small RNA molecules in DNA repair pathways and how these pathways can be used to change the cell fate decision following DNA damage. Importantly, recently we and others have shown that the enzymes involved in miRNA biogenesis play a surprisingly critical role in the DNA repair pathway, independent of their role in miRNA production. We are currently investigating how these enzymes function in the DNA repair pathway.
- The role of large RNA-protein complexes in the regulation of gene expression pathways and how these complexes are remodelled by cellular stress downstream of pivotal cellular signalling events.
Large mRNA-protein (ribonucleoprotein) complexes allow the regulation of gene expression at both the translation and mRNA stability levels. These complexes regulate the production of proteins and thus the cellular response to stress induced by toxic insult. We are investigating how these ribonucleoprotein complexes are regulated downstream of major signalling pathways involved in the response to stress and how this controls gene expression.
- Designing novel mRNA-based therapeutic approaches for non-toxic delivery of genetic material.
The delivery of genetic material to treat human diseases is a major challenge in the development of next generation drugs due to limitations in current technologies. In recent years DNA and viral delivery systems have attracted the most attention; however, they have come under criticism due of low efficacy, genetic transfer risk and poor control over doses delivered. More recently, with the development of modified nucleotides, in vitro transcribed mRNA molecules have been successfully used for the delivery of genetic information without risk of genomic integration. The relatively low half-life of RNA compared to DNA-based methods also allows precise control over final therapeutic protein dosage. However, currently a number of safety issues still remain and need to be addressed before further applications can be realised. We are investigating how these mRNA molecules can be designed to limit their toxicity.
- How do miRNAs regulate gene expression?
Despite much interest in miRNAs, the mechanisms by which they function are not yet fully understood. We know that miRNAs are bound tightly by the Argonaute (Ago1-4) family of proteins, which in turn recruit in the TNRC6 proteins, forming the RNA-induced silencing complex (RISC). Recent data has shown that RISC does not directly repress the expression of targeted mRNAs, but instead recruits the Ccr4-NOT complex to induce translational repression, as well as deadenylation and destabilisation of the mRNA.
Recently, we and others have shown it is via interactions with the two DEAD-box helicases, eIF4A2 and DDX6, that the Ccr4-NOT complex imposes translational repression. We are currently continuing to investigate the precise mechanisms involved and the translational repression signatures operating within cells.