MSc by Research: Why are inhibitors of the protein kinase IRAK4 failing in Clinical Trials?

About the Project

Hyperactivation of the Toll-Like Receptor (TLR) signalling pathway is a major cause of inflammatory and autoimmune diseases, suggesting that specific inhibitors of this pathway may have therapeutic potential for the treatment of diseases such as asthma, arthritis, colitis, lupus, psoriasis, and sepsis.

The activation of TLRs is followed by the recruitment of the adaptor protein MyD88 to the receptor followed by the recruitment of the protein kinase IRAK4 to MyD88 and then the recruitment of IRAK1 and IRAK2 to IRAK4 generating a multi-protein complex known as the “Myddosome”, which drives the production of inflammatory cytokines. We have shown that in a lupus prone strain of mice, the onset of lupus can be prevented by crossing the mice to mice in which IRAK4 or IRAK1 are replaced by kinase-inactive mutants.¹ Moreover, not only can an IRAK4 inhibiting drug given to the mice in their food prevent lupus, but can also reverse the lupus phenotype after it has already developed.^2,3

Despite these and other promising results in mouse models of lupus and other inflammatory diseases, IRAK4 inhibitors have shown little or no efficacy in treating several inflammatory and autoimmune diseases in human patients. Recent studies in my research team have revealed that although the expression of the IRAK4 protein is essential for the TLR signalling pathway to operate in all cells of mouse and human origin that have been investigated, whether the protein kinase activity of IRAK4 is required varies from cell to cell. For example, in mouse bone marrow derived macrophages (BMDM) TLR signalling is blocked completely by IRAK4 inhibitors, but in human epithelial or keratinocyte cell lines, IRAK4’s catalytic activity is not required for the pathway to operate. Moreover, the expression of the IRAK2 protein is essential for the TLR signalling pathway to induce the secretion of inflammatory cytokines in mouse BMDM but the expression of IRAK1 is not.^4,5 In contrast, it is the expression of IRAK1 that is essential for inflammatory cytokine secretion in human epithelial or keratinocyte cell lines. Another major difference is that IRAK3 is only expressed in innate immune cells, but not in other cells of human or mouse origin. The observations raise the question of whether the requirement for IRAK4 catalytic activity depends on which other IRAKs are expressed in a cell and whether they are incorporated into the Myddosome

The aim of the project is to build on this information and to work out whether the protein kinase of IRAK4 is required for TLR signalling in cells in which the Myddosome is composed of a particular combination of IRAK1, IRAK2 and IRAK3.

The project will employ a variety of state-of-the-art techniques used in the study of cell signalling and immunology. They include cell culture, cell stimulation with TLR-activating ligands and IRAK4 inhibiting drugs, cell transfection, generation of CRISPR-Cas9 knockout and stable cell lines, measurement of cytokine levels, immunoblotting with phospho-specific antibodies and mass spectrometry.

The project would be suitable for M.Sc students wishing to gain a strong grounding in the fields of cell signalling and innate immunity.

Our research community thrives on the diversity of students and staff which helps to make the University of Dundee a UK university of choice for postgraduate research. We welcome applications from all talented individuals and are committed to widening access to those who have the ability and potential to benefit from higher education.