Cellular regulation of receptor signalling and cytokine responses (2016–2019)
Macrophages are sentinel cells at the front line of innate immunity with key roles in homeostasis and disease. Arrays of Toll-like receptors (TLRs) on the macrophage surface detect pathogens and danger signals and signalling pathways then control the synthesis and release of pro- and anti-inflammatory cytokines. Dysregulation of cytokine responses is a major and widespread factor underpinning inflammatory, autoimmune and chronic diseases and cancer. Understanding the cellular and therapeutic control of inflammation is of prime importance to medicine worldwide. Our research has uncovered a new PI3K/Akt/mTOR pathway for regulating TLR signalling to control cytokines and suppress inflammation. This mechanism hinges on an unexpected direct liaison between a GTPase, Rab8a, with phosphoinositide 3-kinase gamma as its novel effector. PI3Kgamma is an immune specific kinase, important to human disease and with inhibitors already in clinical trials for cancer and inflammation. This proposal will investigate key mechanistic aspects, identifying the Rab8a-GEF and a putative GPCR crosstalk receptor for Rab/PI3K recruitment and activation. Approaches including pull-downs, mass spectrometry and custom-made Rab8a activation assays will be employed. We will study the range of TLRs that invoke Rab/PI3K regulation, their cytokine responses and the membrane subdomains where TLR and Rab8/PI3k regulation occur using imaging approaches (live cell, super-resolution and EM). Finally, we will examine the consequence of PI3K genetic ablation or pharmacological inhibition during in vivo TLR activation. This project will define mechanisms for recruitment and regulation of this new Rab/PI3K pathway in multiple TLR pathogen-induced signalling pathways and reveal how this new paradigm contributes to the control of inflammation. This research has profound implications for the therapeutic inhibition of PI3Ks in new receptor pathways.