The fundamental role of chemokine receptors is to transmit information about the extracellular environment to the interior of the cell. Chemokine binding and activation of their cognate receptors on the surface of target cells initiates a cascade of intracellular events that culminate in the expression of biological effects. The responsiveness of cells to chemokines is dependent on the environment to which they are exposed, and is controlled in part through desensitisation of their receptors. Recent advances in the field of G-protein coupled receptors, as well as in our appreciation of intracellular transport and signalling networks have led to the hypothesis that cross-talk between different receptor pathways is essential for this control and affects cell behaviour. However, it looks as if pathogens can highjack this cellular control to subvert host defences. With this in mind, I propose to investigate the desensitisation of chemokine receptors by microbial components. The project will focus on CCR1, CCR2 and CCR5, three closely related receptors and their regulation upon cell stimulation with bacterial chemoattractant and toxins. Using monocyte-derived mononuclear phagocytes that endogenously express these receptors as model cells, we plan to 1) characterise pathways of heterologous desensitisation; 2) establish how they affect cell functions; 3) uncover key molecular mechanisms. We will apply morphological and biochemical approaches to establish patterns of desensitisation, determine their specificity by comparing the effects of the different bacterial components, and to define cell biological events involved. We will also make use of inhibitory drugs, small interfering RNAs and mutant proteins to interfere with these events, dissect the molecular basis of cross-desensitisation and together with standard functional assays, assess the impact on cell activities.
Chemokine receptors are surface membrane molecules that act as biological sensors by detecting small soluble attractant proteins, called chemokines. Chemokine receptors are involved in numerous biological functions including host defence, and deregulation of their activity often contributes to pathologies associated with these functions. At the cellular level, binding of chemokines to their cognate receptors switch on signals in the cytosol, which instruct cells to react by changing their behaviour. I have previously shown that regulation of cell surface chemokine receptor expression is a significant mechanism to modulate the cellular activity of these receptors and identified some of the molecular and cell biological events associated with this regulation. It is part of a complex cell biological process named desensitisation that can occur subsequently (homologous) or independently (heterologous) of chemokine stimulation. Indeed, desensitisation can occur following activation of other cell surface molecules by microbial components, including bacterial toxins known to cause septic shock. These toxins alter white blood cell functions by eliciting cytosolic signals that result in abnormal cell activation, and concomitantly induce atypical desensitisation of key chemokine receptors. The present research proposal seeks to establish how heterologous desensitisation may be linked to changes in cellular functions caused by bacterial components. We will focus on three related chemokine receptors, CCR1, CCR2 and CCR5 and will use in vitro differentiation of mononuclear phagocytes as a model system for primary white blood cells. We will apply a combination of morphological, biochemical and cell biological approaches to 1) elucidate the intracellular pathways leading to bacterial-induced desensitisation; 2) evaluate the impact of this desensitisation on basic cell functions; 3) identify molecular mechanisms implicated. I anticipate that this research will add to our understanding of chemokine receptor biology, give insights into the basic cell biological mechanisms of protein trafficking and signalling, the cellular processes that bacterial pathogens exploit, and also provide useful information concerning the regulation of essential immune cells, which may suggest novel anti-inflammatory strategies.
We discovered a pathway of cross-desensitisation of CCR1, 2 and 5 on human monocytes via specific activation of the Toll like receptor 2 (TLR2) that is critical for monocytes function as it blocks their migratory response to chemokines.
|Effective start/end date||1/07/07 → 30/06/10|