Class I PI3Ks in neutrophil function

In recent years, the lab has focused on the role of PI3Ks in the signalling mechanisms which allow cell surface receptors on mammalian neutrophils to control various aspects of neutrophil function. Neutrophils are key players in the front line of our immune system, responsible primarily for the recognition and destruction of bacterial and fungal pathogens. However, they are also involved in the amplification cascades that underlie various inflammatory pathologies, e.g. Acute Respiratory Distress Syndrome (ARDS) and rheumatoid arthritis.

Current projects include investigation of the molecular mechanisms which allow different receptor types to activate PI3Ks. In the past similar investigations in neutrophils led to our understanding of how PI3Kγ is regulated by Gβγ subunits and Ras, as well as how integrins and FcγRs regulate PI3Kβ and PI3Kδ within neutrophils.

​We are also trying to understand the molecular mechanisms which allow the lipid products of activated PI3Ks to regulate key neutrophil responses. The two main PI3K-dependent responses we are currently focusing on are chemotaxis in gradients of soluble stimuli (Fig 1), which is a crucial mechanism allowing recruitment of neutrophils to sites of inflammation and infection, and activation of the NADPH oxidase.

Figure 1. Video of neutrophils chemotaxing towards fMLP added in the top chamber. fMLP is a formylated peptide made by bacteria that allows neutrophils to sense their presence and migrate towards them at sites of infection.
Figure 2. RAW 264.7 cells were stably transfected with the GFP-PX domain from p40phox. This domain binds to PI(3)P with high affinity and specificity. Upon ingestion of IgG-opsonised zymosan particles, the PX domain rapidly accumulates on the phagosome, indicating an increase of levels of PI(3)P in the phagosomal membrane.

​The activation of the NADPH oxidase, or ‘respiratory burst’, is an important weapon used by neutrophils and other phagocytic cells to kill pathogens engulfed by phagocytosis. Work from our laboratory and others has recently discovered that PI(3)P generation by Class III PI3K on phagosomal membranes (Fig 2) is ​an important signal for recruitment of an active NADPH oxidase complex to this location and we are currently trying to understand how this PI(3)P signal is generated by activation of appropriate receptors and how it is used to regulate the oxidase complex.