Final Activity Report Summary - BOOSTIN (PI3K in immunity and inflammation) PI 3-kinases (PI3Ks) are evolutionarily conserved signalling molecules of which there are eight isoforms in mammals. Deregulated signalling by these enzymes is involved in various disease states and PI3Ks are currently actively pursued in industry as targets for new small molecule inhibitors for therapeutic use in, among others, cancer, auto-immunity and inflammation. Signalling through the PI3K pathway usually plays a positive role in cell signalling. We made the seminal observation that the p110 delta isoform of PI3K played both positive and negative roles in dendritic cells (DCs) in signalling by toll-like receptor-4 (TLR-4) in response to stimulation with lipopolysaccharide, also known as endotoxin, which was derived from the outer membrane of gram-negative bacteria. Among the many PI3K isoforms present in DCs, p110 delta turned out to be key mediator for the generation of the phosphatidylinositol(3,4,5)-triphosphate (PIP3) lipid in this context, suggesting a non-redundant isoform selective function of this PI3K. P110 delta achieved its negative role in DCs through a novel mechanism of signalling by depleting the phosphatidylinositol(4,5)-bisphosphate (PIP2) lipid at the cell membrane, thereby affecting PIP2-dependent signalling pathways such as that of the PIP2-binding MyD88-like adapter (Mal). Indeed, membrane binding of Mal was critical for TLR-4 signalling and p110 delta-mediated conversion of PIP2 to PIP3 caused the relocation of Mal from the plasma membrane to cytoplasmic compartments, resulting in diminished TLR4-mediated inflammation. Based on our finding that p110 delta played a negative role in signalling downstream of TLR4 in DCs, inhibition of p110 delta could potentiate the TLR4 response of these cells. LPS-derivatives were used as adjuvants to stimulate DCs in vaccination efforts, and our data suggested that inhibition of p110delta could boost the capacity of DCs to prime immune responses that led to T helper (Th)1-mediated immune responses. In other words, inhibitors of p110 delta could be employed as vaccine adjuvants and boost immune responses of DCs against tumours as well as infections.
