Type III phosphatidylinositol 4 kinases: structure, function, regulation, signalling and involvement in disease

Many important cellular functions are regulated by the selective recruitment of proteins to intracellular membranes mediated by specific interactions with lipid phosphoinositides. The enzymes that generate lipid phosphoinositides therefore must be properly positioned and regulated at their correct cellular locations. Phosphatidylinositol 4 kinases (PI4Ks) are key lipid signalling enzymes, and they generate the lipid species phosphatidylinositol 4-phosphate (PI4P), which plays important roles in regulating physiological processes including membrane trafficking, cytokinesis and organelle identity. PI4P also acts as the substrate for the generation of the signalling phosphoinositides phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 3,4,5-trisphosphate (PIP3). PI4Ks also play critical roles in a number of pathological processes including mediating replication of a number of pathogenic RNA viruses, and in the development of the parasite responsible for malaria. Key to the regulation of PI4Ks is their regulation by a variety of both host and viral protein-binding partners. We review herein our current understanding of the structure, regulatory interactions and role in disease of the type III PI4Ks.