Phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate: Lipids in search of a function

Recent years have seen a rapid accumulation of information which relates to the idea that receptor-controlled effects on inositol lipid metabolism might somehow be involved in the control of stimulated cells (see refs 1-14 for reviews). Most of these studies have been concerned only with phosphatidylinositol (PtdIns) and have tended to ignore the polyphosphoinositides, phosphatidyl-inositol 4-phosphate (PtdIns4P), and phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P₂) (see Fig. 1 for structures). Although relatively few people work on these minor, but very active, lipids at present, recent observations should soon attract others into this field. It was with this in mind that we decided to collect together some thoughts on the published work on polyphosphoinositides, together with ideas and strictures that might inform future work. Detailed background information and discussion of early work can be found in reviews (1,9,15-18), and references to this work will usually be made via these reviews.