Figure 7. Location of different phosphoinositide species in cells.

(A) Different phosphorylated species of PI are enriched in different membrane compartments. PI(3,4,5)P₃ (coloured purple) is only made at the plasma membrane when cells are stimulated by either GPCRs or receptor tyrosine kinases (RTKs). PI(4,5)P₂ (coloured red) and PI4P (coloured blue) are found at the plasma membranes. PI4P is additionally present at the Golgi. PI3P is present in the endosomal compartment and PI(3,5)P₂ is present in multivesicular bodies (MVBs) and lysosomes. (B) Recruitment of proteins by phosphoinositide-binding domains or by patches of positive charge present in proteins by different phosphorylated forms of PI. (C) Activation of AKT by phosphorylation by PDK1 and mTORC2. PIP₃ recruits the PH domains of AKT and PDK1 to the plasma membrane bringing the two proteins together. PDK1 phosphorylates AKT. After a second phosphorylation by membrane target of rapamycin complex 2 (mTORC2), AKT is activated and can move away from the membrane to phosphorylate its target proteins (adapted from Figures 1 and 2 from Hammond G.R.V. and Burke J.E. (2020) Current Opinion in Cell Biology, 63:57–67).