Phosphoinositides (PIs), a small fraction of the cellular lipids, function in almost all cellular physiological processes and especially in intracellular membrane trafficking events. PIs play a critical role in autophagy, but only PI(3)P is well studied. In this issue of The EMBO Journal, Hasegawa et al (2016) identified INPP5E, an inositol polyphosphate 5‐phosphatase, as a novel regulator of autophagy. INPP5E controls the level of PI(3,5)P2 at the lysosome and thereby locally regulates the actin cytoskeleton and autophagosome–lysosome fusion.
See also: J Hasegawa et al (September 2016)
Kinases and phosphatases alter the phosphorylation status of phosphatidylinositol in the 3‐, 4‐, and 5‐positions of the inositol ring to generate distinct phosphoinositides (PIs), widely known as the second messengers in transducing signals from cell surface receptors, like G protein‐coupled receptors (GPCRs) (Marinissen & Gutkind, 2001). PIs are also important for endomembrane identity, for shaping membranes, controlling vesicle trafficking, and organelle physiology. PI(3)P, for example, plays a significant role in endocytic trafficking and is a well‐known regulator of autophagy (Petiot et al, 2000). PI(4)P, PI(4,5)P2, and PI(3,4,5)P3 primarily localize to the plasma membrane, and PI(4)P is not only an intermediate of PI(4,5)P2 synthesis, but also has important functions in controlling plasma membrane ion channels (Hammond et al, 2012). PI(4,5)P2, a substrate of class I phosphoinositide‐3‐kinases and the precursor of PI(3,4,5)P3, is thought to be an important …
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