A Plethora of Functions Condensed into Tiny Phospholipids: The Story of PI4P and PI(4,5)P2

Phosphoinositides (PIs) are small, phosphorylated lipids that serve many functions in the cell. They regulate endo- and exocytosis, vesicular trafficking, actin reorganization, and cell mobility, and they act as signaling molecules. The most abundant PIs in the cell are phosphatidylinositol4-monophosphate (PI4P) and phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2]. PI4P is mostly localized at the Golgi apparatus where it regulates the anterograde trafficking from the Golgi apparatus to the plasma membrane (PM), but it also localizes at the PM. On the other hand, the main localization site of PI(4,5)P2 is the PM where it regulates the formation of endocytic vesicles. The levels of PIs are regulated by many kinases and phosphatases. Four main kinases phosphorylate the precursor molecule phosphatidylinositol into PI4P, divided into two classes (PI4KII alpha, PI4KII beta PI4KIII alpha, and PI4KIII beta), and three main kinases phosphorylate PI4P to form PI(4,5)P-2 (PI4P5KI alpha, PI4P5KI beta, and PI4P5KI gamma). In this review, we discuss the localization and function of the kinases that produce PI4P and PI(4,5)P-2, as well as the localization and function of their product molecules with an overview of tools for the detection of these PIs.

Automated summary

Phosphoinositides (PIs) are phosphorylated lipids that have diverse cellular functions including regulation of trafficking, actin reorganization, and cell signaling. The two most abundant PIs in cells are phosphatidylinositol4-monophosphate (PI4P) and phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], which localize to different cellular compartments and regulate various processes. The levels of PIs are controlled by multiple kinases and phosphatases, and understanding their localization and function is important for studying cellular processes.