Sequential breakdown of 3-phosphorylated phosphoinositides is essential for the completion of macropinocytosis

• Published in: Proceedings of the National Academy of Sciences - PNAS 2014-03, Vol.111 (11), p.3911-3911
• Main Authors: Maekawa, Masashi, Terasaka, Shimpei, Mochizuki, Yasuhiro, Kawai, Katsuhisa, Ikeda, Yuka, Araki, Nobukazu, Skolnik, Edward Y., Taguchi, Tomohiko, Arai, Hiroyuki
• Format: Article
• Language: English
• Subjects: Animals; Biological Sciences; Caenorhabditis elegans - metabolism; Caenorhabditis elegans - physiology; Cell Line; Cellular biology; DNA Primers - genetics; Endocytosis; Humans; Membranes; Microscopy, Electron, Scanning; Microscopy, Fluorescence; Nematodes; Phosphatidylinositol Phosphates - metabolism; Phosphoric Monoester Hydrolases - metabolism; Phosphorylation; Pinocytosis - physiology; PNAS Plus; PNAS Plus: Significance Statements; Protein Tyrosine Phosphatases, Non-Receptor - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; RNA, Small Interfering - genetics
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1311029111

Macropinocytosis is a highly conserved endocytic process by which extracellular fluid and solutes are internalized into cells. Macropinocytosis starts with the formation of membrane ruffles at the plasma membrane and ends with their closure. The transient and sequential emergence of phosphoinositides PI(3,4,5)P3 and PI(3,4)P2 in the membrane ruffles is essential for macropinocytosis. By making use of information in the Caenorhabditis elegans mutants defective in fluid-phase endocytosis, we found that mammalian phosphoinositide phosphatase MTMR6 that dephosphorylates PI(3)P to PI, and its binding partner MTMR9, are required for macropinocytosis. INPP4B, which dephosphorylates PI(3,4)P2 to PI(3)P, was also found to be essential for macropinocytosis. These phosphatases operate after the formation of membrane ruffles to complete macropinocytosis. Finally, we showed that KCa3.1, a Ca(2+)-activated K(+) channel that is activated by PI(3)P, is required for macropinocytosis. We propose that the sequential breakdown of PI(3,4,5)P3 → PI(3,4)P2 → PI(3)P → PI controls macropinocytosis through specific effectors of the intermediate phosphoinositides.