Sequential breakdown of 3-phosphorylated phosphoinositides is essential for the completion of macropinocytosis
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Authors: Maekawa, Masashi; Terasaka, Shimpei; Mochizuki, Yasuhiro; Kawai, Katsuhisa; Ikeda, Yuka; Araki, Nobukazu; Skolnik, Edward Y.; Taguchi, Tomohiko; Arai, Hiroyuki
Abstract
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)P-3 and PI(3,4)P-2 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)P-2 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 Ca2+-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)P-3 -> PI(3,4)P-2 -> PI(3)P -> PI controls macropinocytosis through specific effectors of the intermediate phosphoinositides.
Association of variations in the FTO, SCG3 and MTMR9 genes with metabolic syndrome in a Japanese population
JOURNAL OF HUMAN GENETICS
Authors: Hotta, Kikuko; Kitamoto, Takuya; Kitamoto, Aya; Mizusawa, Seiho; Matsuo, Tomoaki; Nakata, Yoshio; Kamohara, Seika; Miyatake, Nobuyuki; Kotani, Kazuaki; Komatsu, Ryoya; Itoh, Naoto; Mineo, Ikuo; Wada, Jun; Yoneda, Masato; Nakajima, Atsushi; Funahashi, Tohru; Miyazaki, Shigeru; Tokunaga, Katsuto; Masuzaki, Hiroaki; Ueno, Takato; Hamaguchi, Kazuyuki; Tanaka, Kiyoji; Yamada, Kentaro; Hanafusa, Toshiaki; Oikawa, Shinichi; Yoshimatsu, Hironobu; Sakata, Toshiie; Matsuzawa, Yuji; Nakao, Kazuwa; Sekine, Akihiro
Abstract
Metabolic syndrome is defined as a cluster of multiple risk factors, including central obesity, dyslipidemia, hypertension and impaired glucose tolerance, that increase cardiovascular disease morbidity and mortality. Genetic factors are important in the development of metabolic syndrome, as are environmental factors. However, the genetic background of metabolic syndrome is not yet fully clarified. There is evidence that obesity and obesity-related phenotypes are associated with variations in several genes, including NEGR1, SEC16B, TMEM18, ETV5, GNPDA2, BDNF, MTCH2, SH2B1, FTO, MAF, MC4R, KCTD15, SCG3, MTMR9, TFAP2B, MSRA, LYPLAL1, GCKR and FADS1. To investigate the relationship between metabolic syndrome and variations in these genes in the Japanese population, we genotyped 33 single-nucleotide polymorphisms (SNPs) in 19 genes from 1096 patients with metabolic syndrome and 581 control individuals who had no risk factors for metabolic syndrome. Four SNPs in the FTO gene were significantly related to metabolic syndrome: rs9939609 (P=0.00013), rs8050136 (P=0.00011), rs1558902 (P=6.6 x 10(-5)) and rs1421085 (P=7.4 x 10(-5)). rs3764220 in the SCG3 gene (P=0.0010) and rs2293855 in the MTMR9 gene (P=0.0015) were also significantly associated with metabolic syndrome. SNPs in the FTO, SCG3 and MTMR9 genes had no SNP x SNP epistatic effects on metabolic syndrome. Our data suggest that genetic variations in the FTO, SCG3 and MTMR9 genes independently influence the risk of metabolic syndrome. Journal of Human Genetics (2011) 56, 647-651; doi: 10.1038/jhg.2011.74; published online 28 July 2011
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