title: Phosphoinositide-regulated retrograde transport of ricin: crosstalk between hVps34 and sorting nexins.
abstract: The plant toxin ricin is transported from the plasma membrane via early endosomes and the Golgi apparatus to the endoplasmic reticulum. From this compartment, it enters the cytosol and inhibits protein synthesis. Lipid phosphorylation is an important regulator of vesicular transport, and in the present study we have investigated the role of the phosphatidylinositol (PI) 3-kinase hVps34 in retrograde transport of ricin. Our data demonstrate that transport of ricin from endosomes to the Golgi apparatus in human embryonic kidney cells (HEK 293) is dependent on PI(3)P. By using PI 3-kinase inhibitors, by sequestering the hVps34 product PI(3)P and by expressing mutants of hVps34 or small interfering RNA targeted against its messenger RNA, we show that hVps34 and its product PI(3)P are involved in transport of ricin from endosome to Golgi apparatus. Furthermore, we identify two effector proteins in the hVps34-dependent pathway, namely sorting nexin (SNX) 2 and SNX4. Knockdown of SNX2 or SNX4 inhibits ricin transport to the Golgi apparatus to the same extent as when hVps34 is perturbed. Furthermore, inhibition or knockdown of hVps34 redistributes these proteins. Interestingly, knocking down both SNX2 and SNX4 results in a better inhibition than knocking down only one of them, suggesting that they may act on separate pathways.
authors.affiliation: Department of Biochemistry, Institute for Cancer Research, University of Oslo, Faculty Department The Norwegian Radium Hospital, Montebello, N-0310 Oslo, Norway.
authors.forename: Sigrid S
authors.initials: SS
authors.lastname: Skånland
authors.forename: Sébastien
authors.initials: S
authors.lastname: Wälchli
authors.forename: Audrun
authors.initials: A
authors.lastname: Utskarpen
authors.forename: Angela
authors.initials: A
authors.lastname: Wandinger-Ness
authors.forename: Kirsten
authors.initials: K
authors.lastname: Sandvig
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D002867:Chromones / Q000494:pharmacology; D011992:Endosomes / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D021381:Protein Transport; D012276:Ricin / Q000378:metabolism*; D058305:Sorting Nexins; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D018129:Phosphatidylinositol Phosphates; C513979:SNX2 protein, human; C513981:SNX4 protein, human; D058305:Sorting Nexins; D033921:Vesicular Transport Proteins; C055525:phosphatidylinositol 3-phosphate; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D012276:Ricin; D019869:Phosphatidylinositol 3-Kinases; D000077191:Wortmannin