title: A mammalian ortholog of Saccharomyces cerevisiae Vac14 that associates with and up-regulates PIKfyve phosphoinositide 5-kinase activity.
abstract: Multivesicular body morphology and size are controlled in part by PtdIns(3,5)P(2), produced in mammalian cells by PIKfyve-directed phosphorylation of PtdIns(3)P. Here we identify human Vac14 (hVac14), an evolutionarily conserved protein, present in all eukaryotes but studied principally in yeast thus far, as a novel positive regulator of PIKfyve enzymatic activity. In mammalian cells and tissues, Vac14 is a low-abundance 82-kDa protein, but its endogenous levels could be up-regulated upon ectopic expression of hVac14. PIKfyve and hVac14 largely cofractionated, populated similar intracellular locales, and physically associated. A small-interfering RNA-directed gene-silencing approach to selectively eliminate endogenous hVac14 rendered HEK293 cells susceptible to morphological alterations similar to those observed upon expression of PIKfyve mutants deficient in PtdIns(3,5)P(2) production. Largely decreased in vitro PIKfyve kinase activity and unaltered PIKfyve protein levels were detected under these conditions. Conversely, ectopic expression of hVac14 increased the intrinsic PIKfyve lipid kinase activity. Concordantly, intracellular PtdIns(3)P-to-PtdIns(3,5)P(2) conversion was perturbed by hVac14 depletion and was elevated upon ectopic expression of hVac14. These data demonstrate a major role of the PIKfyve-associated hVac14 protein in activating PIKfyve and thereby regulating PtdIns(3,5)P(2) synthesis and endomembrane homeostasis in mammalian cells.
authors.affiliation: Department of Physiology, Wayne State University School of Medicine, 540 E. Canfield, Detroit, MI 48201, USA.
authors.forename: Diego
authors.initials: D
authors.lastname: Sbrissa
authors.forename: Ognian C
authors.initials: OC
authors.lastname: Ikonomov
authors.forename: Jana
authors.initials: J
authors.lastname: Strakova
authors.forename: Rajeswari
authors.initials: R
authors.lastname: Dondapati
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Mlak
authors.forename: Robert
authors.initials: R
authors.lastname: Deeb
authors.forename: Robert
authors.initials: R
authors.lastname: Silver
authors.forename: Assia
authors.initials: A
authors.lastname: Shisheva
mesh_terms: D041721:3T3-L1 Cells; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D004396:Coloring Agents / Q000494:pharmacology; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D020868:Gene Silencing; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells; D050356:Lipid Metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D018613:Microscopy, Confocal; D008954:Models, Biological; D009499:Neutral Red / Q000494:pharmacology; D016716:PC12 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis* / Q000737:chemistry; D010766:Phosphorylation; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation
chemical_list: D004396:Coloring Agents; D018076:DNA, Complementary; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009499:Neutral Red; D019869:Phosphatidylinositol 3-Kinases; D034741:RNA, Small Interfering; D029701:Saccharomyces cerevisiae Proteins; C452435:VAC14 protein, S cerevisiae; C494631:VAC14 protein, human; C492139:PIKFYVE protein, human