title: Synaptojanin 2 functions at an early step of clathrin-mediated endocytosis.
abstract: Synaptojanin 2 is a ubiquitously expressed polyphosphoinositide phosphatase that displays a high degree of homology in its catalytic domains with synaptojanin 1 [1,2]. Neurons of synaptojanin 1-deficient mice display an increase in clathrin-coated vesicles and delayed reentry of recycling vesicles into the fusion-competent vesicle pool, but no defects in early steps of endocytosis [3,4]. Here we show that inhibition of synaptojanin 2 expression via small interfering (si) RNA causes a strong defect in clathrin-mediated receptor internalization in a lung carcinoma cell line. This inhibitory phenotype is rescued by overexpression of wild-type synaptojanin 2, but not of wild-type synaptojanin 1 or mutant synaptojanin 2 that is deficient in 5'-phosphatase activity. In addition, electron-microscopic analysis shows that synaptojanin 2 depletion causes a decrease in clathrin-coated pits and vesicles. These results suggest a role for synaptojanin 2 in clathrin-coated pit formation and imply that lipid hydrolysis is required at an early stage of clathrin-mediated endocytosis. Taken together, our results also indicate that synaptojanin 2 is functionally distinct from synaptojanin 1.
authors.affiliation: Center for Oncology and Cell Biology, North Shore-LIJ Research Institute, 350 Community Drive, Manhasset, NY 11030, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Rusk
authors.forename: Phuong U
authors.initials: PU
authors.lastname: Le
authors.forename: Stefania
authors.initials: S
authors.lastname: Mariggio
authors.forename: Ginette
authors.initials: G
authors.lastname: Guay
authors.forename: Cristiano
authors.initials: C
authors.lastname: Lurisci
authors.forename: Ivan R
authors.initials: IR
authors.lastname: Nabi
authors.forename: Daniela
authors.initials: D
authors.lastname: Corda
authors.forename: Marc
authors.initials: M
authors.lastname: Symons
mesh_terms: D002277:Carcinoma / Q000378:metabolism; D045744:Cell Line, Tumor / Q000378:metabolism; D022163:Clathrin-Coated Vesicles / Q000378:metabolism / Q000648:ultrastructure*; D004705:Endocytosis / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism; D008854:Microscopy, Electron; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics* / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism
chemical_list: D009419:Nerve Tissue Proteins; D034741:RNA, Small Interfering; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases