Synaptojanin 2 functions at an early step of clathrin-mediated endocytosis.
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.
Rusk
Nicole
N
Center for Oncology and Cell Biology, North Shore-LIJ Research Institute, 350 Community Drive, Manhasset, NY 11030, USA.
Le
Phuong U
PU
Mariggio
Stefania
S
Guay
Ginette
G
Lurisci
Cristiano
C
Nabi
Ivan R
IR
Corda
Daniela
D
Symons
Marc
M
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
D009419:Nerve Tissue Proteins; D034741:RNA, Small Interfering; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases