Synaptojanin 2 functions at an early step of clathrin-mediated endocytosis

Curr Biol. 2003 Apr 15;13(8):659-63. doi: 10.1016/s0960-9822(03)00241-0.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Carcinoma / metabolism
  • Cell Line, Tumor / metabolism
  • Clathrin-Coated Vesicles / metabolism
  • Clathrin-Coated Vesicles / ultrastructure*
  • Endocytosis / physiology*
  • Fluorescent Antibody Technique
  • Gene Expression Regulation*
  • Humans
  • Lung Neoplasms / metabolism
  • Microscopy, Electron
  • Nerve Tissue Proteins / genetics*
  • Nerve Tissue Proteins / metabolism*
  • Phosphoric Monoester Hydrolases / genetics*
  • Phosphoric Monoester Hydrolases / metabolism*
  • RNA, Small Interfering / metabolism

Substances

  • Nerve Tissue Proteins
  • RNA, Small Interfering
  • synaptojanin
  • Phosphoric Monoester Hydrolases