Flotillin-1 defines a clathrin-independent endocytic pathway in mammalian cells

Nat Cell Biol. 2006 Jan;8(1):46-54. doi: 10.1038/ncb1342. Epub 2005 Dec 11.

Abstract

Previous studies provide evidence for an endocytic mechanism in mammalian cells that is distinct from both clathrin-coated pits and caveolae, and is not inhibited by overexpression of GTPase-null dynamin mutants. This mechanism, however, has been defined largely in these negative terms. We applied a ferro-fluid-based purification of endosomes to identify endosomal proteins. One of the proteins identified in this way was flotillin-1 (also called reggie-2). Here, we show that flotillin-1 resides in punctate structures within the plasma membrane and in a specific population of endocytic intermediates. These intermediates accumulate both glycosylphosphatidylinositol (GPI)-linked proteins and cholera toxin B subunit. Endocytosis in flotillin-1-containing intermediates is clathrin-independent. Total internal reflection microscopy and immuno-electron microscopy revealed that flotillin-1-containing regions of the plasma membrane seem to bud into the cell, and are distinct from clathrin-coated pits and caveolin-1-positive caveolae. Flotillin-1 small interfering RNA (siRNA) inhibited both clathrin-independent uptake of cholera toxin and endocytosis of a GPI-linked protein. We propose that flotillin-1 is one determinant of a clathrin-independent endocytic pathway in mammalian cells.

MeSH terms

  • Animals
  • COS Cells
  • Caveolins / metabolism
  • Chlorocebus aethiops
  • Cholera Toxin / metabolism
  • Clathrin / metabolism
  • Dynamin II / metabolism
  • Endocytosis*
  • Endosomes / metabolism*
  • HeLa Cells
  • Humans
  • Immunohistochemistry
  • Inositol Phosphates / metabolism
  • Membrane Microdomains / metabolism
  • Membrane Proteins / metabolism*
  • Protein Transport
  • RNA Interference
  • Transfection
  • Transferrin / metabolism

Substances

  • Caveolins
  • Clathrin
  • Inositol Phosphates
  • Membrane Proteins
  • Transferrin
  • flotillins
  • glycerylphosphoinositol
  • Cholera Toxin
  • Dynamin II