Coassembly of flotillins induces formation of membrane microdomains, membrane curvature, and vesicle budding.
Endocytosis has a crucial role in many cellular processes. The best-characterized mechanism for endocytosis involves clathrin-coated pits [1], but evidence has accumulated for additional endocytic pathways in mammalian cells [2]. One such pathway involves caveolae, plasma-membrane invaginations defined by caveolin proteins. Plasma-membrane microdomains referred to as lipid rafts have also been associated with clathrin-independent endocytosis by biochemical and pharmacological criteria [3]. The mechanisms, however, of nonclathrin, noncaveolin endocytosis are not clear [4, 5]. Here we show that coassembly of two similar membrane proteins, flotillin1 and flotillin2 [6-8], is sufficient to generate de novo membrane microdomains with some of the predicted properties of lipid rafts [9]. These microdomains are distinct from caveolin1-positive caveolae, are dynamic, and bud into the cell. Coassembly of flotillin1 and flotillin2 into microdomains induces membrane curvature, the formation of plasma-membrane invaginations morphologically similar to caveolae, and the accumulation of intracellular vesicles. We propose that flotillin proteins are defining structural components of the machinery that mediates a clathrin-independent endocytic pathway. Key attributes of this machinery are the dependence on coassembly of both flotillins and the inference that flotillin microdomains can exist in either flat or invaginated states.
Frick
Manfred
M
Medical Research Council Laboratory of Molecular Biology, Cambridge, UK.
Bright
Nicholas A
NA
Riento
Kirsi
K
Bray
Aurélie
A
Merrified
Christien
C
Nichols
Benjamin J
BJ
D004705:Endocytosis / Q000502:physiology*; D015870:Gene Expression; D006367:HeLa Cells; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism*; D022161:Transport Vesicles / Q000378:metabolism* / Q000648:ultrastructure
D008565:Membrane Proteins; C106354:flotillins