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First published online 14 April 2008
doi: 10.1242/jcs.020792
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Research Article |
1 Graduate Program in Neurosciences, Stanford University School of Medicine, Stanford, CA 94305, USA
2 Department of Chemical and Systems Biology, Stanford University School of Medicine, Clark Center, 318 Campus Drive, Stanford, CA 94305, USA
3 Graduate Program in Biophysics, and Department of Microbiology and Immunology, Beckman Center, 279 Campus Drive, Stanford University Medical School, Stanford, CA 94305, USA
* Author for correspondence (e-mail: tobias1{at}stanford.edu)
Accepted 21 February 2008
Endocytosis and recycling of membrane proteins are key processes for nutrient uptake, receptor signaling and synaptic transmission. Different steps in these fission and fusion cycles have been proposed to be regulated by physiological changes in plasma membrane (PM) phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P2] concentration. Here, we use a chemical enzyme-translocation strategy to rapidly reduce PM PtdIns(4,5)P2 levels while monitoring clathrin-mediated endocytosis and recycling. PtdIns(4,5)P2 hydrolysis blocked transferrin receptor endocytosis and led to a marked increase in the concentration of transferrin receptors in the PM, suggesting that endocytosis is more sensitive to changes in PtdIns(4,5)P2 than recycling. Reduction of PM PtdIns(4,5)P2 levels led to a near complete dissociation of Adaptor protein 2 (AP-2) from the PM but had only a small effect on clathrin assembly. This argues that receptor-mediated PtdIns(4,5)P2 reduction preferentially suppresses AP-2-mediated targeting of cargo to endocytic sites rather than the assembly of clathrin coats or recycling of endocytic vesicles.
Key words: Endocytosis, Phosphoinositides, Recycling