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Molecular and Cellular Biology, October 2004, p. 9102-9123, Vol. 24, No. 20
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.20.9102-9123.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Phosphatidylinositol-4,5-Bisphosphate-Rich Plasma Membrane Patches Organize Active Zones of Endocytosis and Ruffling in Cultured Adipocytes

Shaohui Huang,1 Larry Lifshitz,2 Varsha Patki-Kamath,1 Richard Tuft,2 Kevin Fogarty,2 and Michael P. Czech1*

Program in Molecular Medicine,1 Biomedical Imaging Group, Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts2

Received 22 December 2003/ Returned for modification 1 March 2004/ Accepted 2 July 2004

A major regulator of endocytosis and cortical F-actin is thought to be phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2] present in plasma membranes. Here we report that in 3T3-L1 adipocytes, clathrin-coated membrane retrieval and dense concentrations of polymerized actin occur in restricted zones of high endocytic activity. Ultrafast-acquisition and superresolution deconvolution microscopy of cultured adipocytes expressing an enhanced green fluorescent protein- or enhanced cyan fluorescent protein (ECFP)-tagged phospholipase C{delta}1 (PLC{delta}1) pleckstrin homology (PH) domain reveals that these zones spatially coincide with large-scale PtdIns(4,5)P2-rich plasma membrane patches (PRMPs). PRMPs exhibit lateral dimensions exceeding several micrometers, are relatively stationary, and display extensive local membrane folding that concentrates PtdIns(4,5)P2 in three-dimensional space. In addition, a higher concentration of PtdIns(4,5)P2 in the membranes of PRMPs than in other regions of the plasma membrane can be detected by quantitative fluorescence microscopy. Vesicular structures containing both clathrin heavy chains and PtdIns(4,5)P2 are revealed immediately beneath PRMPs, as is dense F actin. Blockade of PtdIns(4,5)P2 function in PRMPs by high expression of the ECFP-tagged PLC{delta}1 PH domain inhibits transferrin endocytosis and reduces the abundance of cortical F-actin. Membrane ruffles induced by the expression of unconventional myosin 1c were also found to localize at PRMPs. These results are consistent with the hypothesis that PRMPs organize active PtdIns(4,5)P2 signaling zones in the adipocyte plasma membrane that in turn control regulators of endocytosis, actin dynamics, and membrane ruffling.


* Corresponding author. Mailing address: Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation St., Worcester, MA 01605. Phone: (508) 856-2254. Fax: (508) 856-1617. E-mail: Michael.Czech{at}umassmed.edu.


Molecular and Cellular Biology, October 2004, p. 9102-9123, Vol. 24, No. 20
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.20.9102-9123.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.




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