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Vol. 12, Issue 9, 2813-2824, September 2001

Sequential Activities of Phosphoinositide 3-Kinase, PKB/Akt, and Rab7 during Macropinosome Formation in Dictyostelium

Adam Rupper,* Kyung Lee,dagger David Knecht,dagger and James Cardelli*Dagger §

 *Department of Microbiology and Immunology,  Dagger Feist/Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130; and  dagger Department of Molecular and Cellular Biology, University of Connecticut, Storrs, Connecticut 06269-3125

Macropinocytosis plays an important role in the internalization of antigens by dendritic cells and is the route of entry for many bacterial pathogens; however, little is known about the molecular mechanisms that regulate the formation or maturation of macropinosomes. Like dendritic cells, Dictyostelium amoebae are active in macropinocytosis, and various proteins have been identified that contribute to this process. As described here, microscopic analysis of null mutants have revealed that the class I phosphoinositide 3-kinases, PIK1 and PIK2, and the downstream effector protein kinase B (PKB/Akt) are important in regulating completion of macropinocytosis. Although actin-rich membrane protrusions form in these cell lines, they recede without forming macropinosomes. Imaging of cells expressing green fluorescent protein (GFP) fused to the pleckstrin homology domain (PH) of PKB (GFP-PHPKB) indicates that D3 phosphoinositides are enriched in the forming macropinocytic cup and remain associated with newly formed macropinosomes for <1 minute. A fusion protein, consisting of GFP fused to an F-actin binding domain, overlaps with GFP-PHPKB in the timing of association with forming macropinosomes. Although macropinocytosis is reduced in cells expressing dominant negative Rab7, microscopic imaging studies reveal that GFP-Rab7 associates only with formed macropinosomes at approximately the time that F-actin and D3 phosphoinositide levels decrease. These results support a model in which F-actin modulating proteins and vesicle trafficking proteins coordinately regulate the formation and maturation of macropinosomes.

§ Corresponding author. E-mail address: jcarde{at}lsuhsc.edu.

Molecular Biology of the Cell
Vol. 12, 2813-2824, September 2001
Copyright © 2001 by The American Society for Cell Biology


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