Phosphatidylinositol 3'-kinase blocks CD95 aggregation and caspase-8 cleavage at the death-inducing signaling complex by modulating lateral diffusion of CD95.
Activation of phosphatidylinositol 3'-kinase (PI 3'-K) after ligation of CD3 protects Th2 cells from CD95-mediated apoptosis. Here we show that protection is achieved by inhibition of the formation of CD95 aggregates and consequent activation of caspase-8. Inhibition of aggregate formation is mediated by changes in the actin cytoskeleton, which in turn inhibit lateral diffusion of CD95, reducing its diffusion coefficient, D, 10-fold. After cytochalasin D treatment of stimulated cells, the lateral diffusion of CD95 increases to the value measured on unstimulated cells, and CD95 molecules aggregate to process caspase-8 and mediate apoptosis. Regulation of functional receptor formation by modulating lateral diffusion is a novel mechanism for controlling receptor activity.
Varadhachary
A S
AS
Temple University School of Medicine, 3400 North Broad Street, Philadelphia, PA 19140.
Edidin
M
M
Hanlon
A M
AM
Peter
M E
ME
Krammer
P H
PH
Salgame
P
P
D000199:Actins / Q000502:physiology; D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis / Q000276:immunology*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D053181:Caspase 8; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D002999:Clone Cells; D003599:Cytoskeleton / Q000201:enzymology / Q000276:immunology / Q000502:physiology; D004058:Diffusion; D053200:Fas-Associated Death Domain Protein; D006801:Humans; D006868:Hydrolysis; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D011940:Receptor Aggregation / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology*; D013601:T-Lymphocytes / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D019014:fas Receptor / Q000276:immunology / Q000378:metabolism*
D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D061945:Caspase Inhibitors; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D019014:fas Receptor; D019869:Phosphatidylinositol 3-Kinases; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases