Palmitoylation of CD95 facilitates formation of SDS-stable receptor aggregates that initiate apoptosis signaling.
Apoptosis signaling through CD95 (Fas/APO-1) involves aggregation and clustering of the receptor followed by its actin-dependent internalization. Internalization is required for efficient formation of the death-inducing signaling complex (DISC) with maximal recruitment of FADD, caspase-8/10 and c-FLIP occurring when the receptor has reached an endosomal compartment. The first detectable event during CD95 signaling is the formation of SDS-stable aggregates likely reflecting intense oligomerization of the receptor. We now demonstrate that these SDS-stable forms of CD95 correspond to very high molecular weight DISC complexes (hiDISC) and are the sites of caspase-8 activation. hiDISCs are found both inside and outside of detergent-resistant membranes. The formation of SDS-stable CD95 aggregates involves palmitoylation of the membrane proximal cysteine 199 in CD95. Cysteine 199 mutants no longer form SDS-stable aggregates, and inhibition of palmitoylation reduces internalization of CD95 and activation of caspase-8. Our data demonstrate that SDS-stable forms of CD95 are the sites of apoptosis initiation and represent an important early step in apoptosis signaling through CD95 before activation of caspases.
Feig
Christine
C
The Ben May Institute for Cancer Research, University of Chicago, Chicago, IL 60637, USA.
Tchikov
Vladimir
V
Schütze
Stefan
S
Peter
Marcus E
ME
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000737:chemistry; D053455:Caspase 10 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010169:Palmitic Acids / Q000378:metabolism*; D015398:Signal Transduction; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D019014:fas Receptor / Q000737:chemistry* / Q000378:metabolism
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; C506387:Cflar protein, mouse; D010169:Palmitic Acids; D019014:fas Receptor; D012967:Sodium Dodecyl Sulfate; D053455:Caspase 10; D053181:Caspase 8