RGD Reference Report - Amplification of CD95 activation by caspase 8-induced endosomal acidification in rat hepatocytes. - Rat Genome Database

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Amplification of CD95 activation by caspase 8-induced endosomal acidification in rat hepatocytes.

Authors: Reinehr, R  Sommerfeld, A  Keitel, V  Grether-Beck, S  Haussinger, D 
Citation: Reinehr R, etal., J Biol Chem. 2008 Jan 25;283(4):2211-22. Epub 2007 Nov 28.
RGD ID: 2315735
Pubmed: PMID:18045865   (View Abstract at PubMed)
DOI: DOI:10.1074/jbc.M706853200   (Journal Full-text)

Although in rat hepatocytes CD95 is predominantly located inside the cell with almost undetectable immunostaining at the plasma membrane, the addition of CD95-ligand (CD95L) induces hepatocyte apoptosis, which is preceded by a targeting and activation of intracellularly localized CD95 to the plasma membrane including formation of the death-inducing signaling complex. This process involves an NADPH oxidase-dependent generation of reactive oxygen species (ROS) through a ceramide- and protein kinase Czeta-dependent pathway, which leads to an activating phosphorylation of p47(phox). The mechanisms underlying CD95L-induced ceramide formation were addressed in the present study. It was found that CD95L lowered within seconds the apparent vesicular pH from 6.0 to 5.7 in a fluorescein isothiocyanate-dextran-accessible endosomal compartment, which was previously shown to contain acidic sphingomyelinase, and decreased N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide fluorescence, suggestive for an increase of cytosolic [Cl(-)]. Bafilomycin or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid disodium salt largely abolished the CD95L-induced endosomal acidification, ceramide formation, and downstream events, such as p47(phox) phosphorylation, ROS formation, CD95 activation, and apoptosis. These responses were also abolished after knock-down of acidic sphingomyelinase in rat hepatocytes. Interestingly, caspase 8 inhibitors abolished these CD95L-induced signaling events, including the increase in cytosolic [Cl(-)], endosomal acidification, ceramide formation, and ROS generation as well as CD95 targeting to the plasma membrane and CD95 activation. The data suggest that CD95L initiates a rapid caspase 8-dependent endosomal acidification, which triggers ceramide-dependent ROS formation as an upstream event of trafficking of intracellularly stored CD95 to the plasma membrane. It is concluded that a rapid caspase 8 activation in response to CD95L signals to intracellularly stored CD95, which becomes activated and targeted to the plasma membrane. This autoamplification of CD95-activation is required for apoptosis induction.

Gene Ontology Annotations    Click to see Annotation Detail View

Biological Process
TermQualifierEvidenceWithReferenceNotesSourceOriginal Reference(s)
endosomal lumen acidification  IDA 2315735 RGD 
intracellular chloride ion homeostasis  IDA 2315735 RGD 

Cellular Component
TermQualifierEvidenceWithReferenceNotesSourceOriginal Reference(s)
cell surface  IDA 2315735 RGD 

Objects Annotated

Genes (Rattus norvegicus)
Fas  (Fas cell surface death receptor)
Faslg  (Fas ligand)

Additional Information