Modulation of the CD95-Induced Apoptosis: The Role of CD95 N-Glycosylation

Abstract

Protein modifications of death receptor pathways play a central role in the regulation of apoptosis. It has been demonstrated that O-glycosylation of TRAIL-receptor (R) is essential for sensitivity and resistance towards TRAIL-mediated apoptosis. In this study we ask whether and how glycosylation of CD95 (Fas/APO-1), another death receptor, influences DISC formation and procaspase-8 activation at the CD95 DISC and thereby the onset of apoptosis. We concentrated on N-glycostructure since O-glycosylation of CD95 was not found. We applied different approaches to analyze the role of CD95 N-glycosylation on the signal transduction: in silico modeling of CD95 DISC, generation of CD95 glycosylation mutants (at N136 and N118), modulation of N-glycosylation by deoxymannojirimycin (DMM) and sialidase from Vibrio cholerae (VCN). We demonstrate that N-deglycosylation of CD95 does not block DISC formation and results only in the reduction of the procaspase-8 activation at the DISC. These findings are important for the better understanding of CD95 apoptosis regulation and reveal differences between apoptotic signaling pathways of the TRAIL and CD95 systems.

Regulation of hippocampal Fas receptor and death-inducing signaling complex after kainic acid treatment in mice

“…Fas receptor is also expressed as N-glycosylated proteins (García-Fuster et al, 2003;Kamitani et al, 1997), and KA (at 72 h) increased its content in the hippocampus, an effect somewhat opposite to that of Fas aggregates. Interestingly, N-glycosylation of Fas receptor was shown to reduce pro-caspase-8 activation (Shatnyeva et al, 2011), which is in line with p18 fragment downregulation reported in the present study. A recent investigation has also revealed the important role played by Fas receptor (mRNA) in KA-induced hippocampal neuronal death in mice (Ettcheto et al, 2014), but this study did not quantify the status of Fas receptor protein forms.…”

Glycobiology of cell death: when glycans and lectins govern cell fate

“…Whereas TRAIL bears two potential O-glycosylation sites, 18 Fas contains two N-glycosylation sites. 21 In the presence of Fas ligand, Fas-associated N-glycans contribute to stabilize the core DISC structure, DISC-DISC interactions and procaspase-8 oligomerization 21 ( Figure 1b). By contrast, when Fas is aberrantly glycosylated because of localization of the protein tyrosine phosphatase SHP-1 in the endoplasmic reticulum (ER), Fas fails to oligomerize in response to Fas ligand and T-cell homeostasis is impaired.…”

Nucleolin inhibits Fas ligand binding and suppresses Fas-mediated apoptosis in vivo via a surface nucleolin-Fas complex

“…These high-molecular-weight bands represent sialylated and glycosylated Fas (supplemental Figure 5) as previously reported. 32,33 Fas glycosylation does not alter apoptosis sensitivity, 31,32 thus the observed changes do not interfere with our functional studies.…”