Caspase-dependent and -independent Activation of Acid Sphingomyelinase Signaling

Abstract

Recent evidence suggests clustering of plasma membrane rafts into ceramide-enriched platforms serves as a transmembrane signaling mechanism for a subset of cell surface receptors and environmental stresses (Grassme, H., Jekle, A., Riehle, A., Schwarz, H., Berger, J., Sandhoff, K., Kolesnick, R., and Gulbins, E. Translocation of the secretory form of acid sphingomyelinase (ASMase) into microscopic rafts generates therein the ceramide that drives raft coalescence. This process serves to feed forward Fas activation, with ϳ2% of full caspase 8 activation sufficient for maximal ASMase translocation, leading to death-inducing signaling complex formation within ceramide-rich platforms, and apoptosis. Here we report that treatment of Jurkat T cells with UV-C also induces ASMase translocation into rafts within 1 min, catalyzing sphingomyelin hydrolysis to ceramide and raft clustering. In contrast to Fas, UV-induced ASMase translocation and activation were caspase-independent. Nonetheless, ceramide-rich platforms promoted UV-C-induced death signaling, because ASMase inhibition or raft disruption inhibited apoptosis, improving clonogenic cell survival. These studies thus define two distinct mechanisms for biologically relevant ASMase activation within rafts; a Fasmediated mechanism dependent upon caspase 8 and FADD, and a UV-induced mechanism independent of caspase activation. Consistent with this notion, genetic depletion or pharmacologic inhibition of caspase 8 or FADD, which render Jurkat cells incapable of sphingolipid signaling and apoptosis upon Fas ligation, did not impair these events upon UV-C stimulation.

The Role of Sphingolipids and Ceramide in Pulmonary Inflammation in Cystic Fibrosis

“…Ceramide molecules self-associate to small ceramide-enriched membrane microdomains, which have the tendency to spontaneously fuse to large ceramide-enriched membrane domains [36-38]. The formation of ceramide-enriched membrane domains was shown to occur in cells after stimulation via a variety of stimuli including CD95 [39-41], CD40 [42], DR5 [43], FcγRII [44], the PAF-receptor [45], but also after infection with P. aeruginosa [19], Neisseriae gonorrhoeae [46] , Rhinovirus [47], application of stress stimuli such as UV-light [48], cisplatin [49] or Cu 2+ -treatment [50]. The great variety of stimuli that trigger the formation of ceramide-enriched membrane platforms suggests that these membrane domains facilitate signal transduction, but are very likely not part of the specific signal transduction pathway elicited by the these stimuli.…”

Amplification of CD95 Activation by Caspase 8-induced Endosomal Acidification in Rat Hepatocytes

“…amplifies CD95 activation would be that activation of only 2% of total caspase 8 by CD95-activating antibodies was sufficient to induce a maximal ASM activation (55). Furthermore, CD95-dependent ceramide formation in HeLa and 293T cells was reported to require active caspase 8 (56).…”

Ceramide and sphingosine in pulmonary infections

“…Thus, ceramide acts by re-organizing molecules in cells and can control many receptor-mediated and non-receptor-mediated cellular activation processes by changing the biophysics of the membrane. In accordance, ceramide-enriched membrane platforms have been shown to be formed in cells after the application of a variety of stimuli, including CD95 , CD40 (Grassmé et al, 2002), DR5 (Dumitru and Gulbins, 2006), FcγRII (Abdel Shakor et al, 2004), and the PAF-receptor (Göggel et al, 2004); infection with P. aeruginosa (Grassmé et al, 2003a), Neisseriae gonorrhoeae (Grassmé et al, 1997), Neisseria meningitides (Simonis et al, 2014), rhinovirus (Grassmé et al, 2005), or measles virus (Gassert et al, 2009;Avota et al, 2011); or stress stimuli such as UV-light (Charruyer et al, 2005), gamma-irradiation (Rotolo et al, 2005), or treatment with cisplatin (Lacour et al, 2004) or Cu 2+ (Lang et al, 2007).…”