Ceramide Inhibits Inwardly Rectifying K⁺Currents via a Ras- and Raf-1-Dependent Pathway in Cultured Oligodendrocytes

Abstract

Ceramide is a lipid mediator implicated in apoptosis induced by proinflammatory cytokines in many cell types, including oligodendrocytes (OLGs). To determine whether ceramide modulates transmembrane signaling events in OLGs, we studied its effect on intracellular Ca 2ϩ (Ca i ), resting membrane potential and inwardly rectifying K ϩ currents (I Kir ) in cultured neonatal rat OLGs. We report here that (1) exposure to C2-ceramide (cer) rarely increases OLG Ca i , whereas sphingosine elicits sustained increase in Ca i ; (2) cer causes OLG depolarization, an effect mimicked by sphingosine-1-phosphate but not by sphingosine; and (3) cer, but not its inactive analog dihydroceramide, inhibits OLG I Kir . The cer effect is attenuated by Ras antibody Y13-259, by protein kinase C inhibitory peptide (19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36), and by suppression of c-Raf-1 expression with antisense raf-1 oligonucleotides. We conclude that cer-induced OLG depolarization is mediated via inhibition of I Kir by a Ras-and raf-1-dependent pathway, which results in the phosphorylation of the inward rectifier K ϩ channel protein.

Downregulation of the HERG (KCNH2) K+ channel by ceramide: evidence for ubiquitin-mediated lysosomal degradation

“…Previously, we and others have shown that ceramide regulates a number of potassium conductances (Wu et al, 2001;Ramström et al, 2004;Gulbins et al, 1997;Hida et al, 1998;Yu et al, 1999;Li et al, 1999;Chik et al, 2001). The addition of I HERG to this list appears to be expected as a related inwardly rectifying potassium current of lactotrophs and neuroblastoma cells is also inhibited by ceramide (Wu et al, 2001).…”

“…Although ceramide is capable of initiating the ubiquitin/ proteosome pathway (Ogretmen and Hannun, 2004) its action on ion channels is recognised as being mediated primarily by kinase activity, in particular PKC (Ramström et al, 2004;Hida et al, 1998;Chik et al, 2001). PKC activation is reported to result in the internalisation of the ATP-sensitive potassium channel (Hu et al, 2003) and the sodium channel, Na v 1.7 (Yanagita et al, 2000).…”

PDGF upregulates delayed rectifier via Src family kinases and sphingosine kinase in oligodendroglial progenitors

“…Sphingolipids are known modulators of Ca 2ϩ signaling in cells of OLG lineage (16,23). Although PDGFinduced Kv1.5 upregulation was inhibited by chelation of intracellular Ca 2ϩ with BAPTA-AM, it was not prevented by U-73122.…”

Transient Mechanoactivation of Neutral Sphingomyelinase in Caveolae to Generate Ceramide

“…Ceramide can activate several intracellular signaling molecules, including JNK (59) through unknown mechanisms and MAP kinase (60) through the interaction of ceramide-activated protein kinase with Raf (61). Ceramide can also regulate the activity of ion channels (62,63), NRTK and Ras (64), eNOS (65), and, ultimately, transcription factors, such as NFB (66). Interestingly, all of these downstream targets of ceramide also respond to hemodynamic stressors.…”