title: Ceramide activates JNK to inhibit a cAMP-gated K+ conductance and Cl- secretion in intestinal epithelia.
abstract: Sphingomyelinases (SMases) hydrolyze membrane sphingomyelin to ceramide and are expressed by diverse host and microbial cell types populating mucosal surfaces. Exogenous bacterial SMase acts on the basolateral membrane of polarized human intestinal epithelial cells to repress the cAMP-induced Cl(-) secretory response, but how this occurs is unknown. We show here that SMase acts by down-regulating a cAMP-gated basolateral membrane K(+) conductance. Neither phosphocholine, ceramide-1-phosphate, nor sphingosine-1-phosphate recapitulates this effect, indicating that ceramide production is the decisive factor. Basolaterally applied SMase induced the phosphorylation of c-Jun NH(2)-terminal kinase (JNK), and inhibition of JNK rescued the effect of SMase on cAMP-dependant secretion. SMase secreted by normal human fibroblasts specifically recapitulated the effect on cAMP-induced Cl(-) secretion, indicating that cell types inhabiting the subepithelial space can provide such an activity to the basolateral membrane of intestinal enterocytes in trans. Thus, conversion of sphingomyelin to ceramide in basolateral membranes of intestinal cells rapidly activates JNK to inhibit a cAMP-gated K(+) conductance and thereby attenuates Cl(-) secretion. These results define a novel lipid-mediated pathway for regulation of salt and water homeostasis at mucosal surfaces.
authors.affiliation: GI Cell Biology, Children's Hospital, and the Harvard Digestive Diseases Center, Boston, MA 02115, USA. david.saslowsky@childrens.harvard.edu
authors.forename: David E
authors.initials: DE
authors.lastname: Saslowsky
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Tanaka
authors.forename: Krishna P
authors.initials: KP
authors.lastname: Reddy
authors.forename: Wayne I
authors.initials: WI
authors.lastname: Lencer
mesh_terms: D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000502:physiology*; D048670:MAP Kinase Kinase 4 / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism; D015398:Signal Transduction; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D002712:Chlorides; D024642:Potassium Channels, Voltage-Gated; D000242:Cyclic AMP; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D013108:Sphingomyelin Phosphodiesterase; D011188:Potassium