出版社：American Society for Biochemistry and Molecular Biology
摘要：The bioactive molecule sphingosine 1-phosphate (S1P) is abundantlystored in platelets and can be released extracellularly. However,although they have high sphingosine (Sph) kinase activity, plateletslack the de novo sphingolipid biosynthesis necessary to providethe substrates. Here, we reveal a generation pathway for Sph,the precursor of S1P, in human platelets. Platelets incorporatedextracellular 3H-labeled Sph much faster than human megakaryoblasticcells and rapidly converted it to S1P. Furthermore, Sph formedfrom plasma sphingomyelin (SM) by bacterial sphingomyelinase(SMase) and neutral ceramidase (CDase) was rapidly incorporatedinto platelets and converted to S1P, suggesting that plateletsuse extracellular Sph as a source of S1P. Platelets abundantlyexpress SM, possibly supplied from plasma lipoproteins, at thecell surface. Treating platelets with bacterial SMase resultedin Sph generation at the cell surface, conceivably by the actionof membrane-bound neutral CDase. Simultaneously, a time-dependentincrease in S1P levels was observed. Finally, we demonstratedthat secretory acid SMase also induces S1P increases in platelets.
In conclusion, our results suggest that in platelets, Sph issupplied from at least two sources: generation in the plasmafollowed by incorporation, and generation at the outer leafletof the plasma membrane, initiated by cell surface SM degradation.Abbreviations: CDase, ceramidase; Cer, ceramide; FB1, fumonisin B1; NBD, 4-nitrobenzo-2-oxa-1,3-diazole; SM, sphingomyelin; SMase, sphingomyelinase; Sph, sphingosine; S1P, sphingosine 1-phosphate
Supplementary key words ceramide • sphingomyelinase • neutral ceramidase
