title: Stimulation of cellular sphingomyelin import by the chemokine connective tissue-activating peptide III.
abstract: The selective import of phospholipids into cells could be mediated by proteins secreted from the cells into the extracellular compartment. We observed that the supernatants obtained from suspensions of thrombin-activated platelets stimulated the exchange of pyrene (py)-labeled sphingomyelin between lipid vesicles in vitro. The proteins with sphingomyelin transfer activity were purified and identified as the chemokine connective tissue-activating peptide III (CTAP-III) and platelet basic protein. Isolated CTAP-III stimulated the exchange of py-sphingomyelin between lipid vesicles but did not affect the translocations of py-labeled phosphatidylcholine and phosphatidylethanolamine. CTAP-III rapidly increased the transfer of py-sphingomyelin from low density lipoproteins into peripheral blood lymphocytes, other immune cells, and fibroblasts. In the presence of heparin, CTAP-III was unable to insert sphingomyelin into the peripheral blood lymphocytes. The activation energy of the py-sphingomyelin transfer suggested that the translocation proceeded entirely in a hydrophobic environment. [(3)H]Sphingomyelin transferred to the cells by CTAP-III was hydrolyzed to [(3)H]ceramide and [(3)H]sphingosine after activation with tumor necrosis factor alpha. The generation of the [(3)H]sphingolipid messengers was catalyzed by acid sphingomyelinase. Our results identify CTAP-III as the first mediator of the selective (endocytosis-independent) cellular import of sphingomyelin allowing the paracrine modulation of the sphingolipid signaling.
authors.affiliation: Physiologisches Institut der Universität München, Schillerstrasse 44, 80336 München, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Stoeckelhuber
authors.forename: P
authors.initials: P
authors.lastname: Dobner
authors.forename: P
authors.initials: P
authors.lastname: Baumgartner
authors.forename: J
authors.initials: J
authors.lastname: Ehlert
authors.forename: E
authors.initials: E
authors.lastname: Brandt
authors.forename: R
authors.initials: R
authors.lastname: Mentele
authors.forename: D
authors.initials: D
authors.lastname: Adam
authors.forename: B
authors.initials: B
authors.lastname: Engelmann
mesh_terms: D001692:Biological Transport; D001779:Blood Coagulation Factors / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D010455:Peptides; D013109:Sphingomyelins / Q000378:metabolism*
chemical_list: D001779:Blood Coagulation Factors; D010455:Peptides; D013109:Sphingomyelins; C009862:connective tissue-activating peptide; C018329:low affinity platelet factor 4