Platelet-activating factor induces phospholipid turnover, calcium flux, arachidonic acid liberation, eicosanoid generation, and oncogene expression in a human B cell line.
Platelet-activating factor is a potent mediator of the inflammatory response. Studies of the actions of platelet-activating factor have centered mainly around neutrophils, monocytes, and platelets. In this report we begin to uncover the influence of platelet-activating factor on B lymphocytes. Employing the EBV-transformed human B cell line SKW6.4, we demonstrate that platelet-activating factor significantly alters membrane phospholipid metabolism indicated by the incorporation of 32P into phosphatidylcholine, phosphatidylinositol, and phosphatidic acid but not significantly into phosphatidylethanolamine at concentrations ranging from 10(-9) to 10(-6) M. The inactive precursor, lyso-platelet-activating factor, at a concentration as high as 10(-7) M had no effect on any of the membrane phospholipids. We also show that platelet-activating factor from 10(-12) to 10(-6) M induced rapid and significant elevation in intracellular calcium levels, whereas lyso-platelet-activating factor was again ineffective. We further demonstrate the impact of platelet-activating factor binding to B cells by measuring platelet-activating factor induced arachidonic acid release and 5-hydroxyeicosatetraenoic acid production. Moreover, platelet-activating factor was capable of inducing transcription of the nuclear proto-oncogenes c-fos and c-jun. Finally we explored the possible role of 5-hydroxyeicosatetraenoic acid as a regulator of arachidonic acid liberation demonstrating that endogenous 5-lipoxygenase activity modulates platelet-activating factor induced arachidonic acid release perhaps acting at the level of phospholipase A2. In summary, platelet-activating factor is shown here to have a direct and profound effect on a pure B cell line.
Schulam
P G
PG
Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030.
Kuruvilla
A
A
Putcha
G
G
Mangus
L
L
Franklin-Johnson
J
J
Shearer
W T
WT
D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D001402:B-Lymphocytes / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002461:Cell Line, Transformed; D004268:DNA-Binding Proteins / Q000235:genetics; D015777:Eicosanoids / Q000096:biosynthesis; D005786:Gene Expression Regulation; D004854:Herpesvirus 4, Human; D006801:Humans; D006893:Hydroxyeicosatetraenoic Acids / Q000096:biosynthesis; D008563:Membrane Lipids / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D010972:Platelet Activating Factor / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger / Q000096:biosynthesis; D014157:Transcription Factors / Q000235:genetics; D015854:Up-Regulation
D001095:Arachidonic Acids; D004268:DNA-Binding Proteins; D015777:Eicosanoids; D006893:Hydroxyeicosatetraenoic Acids; D008563:Membrane Lipids; D010743:Phospholipids; D010761:Phosphorus Radioisotopes; D010972:Platelet Activating Factor; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D014157:Transcription Factors; D016718:Arachidonic Acid; C022022:5-hydroxy-6,8,11,14-eicosatetraenoic acid; D002118:Calcium