Growth factor-like action of lysophosphatidic acid on human B lymphoblasts.
Proliferation and immunoglobulin secretion of B lymphocytes are regulated by specific antigens and numerous accessory immunomodulatory factors. Lysophosphatidic acid (LPA) is a glycerophospholipid mediator that is released from activated blood platelets, attains high levels in serum, and exerts potent stimulatory effects on, e.g., neutrophils, monocytes, and T lymphocytes. LPA is also generated by a secretory, cytokine-inducible phospholipase A2 present in high concentrations in inflammatory exudates and septic states. We investigated effects of LPA on human Epstein-Barr virus-immortalized B lymphoblasts, a model for immunoglobulin-secreting B cells. Intracellular Ca2+ was determined with fura 2 and the formation of inositol 1,4, 5-trisphosphate by anion-exchange chromatography. LPA stimulated an increase in inositol 1,4,5-trisphosphate levels and induced a transient rise in intracellular free Ca2+ concentration from 105 +/- 17 to 226 +/- 21 nM. This Ca2+ signal resulted from Ca2+ mobilization and Ca2+ influx and was subject to homologous desensitization. Pertussis toxin inhibited these responses by approximately 70%. Furthermore, LPA stimulated a 27.5% increase in guanosine 5'-O-(3-thiotriphosphate) binding to permeabilized B lymphoblasts, which suggests the direct activation of pertussis toxin-sensitive G proteins by LPA. LPA stimulated a strong increase in the specific phosphorylation of the mitogen-activated protein kinase (immunoblot analysis) that was prevented by the MEK inhibitor PD-98059. Finally, LPA triggered a 2-fold increase in DNA synthesis ([3H]thymidine incorporation) and a 2-fold increase in B lymphoblast number and evoked a 20- to 50-fold increase in immunoglobulin formation. By RT-PCR we detected specific mRNA transcripts for the recently cloned human LPA receptor. Thus our data suggest that LPA behaves as a B cell growth factor.
Rosskopf
D
D
Institut fur Pharmakologie, Universitatsklinikum, D-45122 Essen, Germany.
Daelman
W
W
Busch
S
S
Schurks
M
M
Hartung
K
K
Kribben
A
A
Michel
M C
MC
Siffert
W
W
D000917:Antibody Formation; D001402:B-Lymphocytes / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002461:Cell Line, Transformed; D002852:Chromatography, Ion Exchange; D004247:DNA / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006133:Growth Substances / Q000494:pharmacology*; D004854:Herpesvirus 4, Human; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D018655:Lymphocyte Count; D008246:Lysophospholipids / Q000494:pharmacology*; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases; D037342:Pertussis Toxin; D047428:Protein Kinase Inhibitors; D015398:Signal Transduction; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005419:Flavonoids; D006133:Growth Substances; D008246:Lysophospholipids; D047428:Protein Kinase Inhibitors; D010566:Virulence Factors, Bordetella; D015544:Inositol 1,4,5-Trisphosphate; D004247:DNA; D037342:Pertussis Toxin; D020929:Mitogen-Activated Protein Kinase Kinases; D019204:GTP-Binding Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D002118:Calcium