title: Leptin potentiates ADP-induced [Ca(2+)](i) increase via JAK2 and tyrosine kinases in a megakaryoblast cell line.
abstract: Plasma leptin levels are elevated in most of obese individuals, and obesity is associated with high incidence of cardiovascular diseases. It has been reported that leptin is an independent risk factor for the coronary artery disease in obese patients and that leptin is involved in the pathogenesis of cardiovascular diseases. We previously reported that leptin promotes platelet aggregation. The present study aimed to elucidate the mechanisms underlying this effect of leptin using a megakaryoblast cell line, MEG-01 cells. Leptin receptors mRNAs expression in MEG-01 cells were analyzed by RT-PCR. Leptin-induced tyrosine-phosphorylation of proteins was analyzed by immunoblotting with an anti-phosphotyrosine antibody. ADP-induced increases in cytosolic Ca(2+) concentration ([Ca(2+)](i)) in the presence and absence of leptin were measured by dual-wavelength fura-2 microfluorometry. Both Ob-Ra and Ob-Rb, were expressed and leptin-induced tyrosine-phosphorylation of several proteins in MEG-01 cells. Leptin-potentiated increases in [Ca(2+)](i) induced by ADP. ADP at a subthreshold concentration and leptin acted synergistically in producing [Ca(2+)](i) increases. These effects of leptin on [Ca(2+)](i) were inhibited by blockers of JAK2 and tyrosine kinases. Furthermore, leptin increased the tyrosine-phosphorylation of Gq alpha-subunits. The results indicate that leptin enhances ADP-induced [Ca(2+)](i) increases via JAK2 and tyrosine kinases in a megakaryoblast cell line. This mechanism may underlie the potentiation of platelet aggregation by leptin.
authors.affiliation: Department of Physiology, Division of Integrative Physiology, Jichi Medical School, School of Medicine, Minamikawachimachi, Kawachi, Tochigi 329-0498, Japan. nakata@jichi.ac.jp
authors.forename: Masanori
authors.initials: M
authors.lastname: Nakata
authors.forename: Ikuro
authors.initials: I
authors.lastname: Maruyama
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Yada
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology*; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D053614:Janus Kinase 2; D020738:Leptin / Q000494:pharmacology*; D008533:Megakaryocytes / Q000187:drug effects / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics*; D054411:Receptors, Leptin; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020032:Tyrphostins / Q000494:pharmacology
chemical_list: D017931:DNA Primers; D004791:Enzyme Inhibitors; C515448:LEPR protein, human; D020738:Leptin; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide; D000244:Adenosine Diphosphate; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D002118:Calcium