Cyclic AMP raises intracellular Ca(2+) in human megakaryocytes independent of protein kinase A.
The immature megakaryoblastic cell line MEG-01 responds to iloprost with an increase in cytosolic Ca(2+) and cAMP. The Ca(2+) response is almost absent in CHRF-288-11 cells, but cAMP formation is preserved in this more mature megakaryoblastic cell line. Also, in human hematopoietic stem cells, iloprost induces a Ca(2+) response and cAMP formation. The Ca(2+) response is downregulated during megakaryocytopoiesis, but cAMP formation remains unchanged. The Ca(2+) increase may be caused by cAMP-mediated inhibition of Ca(2+) sequestration, because it is (1) independent of Ca(2+) entry; (2) mimicked by forskolin, an activator of adenylyl cyclase, and isobutylmethylxanthine, an inhibitor of phosphodiesterases; and (3) preserved in the presence of inhibitors of protein kinase A and inositol-1,4,5-triphosphate receptors. The small GTPase Rap1 has been implicated in the control of Ca(2+) sequestration. Indeed, Rap1 activation parallels the iloprost- and forskolin-induced Ca(2+) increase and is unaffected by the calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N',-tetraacetic acid-AM. These findings reveal a novel mechanism for elevating cytosolic Ca(2+) by cAMP, possibly via GTP-Rap1.
den Dekker
Els
E
Thrombosis and Haemostasis Laboratory, Department of Haematology, University Medical Center Utrecht, The Netherlands. e.dendekker@lab.azu.nl
Heemskerk
Johan W M
JW
Gorter
Gertie
G
van der Vuurst
Hans
H
Donath
José
J
Kroner
Christine
C
Mikoshiba
Katsuhiko
K
Akkerman
Jan-Willem N
JW
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D002460:Cell Line; D002614:Chelating Agents / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D016285:Iloprost / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008533:Megakaryocytes / Q000187:drug effects* / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors; D014665:Vasodilator Agents / Q000494:pharmacology*; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
D015220:Calcium Channels; D002614:Chelating Agents; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D010726:Phosphodiesterase Inhibitors; D018160:Receptors, Cytoplasmic and Nuclear; D014665:Vasodilator Agents; D005576:Colforsin; D004533:Egtazic Acid; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D020827:rap1 GTP-Binding Proteins; D016285:Iloprost; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine