Crosstalk between thrombin and adenylyl cyclase-stimulating agonists in proliferating human erythroid progenitor cells.
Human erythroid progenitor cells grown in a suspension culture system were used to study possible interactions between different guanine nucleotide-binding protein (G-protein)-coupled receptor-effector systems during normal cell differentiation. Agonist-stimulated adenylyl cyclase was not inhibited by any one of a panel of ligands (ADP, UTP, platelet-activating factor, thrombin, alpha2-adrenoceptor agonists, interleukin 8, lysophosphatidic acid) most of which are known, in other cells, to reduce cAMP formation by a Gi-mediated, pertussis toxin-sensitive mechanism. The first four of these ligands are also known to cause transient changes in intracellular [Ca2+] in erythroid cells. Rather than inhibiting, thrombin (but not ADP, UTP or PAF) specifically caused a fivefold increase in the maximum adenosine- or prostaglandin E1-stimulated cAMP formation, without any shift of the concentration/response curves. Thrombin did not enhance forskolin- and AlF4-stimulated cyclase activity and had only a marginal effect on isoprenaline-dependent stimulation. The effect of thrombin seemed to be unrelated to intracellular Ca2+ release but could be partially mimicked by phorbol ester (PMA)-induced stimulation of protein kinase C (PKC) and was inhibited by staurosporin or by inactivation of PKC after long-term incubation with PMA. The activity of thrombin was restricted to proliferating, colony-forming progenitor cells while proerythroblasts were completely unresponsive. Our results suggest that the interaction of thrombin with Gs-linked receptors requires phosphorylation of a target protein that is different from adenylyl cyclase, Gs or Gi but may be involved in the regulation of receptor desensitization.
Porzig
H
H
Department of Pharmacology, Universität Bern, Switzerland.
Gutknecht
R
R
Thalmeier
K
K
D000241:Adenosine / Q000494:pharmacology*; D000262:Adenylyl Cyclases / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002455:Cell Division; D000242:Cyclic AMP / Q000096:biosynthesis; D015672:Erythroid Precursor Cells / Q000187:drug effects / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000502:physiology; D006801:Humans; D011493:Protein Kinase C / Q000502:physiology; D015398:Signal Transduction; D013917:Thrombin / Q000494:pharmacology*
D000242:Cyclic AMP; D011493:Protein Kinase C; D013917:Thrombin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D000241:Adenosine; D002118:Calcium