Ca2+/calmodulin-dependent and -independent down-regulation of c-myb mRNA levels in erythropoietin-responsive murine erythroleukemia cells. The role of calcineurin.
Down-regulation of c-myb mRNA levels by [Ca2+]i-increasing agents (A23187, thapsigargin, cyclopiazonic acid) and erythropoietin was comparatively studied in the erythropoietin-responsive murine erythroleukemia cell line, ELM-I-1. The Ca2+-induced suppression of c-myb mRNA could be inhibited by the calmodulin antagonists trifluoperazine and calmidazolium, as well as by cyclosporin A, an inhibitor of the Ca2+/calmodulin-dependent protein phosphatase 2B (calcineurin). KN-62, an inhibitor of Ca2+/calmodulin-dependent protein kinases, did not antagonize the Ca2+-mediated decrease in c-myb mRNA. In cyclosporin A-treated ELM-I-1 cells, a close correlation could be demonstrated between the antagonization of the Ca2+ effect on c-myb mRNA levels and inhibition of the calcineurin phophatase activity. On the other hand, FK506, which did not inhibit calcineurin activity in ELM-I-1 cells, failed to prevent the Ca2+-mediated decrease in c-myb mRNA. The erythropoietin-induced down-regulation of c-myb mRNA levels could be demonstrated also in the presence of EGTA and was resistant to calmodulin antagonists and cyclosporin A. In addition, no increase in [Ca2+]i was observed in ELM-I-1 cells in response to erythropoietin. Cyclosporin A inhibited the Ca2+-induced hemoglobin production, while the erythropoietin-mediated increase in hemoglobin synthesis was not affected. The results indicate that the Ca2+-induced decrease in c-myb mRNA and increase in hemoglobin synthesis is mediated by calcineurin, while these effects of erythropoietin occur independently of Ca2+ in ELM-I-1 cells. Calcineurin may be involved in the regulation of c-myb expression in erythroid precursor cells and Ca2+ signals via calcineurin may positively modulate the differentiation inducing action of erythropoietin.
Schaefer
A
A
Department of Toxicology, Hamburg University Medical School, Grindelallee 117, D-20146 Hamburg, Federal Republic of Germany.
Magócsi
M
M
Stöcker
U
U
Fandrich
A
A
Marquardt
H
H
D000818:Animals; D019703:Calcineurin; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D016572:Cyclosporine / Q000494:pharmacology; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004921:Erythropoietin / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D016259:Genes, myc / Q000187:drug effects; D006454:Hemoglobins / Q000096:biosynthesis; D004915:Leukemia, Erythroblastic, Acute / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D009857:Oncogenes / Q000187:drug effects; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism*; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D016559:Tacrolimus / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D004791:Enzyme Inhibitors; D006454:Hemoglobins; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D004921:Erythropoietin; D016572:Cyclosporine; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D002118:Calcium; D016559:Tacrolimus