title: Cyclic AMP and calcium interplay as second messengers in melatonin-dependent regulation of Plasmodium falciparum cell cycle.
abstract: The host hormone melatonin increases cytoplasmic Ca(2+) concentration and synchronizes Plasmodium cell cycle (Hotta, C.T., M.L. Gazarini, F.H. Beraldo, F.P. Varotti, C. Lopes, R.P. Markus, T. Pozzan, and C.R. Garcia. 2000. Nat. Cell Biol. 2:466-468). Here we show that in Plasmodium falciparum melatonin induces an increase in cyclic AMP (cAMP) levels and cAMP-dependent protein kinase (PKA) activity (40 and 50%, respectively). When red blood cells infected with P. falciparum are treated with cAMP analogue adenosine 3',5'-cyclic monophosphate N6-benzoyl/PKA activator (6-Bz-cAMP) there is an alteration of the parasite cell cycle. This effect appears to depend on activation of PKA (abolished by the PKA inhibitors adenosine 3',5'-cyclic monophosphorothioate/8 Bromo Rp isomer, PKI [cell permeable peptide], and H89). An unexpected cross talk was found to exist between the cAMP and the Ca(2+)-dependent signaling pathways. The increases in cAMP by melatonin are inhibited by blocker of phospholipase C U73122, and addition of 6-Bz-cAMP increases cytosolic Ca(2+) concentration, through PKA activation. These findings suggest that in Plasmodium a highly complex interplay exists between the Ca(2+) and cAMP signaling pathways, but also that the control of the parasite cell cycle by melatonin requires the activation of both second messenger controlled pathways.
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Flávio H
authors.initials: FH
authors.lastname: Beraldo
authors.forename: Fabiana M
authors.initials: FM
authors.lastname: Almeida
authors.forename: Aline M
authors.initials: AM
authors.lastname: da Silva
authors.forename: Célia R S
authors.initials: CR
authors.lastname: Garcia
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008550:Melatonin / Q000494:pharmacology*; D018613:Microscopy, Confocal; D008954:Models, Biological; D010271:Parasites / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D010963:Plasmodium falciparum / Q000166:cytology* / Q000187:drug effects* / Q000201:enzymology; D015290:Second Messenger Systems; D015398:Signal Transduction / Q000187:drug effects; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
chemical_list: D004791:Enzyme Inhibitors; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D010738:Type C Phospholipases; D008550:Melatonin; D002118:Calcium