Calmodulin-dependent regulation of the catalytic function of the human serotonin transporter in placental choriocarcinoma cells.
We investigated the involvement of calmodulin-dependent cellular processes in the regulation of the human serotonin transporter in placental choriocarcinoma cells. Treatment of JAR and BeWo cells with the selective calmodulin antagonist 1,3-dihydro-1-[1-((4-methyl-4H, 6H-pyrrolo[1,2-a][4,1]-benzoxapin-4-yl)-methyl)-4-piperindinyl+ ++]- 2H-benzimidazol-2-one (CGS93-43B (CGS)) for 1 h decreased the imipramine-sensitive serotonin transport activity markedly. The inhibitory effect was specific and was reproducible with other calmodulin antagonists. The basal serotonin transport activity as well as the activity that was stimulated by cholera toxin were inhibited to a similar extent. The CGS-induced inhibition was accompanied by a decrease in the maximal velocity and in the affinities of the transporter for Na+ and Cl- and an increase in the affinity for serotonin. There was, however, no change in the Na+/Cl-/serotonin stoichiometry. The inhibition of the transport activity induced by the treatment of intact cells with CGS was observable in plasma membrane vesicles isolated from these cells. Treatment with CGS had no effect on steady state levels of the serotonin transporter mRNAs nor on the transporter density in the plasma membrane. We conclude that the serotonin transporter is regulated by calmodulin-dependent processes in human placental choriocarcinoma cells involving posttranslational modification, most likely phosphorylation/dephosphorylation, of the transporter protein.
Jayanthi
L D
LD
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100.
Ramamoorthy
S
S
Mahesh
V B
VB
Leibach
F H
FH
Ganapathy
V
V
D000409:Alanine / Q000378:metabolism; D001562:Benzimidazoles / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000502:physiology*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002822:Choriocarcinoma / Q000378:metabolism*; D003042:Cocaine / Q000031:analogs & derivatives / Q000378:metabolism; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D010920:Placenta / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D014594:Uterine Neoplasms / Q000378:metabolism*
D001562:Benzimidazoles; D002147:Calmodulin; D002352:Carrier Proteins; D007457:Iodine Radioisotopes; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins; C052087:CGS 9343B; D012701:Serotonin; C069723:2beta-carbomethoxy-3beta-(4-iodophenyl)tropane; D007930:Leucine; D003042:Cocaine; D000409:Alanine