Chronic olanzapine activates the Stat3 signal transduction pathway and alters expression of components of the 5-HT2A receptor signaling system in rat frontal cortex.
The mechanisms underlying desensitization of serotonin 2A (5-HT(2A)) receptor signaling by antagonists are unclear but may involve changes in gene expression mediated via signal transduction pathways. In cells in culture, olanzapine causes desensitization of 5-HT(2A) receptor signaling and increases the levels of regulators of G protein signaling (RGS) 7 protein dependent on phosphorylation/activation of the Janus kinase 2 (Jak2)/signal transducers and activators of transcription 3 (Stat3) signaling pathway. In the current study, the 5-HT(2A) receptor signaling system in rat frontal cortex was examined following 7 days of daily treatment with 0.5, 2.0 or 10.0 mg/kg i.p. olanzapine. Olanzapine increased phosphorylation of Stat3 in rats treated daily with 10 mg/kg olanzapine and caused a dose-dependent desensitization of 5-HT(2A) receptor-mediated phospholipase C activity. There were dose-dependent increases in the levels of membrane-associated 5-HT(2A) receptor, G(alpha11) and G(alphaq) protein levels but no changes in the G(beta) protein levels. With olanzapine treatment, RGS4 protein levels increase in the membrane-fraction and decrease in the cytosolic fraction by similar amounts suggesting a redistribution of RGS4 protein within neurons. RGS7 protein levels increase in both the membrane and cytosolic fractions in rats treated daily with 10mg/kg olanzapine. The olanzapine-induced increase in Stat3 activity could underlie the increase in RGS7 protein expression in vivo as previously demonstrated in cultured cells. Furthermore, the increases in membrane-associated RGS proteins could play a role in desensitization of signaling by terminating the activated G(alphaq/11) proteins more rapidly.
Department of Pharmacology, Loyola University Medical Center, Maywood, IL 60153, USA. nmuma@ku.edu
N A
NA
Muma
R K
RK
Singh
M S
MS
Vercillo
D N
DN
D'Souza
B
B
Zemaitaitis
F
F
Garcia
K J
KJ
Damjanoska
Y
Y
Zhang
G
G
Battaglia
L D
LD
Van de Kar
D000818:Animals; D001569:Benzodiazepines / Q000494:pharmacology*; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D005625:Frontal Lobe / Q000187:drug effects / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000378:metabolism; D008297:Male; D000077152:Olanzapine; D051381:Rats; D017207:Rats, Sprague-Dawley; D044402:Receptor, Serotonin, 5-HT2A / Q000187:drug effects / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000502:physiology*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D010738:Type C Phospholipases / Q000378:metabolism
D001569:Benzodiazepines; D019204:GTP-Binding Proteins; D000077152:Olanzapine; D044402:Receptor, Serotonin, 5-HT2A; D050796:STAT3 Transcription Factor; D017367:Selective Serotonin Reuptake Inhibitors; D010738:Type C Phospholipases; C494088:Stat3 protein, rat