Phosphorylation of STAT3 by the human serotonin 2C receptor
Serotonin (5-HT) is a modulatory neurotransmitter in the central nervous system that plays a role in many physiological responses by binding to 14 different receptor subtypes. The 5-HT2C receptor subtype (5-HT 2CR), a 7-transmembrane spanning G protein-coupled receptor, is involved in neuronal excitability, spatial learning, mood, executive function, glucose and energy homeostasis, and appetite. This receptor activates signaling pathways downstream of the Gαq/11 protein, as well as other intracellular proteins that activate G protein-independent pathways. The structurally similar 5-HT2AR can additionally activate the JAK/STAT pathway, and has been shown to do so following chronic treatment with the atypical antipsychotic and 5-HT2A and 5-HT2C receptor antagonist, olanzapine. The purpose of the present study to was to investigate the ability of the 5-HT2CR to activate the JAK/STAT pathway. Human Embryonic Kidney (HEK) 293 cells stably expressing the 5-HT2C-IDIR were treated with vehicle, serotonin, olanzapine, or the 5-HT2CR inverse agonist, SB206553. For in vivo analysis, adult male C57BL/6 mice were treated with SB206553, the 5-HT2CR agonist MK-212, or saline. Phospho-STAT3 levels in the hypothalamus, amygdala, and hippocampus of mice from each treatment group were examined by immunohistochemistry and western blot. Proteins from cell lysates and brain tissue were separated by SDS-PAGE and levels of phosphorylated JAK2 and STAT3 were analyzed via immunoblot. Constitutive phosphorylation of STAT3 was observed in cells containing the 5-HT2C-IDI receptor, while STAT3 phosphorylation was not observed in untransfected cells or cells treated with SB206553 or olanzapine. Within transfected cells, treatment with 5-HT increased the levels of phosphorylated STAT3 while JAK2 phosphorylation was unaffected in all treatment groups, indicating that agonist binding enhances phosphorylation of STAT3 independently of JAK2 activation. STAT3 phosphorylation in mice was unaffected in all treatment groups in both immunohistochemical and western blot analysis. This discrepancy may be due to the time course or dosage of treatment, or the functional selectivity of the agonist MK-212, and requires further evaluation. This is the first report of the 5-HT 2CR activating this pathway and suggests that this receptor may be involved in growth, cell differentiation, the immune response, and transcription of other STAT activated genes.
Mary E Curtis,
"Phosphorylation of STAT3 by the human serotonin 2C receptor"
ETD Collection for Tennessee State University.