Comparison of STAT3 Phosphorylation Between IDI Versus INI Isoforms and Acute Versus Chronic Treatment of the Human Serotonin 2C Receptor
Serotonin (5-HT) is an indolamine neurotransmitter involved in a variety of functions including regulation of mood, appetite, sleep, learning and memory, and neuronal excitability. 5-HT elicits its effects by binding to at least 14 different receptor subtypes that mediate both excitatory and inhibitory neurotransmission. The many classes of serotonin receptors have been subjected to significant studies in order to discern the functionality and produce effective therapeutic targets. One of the receptors, the 5-HT2C receptor, has been studied and used as a target for antipsychotic medication. 5-HT2C subtype receptor exists as a 7-transmembrane spanning G protein-coupled receptor (GPCR) found in the central nervous system, and is the only GPCR known to undergo RNA editing, creating 14 known isoforms in the human brain which affect its ability to couple with G proteins and other signaling proteins. The structurally similar 5-HT2A receptor has been shown to activate the G protein independent JAK/STAT pathway. The purpose of this study was to determine if the human 5-HT2C receptor also activates the JAK/STAT pathway. Human Embryonic Kidney (HEK) 293 cells were transfected with human 5-HT2C receptors in INI or IDI isoforms to produce stable cell lines. Cells were then treated with vehicle (control), 5-HT, olanzapine (antagonist), and SB206553 (inverse agonist) for 30 minutes or 1 hour. Treated cells were lysed, proteins were separated by SDS-PAGE, and levels of phosphorylated JAK2 and STAT3 were analyzed using western blots. In cells treated for 30 minutes with vehicle, phosphorylation of STAT3 was observed in cells transfected with the 5-HT2C receptor but not in untransfected cells indicating constitutive phosphorylation of STAT3 by the 5-HT2C receptor. Upon treatment with serotonin, phosphorylated levels of STAT3 were increased in cells expressing the 5-HT2C receptor while STAT3 phosphorylation was completely blocked with cells treated with olanzapine or SB206553. Phosphorylated levels of JAK2 were unaffected across all treatments. Phosphorylated STAT3 levels showed similar patterns in cells expressing the 5-HT2C receptor when treated for 1 hour with serotonin but olanzapine loses its inverse agonist properties. These findings indicate that both IDI and INI 2C receptors are activating STAT3, possibly independently of JAK2, but with differences between acute and chronic treatment. Human serotonin 2C receptor may be involved in cell growth, differentiation, transcription of other STAT genes, and immune response. Future studies will examine different edited isoforms of the 5-HT2C receptor and whether STAT3 activation is dependent or independent of G-protein activation to elucidate the phosphorylation mechanism of STAT3 by the human 5-HT2C receptors.
"Comparison of STAT3 Phosphorylation Between IDI Versus INI Isoforms and Acute Versus Chronic Treatment of the Human Serotonin 2C Receptor"
ETD Collection for Tennessee State University.