Coupling of neuronal 5‐HT₇ receptors to activation of extracellular‐regulated kinase through a protein kinase A‐independent pathway that can utilize Epac

Abstract

The roles of 3¢,5¢-cyclic adenosine monophosphate (cAMP) and protein kinase A in 5-hydroxytryptamine (5-HT) 7 receptormediated activation of extracellular-regulated kinase (ERK) were studied in cultured hippocampal neurons and transfected PC12 cells. Activation of ERK by neuronal G s -coupled receptors has been thought to proceed through a protein kinase A-dependent pathway. In fact we identified coupling of 5-HT 7 receptors to activation of adenylyl cyclase and protein kinase A. However, no inhibition of agonist-stimulated ERK activation was found when cells were treated with H-89 and KT5720 at concentrations sufficient to completely inhibit activation of protein kinase A. However, activation of ERK was found to be sensitive to the adenylyl cyclase inhibitor 9-(tetrahydrofuryl)-adenine, suggesting a possible role for a cAMP-guanine nucleotide exchange factor (cAMP-GEF). Co-treatment of cells with 8-(4-chlorophenylthio)-2¢-O-methyladenosine 3¢,5¢-cyclic monophosphate, a direct activator of the cAMP-GEFs Epac1 and 2, reversed the inhibition of agonist-stimulated ERK activation induced by adenylyl cyclase inhibition. Additionally, over-expression of Epac1 enhanced 5-HT 7 receptor-mediated activation of ERK. These results demonstrate that the activation of ERK mediated by neuronal G s -coupled receptors can proceed through cAMP-dependent pathways that utilize cAMP-GEFs rather than protein kinase A.

Low Nociceptor GRK2 Prolongs Prostaglandin E2Hyperalgesia via Biased cAMP Signaling to Epac/Rap1, Protein Kinase Cε, and MEK/ERK

“…It is also possible, however, that PKC and MEK are part of the same pathway and one is downstream of the other. At present, there is no evidence that activation of Epac by cAMP can lead to direct activation of MEK/ERK pathway in vitro (Enserink et al, 2002;Lin et al, 2003;Gelinas et al, 2008). Consistently, we observed a small 8-pCPTinduced increase in p-ERK in GRK2-deficient cells but not in WT cells.…”

Fluoxetine inhibits the extracellular signal regulated kinase pathway and suppresses growth of cancer cells

“…It has been shown that serotonin activates ERK1/2 kinases through 5-HT1A receptors in cultured human peripheral blood mononuclear cells, 24 and through 5-HT1B in neuroblastoma cells. 25 In smooth muscle cells, 26,27 mesangial cells 7,28 and PC12 cells 29 30 Serotonin-stimulated 5-HT7 receptors were found to activate ERK1/2 kinases in hippocampal neurons, 31 in COS-7 and HEK293 cells. 32 Upon stimulation, ERK1/2 are phosphorylated and translocate to the cell nucleus where they can phosphorylate and activate transcription factors including c-Myc, 33 and ELK or, through the cytoplasmic kinase p90Rsk, the transcription factor cAMP response binding protein (CREB).…”

The 5-HT7 receptor triggers cerebellar long-term synaptic depression via PKC-MAPK

“…cAMP causes in turn activation of MAPK such as the extracellular-regulated kinase (ERK1/2; Lin et al, 2003). In addition, there is evidence that 5-HT7R can also activate PKC indicating that the same receptor may contribute to different signaling pathways besides the canonical PKA downstream pathway (Lieb et al, 2005).…”