5-HT4R, 5-HT6R, and 5-HT7AR are three constitutively active Gs-coupled 5-HT receptors that have key roles in brain development, learning, memory, cognition, and other physiological processes in the central nervous system. In addition to Gs signaling cascade mediated by these three 5-HT receptors, the ERK1/2 signaling which is dependent on cyclic adenosine monophosphate (cAMP) production and protein kinase A (PKA) activation downstream of Gs signaling has also been widely studied. In this study, we investigated these two signaling pathways originating from the three Gs-coupled 5-HT receptors in AD293 cells. We found that the phosphorylation and activation of ERK1/2 are ligand-induced, in contrast to the constitutively active Gs signaling. This indicates that Gs signaling alone is not sufficient for ERK1/2 activation in these three 5-HT receptors. In addition to Gs, we found that β-arrestin and Fyn are essential for the activation of ERK1/2. Together, these results put forth a novel mechanism for ERK1/2 activation involving the cooperative action of Gs, β-arrestin, and Fyn.
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This work was supported in part by the National Natural Science Foundation (31770796 to Yi Jiang), the National Science and Technology Major Project (2018ZX09711002-002-002 to Yi Jiang), the Ministry of Science and Technology of China (XDB08020303 to H. Eric Xu), the K.C. Wong Education Foundation (to Yi JIANG), the Youth Innovation Promotion Association of CAS (to Yi Jiang), and the Outstanding Young Scientist Foundation (CAS, to Yi Jiang).
PL conducted the experiments and wrote the first draft of the paper; Y-lY, TW, LH, X-xW, MW, and G-gZ performed the experiments; PL, YS, and YJ analyzed the results; HEX and YJ supervised the project and wrote the manuscript, with contributions from all the authors.
The authors declare no competing interests.