Melatonin MT1 and MT2 receptor ERK signaling is differentially dependent on Gi/o and Gq/11 proteins

J Pineal Res. 2020 May;68(4):e12641. doi: 10.1111/jpi.12641. Epub 2020 Mar 6.

Abstract

G protein-coupled receptors (GPCRs) transmit extracellular signals into cells by activating G protein- and β-arrestin-dependent pathways. Extracellular signal-regulated kinases (ERKs) play a central role in integrating these different linear inputs coming from a variety of GPCRs to regulate cellular functions. Here, we investigated human melatonin MT1 and MT2 receptors signaling through the ERK1/2 cascade by employing different biochemical techniques together with pharmacological inhibitors and siRNA molecules. We show that ERK1/2 activation by both receptors is exclusively G protein-dependent, without any participation of β-arrestin1/2 in HEK293 cells. ERK1/2 activation by MT1 is only mediated though Gi/o proteins, while MT2 is dependent on the cooperative activation of Gi/o and Gq/11 proteins. In the absence of Gq/11 proteins, however, MT2 -induced ERK1/2 activation switches to a β-arrestin1/2-dependent mode. The signaling cascade downstream of G proteins is the same for both receptors and involves activation of the PI3K/PKCζ/c-Raf/MEK/ERK cascade. The differential G protein dependency of MT1 - and MT2 -mediated ERK activation was confirmed at the level of EGR1 and FOS gene expression, two ERK1/2 target genes. Gi/o /Gq/11 cooperativity was also observed in Neuroscreen-1 cells expressing endogenous MT2 , whereas in the mouse retina, where MT2 is engaged into MT1 /MT2 heterodimers, ERK1/2 signaling is exclusively Gi/o -dependent. Collectively, our data reveal differential signaling modes of MT1 and MT2 in terms of ERK1/2 activation, with an unexpected Gi/o /Gq/11 cooperativity exclusively for MT2 . The plasticity of ERK activation by MT2 is highlighted by the switch to a β-arrestin1/2-dependent mode in the absence of Gq/11 proteins and by the switch to a Gi/o mode when engaged into MT1 /MT2 heterodimers, revealing a new mechanism underlying tissue-specific responses to melatonin.

Keywords: ERK; GPCR; Gi/o protein; Gq/11 protein; MT1; MT2; melatonin receptors.

MeSH terms

  • Animals
  • GTP-Binding Proteins / metabolism*
  • HEK293 Cells
  • Humans
  • MAP Kinase Signaling System / physiology*
  • Mice
  • Mice, Inbred C57BL
  • Receptor, Melatonin, MT1 / metabolism*
  • Receptor, Melatonin, MT2 / metabolism*
  • Receptors, G-Protein-Coupled / metabolism

Substances

  • Receptor, Melatonin, MT1
  • Receptor, Melatonin, MT2
  • Receptors, G-Protein-Coupled
  • GTP-Binding Proteins