Specificity and nanomolar potency of melatonin on G-protein coupled melatonin MT1 and MT2 receptors expressed in HEK-293T human embryo kidney cells

Abstract

This is a pre-registered study, i.e. a study whose hypotheses and experiments designed to address these hypotheses have been deposited in a database before starting the experiments. The study aims at assessing the Gs versus Gi coupling and the potency of melatonin in the human version of melatonin MT1 and MT2 G-protein-coupled receptors expressed in HEK-293T cells. The results show that these receptors are Gi but not Gs coupled. By using a standard procedure of modulation of 0.5 µM forskolin-induced cAMP levels, it was found that the potency on MT2 receptor-mediated actions is in the low nanomolar range, but the potency on MT1 receptor is in the high nanomolar range. The potency of melatonin to stimulate the MT2 receptor is similar to that of a selective agonist, N-[2-(2-methoxy-6H-isoindolo[2,1-a]indol-11-yl)ethyl]butanamide (IIK7). Overall, the data on the potency of melatonin on its receptors will provide a new look for melatonin research. It is important to consider this finding for appropriately addressing physiological or therapeutic effects based on melatonin potency. Thus, the low doses of melatonin used in the existing prolonged release preparations or in other supplements should be revisited.

Expression of Melatonin and Dopamine D3 Receptor Heteromers in Eye Ciliary Body Epithelial Cells and Negative Correlation with Ocular Hypertension

“…Thus, activation of these receptors leads to a decrease in cytosolic cAMP levels. We have confirmed that this is the case in single transfected cells (Appendix A Figure A1B,C; see also our recent report [52]), thereby reproducing data reported in References [34,53]. HEK-293T cells expressing D 3 R or MT 1 and incubated with the selective agonists, 7-OH-PIPAT for D 3 and melatonin for MT 1 , led to significant decreases in the forskolin-induced cytosolic cAMP levels.…”

“…Based on prototypic heteromer prints that occur similarly in heterologous expression systems and natural cell lines, and by further confirmation in natural sources by PLA, we discovered novel physiologically relevant receptor-receptor interactions. The D 3 R, expressed in ciliary body epithelial cells, may interact with either MT 1 R or MT 2 R. Canonical coupling of melatonin receptors individually expressed in a heterologous system is to Gi (see References [25,52] and references therein). Dopamine receptors are either coupled to Gs (D 1 and D 5 ) or Gi (D 2 , D 3 and D 4 ).…”

The potential anti-cancer effects of melatonin on breast cancer

“…These are membrane-bound GTP-binding protein (G-protein) coupled receptors (GPCRs). They modulate the activity of the variety of G-proteins, including Giα2, Giα3, Gαq, and Gα11 [20,21]. Moreover, melatonin acts directly to the DNA binding nuclear receptors (NRs) [retinoid-related orphan receptor (ROR)-α/isoforms of nuclear receptors of retinoic acid receptor superfamily (RZR)].…”