Melatonin receptor heterodimerization in a photoreceptor-like cell line endogenously expressing melatonin receptors

Abstract

Purpose: Melatonin signaling plays an important role in the modulation of retinal physiology and photoreceptor viability during aging. In this study, we investigated whether 661W cells-a photoreceptor-like cell that endogenously expresses melatonin receptor type 1 (MT₁) and melatonin receptor type 2 (MT₂) receptors-represent a useful model for studying the biology of heterodimerization and signaling of MT_1/2 receptors.

Methods: 661W cells were cultured, and MT₁/MT₂ heterodimerization in 661W cells was assessed with proximity ligation assay. MT₂ was removed from the 661W cells using the MT₂-CRISPR/Cas9 system. Melatonin receptor signaling was investigated by measuring cAMP levels and activation of the AKT-FoxO1 pathway.

Results: The results demonstrated that heterodimerization of MT₁ and MT₂ receptors occurs in 661W cells. The pathways activated by MT₁/MT₂ heterodimer (MT_1/2h) in 661W cells are similar to those previously reported in mouse photoreceptors. Disruption of the heterodimer formation by genetically ablating MT₂ from 661W cells abolished the activation of melatonin signaling in these cells.

Conclusions: The data indicated that in 661W cells, MT₁ and MT₂ receptors are functional only when they are associated in a heteromeric complex, as occurs in mouse photoreceptors. 661W cells represent a useful model for studying the mechanism underlying MT₁/MT₂ heterodimerization.