Scaffolds between MT2 melatonin receptors, Gi, βarrestins, MEK and ERK form in differentiating bone stem cells and these processes require internalization; domains found in the C‐tail of the receptor

Melatonin induces bone stem cell differentiation into osteoblasts dependent upon desensitized MT 2 receptors (MT 2 R), internalization processes and MEK (1/2). Since GPCRs can modulate MEK/ERK (1/2) through a β‐arrestin‐dependent pathway, the objectives of this study were (1) to assess if scaffolds between MT 2 R, G‐proteins, β‐arrestins, and MEK and ERK (1/2) could form in the bone stem cell using immunoprecipitation analysis, (2) to determine if melatonin could still modulate ERK translocation in the cell even if MT 2 R are desensitized using immunocytochemistry and (3) to determine the MT 2 R domains involved with its desensitization using mutagenesis. Our results show that human MT 2 R scaffold with β arrestins, and MEK/ERK (1/2) that are blocked in the presence of luzindole. Our data also show that melatonin can promote ERK translocation from the cytoplasm to the nucleus even if all other measures suggest that the MT 2 R are desensitized. Also, our data show that truncation mutations in the C‐tail of MT 2 R (MT 2 Y7.64GFP) prevent melatonin‐induced MT 2 R internalization. Perhaps, the C‐tail functions to internalize these MT 2 R/β‐arrestin scaffolds to activate ERK and thus promote melatonin‐induced bone stem cell differentiation into an osteoblast. This study was supported by the Pennsylvania Health Assessment Fund awarded to PWE, and the AFPE fellowship awarded to NMR