Heterodimerization and Subcellular Distribution of Melatonin and Cannabinoid Type 1 Receptors

Membrane receptors belonging to the G proteins coupled receptors (GPCRs) form the largest family of proteins in the human genome with more than 800 members. Until recently GPCRs functions were thought to occur only at the plasma membrane after activation upon binding of their cognate ligand. However evidences show that many functional GPCRs are found in intracellular compartments opening new direction of research to understand their roles in a cellular context. Among these intracellular compartments mitochondria are the latest organelle in which some GPCRs were identified. Melatonin receptor type 1 (MT1) and cannabinoid receptor type 1 (CB1) were identified in mouse neuronal mitochondria where they were shown to exert an inhibitory action on cytochrome c release (MT1) or on the respiratory chain (CB1). Using several techniques my current results describe a new cross-talk between MT1 and CB1 receptors. Confocal analysis of immunofluorescence experiments of cells coexpressing both receptors showed a high degree of colocalisation. A combination of coimmunoprecipitation experiments performed on extracts of transfected HEK293T or HeLa cell lines and immunodetection of receptors by Western-blot revealed that MT1 and CB1 receptors can physically interact to form heterodimers in absence of ligand. Heterodimers formation was also confirmed by Proximity Ligation Assay (PLA) experiments in live HEK293T and HeLa cells. Confocal analysis revealed a colocalisation of PLA staining with the mitochondrial marker TOMM20. Experiments in relation with the functional role of MT1 and CB1 in mitochondria are ongoing.