BACKGROUND AND PURPOSE:

Heteromerization of G protein-coupled receptors is key on the integration of extracellular signals and the subsequent cell response via several mechanisms including heteromer-selective ligand binding, trafficking and/or downstream signaling. Considering the modulatory impact of the lysophosphatidylinositol G protein-coupled receptor 55 (GPR55) on the function of cannabinoid receptor subtype 2 (CB2 R) in human neutrophils, a potential heteromerization of CB2 R and GPR55 was hypothesized.

EXPERIMENTAL APPROACH:

Direct interaction of human GPR55 and CB2 R heterologously expressed in HEK293 cells was assessed by co-immunoprecipitation and bioluminescence resonance energy transfer (BRET) assays. Moreover, the cross-talk on signaling was investigated at downstream levels by label-free real-time methods (Epic dynamic mass redistribution and CellKey impedance assays), ERK1/2-MAP kinase activation and gene reporter assays.

KEY RESULTS:

GPR55 and CB2 R colocalize on the surface of human embryonic HEK293 cells, co-precipitate in membrane extracts and form heteromers in living HEK293 cells. Whereas heteromerization leads to a reduction of GPR55-mediated activation of transcription factors (NFAT, NF-κB and CRE), the ERK1/2-MAP kinase activation is potentiated in the presence of CB2 R. CB2 R-mediated signaling is also affected by co-expression with GPR55. Moreover, label-free assays confirmed a cross-talk between the two receptors.

CONCLUSIONS AND IMPLICATIONS:

In HEK293 cells expressing GPR55 and cannabinoid CB2 R receptors, heteromers that are unique signaling units are formed. The signaling by agonists of either receptor is governed i) by the presence or absence of the partner receptors (with the consequent formation of heteromers) and ii) by the activation state of the partner receptor.
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