Characterization of a metabotropic glutamate receptor type 5-green fluorescent protein chimera (mGluR5-GFP): Pharmacology, surface expression, and differential effects of Homer-1a and Homer-1c

Metabotropic glutamate receptor 5 (mGluR5) can modulate synaptic transmissi on by increasing intracellular Ca2+ and it plays a role in several forms of synaptic plasticity. We have constructed a fusion of human mGluR5 and gree n fluorescent protein (mGluR5-GFP). Expression of mGluR5-GFP in clonal cell lines yielded a functional fluorescent receptor with pharmacological profi les similar to wild-type mGluR5. mGluR5-GFP coimmunoprecipitated with Homer -1c, indicating that addition of GFP to the C-terminal did not prevent Home r binding. Coexpression of wild-type mGluR5 or mGluR5-GFP with Homer 1c, bu t not Homer-1a, resulted in reduced receptor surface localization and the f ormation of intracellular clusters. Neither Homer-1a nor Homer-1c had any e ffect on mGluR1 or mGluR1-GFP distribution. mGluR5-GFP expressed alone or i n combination with Homer-1a formed dimers in HEK cells. Coexpression with H omer-1c, however, prevented mGluR5-GFP dimerization. Neither Homer altered the agonist profiles of mGluR5 or mGluR5-GFP. These data indicate that the functional expression of mGluR5 is regulated by Homer-1c and demonstrate th at mGluR5-GFP provides a useful tool to study the molecular pharmacology an d cell biology of mGluRs in real-time.