EXPRESSION OF DOPAMINE D-3 RECEPTOR DIMERS AND TETRAMERS IN BRAIN ANDIN TRANSFECTED CELLS

The expression and characteristics of the dopamine D-3 receptor protei n were studied in brain and in stably transfected GH3 cells, Monoclona l antibodies were used for immunoprecipitation and immunoblot experime nts. Immunoprecipitates obtained from primate and rodent brain tissues contain a low molecular weight D-3 protein and one or two larger prot ein species whose molecular mass are integral multiples of the low mol ecular weight protein and thus appear to have resulted from dimerizati on and tetramerization of a D-3 monomer, Whereas D-3 receptor multimer s were found to be abundantly expressed in brain, the major D-3 immuno reactivity expressed in stable D-3-expressing rat GH3 cells was found to be a monomer, However, multimeric D-3 receptor species with electro phoretic mobilities similar to those expressed in brain were also seen in D-3-expressing GH3 cells when a truncated D-3-like protein (named D-3nf) was coexpressed in these cells, Furthermore, results from immun oprecipitation experiments with D-3- and D-3nf-specific antibodies sho w that the higher order D-3 proteins extracted from brain and D-3/D-3n f double transfectants also contain D-3nf immunoreactivity, and immuno cytochemical studies show that the expression of D-3 and D-3nf immunor eactivities overlaps substantially in monkey and rat cortical neurons. Altogether, these data show oligomeric D-3 receptor protein expressio n in vivo and they suggest that at least some of these oligomers are h eteroligomeric protein complexes containing D-3 and the truncated D-3n f protein.