Proposed schizophrenia-related gene polymorphism: expression of the Ser9Gly mutant human dopamine D3 receptor with the Semliki Forest virus system.

Homozygotes for a BalI polymorphism resulting in the Ser9Gly mutation in the human dopamine D3 receptor gene are suggested to display a twofold higher risk of schizophrenia. The cDNAs for this mutant and the wildtype receptor were introduced into the pSFV1C vector and recombinant Semliki Forest virus particles generated. CHO cells infected with SFV-D3 virus resulted in high level expression of recombinant receptor. Double infections with wildtype and Ser9Gly dopamine D3 SFV stocks generated an artificial heterozygote in CHO cells. Receptor binding analysis of several structurally different dopamine D3 ligands showed similar pharmacological properties for all compounds tested except for dopamine and the D3-selective ligand GR99841. A significantly higher dopamine binding affinity for the Ser9Gly homozygote was detected. The heterozygote binding did not differ from the wildtype. However, both the homo- and heterozygote for Ser9Gly showed significantly higher binding activity for GR99841 compared to the D3 wildtype.