RECOMBINATION OF ENDOGENOUS D-2 DOPAMINE-RECEPTOR GENE WITH A METALLOTHIONEIN PROMOTER IN GH4C1 CELLS CONFERS FUNCTIONAL AND INDUCIBLE D-2 RESPONSE

We have previously shown that expression of a functional endogenous D- 2 short dopamine receptor is obtained in GH4C1 cells following transfe ction with a plasmid that confers resistance to neomycin (pRSVNeo) (Al lard et al. (1993) Biochem. Biophys. Res. Commun. 193, 801-807). In or der to better understand the mechanisms responsible for such a phenome non, we cloned and sequenced the 5' region of the D-2 gene present in native GH4C1 cells as well as the cDNA of transfected cells. No homolo gy with the published sequence of the rat D-2 dopamine receptor promot er was found; however, this region has perfect homology with the mouse metallothionein promoter. In cells expressing D-2 receptor, the promo ter is fully functional and can regulate dopaminergic D-2 receptor mRN A levels and receptor expression in a dose-dependent manner in the pre sence of Zn2+ or Cd2+. The receptor level is raised from 500 to 3000 f mol/mg of protein in the presence of 100 mu M of Zn2+. These results s uggest that in GK4C1 cells, a recombination between the mouse metallot hionein promoter and the D2 dopamine receptor took place. This system provides us with a cell line expressing an endogenous dopamine D-2 rec eptor in which the level of expression can be easily modulated.