ALTERNATIVE SPLICING OF THE DOPAMINE D2 RECEPTOR DIRECTS SPECIFICITY OF COUPLING TO G-PROTEINS

Two isoforms of the dopamine D2 receptor have been characterized, D2L (long) and D2S (short), generated by alternative splicing from the sam e gene, They differ by an in-frame insert of 29 amino acids specific t o D2L within the putative third intracytoplasmic loop of the receptor, We have previously demonstrated (Montmayeur, J.-P., Guiramand, J., an d Borelli, E. (1993) Mol. Endocrinol. 7, 161-170) that D2S and D2L, al though presenting very similar pharmacological profiles, couple differ ently to the alpha-subunit of guanine nucleotide-binding regulatory pr oteins (G-prateins). In particular, D2L, but not D2S, requires the pre sence of the alpha-subunit of the inhibitory G protein (G alpha i2) to elicit greater inhibition of adenylyl cyclase activity, The insert pr esent in D2L must therefore confer the specificity of interaction with G alpha i2. Thus, we introduced substitution mutations within the D2L insert, These mutant receptors were expressed in JEG3 cells, a G alph a i2-deficient cell line, scoring for those presenting an increased in hibition of adenylyl cyclase by dopamine, Our analysis identified two mutants, S259/262A and D249V, with these properties, These results dea rly show that the insert present in D2L plays a critical role in the s electivity for the G-proteins interacting with the receptor.