Alternative Splicing of the Dopamine D2 Receptor Directs Specificity of Coupling to G-proteins

The results clearly show that the insert present in D2L plays a critical role in the selectivity for the G-proteins interacting with the receptor.

Abstract

Two isoforms of the dopamine D2 receptor have been characterized, D2L (long) and D2S (short), generated by alternative splicing from the same gene. They differ by an in-frame insert of 29 amino acids specific to D2L within the putative third intracytoplasmic loop of the receptor. We have previously demonstrated (Montmayeur, J.-P., Guiramand, J., and Borelli, E. (1993) Mol. Endocrinol. 7, 161-170) that D2S and D2L, although presenting very similar pharmacological profiles, couple differently to the alpha-subunit of guanine nucleotide-binding regulatory proteins (G-proteins). In particular, D2L, but not D2S, requires the presence of the alpha-subunit of the inhibitory G-protein (G alpha i2) to elicit greater inhibition of adenylyl cyclase activity. The insert present 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 alpha i2-deficient cell line, scoring for those presenting an increased inhibition of adenylyl cyclase by dopamine. Our analysis identified two mutants, S259/262A and D249V, with these properties. These results clearly show that the insert present in D2L plays a critical role in the selectivity for the G-proteins interacting with the receptor.