L-DOPA Receptor GPR143 Functionally Couples with Adrenergic a_1B Receptor at the Second Transmembrane Interface

Adrenergic receptors (ADRs) are widely distributed in the peripheral and central nervous systems. We previously reported that L-3,4-dihydroxyphenylalanine (L-DOPA), the precursor of dopamine, sensitizes adrenergic a(1) receptor (ADRA1) through a G protein-coupled receptor GPR143. Chi-meric analysis, in which the transmembrane (TM) domains of GPR143 were replaced with those of GPR37, revealed that the second TM region was essential for the potentiation of phenyl-ephrine-induced extracellular signal-regulated kinase (ERK) phosphorylation by GPR143. In HEK293T cells expressing ADRA1B, phenylephrine-induced ERK phosphorylation was augmented by the co-expression of GPR143, compared to the mock vector. Immunoprecipitation analysis revealed that a synthetic transactivator of the transcription peptide fused with TM2 of GPR143 (TAT-TM2) disrupts the interaction between GPR143 and ADRA1B. This TAT-TM2 peptide sup-pressed the augmentation of phenylephrine-induced ERK phosphorylation by GPR143 in HEK293T cells co-expressing ADRA1B and GPR143. These results indicate that the in-teraction between GPR143 and ADRA1B is required for the potentiation of ADRA1B-mediated signaling by GPR143. The TM2 region of GPR143 is a crucial dimeric interface for the functional coupling between ADRA1B and GPR143.