Role of a Gαi2 protein splice variant in the formation of an intracellular dopamine D2 receptor pool

Abstract

Treatment of D2-receptor-expressing cells with specific drugs upregulates the receptor number at the cell surface independently of protein synthesis, leading to the concept of an intracellular receptor pool. However, how this pool is operating is still an enigma. Here, we report that a splice variant of the Gαi2 protein, protein sGαi2, plays a crucial role in the maintenance of this D2-receptor pool. Co-expression of sGi2 with D2 receptor reduced receptor localization to cell surface by one-third. This effect is associated with specific intracellular protein-protein interaction and the formation of a sGi2–D2-receptor complex. It has been suggested that the formation of this complex serves to prevent D2 receptors from reaching the cell membrane. Treatment of D2-receptor-expressing cells with agonists increased the number of cell surface D2 receptors and coincided with a reduction in these receptors from intracellular complexes, suggesting that agonist treatment released D2 receptors from the complex allowing them to localize to the cell membrane. Thus, in addition to elucidating how the intracellular pool of D2 receptor functions, our findings uncover a novel mechanism regulating the density of cell surface D2 receptors.

Signaling by dopamine regulates D2 receptors trafficking at the membrane

“…Interestingly, antibodies to both proteins revealed a strong labeling of intracellular compartments corresponding very likely to Golgi and endoplasmic reticulum ( Fig. 2A and B); 5,28 in addition, we observed an overlapping staining of D2Rs and sGi2 in primary striatal neurons in these compartments (Fig. 2C).…”

A dynamic expression pattern of sGαi2 protein during early period of postnatal rat brain development

“…In addition, it has been argued that protein–protein interaction is a crucial step during the maturation of synapses. Therefore, recent demonstration of sGαi2 protein capability in protein–protein interaction (Lopez‐Aranda et al, 2007) further strengthen the concept of participation of this protein in the synaptic maturation process.…”

“…The antibodies to sGαi2 were affinity purified as described earlier (Khan et al, 1993) and used in this study. Specificity of this affinity‐purified antibody has been determined with the use of brain tissues and transfected cells (Khan and Gutierrez, 2004; Lopez‐Aranda et al, 2007). The results of specificity tests of this antibody are published (see Fig.…”

“…Although the G(i2 mediated receptor signal transduction cascade operates exclusively at the plasma membrane, we and others have shown that its splice variant, sGai2, is an intracellular protein and is not localized at cellular plasma membrane (Khan and Gutierrez, 2004;Lopez-Aranda et al, 2007;Montmayeur and Borrelli, 1994;Picetti and Borrelli, 2000). The sG i2 transcript encodes a protein with different carboxyl-terminus where 24 amino acids carboxyl-terminal of G(i2 are replaced by a longer peptide of 35 amino acids.…”

“…It has also been shown that G proteins can influence the transport in secretory (Melancon et al, 1987) and endocytotic (Mayorga et al, 1989) pathways. Recently, it was shown that the sGαi2 protein not only participated in the formation of intracellular reservoir of D2 receptor but also regulated the receptor density of cell surface (Lopez‐Aranda et al, 2007). This activity was accounted to the protein–protein interaction of sGαi2 protein and intracellular entrapment of D2 receptor.…”