Sorting nexin‐25 interacts with D1 and D2 dopamine receptors to regulate receptor expression and signaling

Abstract

Our studies employing co‐immunoprecipitation assays for dopamine receptors (DARs) coupled with mass spectrometry‐based sequencing have identified sorting nexin‐25 as a member of the DAR signalplex. Mammalian sorting nexins (SNXs) have been suggested to regulate intracellular trafficking, internalization, and endosomal recycling or sorting of membrane‐bound cargo. The physiological role of SNX25 is unknown. Using RT‐PCR we have found that SNX25 is expressed in multiple tissues including brain and kidney and that the endogenous isoform is longer than the one indicated in GenBank. The full‐length SNX25 contains two putative transmembrane‐spanning regions and confocal microscopy shows that it is localized in distinct clusters at or near the plasma membrane. When SNX25 is over‐expressed with DARs, the receptors show changes in expression patterns and appear localized to the SNX25 clusters. Over‐expression of SNX25 perturbed both endocytosis and recycling of the D2 DAR. Radioligand binding also show that the expression levels of both D1 and D2 DARs are increased with SNX25 over‐expression. Decreasing the levels of endogenous SNX25 using siRNA causes a subsequent decrease in DAR expression. These data suggest that SNX25 plays a role in DAR trafficking through intracellular membrane compartments and regulates both receptor expression and signaling.