Multi-component signaling complexes of the δ-opioid receptor with STAT5B and G proteins

Besides mediating opioid responses in the nervous system and the peripheral tissues, opioid receptors are implicated in signaling mechanisms shared by cytokine receptors. Recent observations have shown that the Signal Transducer and Activator of Transcription 5A (STAT5A) interacts with the μ-opioid receptor (μ-OR) and is phosphorylated upon μ-OR stimulation (Mazarakou and Georgoussi, 2005). In the present study we demonstrate that another member of the STAT family, STAT5B, associates constitutively with the C-terminal tail of the δ-opioid receptor (δ-CT). [D-Ser2, Leu5, Thr6]-enkephalin-exposure of HEK293 cells, expressing stably the δ-opioid receptor (δ-OR), leads to receptor-dependent STAT5B tyrosine phosphorylation and transcriptional activation. This phosphorylation occurs in a G protein-dependent manner and is carried out by a c-Src kinase. Co-immunoprecipitation studies indicate that STAT5B forms pairs with selective Gα and Gβγ subunits of G proteins and activated c-Src kinase in HEK293 cells. These interactions are formed either constitutively, or upon receptor stimulation. We also demonstrate that the δ-CT serves as a platform for the formation of a multi-component signaling complex (signalosome), consisting of STAT5B, c-Src and selective G protein members. We can thus conclude that STAT5B signaling can be modulated by its coupling with a specific subset of G protein subunits, revealing a novel signaling mechanism for the transcriptional regulation of STAT5B-dependent genes.