Signal Transducer and Activator of Transcription 3 Activation by the δ-Opioid Receptor via Gα₁₄Involves Multiple Intermediates

Abstract

The hematopoietic-specific G␣ 14 links a variety of G proteincoupled receptors to phospholipase C␤ (PLC␤) stimulation. Recent studies reveal that several G␣ subunits are capable of activating signal transducer and activator of transcription (STAT) proteins. In the present study, we investigated the mechanism by which G␣ 14 mediates receptor-induced stimulation of STAT3. In human embryonic kidney 293 cells, coexpression of G␣ 14 with ␦-opioid receptor supported [D-Pen 2 ,]enkephalin (DPDPE)-induced STAT3 phosphorylations at both Tyr 705 and Ser 727 in a pertussis toxin-insensitive manner. The constitutively active G␣ 14 QL mutant also induced STAT3 phosphorylations at these sites and promoted STAT3-dependent luciferase activity. Requirements for PLC␤, protein kinase C (PKC), and calmodulin-dependent kinase II (CaMKII) in G␣ 14 QL-induced STAT3 activation were demonstrated by their respective inhibitors as well as by coexpression of their dominant-negative mutants. Inhibition of c-Src and Janus kinase 2 and 3 activities abolished STAT3 activation induced by G␣ 14 QL, but no physical association between G␣ 14 QL and c-Src could be detected by coimmunoprecipitation. Various intermediates along the extracellular signal-regulated kinase signaling cascade were apparently required for G␣ 14 QL-induced STAT3 activation; they included Ras/Rac1, Raf-1, and mitogen-activated protein kinase kinase-1/2. In contrast, functional blockade of c-Jun N-terminal kinase, p38 mitogen-activated protein kinase, and phosphatidylinositol-3 kinase had no effect on G␣ 14 QL-induced responses. PLC␤, PKC, and CaMKII were shown to be involved in G␣ 14 QL-mediated c-Src phosphorylation. Similar results were obtained with human erythroleukemia cells upon DPDPE treatment. These results demonstrate for the first time that G␣ 14 activation can lead to STAT3 stimulation via a complex signaling network involving multiple intermediates.

Prostacyclin receptor-induced STAT3 phosphorylation in human erythroleukemia cells is mediated via Gαs and Gα16 hybrid signaling

“…indeed plays a critical role in STAT3 Ser 727 phosphorylation in human T cells (Fung et al, 2003) (Lo et al, 2003;Lo and Wong, 2004). Our results do conform to such a postulation (Fig.…”

“…One particular feature of HEL cells is the endogenous expression of both Gα 16 and Gα 14 , members of the G q family of G proteins (Lo et al, 2003;Lo and Wong, 2004). Since these promiscuous Gα subunits (Ho et al, 2001;Offermanns and Simon, 1995) are capable of mediating GPCR-induced activation of STAT3 (Lo et al, 2003;Lo and Wong, 2004), they could provide a functional linkage between hIP and STAT3. We thus adopted a well established transient recombinant system (Yung et al, 1999) to examine the ability of these PTX-insensitive G q proteins to interact with hIP.…”

“…Gα o and Gα i2 (Ram et al, 2000) and PTX-insensitive Gα s (Liu et al, 2006), Gα 16 (Lo et al, 2003), and Gα 14 (Lo and Wong, 2004). In HEL cells, the G 16 -coupled complement C5a receptor (C5aR) activates STAT3 through multiple pathways including the PLCβ/PKC/Raf-1/MEK/ERK axis (Lo et al, 2003).…”

“…2A Since hIP can interact productively with Gα q members to activate PLCβ ( Fig. 2A), and that G q members can activate STAT3 through the PLCβ signaling cascades (Lo et al, 2003;Lo and Wong, 2004), cicaprost might well employ the PLCβ pathway to activate STAT3. To determine if cicaprost-induced STAT3 activation can be mediated along the PLCβ cascade, HEL cells were pretreated with various inhibitors (10 µM U73122, 10 µM KN62 or 100 nM calphostin C) or their inactive analogues (10 µM U73343 or 10 µM KN92) for 30 min prior to cicaprost treatment.…”

CCR1-Mediated STAT3 Tyrosine Phosphorylation and CXCL8 Expression in THP-1 Macrophage-like Cells Involve Pertussis Toxin-Insensitive Gα14/16 Signaling and IL-6 Release

“…CCR1 agonists were found to induce gene expression of the STAT-inducible protooncogene, c-fos (18). c-Fos expression and transcriptional activation is induced upon Ga 16 activation (19), and constitutively active mutants of Ga 14 and Ga 16 were demonstrated to enhance the activity of STAT3 in cotransfection systems (20,21). The coexistence of Ga 14/16 and CCR1, as well as their demonstrated functional coupling in THP-1 macrophage-like cells (2,(22)(23)(24)(25)(26), suggests that CCR1 may use Ga 14/16 to stimulate STAT3.…”