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Regulation of STAT3 activity by G16-coupled receptors
Eddy H T Wu1, Rico K H Lo, Yung H Wong
1Department of Biochemistry, The Molecular Neuroscience Center, and The Biotechnology Research Institute, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Abstract:
A number of G protein-coupled receptors (GPCRs) have been shown to stimulate signal transducers and activators of transcription (STAT) activities while STAT3 activation by G alpha(o) can lead to neoplastic transformation in fibroblasts. In the present study we examined the ability of GPCRs to activate STAT3 via G alpha(16), a G alpha subunit which is primarily expressed in hematopoietic cells. In HEK 293 cells expressing a STAT3-driven luciferase reporter, the G alpha(16)-coupled ORL(1) and fMLP receptors stimulated luciferase activity upon activation by their agonists. Agonist-induced STAT3 activity required coexpression of G alpha(16) and was resistant to PTX treatment. Upon activation of the ORL(1) and fMLP receptors, phosphorylation of STAT3 at Tyr(705) was detected by immunoblot analysis. Additional experiments indicated that GPCR-mediated STAT3 activation was dependent on JAK and Raf1 signaling, but did not require phosphatidylinositol 3-kinase. This is the first study that demonstrates the stimulatory effect of ORL(1) and fMLP receptors on STAT3 activity.
Insights
G protein-coupled receptors (GPCRs) can activate signal transducers and activators of transcription 3 (STAT3). This study shows that GPCRs, specifically ORL(1) and fMLP receptors, activate STAT3 via G alpha(16) in hematopoietic cells.
Area of Science:
- Molecular Biology
- Cell Signaling
- Immunology
Background:
- G protein-coupled receptors (GPCRs) are known to modulate Signal Transducers and Activators of Transcription (STAT) pathways.
- STAT3 activation by G alpha(o) signaling has been linked to neoplastic transformation.
- The role of G alpha(16) in GPCR-mediated STAT activation, particularly in hematopoietic cells, remains underexplored.
Purpose of the Study:
- To investigate the ability of GPCRs to activate STAT3 through the G alpha(16) subunit.
- To determine if specific GPCRs, namely ORL(1) and fMLP receptors, can stimulate STAT3 activity via G alpha(16).
Main Methods:
- Utilized HEK 293 cells co-expressing a STAT3-driven luciferase reporter and G alpha(16).
- Assessed receptor activation using specific agonists for ORL(1) and fMLP receptors.
- Confirmed STAT3 phosphorylation at Tyr(705) via immunoblot analysis.
- Investigated signaling pathway involvement using JAK and Raf1 inhibitors, and assessed phosphatidylinositol 3-kinase (PI3K) requirement.
Main Results:
- Activation of G alpha(16)-coupled ORL(1) and fMLP receptors by their agonists significantly stimulated STAT3-driven luciferase activity.
- Agonist-induced STAT3 activation was dependent on the coexpression of G alpha(16) and was resistant to pertussis toxin (PTX) treatment.
- Phosphorylation of STAT3 at Tyr(705) was observed upon ORL(1) and fMLP receptor activation.
- GPCR-mediated STAT3 activation was found to be dependent on Janus Kinase (JAK) and Raf1 signaling pathways, but independent of PI3K.
Conclusions:
- This study provides the first evidence that ORL(1) and fMLP receptors can stimulate STAT3 activity through G alpha(16) signaling.
- GPCR-mediated STAT3 activation involves JAK and Raf1, highlighting a novel signaling axis in hematopoietic cells.
- These findings contribute to understanding GPCR signaling networks in immune cell function and potential disease states.