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Jak2 acts as both a STAT1 kinase and as a molecular bridge linking STAT1 to the angiotensin II AT1 receptor
M S Ali1, P P Sayeski, K E Bernstein
1Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Abstract:
Angiotensin II activates the Jak-STAT pathway via the AT(1) receptor. We studied two mutant AT(1) receptors, termed M5 and M6, that contain Y to F substitutions for the tyrosine residues naturally found in the third intracellular loop and the carboxyl terminus. After binding ligand, both the M5 and M6 AT(1) receptors trigger STAT1 tyrosine phosphorylation equivalent to that observed with the wild type receptor, indicating that angiotensin II-mediated phosphorylation of STAT1 is independent of these receptor tyrosine residues. In response to angiotensin II, Jak2 autophosphorylates on tyrosine, and Jak2 and STAT1 physically associate, a process that depends on the SH2 domain of STAT1 in vitro. Evaluation of the wild type, M5, and M6 AT(1) receptors showed that angiotensin II-dependent AT(1) receptor-Jak2-STAT1 complex formation is dependent on catalytically active Jak2, not on the receptor tyrosine residues in the third intracellular loop and carboxyl tail. Immunodepletion of Jak2 virtually eliminated the ligand-dependent binding of STAT1 to the AT(1) receptor. These data indicate that the association of STAT1 with the AT(1) receptor is not strictly bimolecular; it requires Jak2 as both a STAT1 kinase and as a molecular bridge linking STAT1 to the AT(1) receptor.
Insights
Angiotensin II activates the Jak-STAT pathway. The AT(1) receptor
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Receptor-mediated signal transduction
Background:
- Angiotensin II is a key hormone regulating blood pressure.
- The Jak-STAT pathway is crucial for cellular responses to various stimuli.
- The AT(1) receptor's role in Jak-STAT activation is not fully understood.
Purpose of the Study:
- To investigate the role of specific tyrosine residues in the AT(1) receptor during Angiotensin II-induced Jak-STAT activation.
- To elucidate the mechanism of STAT1 association with the AT(1) receptor.
Main Methods:
- Site-directed mutagenesis of AT(1) receptor tyrosine residues.
- Western blotting to assess STAT1 and Jak2 phosphorylation.
- Co-immunoprecipitation to study protein-protein interactions.
Main Results:
- STAT1 phosphorylation by Angiotensin II is independent of AT(1) receptor tyrosine residues.
- Jak2 kinase activity and its SH2 domain are essential for STAT1 association with the AT(1) receptor.
- Jak2 acts as a molecular bridge between STAT1 and the AT(1) receptor.
Conclusions:
- Angiotensin II-mediated STAT1 activation relies on Jak2's catalytic activity and scaffolding function.
- Specific tyrosine residues in the AT(1) receptor are not required for Jak-STAT pathway activation.
- Jak2 is essential for the physical association of STAT1 with the AT(1) receptor.