Angiotensin II-induced Tyrosine Phosphorylation of Signal Transducers and Activators of Transcription 1 Is Regulated by Janus-activated Kinase 2 and Fyn Kinases and Mitogen-activated Protein Kinase Phosphatase 1

Abstract

Angiotensin II (Ang II) AT 1 receptors on vascular smooth muscle cells (VSMCs) are coupled to the Janusactivated kinase (JAK)/signal transducers and activators of transcription (STAT) pathway. We have shown previously that Ang II stimulation of VSMCs results in the tyrosine phosphorylation of JAK2 and STAT1 and the translocation of STAT1 to the nucleus. In the present study, we demonstrate using specific enzyme inhibitors and antisense oligonucleotides that both JAK2 and p59 Fyn tyrosine kinases are required for the Ang II-induced tyrosine phosphorylation and nuclear translocation of STAT1 in VSMCs. Neither tyrosine kinase, however, appears to function upstream from the other in a phosphorylation cascade. Rather, p59 Fyn functions as an Ang II-activated docking protein for both JAK2 and STAT1, a docking interaction that may facilitate JAK2-mediated STAT1 tyrosine phosphorylation. In this study, we have also identified the nuclear dual-specificity phosphatase mitogen-activated protein kinase phosphatase 1 as the enzyme responsible for STAT1 tyrosine dephosphorylation in VSMCs.Cytokine signal transduction in hematopoietic cells includes the activation of latent transcription factors termed signal transducers and activators of transcription (STATs).1 Seven mammalian STATs are known, referred to as STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B, and STAT6 (1). STAT proteins are activated by direct phosphorylation by cytokine receptor-associated tyrosine kinases called Janus-activated kinases (JAKs). The JAK family of tyrosine kinases includes four members known as JAK1, JAK2, JAK3, and Tyk2 (2, 3). JAKs are activated by cytokine-induced tyrosine phosphorylation. The STATs are subsequently tyrosine-phosphorylated by JAKs, accompanied by STAT homo-or heterodimerization and the translocation of STAT dimers to the nucleus, where STATs activate gene transcription through binding to specific response elements in gene promoters. Recent reports have also implicated the Src family of tyrosine kinases in the phosphorylation and activation of STAT proteins (4 -9). A role for serine phosphorylation in the activation of STATs has also been suggested (10, 11). STAT activation is transient in nature and is likely terminated by STAT tyrosine dephosphorylation because the tyrosine phosphatase inhibitor pervanadate prolongs STAT activation in cells treated with the inhibitor (12-14). However, the specific tyrosine phosphatase (or phosphatases) that participates in STAT dephosphorylation has not been identified.The JAK/STAT pathway is also utilized in signaling by the G-protein-coupled angiotensin II (Ang II) AT 1 receptor in both vascular smooth muscle cells (VSMCs) and cardiac myocytes (15-23). We have shown previously that Ang II stimulation of VSMCs induces the rapid and transient tyrosine phosphorylation of JAK2. Ang II-induced JAK2 phosphorylation is accompanied by an increased association of the enzyme with the AT 1 receptor and an increase in enzyme catalytic activity. In addition, Ang II induces the tyrosine phosphorylation of ST...

Hyperglycemia Enhances Angiotensin II-induced Janus-activated Kinase/STAT Signaling in Vascular Smooth Muscle Cells

“…We have shown previously that STAT1 is tyrosine-phosphorylated and that STAT3 is both tyrosine-and serine-phosphorylated in VSMCs in response to Ang II stimulation (12,14,15). To determine whether HG alters either the basal or the Ang II-induced tyrosine or serine phosphorylation of STAT1 or STAT3, we carried out immunoblotting experiments with phosphospecific antibodies that recognize either the tyrosine-or the serine-phosphorylated, but not the nonphosphorylated, forms of STAT1 and STAT3.…”

“…Immunoprecipitation and Immunoblotting-Immunoprecipitation and immunoblotting were carried out as described previously (13)(14)(15).…”

“…We have also demonstrated that Ang II-induced JAK2 tyrosine phosphorylation is regulated by the protein-tyrosine phosphatases known as SHP-1 and SHP-2 (13) and that phosphorylation of JAK2 is accompanied by the tyrosine and/or serine phosphorylation of STAT1 and STAT3 and translocation of the two proteins to the nucleus (12,14,15). This signaling cascade appears to be essential to Ang II induction of VSMC proliferation, because treatment of VSMCs with the JAK2 inhibitor, AG-490, or electroporation of anti-STAT1 or anti-STAT3-neutralizing antibodies completely blocks Ang II induction of cell proliferation (8).…”

GIT1 Mediates Src-dependent Activation of Phospholipase Cγ by Angiotensin II and Epidermal Growth Factor

“…AngII-mediated growth effects in VSMC also require the rapid activation of phospholipase C␥ (PLC␥) and mobilization of intracellular calcium (12)(13)(14). Early growth response genes induced by AngII such as c-fos and c-myc require calcium mobilization and activation of AP-1-dependent transcription.…”

Expression of G Protein-Coupled Receptor 19 in Human Lung Cancer Cells Is Triggered by Entry into S-Phase and Supports G2–M Cell-Cycle Progression

“…Further progress in this area is contingent on the identification of the cognate agonist(s) of GPR19. Finally, a function other than direct signaling via G proteins might also be conceivable for GPR19, e.g., recruiting G protein-independent pathways via b-arrestins (50), via direct binding of tyrosine kinases (51), or by acting as a scaffolding protein (52).…”