Janus kinase 2 (Jak2) must be catalytically active to associate with the AT1 receptor in response to angiotensin II.

Angiotensin II evokes a variety of biological responses by binding to a seven transmembrane cell surface receptor termed AT1. Ligand binding to the AT1 receptor induces the physical association and activation of the intracellular kinase Jak2. To elucidate the mechanism of this association, COS-7 cells were co-transfected with the AT1 receptor and either wild type Jak2 or a catalytically inactive Jak2. AT1 receptor-Jak2 association was assessed in vitro by a GST-AT1 receptor fusion protein binding assay and in vivo by direct co-immunoprecipitation of the receptor-Jak2 complex. Both studies showed that Jak2 must be catalytically active to form a complex with the AT1 receptor, and that complex formation is associated with Jak2 tyrosine phosphorylation. These results were confirmed using the Jak2 specific inhibitor AG-490. We also found that over-expression of wild type Jak2 in COS-7 cells leads to in vivo complex formation of spontaneously autophosphorylated Jak2 with the AT1 receptor. No such complex formation was observed with a dominant negative Jak2. Thus, the physical association of Jak2 with the AT1 receptor is regulated by an angiotensin II mediated autophosphorylation event.