cAbl tyrosine kinase mediates reactive oxygen species- and caveolin-dependent AT₁ receptor signaling in vascular smooth muscle: Role in vascular hypertrophy

Important output signals of the angiotensin subtype 1 receptor (AT ₁R) in vascular smooth muscle cells (VSMCs) are mediated by angiotensin II (Ang II)-stimulated transactivation of the epidermal growth factor receptor (EGF-R), which is critical for vascular hypertrophy. Ang II-induced EGF-R transactivation is mediated through cSrc, a proximal target of reactive oxygen species (ROS) derived from NAD(P)H oxidase (NOX) and is dependent on AT₁R trafficking through caveolin1 (Cav1)-enriched lipid rafts. Underlying molecular mechanisms are incompletely understood. The nonreceptor tyrosine kinase, proto-oncogene cAb1 is a substrate of Src and is a major mediator for ROS-dependent tyrosine phosphorylation of Cav1. We thus hypothesized that cAb1 is important for ROS-, cSrc-, and Cav1-dependent growth-related AT₁R signal transduction. Here we show that Ang II induces tyrosine phosphorylation of cAbl in rat VSMCs and mouse aorta, and that Ang II promotes association of cAbl with AT₁R, both of which are Src-dependent. Pretreatment of rat VSMCs with the NOX inhibitor diphenylene iodonium or the antioxidants N-acetylcysteine or ebselen significantly inhibited Ang II-induced cAbl phosphorylation. Cell fractionation shows that both EGF-Rs and cAbl are found basally in Cav1-enriched membrane fractions. Knockdown of cAbl protein using small interference RNA inhibits Ang II-stimulated: (1) trafficking of AT₁R into, and EGF-R out of, Cav1-enriched lipid rafts; (2) EGF-R transactivation; (3) appearance of the transactivated EGF-R and phospho-Cav1 at focal adhesions; and (4) vascular hypertrophy. These studies provide a novel role of cAbl in the spatial and temporal organization of growth-related AT₁R signaling in VSMCs and suggest that cAbl may be generally important in signaling of G-protein coupled receptors.