Reactive Oxygen Species‐Dependent PKB Activation Contributes to Insulin‐Like Growth Factor 1‐Induced Phosphorylation of Histone Deacetylase 5 in Vascular Smooth Muscle Cells

Abstract

Insulin‐like growth factor 1 (IGF‐1), a potent mitogenic and vasoactive factor, has been shown to play an important role in the development of cardiovascular diseases. This occurs through the generation of reactive oxygen species (ROS) as well as through the hyperactivation of mitogenic and growth promoting signaling pathways and the subsequent alteration in gene expression. Histone deacetylases (HDACs), by their ability to modify the acetylation status of lysine residues in histone and non‐histone proteins, regulate gene transcription. Recent studies have demonstrated that a heightened activation of HDACs, notably HDAC5, is associated with vascular disorders such as atherosclerosis. However, a role of IGF‐1 in HDAC activation by phosphorylation remains poorly characterized. Therefore, in the present studies, we examined the effect of IGF‐1 on the phosphorylation of HDAC5 in vascular smooth muscle cells (VSMCs) and identified the signalling pathways involved in this process. Treatment of A10 VSMCs with IGF‐1 enhanced the phosphorylation of HDAC5 at serine 498 in a time and dose‐dependent fashion. Pretreatment of cells with AG1024, a selective pharmacological inhibitor of IGF‐1 receptor, significantly inhibited IGF‐1‐induced HDAC5 phosphorylation in A10 VSMCs whereas AG1478, a selective inhibitor of epidermal growth factor receptor, did not have an inhibitory effect on the levels of phospho‐HDAC5. Pharmacological blockade of the MAPK pathway with PD98059 and UO126 had no effect on HDAC5 phosphorylation, however wortmannin and SC‐66, inhibitors of the PI3K/PKB pathways, almost completely attenuated IGF‐1‐induced HDAC5 phosphorylation. In addition, pretreatment of A10 VSMCs with Diphenyleneiodonium (DPI) and apocynin, two NAD(P)H oxidase inhibitors, as well as the antioxidant N‐Acetyl‐Cysteine (NAC), resulted in an attenuation of IGF‐1‐induced phosphorylation of HDAC5 as well as PKB. In summary, these data demonstrate that IGF‐1 induces the phosphorylation of HDAC5 in a ROS‐ and PKB‐dependent fashion in VSMCs.Support or Funding InformationSupported by a grant from the Canadian Institutes of Health Research.