Essential Role of Pituitary Tumor Transforming Gene 1 (PTTG1) in Vascular Endothelial Cell Activation and Remodeling

Abstract

ObjectivePituitary tumor‐transforming gene‐1 (PTTG1) is a transforming gene that was first discovered in rat pituitary tumor cells. It possesses transcriptional activity and has securin functions. As a transcription factor, PTTG1 has been shown to mediate angiogenic process by activation of cell proliferation, migration, and tube formation of human endothelial cells (ECs). The purpose of this study is to determine whether PTTG1 is involved in inflammatory responses in vascular ECs, and if so, to elucidate the mechanism (s) involved.Methods and ResultsAnalyses of multiple microarray datasets derived indicated that mRNA levels of pituitary tumor transforming gene (PTTG1) are highly interrelated with shear stress‐induced vascular remodeling in vascular ECs. Our results show that the expression of PTTG1 is significantly down‐regulated in vascular ECs in response to laminar shear stress, indicating that PTTG1 may participate in the inflammatory process of endothelial cell activation. Indeed, treatment of ECs with inflammatory cytokines, such as interleukin‐1β (IL‐1β) and tumor necrosis factor‐alpha (TNF‐α), the expression of PTTG1 in vascular ECs was markedly increased in a dose and time‐dependent manner, as determined by both quantitative real‐time PCR (qRT‐PCR) and western blot analysis. Furthermore, we show that treatment of vascular ECs with either simvastatin or fluvastatin substantially decreased PTTG1 expression in a time and dose dependent manner. To determine the functional significance of PTTG1 in endothelial activation, we performed a loss‐of‐function study by using PTTG1 specific small interference RNA (siRNA). Our results demonstrate that knockdown of PTTG1 in vascular ECs substantially attenuates both IL‐1β and TNF‐α‐induced inflammatory responses. The expression of inflammatory cytokines and chemokines, such as IL‐6, IL‐8, and MCP‐1, was markedly inhibited in PTTG1 knockdown ECs. To further elucidate the functional significance of PTTG1 in vivo, we assessed the expression of PTTG1 in carotid arteries subjected to a carotid artery ligation‐induced injury. Our results demonstrate that the expression of PTTG1 was markedly decreased in the injured vessels. Furthermore, we found that in a mouse model of carotid artery ligation induced injury, PTTG1 gene deficiency substantially attenuated vascular remodeling, as manifested by decreased neointimal formation, microphage infiltration, and expression of inflammatory cytokines and adhesion molecules in the injured endothelium.ConclusionTogether, our results for the first time identify PTTG1 as a critical regulator implicated in vascular inflammation and remodeling, and suggest that targeted inhibition of PTTG1 in vasculature may represent a novel therapeutic strategy for preventing inflammatory cardiovascular diseases, such as atherosclerosis and restenosis.Support or Funding InformationSupported by the US National Institutes of Health (HL103869) to J. Sun