title: Iroquois homeobox transcription factor (Irx5) promotes G1/S-phase transition in vascular smooth muscle cells by CDK2-dependent activation.
abstract: The Iroquois homeobox (Irx5) gene is essential in embryonic development and cardiac electrophysiology. Although recent studies have reported that IRX5 protein is involved in regulation of the cell cycle and apoptosis in prostate cancer cells, little is known about the role of IRX5 in the adult vasculature. Here we report novel observations on the role of IRX5 in adult vascular smooth muscle cells (VSMCs) during proliferation in vitro and in vivo. Comparative studies using primary human endothelial cells, VSMCs, and intact carotid arteries to determine relative expression of Irx5 in the peripheral vasculature demonstrate significantly higher expression in VSMCs. Sprague-Dawley rat carotid arteries were subjected to balloon catherization, and the presence of IRX5 was examined by immunohistochemistry after 2 wk. Results indicate markedly elevated IRX5 signal at 14 days compared with uninjured controls. Total RNA was isolated from injured and uninjured arteries, and Irx5 expression was measured by RT-PCR. Results demonstrate a significant increase in Irx5 expression at 3-14 days postinjury compared with controls. Irx5 genetic gain- and loss-of-function studies using thymidine and 5-bromo-2'-deoxyuridine incorporation assays resulted in modulation of DNA synthesis in primary rat aortic VSMCs. Quantitative RT-PCR results revealed modulation of cyclin-dependent kinase inhibitor 1B (p27(kip1)), E2F transcription factor 1 (E2f1), and proliferating cell nuclear antigen (Pcna) expression in Irx5-transduced VSMCs compared with controls. Subsequently, apoptosis was observed and confirmed by morphological observation, caspase-3 cleavage, and enzymatic activation compared with control conditions. Taken together, these results indicate that Irx5 plays an important role in VSMC G1/S-phase cell cycle checkpoint control and apoptosis.
authors.affiliation: Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia; Department of Physiology, Morehouse School of Medicine, Atlanta, Georgia; and.
authors.forename: Dong
authors.initials: D
authors.lastname: Liu
authors.affiliation: Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia; Department of Medicine, Morehouse School of Medicine, Atlanta, Georgia.
authors.forename: Vaishnavi
authors.initials: V
authors.lastname: Pattabiraman
authors.affiliation: Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia; Department of Physiology, Morehouse School of Medicine, Atlanta, Georgia; and.
authors.forename: Methode
authors.initials: M
authors.lastname: Bacanamwo
authors.affiliation: Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia; Department of Physiology, Morehouse School of Medicine, Atlanta, Georgia; and Landerson@msm.edu.
authors.forename: Leonard M
authors.initials: LM
authors.lastname: Anderson
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002339:Carotid Arteries / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004268:DNA-Binding Proteins / Q000378:metabolism; D050687:E2F1 Transcription Factor / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology*; D059585:G1 Phase Cell Cycle Checkpoints / Q000502:physiology*; D018398:Homeodomain Proteins / Q000378:metabolism*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016196:S Phase / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D050687:E2F1 Transcription Factor; C493755:E2f1 protein, rat; D018398:Homeodomain Proteins; C539715:Irx5 protein, rat; D014157:Transcription Factors; D050760:Cyclin-Dependent Kinase Inhibitor p27; C495892:Cdk2 protein, rat; D051357:Cyclin-Dependent Kinase 2; D053148:Caspase 3
keywords: DNA synthesis; Irx5; apoptosis; cell cycle; cyclin-dependent kinase 2; vascular smooth muscle cell