title: Bidirectional regulation of upstream IGF-I/insulin receptor signaling and downstream FOXO1 in cardiomyocytes.
abstract: Signaling pathways of IGF-I and insulin receptors play important roles in the regulation of myocardial function. FOXO1 is a member of the forkhead transcriptional factor family, but how insulin and IGF-I receptor signaling regulate FOXO1 in cardiomyocytes is not well understood. This study was carried out to elucidate how IGF-I and insulin receptor signaling modulate FOXO1 in cardiomyocytes. In cardiomyocytes, activation of IGF-I receptor and insulin receptor lead to rapid phosphorylation of FOXO1. Inhibition of phosphatidylinositol 3-kinase/Akt pathway suppressed the effect of insulin and IGF-I on FOXO1 phosphorylation. Prolonged incubation with IGF-I increased ubiquitination of FOXO1 and down-regulated the abundance of FOXO1 proteins, which suggested that IGF-I might modulate FOXO1 degradation. To explore whether FOXO1 could modulate IGF-I and insulin signaling, a constitutively active FOXO1 was overexpressed in cardiomyocytes. The abundance of insulin receptor and IGF-I receptor was significantly upregulated in the cells overexpressing active FOXO1, accompanied by increased receptor phosphorylation upon insulin/IGF-I stimulation. Interestingly, overexpression of constitutively active FOXO1 also led to activation of MEK and Akt phosphorylation. IGF-I-stimulated MEK and Akt phosphorylation were augmented byoverexpression of constitutively active FOXO1. These findings indicate bidirectional regulation of insulin/IGF-I receptor signaling and FOXO1 in cardiomyocytes. FOXO1 may provide feedback control through upregulation of insulin and IGF-I receptor signaling.
authors.affiliation: Department of Medicine, Biological Chemistry, Physiology and Biophysics, Center for Diabetes Research and Treatment, University of California, Irvine, CA 92697, USA.
authors.forename: Tsun-Jui
authors.initials: TJ
authors.lastname: Liu
authors.forename: Hui-Chin
authors.initials: HC
authors.lastname: Lai
authors.forename: Chih-Tai
authors.initials: CT
authors.lastname: Ting
authors.forename: Ping H
authors.initials: PH
authors.lastname: Wang
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D005822:Genetic Vectors / Q000008:administration & dosage; D015151:Immunoblotting / Q000379:methods; D047468:Immunoprecipitation / Q000379:methods; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D051058:Oncogene Protein v-akt / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011972:Receptor, Insulin / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014161:Transduction, Genetic / Q000379:methods; D000071161:Forkhead Box Protein O1
chemical_list: D051858:Forkhead Transcription Factors; D007334:Insulin-Like Growth Factor I; D048369:MAP Kinase Kinase 1; D009419:Nerve Tissue Proteins; D051058:Oncogene Protein v-akt; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin; C074639:Foxo1 protein, rat; D000071161:Forkhead Box Protein O1