Bidirectional regulation of upstream IGF-I/insulin receptor signaling and downstream FOXO1 in cardiomyocytes.
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.
Mesh Terms:
Adenoviridae, Animals, Animals, Newborn, Cells, Cultured, Forkhead Transcription Factors, Gene Expression Regulation, Genetic Vectors, Immunoblotting, Immunoprecipitation, Insulin-Like Growth Factor I, MAP Kinase Kinase 1, Myocytes, Cardiac, Nerve Tissue Proteins, Oncogene Protein v-akt, Phosphorylation, Rats, Rats, Sprague-Dawley, Receptor, IGF Type 1, Receptor, Insulin, Signal Transduction, Transduction, Genetic
Adenoviridae, Animals, Animals, Newborn, Cells, Cultured, Forkhead Transcription Factors, Gene Expression Regulation, Genetic Vectors, Immunoblotting, Immunoprecipitation, Insulin-Like Growth Factor I, MAP Kinase Kinase 1, Myocytes, Cardiac, Nerve Tissue Proteins, Oncogene Protein v-akt, Phosphorylation, Rats, Rats, Sprague-Dawley, Receptor, IGF Type 1, Receptor, Insulin, Signal Transduction, Transduction, Genetic
J. Endocrinol.
Date: Jan. 01, 2007
PubMed ID: 17210752
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