Insulin-like Growth Factor 1 Regulates the Expression of ATP-Binding Cassette Transporter A1 in Pancreatic Beta Cells

• Published in: Hormone and metabolic research Vol. 48; no. 5; p. 338
• Main Authors: Lyu, J, Imachi, H, Iwama, H, Zhang, H, Murao, K
• Format: Journal Article
• Language: English
• Published: Germany 01.05.2016
• Subjects: Animals; ATP Binding Cassette Transporter 1 - genetics; ATP Binding Cassette Transporter 1 - metabolism; Biological Transport - drug effects; Cell Line, Tumor; Cholesterol - metabolism; Insulin-Like Growth Factor I - pharmacology; Insulin-Secreting Cells - drug effects; Insulin-Secreting Cells - metabolism; Nerve Tissue Proteins - metabolism; Phosphatidylinositol 3-Kinases - metabolism; Promoter Regions, Genetic; Proto-Oncogene Proteins c-akt - metabolism; Rats, Wistar; Signal Transduction - drug effects
• ISSN: 1439-4286
• DOI: 10.1055/s-0035-1569272

ATP-binding cassette transporter A1 (ABCA1) in pancreatic beta cells influences insulin secretion and cholesterol homeostasis. The present study investigates whether insulin-like growth factor 1 (IGF-1), which mediates stimulation of ABCA1 gene expression, could also interfere with the phosphatidylinositol 3-kinase (PI3-K) cascade.ABCA1 expression was examined by real-time polymerase chain reaction (PCR), Western blot analysis, and a reporter gene assay in rat insulin-secreting INS-1 cells incubated with IGF-1. The binding of forkhead box O1 (FoxO1) protein to the ABCA1 promoter was assessed by a chromatin immunoprecipitation (ChIP) assay. ABCA1 protein levels increased in response to rising concentrations of IGF-1. Real-time PCR analysis showed a significant increase in ABCA1 mRNA expression. However, both effects were suppressed after silencing the IGF-1 receptor. In parallel with its effect on endogenous ABCA1 mRNA levels, IGF-1 induced the activity of a reporter construct containing the ABCA1 promoter, while it was abrogated by LY294002, a specific inhibitor of PI3-K. Constitutively active Akt stimulated activity of the ABCA1 promoter, and a dominant-negative mutant of Akt or mutagenesis of the FoxO1 response element in the ABCA1 promoter abolished the ability of IGF-1 to stimulate promoter activity. A ChIP assay showed that FoxO1 mediated its transcriptional activity by directly binding to the ABCA1 promoter region. The knockdown of FoxO1 disrupted the effect of IGF-1 on ABCA1 expression. Furthermore, IGF-1 promoted cholesterol efflux and reduced the pancreatic lipotoxicity. These results demonstrate that the PI3-K/Akt/FoxO1 pathway contributes to the regulation of ABCA1 expression in response to IGF-1 stimulation.