Ceruloplasmin Expression in Rat Liver Cells is Attenuated by Insulin: Role of FoxO Transcription Factors

Abstract

The phosphoinositide 3'-kinase (PI3 K)/Akt pathway controls the activity of a number of proteins important in the regulation of apoptosis and cell proliferation. FoxO (forkhead box, class O) transcription factors, substrates of the Ser/Thr kinase Akt, control the expression of several target genes that are crucial to the defense against oxidative stress, the regulation of cell cycle, and apoptosis in mammalian cells. Here, expression of ceruloplasmin (CP), the major copper-containing protein in blood released by the liver, was investigated. We observed a significant downregulation of CP mRNA levels after insulin treatment in H4IIE rat hepatoma cells. The PI3K inhibitor wortmannin counteracted this insulin effect on CP mRNA levels, indicating that the PI3K/Akt cascade is involved in the regulation of CP expression. Stimulation of FoxO1 was induced in H4IIE rat hepatoma cells expressing a conditionally active FoxO1 construct, resulting in significant upregulation of CP mRNA levels. This upregulation was prevented in the presence of insulin. In parallel, mRNAs of established FoxO target genes were analyzed: like CP mRNA, selenoprotein P and glucose 6-phosphatase mRNAs were upregulated by FoxO1, which was prevented by insulin. The same effects of insulin on CP mRNA levels were detected in primary rat hepatocytes. Furthermore, CP release into cell culture media was analyzed with primary hepatocytes and found to be attenuated by insulin. In line with its insulin-mimetic effects on cultured cells, Cu (2+) imitated the effect of insulin on CP expression and caused a downregulation of CP mRNA levels in rat hepatoma cells.

Regulation of FOXO3 by phosphorylation and methylation in hepatitis C virus infection and alcohol exposure

“…FOXO transcription factors regulate hepatic growth and metabolism and respond to stress conditions . FOXO1 is activated by HCV infection, contributing to insulin resistance, and FOXO3 activity was noted to be increased in HCV infection where it modulated innate immune signaling .…”

Stress and biological aging

“…For example, oxidative stress may result in stimulation of signaling cascades that trigger activation of at least two different groups of transcription factors whose target genes encode protective proteins, nuclear factor erythroid 2-related factor 2 (Nrf2) and forkhead box class O (FoxO) family transcription factors. Whereas Nrf2 is involved in regulating the expression of phase II xenobiotic metabolism enzymes, including glutathione S-transferases and other enzymes involved in the cellular defense against xenobiotics [38], FoxO transcription factors stimulate the expression of genes encoding antioxidant enzymes, both intracellular, such as superoxide dismutases (SOD) [26] and catalases [37] and extracellular proteins, such as selenoprotein P [51,55] and ceruloplasmin [28,49]. Triggering these pathways by exposure to mild oxidative stress will render cells protected and more resistant to subsequent intense stress [46].…”

Reactive Oxygen Species as Initiators and Mediators of Cellular Signaling Processes

“…Another family of transcription factors known to be redox-regulated and to control the expression of antioxidant enzymes are the forkhead box, class O (FoxO) transcription factors. These factors regulate expression of proapoptotic genes, genes involved in fuel metabolism, and antioxidants such as catalase, MnSOD [ 89 ], selenoprotein P [ 90 , 91 ] and ceruloplasmin [ 92 ], to name a few. Nrf2 and FoxOs, and the mode of redox regulation in these cases, will be discussed briefl y.…”