Long-term effects of tumor necrosis factor-α treatment on insulin signaling pathway in HepG2 cells and HepG2 cells overexpressing constitutively active Akt/PKB

✍ Scribed by Dhananjay Gupta; Shailly Varma; Ramji L. Khandelwal

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 675 KB
• Volume: 100
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.21080

✦ Synopsis

Abstract

Tumor necrosis factor‐α (TNF‐α) mediated attenuation of insulin signaling pathway is an important cause in several disorders like obesity, obesity linked diabetes mellitus. TNF‐α actions vary depending upon concentration and time of exposure in various cells. In the present study, the effects of long‐term TNF‐α (1 ng/ml) exposure on the components of insulin signaling pathway in HepG2 and HepG2 cells overexpressing constitutively active Akt1/PKB‐α (HepG2‐CA‐Akt/PKB) have been investigated. In parental HepG2 cells, TNF‐α treatment for 24 h reduced the phosphorylation of Akt1/PKB‐α and GSK‐3β and under these conditions cells also showed reduced insulin responsiveness in terms of Akt1/PKB‐α and GSK‐3β phosphorylation. TNF‐α pre‐incubated HepG2‐CA‐Akt/PKB cells showed lower reduction in Akt1/PKB‐α and GSK‐3β phosphorylation and insulin responsiveness after 24 h as compared to parental HepG2 cells. We report that the long‐term TNF‐α pre‐incubation in both parental HepG2 and HepG2‐CA‐Akt/PKB‐α cells leads to the reduction in the levels of IRS‐1 without altering the levels of IRS‐2. In order to understand the reason for the differential insulin resistance in both the cell types, the effect of long‐term TNF‐α treatment on the proteins upstream to Akt/PKB was investigated. TNF‐α pre‐incubation also showed reduced insulin‐stimulated Tyr phosphorylation of insulin receptor (IR‐β) in both the cell types, moreover hyperphosphorylation of IRS‐1 at Ser 312 residue was observed in TNF‐α pre‐incubated cells. As hyperphosphorylation of IRS‐1 at Ser 312 can induce its degradation, it is possible that reduced insulin responsiveness after long‐term TNF‐α pre‐incubation observed in this study is due to the decrease in IRS‐1 levels. J. Cell. Biochem. 100: 593–607, 2007. © 2006 Wiley‐Liss, Inc.