Journal Article

Regulation of glucose homeostasis through a XBP-1–FoxO1 interaction

White, Morris F, Zhou, Yingjiang, Lee, Jaemin, Lee, Justin, Chung, Jason, Park, Sang Won, Ozcan, Umut, Sun, Cheng, Fisher, Simon J, Biddinger, Sudha B, Reno, Candace M

2011

Overview

Insulin dials down endogenous hepatic glucose production after a meal by deactivating the transcription factor FoxO1. In a mouse model of insulin resistance, Umut Ozcan and his colleagues now show that hepatic overexpression of Xbp-1s, a factor involved in the cell stress response, leads to the protein degradation of FoxO1, thus reducing serum glucose levels. These results suggest a way to bypass one aspect of insulin resistance. To date, the only known role of the spliced form of X-box–binding protein-1 (XBP-1s) in metabolic processes has been its ability to act as a transcription factor that regulates the expression of genes that increase the endoplasmic reticulum (ER) folding capacity, thereby improving insulin sensitivity. Here we show that XBP-1s interacts with the Forkhead box O1 (FoxO1) transcription factor and directs it toward proteasome-mediated degradation. Given this new insight, we tested modest hepatic overexpression of XBP-1s in vivo in mouse models of insulin deficiency or insulin resistance and found it improved serum glucose concentrations, even without improving insulin signaling or ER folding capacity. The notion that XBP-1s can act independently of its role in the ER stress response is further supported by our finding that in the severely insulin resistant ob/ob mouse strain a DNA-binding–defective mutant of XBP-1s, which does not have the ability to increase ER folding capacity, is still capable of reducing serum glucose concentrations and increasing glucose tolerance. Our results thus provide the first evidence to our knowledge that XBP-1s, through its interaction with FoxO1, can bypass hepatic insulin resistance independent of its effects on ER folding capacity, suggesting a new therapeutic approach for the treatment of type 2 diabetes.

• Publisher: Nature Publishing Group US,Nature Publishing Group
• Subject: 631/443/163 / 631/80/474/2085 / 692/699/2743/137/773 / 692/699/2743/393 / Animals / Biomedical and Life Sciences / Biomedicine / Blood Glucose - analysis / Cancer Research / Deoxyribonucleic acid / Disease Models, Animal / DNA / DNA-Binding Proteins - genetics / DNA-Binding Proteins - physiology / Forkhead Box Protein O1 / Forkhead Transcription Factors - physiology / Gene expression / Genetic aspects / Glucose / Glucose - metabolism / Health aspects / Homeostasis / Hydrolysis / Infectious Diseases / Insulin / Insulin Resistance / Liver - metabolism / Metabolic Diseases / Mice / Molecular Medicine / Mutation / Neurosciences / Phosphorylation / Physiological aspects / Protein folding / Receptor, Insulin - metabolism / Regulatory Factor X Transcription Factors / Risk factors / Signal Transduction / Stress response / Transcription factors / Transcription Factors - genetics / Transcription Factors - physiology / Type 2 diabetes / X-Box Binding Protein 1