Gab1 involvement in glucose homeostasis regulation by hepatocytes

Abstract

The invention is directed to the regulation of glucose homeostasis by modulating the activity of Grb2-associated binder 1 (Gab1) in hepatocytes. This invention also provides for a method for identifying compounds capable of modulating the glucose homeostasis regulatory activity of Gab1. In one aspect, the invention provides a method for identifying a compound that can effectively modulate glucose homeostasis wherein Gab1 mediated MapK activity indicates that the candidate compound is an effective compound that modulates glucose homeostasis. In another aspect, the invention provides a method for identifying a compound that can effectively modulate the glucose homeostasis regulating activity of Gab1 wherein MAPK is activated to phosphorylate Serine residue 612 of IRS-1, indicating that the candidate compound is an effective compound that modulates glucose homeostasis. In another aspect of the invention is provided a method for diagnosing Gab1 related disorders.

1 . A method of identifying a modulator of Gab1 comprising:
 providing a first group comprising cells that express Gab1 protein and a second group comprising cells modified to lack Gab1 protein expression;   contacting said first group and second group with a candidate agent;   comparing the extracellular glucose concentration of said first and second groups after contact with said candidate agent to a baseline value indicated by the difference in extracellular glucose concentration between the first and second groups without contact with said candidate agent; and   identifying the candidate agent as a modulator of Gab1 if a change in glucose concentration between the first and second groups is found after contact with the candidate agent compared to the baseline value.   
     
     
         2 . The method of  claim 1 , wherein the cells of the first and second groups comprise mammalian cells. 
     
     
         3 . The method of  claim 2 , wherein the cells of the first and second groups comprise murine cells. 
     
     
         4 . The method of  claim 3 , wherein the cells modified to lack Gab1 protein expression are from a transgenic mouse whose genome comprises a homozygous disruption of the endogenous Gab1 gene. 
     
     
         5 . The method of  claim 1 , wherein the cells of said first and second groups are from the same organ type. 
     
     
         6 . The method of  claim 4 , wherein the organ type is liver. 
     
     
         7 . The method of  claim 1 , wherein said providing and said contacting are performed in vitro. 
     
     
         8 . The method of  claim 1 , wherein said providing and said contacting are performed in vivo. 
     
     
         9 . The method of  claim 8 , wherein said first and second groups are mice. 
     
     
         10 . The method of  claim 9 , wherein said second group is a transgenic mouse whose genome comprises a homozygous disruption of the endogenous Gab1 gene. 
     
     
         11 . The method of  claim 10 , further comprising administering a known amount of glucose to the mice. 
     
     
         12 . The method of  claim 11 , wherein the extracellular glucose concentration is measured as plasma glucose levels. 
     
     
         13 . The method of  claim 1 , wherein the candidate agent is identified as a positive modulator of Gab1 if said change in glucose concentration is an increase. 
     
     
         14 . The method of  claim 1 , wherein the candidate agent is identified as a negative modulator of Gab1 if said change in glucose concentration is a decrease. 
     
     
         15 . A transgenic mouse whose genome comprises a homozygous disruption of the endogenous Gab1 gene, wherein said disruption results in the functional inactivation of the Gab1 gene, and wherein said mouse exhibits hypoglycemia relative to a mouse whose genome comprises the functional endogenous Gab1 gene. 
     
     
         16 . The transgenic mouse of  claim 15 , wherein the homozygous disruption is specifically in the hepatic cells of the mouse. 
     
     
         17 . The transgenic mouse of  claim 15 , wherein the disruption in the Gab1 gene is a deletion of SEQ ID NO: 3. 
     
     
         18 . The transgenic mouse of  claim 17 , wherein the Gab1 gene is replaced with a replacement gene. 
     
     
         19 . The transgenic mouse of  claim 18 , wherein the replacement gene comprises a neomycin resistance gene. 
     
     
         20 . The transgenic mouse of  claim 17 , wherein the replacement gene further comprises a thymidine kinase gene.