oa Characterization of insulin signaling pathway in calnexin knockout cells

Background: Calnexin is a lectin-like chaperone in the endoplasmic reticulum (ER) lumen, which along with calreticulin are involved in folding, maturation and trafficking of many glycoproteins. Insulin receptor and glucose transporters are among some of the proteins which are synthesized and folded in the ER. Previously, calreticulin was reported to play a role in the folding of GLUT-4 transporter as well as its stability. Furthermore, our lab reported that loss of calreticulin function results in increased insulin receptor synthesis, increased phosphorylation of Akt upon stimulation by insulin and increased glucose uptake. To date no data are available on the changes in insulin receptor pathway upon loss of calnexin chaperone. Objectives: The aim of this study is to examine changes in insulin receptor expression and insulin-mediated phosphorylation of Akt upon loss of calnexin function. Methods: Mouse embryonic fibroblast cells were serum starved overnight, then stimulated with insulin for 10 mins at 37°C. Cell lysate were prepared and Western blots with antibodies of different proteins in insulin signaling pathways were performed. Results: Our results showed a significant increase in insulin receptor expression in calnexin deficient cells. Furthermore, we observed a significant increase in the phosphorylation of Akt illustrating activation of insulin receptor pathway upon loss of calnexin function. Conclusions: In conclusion our data illustrates that loss of either of lectin like chaperones (calreticulin and calnexin) results in the activation of insulin receptor pathways via release of a negative suppressor of insulin receptor gene expression. Further research is needed to decipher the mechanism of this regulation.