Chronic endothelin-1 treatment leads to heterologous desensitization of insulin signaling in 3T3-L1 adipocytes

We recently reported that insulin and endothelin-1 (ET-1) can stimulate GLU T4 translocation via the heterotrimeric G protein G alphaq/11 and through P I3-kinase-mediated pathways in 3T3-L1 adipocytes. Because both hormones sti mulate glucose transport through a common downstream pathway, we determined whether chronic ET-1 pretreatment would desensitize these cells to acute i nsulin signaling. We found that ET-1 pretreatment substantially inhibited i nsulin-stimulated 2-deoxyglucose uptake and GLUT4 translocation. Cotreatmen t with the ETA receptor antagonist BQ 610 prevented these effects, whereas inhibitors of G alphai or G beta gamma were without effect. Chronic ET-1 tr eatment inhibited insulin-stimulated tyrosine phosphorylation of G alphaq/1 1 and IRS-I, as well as their association with P13-kinase and blocked the a ctivation of PI3-kinase activity and phosphorylation of Akt. In addition, c hronic ET-1 treatment caused IRS-1 degradation, which could be blocked by i nhibitors of PI3-kinase or p70 SG-kinase. Similarly, expression of a consti tutively active Gag mutant, but not the wild-type Gag, led to IRS-1 degrada tion and inhibited insulin-stimulated phosphorylation of IRS-1, suggesting that the ET-1-induced decrease in IRS-1 depends on G alphaq/11 and PI3-kina se. Insulin-stimulated tyrosine phosphorylation of SHC was also reduced in ET-1 treated cells, resulting in inhibition of the MAPK pathway. In conclus ion, chronic ET-1 treatment of 3T3-L1 adipocytes leads to heterologous dese nsitization of metabolic and mitogenic actions of insulin, most likely thro ugh the decreased tyrosine phosphorylation of the insulin receptor substrat es IRS-1, SHC, and G alphaq/11.