Activation of the insulin-like growth factor 1 signaling pathway by the antiapoptotic agents aurintricarboxylic acid and Evans blue

Aurintricarboxylic acid (ATA), an endonuclease inhibitor, prevents the deat h of a variety of cell types in culture. Previously we have shown that ATA, similar to insulin-like growth factor I (IGF-I), protected MCF-7 cells aga inst apoptotic death induced by the protein synthesis inhibitor cycloheximi de. Here we show that ATA and a polysulfonated aromatic compound, Evans blu e (EB), similar to IGF-I, promote survival and increase proliferation of MC F-7 cells in serum-free culture medium. This may suggest a common signaling pathway shared by the aromatic polyanions and IGF-I. Therefore, the abilit y of these aromatic compounds to activate the signal transduction pathway o f IGF-I was examined. We found that ATA and EB mimicked the IGF-I effect on tyrosine phosphorylation of the IGF-I receptor (IGF-IR) and its major subs trates, insulin receptor substrate-1 (IRS-1) and IRS-P: induced the associa tion of these substrates with phosphatidylinositol 3-kinase and Grb2; and a ctivated Akt kinase and p42/p44 mitogen-activated protein kinases. ATA and EB competed for IGF-I binding to the IGF-IR. ATA was found to be selective for the IGF-IR, whereas EB also activated the insulin receptor. Upon fracti onation of commercial ATA by size exclusion chromatography, we found that f ractions that enhanced the intensity of tyrosyl-phosphorylated IRS-1/IRS-2 also increased the survival of MCF-7 cells in the presence of cycloheximide , whereas fractions devoid of IRS phosphorylation activity had no survival ability. Taken together, these results suggest that the survival/proliferat ion-promoting effects of ATA and EB in MCF-7 cells are transduced via the I GF-IR signaling pathway.