Aurintricarboxylic acid induces a distinct activation of the IGF-I receptor signaling within MDA-231 cells.
Aurintricarboxylic acid (ATA), a polymeric carboxylated triphenylmethane derivate, prevents apoptotic death in a variety of cell systems. Recently, we have shown that the survival promoting effect of ATA is transduced via activation of the IGF-I receptor (IGF-IR) signaling pathway. In breast cancer MDA-231 cells exposed either to the protein synthesis inhibitors cycloheximide or ricin or to the anticancer drug adriamycin, we have found that ATA, but not IGF-1, is a powerful antiapoptotic agent. The purpose of this study was to compare the ability of ATA and IGF-I to activate the IGF-IR signaling cascade and to correlate this ability to their survival potency. MDA-231 cells were exposed to ATA or IGF-I, up to 7 h, and the dynamics of activation of the IGF-IR signaling cascade was evaluated. Our results show that: 1) The amount of tyrosine phosphorylated IGF-IR proteins was greater after exposure to ATA, compared with IGF-I. 2) Two phosphorylated IGF-IR beta-subunits (a 95-kDa and a 75-kDa) were induced after exposure to ATA, whereas IGF-1 induced only the 95-kDa form. Immunoprecipitation of both receptor forms by antibodies against the alpha-subunit and against the carboxy terminus of the beta-subunit of the IGF-IR suggests that the 75-kDa form could be the beta-chain truncated at the amino terminus above the alpha-beta disulphide bridges. 3) The ATA-activated IGF-IR forms underwent slow dephosphorylation, compared with a rapid dephosphorylation of the IGF-I activated receptor. 4) The insulin receptor substrate-1/2-associated PI3K, Shc proteins, and the kinases Akt and Erk1/2, downstream mediators of the antiapoptotic signaling by IGF-IR, were activated to a higher extent and for a longer time period by ATA, compared with IGF-I. Taken together, the sustained activation of the IGF-IR signaling pathway by ATA may explain its stronger antiapoptotic effect. We suggest that this enhanced activity, and the different susceptibility of the IGF-IR to certain proteases and phosphatases, may indicate a distinct conformation of the ATA-activated IGF-IR.
Haimsohn
Michal
M
Institue of Endocrinology, Sheba Medical Center, Tel Hashomer, 52621, Israel.
Beery
Rachel
R
Karasik
Avraham
A
Kanety
Hannah
H
Geier
Avraham
A
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001312:Aurintricarboxylic Acid / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D003513:Cycloheximide / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D005260:Female; D006801:Humans; D010766:Phosphorylation; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D017526:Receptor, IGF Type 1 / Q000187:drug effects*; D012276:Ricin / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured
D000903:Antibiotics, Antineoplastic; D011500:Protein Synthesis Inhibitors; D001312:Aurintricarboxylic Acid; D004317:Doxorubicin; D012276:Ricin; D003513:Cycloheximide; D017526:Receptor, IGF Type 1