Down-regulation of insulin receptor by antibodies against the type I insulin-like growth factor receptor: implications for anti-insulin-like growth factor therapy in breast cancer.
Insulin-like growth factor-I (IGF-I), IGF-II, and insulin have all been implicated in regulating several aspects of the malignant phenotype via the type I IGF receptor (IGF1R) and insulin receptor (IR). We have previously shown that a chimeric single-chain antibody against IGF1R (scFv-Fc) and a murine antibody EM164 down-regulate IGF1R, making breast cancer cells unresponsive to IGF-I. To determine if IR signaling is affected, we examined regulation of IR in MCF-7 cells after exposure to these antibodies. Surprisingly, both scFv-Fc and EM164 resulted in decreased levels of IR in vitro and in vivo despite their lack of reactivity against IR. Twenty-four-hour pretreatment with EM164 also inhibited insulin-mediated phosphorylation of IR and insulin-stimulated proliferation of MCF-7 cells. Neither scFv-Fc nor EM164 caused down-regulation of IR in cells that express very low levels of IGF1R or no IGF1R. Expression of IGF1R was required for IR down-regulation, which was specific as neither antibody caused down-regulation of beta1 integrin or epidermal growth factor receptor. Reagents that disrupt lipid rafts inhibited IR down-regulation by the antibodies, suggesting that IR in close physical proximity to IGF1R in lipid rafts was being endocytosed. Our data show that down-regulation of IR by monoclonal antibodies against IGF1R requires the coexpression of IGF1R and may be due to endocytosis of hybrid IR/IGF1R or holo-IR. Thus, antibodies against IGF1R provide inhibition of both IGF and insulin signaling in cancer cells.
University of Minnesota Cancer Center, Minneapolis, Minnesota 55455, USA. sachd003@umn.edu
Deepali
D
Sachdev
Rajeeva
R
Singh
Yoko
Y
Fujita-Yamaguchi
Douglas
D
Yee
D000818:Animals; D000906:Antibodies / Q000276:immunology / Q000494:pharmacology*; D000918:Antibody Specificity; D001943:Breast Neoplasms / Q000276:immunology / Q000378:metabolism / Q000628:therapy*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D005260:Female; D006801:Humans; D007128:Immunoglobulin Fragments / Q000276:immunology / Q000494:pharmacology; D021962:Membrane Microdomains / Q000378:metabolism; D051379:Mice; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000276:immunology*; D011972:Receptor, Insulin / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000276:immunology; D023041:Xenograft Model Antitumor Assays
D000906:Antibodies; D007128:Immunoglobulin Fragments; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin