title: Inhibition of insulin-like growth factor I receptor signaling by the vitamin D analogue EB1089 in MCF-7 breast cancer cells: A role for insulin-like growth factor binding proteins.
abstract: Insulin-like growth factors I and II (IGF-I and IGF-II) are potent mitogens involved in growth regulation of breast epithelial cells and are implicated in the pathophysiology of breast cancer. Their bioactivity is enhanced or inhibited by specific IGF-binding proteins (IGFBPs). Vitamin D-related compounds (VDRCs) have been shown to inhibit proliferation and induce apoptosis of MCF-7 breast carcinoma cells. We have previously demonstrated that VDRCs antagonize the growth-promoting activity of IGF-I by stimulating autocrine production of IGFBP-5 in MCF-7 cells, but the effect of VDRCs on IGF-I receptor (IGF-IR) intracellular signaling has not been elucidated. We report here that the vitamin D analogue EB1089 interferes with the IGF-IR signaling pathway by attenuating IGF-I-induced tyrosine phosphorylation of IRS-1, and to a lesser extent, IRS-2. It does not affect protein levels of IRS-1, IRS-2 or IGF-IR. However, EB1089 does not inhibit tyrosine phosphorylation of IRS-1 induced by des(1-3) IGF-I, an IGF-I analogue with greatly reduced affinity for IGFBPs. Furthermore, we demonstrate that an antisense IGFBP-5 oligodeoxynucleotide attenuates EB1089-induced inhibition of IGF-I-stimulated tyrosine phosphorylation of IRS-1 and EB1089-induced IGFBP-5 accumulation. These data strongly suggest that IGFBP-5 plays a functional role in the interfering action of EB1089 with the IGF-IR signal transduction pathway.
authors.affiliation: Lady Davis Institute for Medical Research of the Jewish General Hospital and Departments of Medicine and Oncology, McGill University, Montreal, Quebec H3T 1E2, Canada.
authors.forename: F
authors.initials: F
authors.lastname: Rozen
authors.forename: M
authors.initials: M
authors.lastname: Pollak
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use*; D019898:Autocrine Communication; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000627:therapeutic use; D004354:Drug Screening Assays, Antitumor; D005260:Female; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins / Q000502:physiology*; D008970:Molecular Weight; D010766:Phosphorylation; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D018969:Insulin-Like Growth Factor Binding Proteins; D017526:Receptor, IGF Type 1; D002117:Calcitriol; C078903:seocalcitol