title: The role of insulin-like growth factor binding protein-3 in the breast cancer cell response to DNA-damaging agents.
abstract: Following exposure to radiation and chemotherapeutic agents, the epidermal growth factor receptor (EGFR) can modulate the repair of DNA double-strand breaks (DSB) by forming protein complexes that include the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs). This is one of the key mechanism by which tumors become resistant to DNA-damaging therapies. Our previous studies have shown that insulin-like growth factor binding protein-3 (IGFBP-3) is a substrate for DNA-PKcs, and can transactivate EGFR. We therefore questioned whether IGFBP-3 might interact with the EGFR-DNA-PK complex that regulates the DNA damage response. The aim of this study was to delineate the role of IGFBP-3 in the response of breast cancer cells to DSB-inducing chemotherapeutic agents. In the estrogen receptor-negative breast cancer cell lines MDA-MB-468 and Hs578T, which express IGFBP-3 highly, nuclear localization of EGFR and IGFBP-3 was enhanced by treatment with cytotoxic drugs etoposide or doxorubicin and reduced by the EGFR kinase inhibitor gefitinib. Enhanced association among IGFBP-3, EGFR and DNA-PKcs, following the exposure to DNA-damaging drugs was supported by both co-immunoprecipitation analysis and direct visualization by proximity ligation assay. The activation of DNA-PKcs at Ser2056, DNA repair as measured by a nonhomologous end-joining assay, and the increase in EGFR and DNA-PKcs interaction induced by DNA-damaging agents, were all decreased by IGFBP-3 silencing, suggesting that IGFBP-3 has an obligatory role in the DNA repair response to DNA-damaging therapy. In conclusion, IGFBP-3 co-translocation to the nucleus of breast cancer cells and its formation of a complex with DNA-PKcs and EGFR in response to DNA damage shows its potential involvement in the regulation of DNA repair. This suggests the possibility of a therapeutic approach for sensitizing breast cancer to chemo- or radiotherapy by targeting the DNA repair function of IGFBP-3.
authors.affiliation: Hormones and Cancer Division, Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St Leonards, Australia.
authors.forename: M Z
authors.initials: MZ
authors.lastname: Lin
authors.affiliation: Hormones and Cancer Division, Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St Leonards, Australia.
authors.forename: K A
authors.initials: KA
authors.lastname: Marzec
authors.affiliation: Hormones and Cancer Division, Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St Leonards, Australia.
authors.forename: J L
authors.initials: JL
authors.lastname: Martin
authors.affiliation: Hormones and Cancer Division, Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St Leonards, Australia.
authors.forename: R C
authors.initials: RC
authors.lastname: Baxter
mesh_terms: D021581:Active Transport, Cell Nucleus; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology*; D005260:Female; D000077156:Gefitinib; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000502:physiology*; D021962:Membrane Microdomains / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D011799:Quinazolines / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; C515497:IGFBP3 protein, human; D018972:Insulin-Like Growth Factor Binding Protein 3; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D005047:Etoposide; D004317:Doxorubicin; C512478:EGFR protein, human; D066246:ErbB Receptors; D051747:DNA-Activated Protein Kinase; D000077156:Gefitinib