title: IGFBP-3 binds GRP78, stimulates autophagy and promotes the survival of breast cancer cells exposed to adverse microenvironments.
abstract: Despite the established role of insulin-like growth factor binding protein-3 (IGFBP-3) as a growth inhibitor in vitro, a high level of IGFBP-3 in breast tumor tissue is associated with the stimulation of xenograft growth in mice and poor prognosis in patients. To understand the contribution of IGFBP-3 to breast cancer progression, tandem affinity purification was used to identify novel interacting proteins. The endoplasmic reticulum protein, glucose-regulated protein 78 (GRP78), was shown to bind to IGFBP-3, confirmed by colocalization, coimmunoprecipitations, glutathione S-transferase (GST) pulldowns and a nanomolar binding affinity. GST pulldowns also indicated that the GRP78 ATPase domain mediated the interaction with IGFBP-3. The critical roles of GRP78 in the unfolded protein response and macroautophagy led to an investigation of possible links between IGFBP-3, GRP78 and cellular stress responses. IGFBP-3 was found to stimulate the survival of breast cancer cells subjected to glucose starvation and hypoxia. Pharmacological inhibitors and small interfering RNA knockdown established that the increased survival of IGFBP-3-expressing cells was dependent on an intact autophagy response, as well as GRP78. The contribution of autophagy was confirmed by the demonstration that IGFBP-3 expression increases both the formation of autophagic puncta and flux through the system. In conclusion, we have shown that IGFBP-3 stimulates autophagy and thereby promotes the survival of breast cancer cells exposed to conditions that represent the adverse microenvironments encountered by solid tumor cells in vivo.
authors: Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St Leonards, New South Wales, Australia. sgrkovic@yahoo.com.au
authors: S
authors: S
authors: Grkovic
authors: V C
authors: VC
authors: O'Reilly
authors: S
authors: S
authors: Han
authors: M
authors: M
authors: Hong
authors: R C
authors: RC
authors: Baxter
authors: S M
authors: SM
authors: Firth
mesh_terms: D000818:Animals; D001343:Autophagy / Q000502:physiology; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D057809:HEK293 Cells; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000378:metabolism*; D061986:MCF-7 Cells; D015398:Signal Transduction; D016019:Survival Analysis; D059016:Tumor Microenvironment
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; C515497:IGFBP3 protein, human; D018972:Insulin-Like Growth Factor Binding Protein 3