title: Insulin-like growth factor binding protein-3 prevents retinoid receptor heterodimerization: implications for retinoic acid-sensitivity in human breast cancer cells.
abstract: Insulin-like growth factor binding protein-3 (IGFBP-3) has both IGF-dependent and -independent effects on cell growth, which are frequently growth-inhibitory. Interestingly, the development of a more aggressive phenotype in breast cancer cells (BCCs) correlates positively with elevated expression of IGFBP-3 and is often associated with all-trans-retinoic acid (atRA)-resistance. IGFBP-3 was previously demonstrated to interact directly with retinoid X receptor (RXR). In this study we have shown that IGFBP-5 also interacts with RXR and that both IGFBPs interact with retinoic acid receptor (RAR). To investigate whether the presence of IGFBP-3 regulates breast cancer cell responsiveness to atRA, we immuno-neutralized the IGFBP-3 expressed by the atRA-resistant Hs578T and MDA-MB-231 BCCs (which express IGFBP-3 constitutively) and showed that they become more sensitive to the growth-inhibitory effects of atRA. Similarly, in Hs578T cells expressing a reporter gene under the control of an RAR response element (RARE), depletion of IGFBP-3 resulted in the induction of reporter gene expression in response to atRA. In investigating possible mechanisms for IGFBP-3 regulation of atRA-sensitivity, we found that IGFBP-3 blocked the formation of RAR:RXR heterodimers and disrupted the ligand-inducible receptor complex. Thus, IGFBP-3 has the potential to reduce the RARE-mediated transactivation of target genes and modulate the atRA-response in BCCs.
authors.affiliation: Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, NSW, Australia. lyns@med.usyd.edu.au
authors.forename: Lynette J
authors.initials: LJ
authors.lastname: Schedlich
authors.forename: Michelle K
authors.initials: MK
authors.lastname: O'Han
authors.forename: Gary M
authors.initials: GM
authors.lastname: Leong
authors.forename: Robert C
authors.initials: RC
authors.lastname: Baxter
mesh_terms: D000970:Antineoplastic Agents; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D019281:Dimerization; D019008:Drug Resistance, Neoplasm; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D047488:Retinoid X Receptors; D014157:Transcription Factors / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D018972:Insulin-Like Growth Factor Binding Protein 3; D018975:Insulin-Like Growth Factor Binding Protein 5; C000607071:RARA protein, human; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D047488:Retinoid X Receptors; D014157:Transcription Factors; D014212:Tretinoin