title: Molecular basis of the interaction between IGFBP-3 and retinoid X receptor: role in modulation of RAR-signaling.
abstract: IGFBP-3 interacts with the retinoid X receptor-alpha (RXRalpha) and retinoic acid receptor-alpha (RARalpha) and thereby interferes with the formation of RXR:RAR heterodimers. Here we identify the domains in RXRalpha and IGFBP-3 that participate in this interaction. When different regions of RXRalpha were expressed independently, we found that only the DNA-binding domain (C-domain) bound IGFBP-3. Residues in the second Zn-finger loop (Gln49, Arg52), which contribute to C-domain dimerization on DR1 response elements, proved essential to IGFBP-3 binding. In complementary studies, we found that residues within the N-terminal domain of IGFBP-3 (Thr58, Arg60) and motifs in its C-terminal domain ((220)LysLysLys, (228)LysGlyArgLysArg) were required for interaction with RXRalpha and RARalpha. Unlike wild-type IGFBP-3, the non-retinoid receptor-binding mutants of IGFBP-3 were unable to attenuate all-trans-retinoic acid-induced transactivation of the RAR response element by RXR:RAR heterodimers. We conclude that residues in both the N- and C-terminal domains of IGFBP-3 are involved in binding the retinoid receptors, and that this interaction is essential to the modulation of RAR-signaling by IGFBP-3.
authors.affiliation: Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St. Leonards, NSW 2065, Australia. lyns@med.usyd.edu.au
authors.forename: Lynette J
authors.initials: LJ
authors.lastname: Schedlich
authors.forename: Lloyd D
authors.initials: LD
authors.lastname: Graham
authors.forename: Michelle K
authors.initials: MK
authors.lastname: O'Han
authors.forename: Anita
authors.initials: A
authors.lastname: Muthukaruppan
authors.forename: Xiaolang
authors.initials: X
authors.lastname: Yan
authors.forename: Sue M
authors.initials: SM
authors.lastname: Firth
authors.forename: Robert C
authors.initials: RC
authors.lastname: Baxter
mesh_terms: D001665:Binding Sites; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018168:Receptors, Retinoic Acid / Q000737:chemistry* / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D047490:Retinoid X Receptor alpha / Q000737:chemistry* / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D047490:Retinoid X Receptor alpha