Modulation of the Actions of IGFs by IGFBP-5 in the Mammary Gland

Abstract

IGFBP-5 has been associated with cell death in a number of systems; recently, the first evidence that it is involved in apoptosis of the mammary gland has been provided by studies, both in vivo and in vitro, involving the addition of exogenous IGFBP-5 and from a transgenic mouse expressing IGFBP-5 on a mammary-specific promoter. These studies have indicated that the effects are mediated in part by inhibition of IGF-signalling and involving members of the Bcl-2 family, but a role for IGF-independent effects cannot be ruled out. These IGF-independent effects involve potential interactions with components of the extracellular matrix involved in tissue remodelling such as components of the plasminogen system. In addition, intracellular events involving nuclear localisation of IGFBP-5 have been shown to have potential to inhibit cell proliferation. IGFBP-5 binds to a considerable number of molecules in the extracellular matrix, but the specific roles of these interactions in modulating its biological effects are poorly understood. The development of IGFBP-5 mutants, with differential binding characteristics, will aid in elucidating the precise roles of IGFBP-5 and potentially offer new therapeutic approaches based on IGF-independent effects in addition to its classical role of modulating IGF actions.

Mammary gland - IGFBP-5 - Apoptosis - Extracellular Matrix - IGF-action

References

• 1 Firth S M, Baxter R C. Cellular actions of the insulin-like growth factor binding proteins.  Endocr Rev. 2002;  23 824-854
• 2 Wood T L, Yee D. Introduction: IGFs and IGFBPs in the normal mammary gland and in breast cancer.  J Mammary Gland Biol Neoplasia. 2000;  5 1-5
• 3 Flint D J, Tonner E, Allan G J. Insulin-like growth factor binding proteins: IGF-dependent and -independent effects in the mammary gland.  J Mammary Gland Biol Neoplasia. 2000;  5 65-73
• 4 Muta K, Krantz S B. Apoptosis of human erythroid colony-forming cells is decreased by stem cell factor and insulin-like growth factor I as well as erythropoietin.  J Cell Physiol. 1993;  156 264-271
• 5 Harrington E A, Bennett M R, Fanidi A, Evan G I. c-Myc-induced apoptosis in fibroblasts is inhibited by specific cytokines.  Embo J. 1994;  13 3286-3295
• 6 Sell C, Baserga R, Rubin R. Insulin-like growth factor I (IGF-I) and the IGF-I receptor prevent etoposide-induced apoptosis.  Cancer Res. 1995;  55 303-306
• 7 Kulik G, Klippel A, Weber M J. Antiapoptotic signalling by the insulin-like growth factor I receptor, phosphatidylinositol 3-kinase, and Akt.  Mol Cell Biol. 1997;  17 1595-1606
• 8 Chan J M, Stampfer M J, Giovannucci E, Gann P H, Ma J, Wilkinson P, Hennekens C H, Pollak M. Plasma insulin-like growth factor-I and prostate cancer risk: a prospective study.  Science. 1998;  279 563-566
• 9 Signorello L B, Brismar K, Bergstrom R, Andersson S O, Wolk A, Trichopoulos D, Adami H O. Insulin-like growth factor-binding protein-1 and prostate cancer.  J Natl Cancer Inst. 1999;  91 1965-1967
• 10 Wolk A, Mantzoros C S, Andersson S O, Bergstrom R, Signorello L B, Lagiou P, Adami H O, Trichopoulos D. Insulin-like growth factor 1 and prostate cancer risk: a population-based, case-control study.  J Natl Cancer Inst. 1998;  90 911-915
• 11 Ma J, Pollak M N, Giovannucci E, Chan J M, Tao Y, Hennekens C H, Stampfer M J. Prospective study of colorectal cancer risk in men and plasma levels of insulin-like growth factor (IGF)-I and IGF-binding protein-3.  J Natl Cancer Inst. 1999;  91 620-625
• 12 Pollak M. The question of a link between insulin-like growth factor physiology and neoplasia.  Growth Horm IGF Res. 2000;  10 Suppl B S21-24
• 13 Stambolic V, Tsao M S, Macpherson D, Suzuki A, Chapman W B, Mak T W. High incidence of breast and endometrial neoplasia resembling human Cowden syndrome in pten+/- mice.  Cancer Res. 2000;  60 3605-3611
• 14 Li Y, Podsypanina K, Liu X, Crane A, Tan L K, Parsons R, Varmus H E. Deficiency of Pten accelerates mammary oncogenesis in MMTV-Wnt-1 transgenic mice.  BMC Mol Biol. 2001;  2 2
• 15 Zumkeller W. IGFs and IGFBPs: surrogate markers for diagnosis and surveillance of tumour growth.  Mol Pathol. 2001;  54 285-288
• 16 Ellis M J, Leav B A, Yang Z, Rasmussen A, Pearce A, Zweibel J A, Lippman M E, Cullen K J. Affinity for the insulin-like growth factor-II (IGF-II) receptor inhibits autocrine IGF-II activity in MCF-7 breast cancer cells.  Mol Endocrinol. 1996;  10 286-297
• 17 Hankins G R, De Souza A T, Bentley R C, Patel M R, Marks J R, Iglehart J D, Jirtle R L. M6P/IGF2 receptor: a candidate breast tumor suppressor gene.  Oncogene. 1996;  12 2003-2009
• 18 Farrelly N, Lee Y J, Oliver J, Dive C, Streuli C H. Extracellular matrix regulates apoptosis in mammary epithelium through a control on insulin signaling.  J Cell Biol. 1999;  144 1337-1348
• 19 Hadsell D L, Greenberg N M, Fligger J M, Baumrucker C R, Rosen J M. Targeted expression of des(1 - 3) human insulin-like growth factor I in transgenic mice influences mammary gland development and IGF-binding protein expression.  Endocrinology. 1996;  137 321-330
• 20 Neuenschwander S, Schwartz A, Wood T L, Roberts C T Jr, Henninghausen L, LeRoith D. Involution of the lactating mammary gland is inhibited by the IGF system in a transgenic mouse model.  J Clin Invest. 1996;  97 2225-2232
• 21 Moorehead R A, Fata J E, Johnson M B, Khokha R. Inhibition of mammary epithelial apoptosis and sustained phosphorylation of Akt/PKB in MMTV-IGF-II transgenic mice.  Cell Death Differ. 2001;  8 16-29
• 22 Tonner E, Barber M C, Travers M T, Logan A, Flint D J. Hormonal control of insulin-like growth factor-binding protein-5 production in the involuting mammary gland of the rat.  Endocrinology. 1997;  138 5101-5107
• 23 Brisken C, Ayyannan A, Nguyen C, Heineman A, Reinhardt F, Tan J, Dey S K, Dotto G P, Weinberg R A, Jan T. IGF-2 is a mediator of prolactin-induced morphogenesis in the breast.  Dev Cell. 2002;  3 877-887
• 24 Hovey R C, Harris J, Hadsell D L, Lee A V, Ormandy C J, Vonderhaar B K. Local insulin-like growth factor-II mediates prolactin-induced mammary gland development.  Mol Endocrinol. 2003;  17 460-471
• 25 Chapman R S, Lourenco P, Tonner E, Flint D, Selbert S, Takeda K, Akira S, Clarke A R, Watson C J. The role of Stat3 in apoptosis and mammary gland involution. Conditional deletion of Stat3.  Adv Exp Med Biol. 2000;  480 129-138
• 26 Chapman R S, Duff E K, Lourenco P C, Tonner E, Flint D J, Clarke A R, Watson C J. A novel role for IRF-1 as a suppressor of apoptosis.  Oncogene. 2000;  19 6386-6391
• 27 Dupont J, Renou J P, Shani M, Hennighausen L, LeRoith D. PTEN overexpression suppresses proliferation and differentiation and enhances apoptosis of the mouse mammary epithelium.  J Clin Invest. 2002;  110 815-825
• 28 Bagheri-Yarmand R, Vadlamudi R K, Kumar R. Activating transcription factor 4 overexpression inhibits proliferation and differentiation of mammary epithelium resulting in impaired lactation and accelerated involution.  J Biol Chem. 2003;  278 17 421-17 429
• 29 Guenette R S, Tenniswood M. The role of growth factors in the suppression of active cell death in the prostate: an hypothesis.  Biochem Cell Biol. 1994;  72 553-559
• 30 Phillips I D, Becks G P, Logan A, Wang J F, Smith C, Hill D J. Altered expression of insulin-like growth factor-I (IGF-I) and IGF binding proteins during rat thyroid hyperplasia and involution.  Growth Factors. 1994;  10 207-222
• 31 Liu X J, Malkowski M, Guo Y, Erickson G F, Shimasaki S, Ling N. Development of specific antibodies to rat insulin-like growth factor- binding proteins (IGFBP-2 to -6): analysis of IGFBP production by rat granulosa cells.  Endocrinology. 1993;  132 1176-1183
• 32 van Kleffens M, Groffen C, Rosato R R, van den Eijnde S M, van Neck J W, Lindenbergh-Kortleve D J, Zwarthoff E C, Drop S L. mRNA expression patterns of the IGF system during mouse limb bud development, determined by whole mount in situ hybridization.  Mol Cell Endocrinol. 1998;  138 151-161
• 33 Allan G J, Flint D J, Patel K. Insulin-like growth factor axis during embryonic development.  Reproduction. 2001;  122 31-39
• 34 Allan G J, Flint D J, Darling S M, Geh J, Patel K. Altered expression of insulin-like growth factor-1 and insulin like growth factor binding proteins-2 and 5 in the mouse mutant Hypodactyly (Hd) correlates with sites of apoptotic activity.  Anat Embryol (Berl). 2000;  202 1-11
• 35 Jones J I, Gockerman A, Busby W H Jr, Camacho-Hubner C, Clemmons D R. Extracellular matrix contains insulin-like growth factor binding protein-5: potentiation of the effects of IGF-I.  J Cell Biol. 1993;  121 679-687
• 36 Miyake H, Pollak M, Gleave M E. Castration-induced up-regulation of insulin-like growth factor binding protein-5 potentiates insulin-like growth factor-I activity and accelerates progression to androgen independence in prostate cancer models.  Cancer Res. 2000;  60 3058-3064
• 37 Clemmons D R. Role of insulin-like growth factor binding proteins in controlling IGF actions.  Mol Cell Endocrinol. 1998;  140 19-24
• 38 Nam T J, Busby W H Jr, Rees C, Clemmons D R. Thrombospondin and osteopontin bind to insulin-like growth factor (IGF)-binding protein-5 leading to an alteration in IGF-I-stimulated cell growth?.  Endocrinology. 2000;  141 1100-1106
• 39 Yee D. The insulin-like growth factor system as a target in breast cancer.  Breast Cancer Res Treat. 1994;  32 85-95
• 40 Figueroa J A, Yee D. The insulin-like growth factor binding proteins (IGFBPs) in human breast cancer.  Breast Cancer Res Treat. 1992;  22 81-90
• 41 Ewton D Z, Coolican S A, Mohan S, Chernausek S D, Florini J R. Modulation of insulin-like growth factor actions in L6A1 myoblasts by insulin-like growth factor binding protein (IGFBP)-4 and IGFBP-5: a dual role for IGFBP-5.  J Cell Physiol. 1998;  177 47-57
• 42 Marshman E, Green K A, Flint D J, White A, Streuli C H, Westwood M. Insulin-like growth factor binding protein 5 and apoptosis in mammary epithelial cells.  J Cell Sci. 2003;  116 675-682
• 43 Butt A J, Dickson K A, McDougall F, Baxter R C. Insulin-like Growth Factor-binding Protein-5 Inhibits the Growth of Human Breast Cancer Cells in Vitro and in Vivo .  J Biol Chem. 2003;  278 29 676-29 685
• 44 Allan G J, Tonner E, Barber M C, Travers M T, Shand J H, Vernon R G, Kelly P A, Binart N, Flint D J. Growth hormone, acting in part through the insulin-like growth factor axis, rescues developmental, but not metabolic, activity in the mammary gland of mice expressing a single allele of the prolactin receptor.  Endocrinology. 2002;  143 4310-4319
• 45 Tonner E, Barber M C, Allan G J, Beattie J, Webster J, Whitelaw C B, Flint D J. Insulin-like growth factor binding protein-5 (IGFBP-5) induces premature cell death in the mammary glands of transgenic mice.  Development. 2002;  129 4547-4557
• 46 Cheng H L, Shy M, Feldman E L. Regulation of insulin-like growth factor-binding protein-5 expression during Schwann cell differentiation.  Endocrinology. 1999;  140 4478-4485
• 47 Kanatani M, Sugimoto T, Nishiyama K, Chihara K. Stimulatory effect of insulin-like growth factor binding protein-5 on mouse osteoclast formation and osteoclastic bone-resorbing activity.  J Bone Miner Res. 2000;  15 902-910
• 48 Zimmermann E M, Li L, Hou Y T, Cannon M, Christman G M, Bitar K N. IGF-I induces collagen and IGFBP-5 mRNA in rat intestinal smooth muscle.  Am J Physiol. 1997;  273 G875-882
• 49 Richman C, Baylink D J, Lang K, Dony C, Mohan S. Recombinant human insulin-like growth factor-binding protein-5 stimulates bone formation parameters in vitro and in vivo. .  Endocrinology. 1999;  140 4699-4705
• 50 Meadows K A, Holly J M, Stewart C E. Tumor necrosis factor-alpha-induced apoptosis is associated with suppression of insulin-like growth factor binding protein-5 secretion in differentiating murine skeletal myoblasts.  J Cell Physiol. 2000;  183 330-337
• 51 James P L, Stewart C E, Rotwein P. Insulin-like growth factor binding protein-5 modulates muscle differentiation through an insulin-like growth factor-dependent mechanism.  J Cell Biol. 1996;  133 683-693
• 52 Ball R K, Friis R R, Schoenenberger C A, Doppler W, Groner B. Prolactin regulation of beta-casein gene expression and of a cytosolic 120-kd protein in a cloned mouse mammary epithelial cell line.  Embo J. 1988;  7 2089-2095.
• 53 Phillips K, Park M A, Quarrie L H, Boutinaud M, Lochrie J D, Flint D J, Allan G J, Beattie J. Hormonal control of IGF-binding protein (IGFBP)-5 and IGFBP-2 secretion during differentiation of the HC11 mouse mammary epithelial cell line.  J Mol Endocrinol. 2003;  31 197-208
• 54 Fielder P J, Thordarson G, English A, Rosenfeld R G, Talamantes F. Expression of a lactogen-dependent insulin-like growth factor-binding protein in cultured mouse mammary epithelial cells.  Endocrinology. 1992;  131 261-267
• 55 Bramani S, Song H, Beattie J, Tonner E, Flint D J, Allan G J. Amino acids within the extracellular matrix (ECM) binding region (201 - 218) of rat insulin-like growth factor binding protein (IGFBP)-5 are important determinants in binding IGF-I.  J Mol Endocrinol. 1999;  23 85-96
• 56 Song H, Beattie J, Campbell I W, Allan G J. Overlap of IGF- and heparin-binding sites in rat IGF-binding protein-5.  J Mol Endocrinol. 2000;  24 43-51
• 57 Song H, Shand J H, Beattie J, Flint D J, Allan G J. The carboxy-terminal domain of IGF-binding protein-5 inhibits heparin binding to a site in the central domain.  J Mol Endocrinol. 2001;  26 229-239
• 58 Clemmons D R. Use of mutagenesis to probe IGF-binding protein structure/function relationships.  Endocr Rev. 2001;  22 800-817
• 59 Hwa V, Oh Y, Rosenfeld R G. The insulin-like growth factor-binding protein (IGFBP) superfamily.  Endocr Rev. 1999;  20 761-787
• 60 Schneider M R, Wolf E, Hoeflich A, Lahm H. IGF-binding protein-5: flexible player in the IGF system and effector on its own.  J Endocrinol. 2002;  172 423-440
• 61 Zheng B, Clarke J B, Busby W H, Duan C, Clemmons D R. Insulin-like growth factor-binding protein-5 is cleaved by physiological concentrations of thrombin.  Endocrinology. 1998;  139 1708-1714
• 62 Thrailkill K M, Quarles L D, Nagase H, Suzuki K, Serra D M, Fowlkes J L. Characterization of insulin-like growth factor-binding protein 5-degrading proteases produced throughout murine osteoblast differentiation.  Endocrinology. 1995;  136 3527-3533
• 63 Imai Y, Busby W H Jr, Smith C E, Clarke J B, Garmong A J, Horwitz G D, Rees C, Clemmons D R. Protease-resistant form of insulin-like growth factor-binding protein 5 is an inhibitor of insulin-like growth factor-I actions on porcine smooth muscle cells in culture.  J Clin Invest. 1997;  100 2596-2605
• 64 Nam T J, Busby W H Jr, Clemmons D R. Human fibroblasts secrete a serine protease that cleaves insulin-like growth factor-binding protein-5.  Endocrinology. 1994;  135 1385-1391
• 65 Busby W H Jr, Nam T J, Moralez A, Smith C, Jennings M, Clemmons D R. The complement component C1s is the protease that accounts for cleavage of insulin-like growth factor-binding protein-5 in fibroblast medium.  J Biol Chem. 2000;  275 37 638-37 644
• 66 Carrick F E, Forbes B E, Wallace J C. BIAcore analysis of bovine insulin-like growth factor (IGF)-binding protein-2 identifies major IGF binding site determinants in both the amino- and carboxyl-terminal domains.  J Biol Chem. 2001;  276 27 120-27 128
• 67 Galanis M, Firth S M, Bond J, Nathanielsz A, Kortt A A, Hudson P J, Baxter R C. Ligand-binding characteristics of recombinant amino- and carboxyl-terminal fragments of human insulin-like growth factor-binding protein-3.  J Endocrinol. 2001;  169 123-133
• 68 Vorwerk P, Hohmann B, Oh Y, Rosenfeld R G, Shymko R M. Binding properties of insulin-like growth factor binding protein-3 (IGFBP-3), IGFBP-3 N- and C-terminal fragments, and structurally related proteins mac25 and connective tissue growth factor measured using a biosensor.  Endocrinology. 2002;  143 1677-1685
• 69 Hobba G D, Forbes B E, Parkinson E J, Francis G L, Wallace J C. The insulin-like growth factor (IGF) binding site of bovine insulin-like growth factor binding protein-2 (bIGFBP-2) probed by iodination.  J Biol Chem. 1996;  271 30 529-30 536
• 70 Hobba G D, Lothgren A, Holmberg E, Forbes B E, Francis G L, Wallace J C. Alanine screening mutagenesis establishes tyrosine 60 of bovine insulin-like growth factor binding protein-2 as a determinant of insulin-like growth factor binding.  J Biol Chem. 1998;  273 19 691-19 698
• 71 Kalus W, Zweckstetter M, Renner C, Sanchez Y, Georgescu J, Grol M, Demuth D, Schumacher R, Dony C, Lang K, Holak T A. Structure of the IGF-binding domain of the insulin-like growth factor- binding protein-5 (IGFBP-5): implications for IGF and IGF-I receptor interactions.  Embo J. 1998;  17 6558-6572
• 72 Imai Y, Moralez A, Andag U, Clarke J B, Busby J, Clemmons D R. Substitutions for hydrophobic amino acids in the N terminal domains of IGFBP 3 and 5 markedly reduce IGF-I binding and alter their biologic actions.  J Biol Chem. 2000;  275 18 188-18 194
• 73 Clemmons D R. IGF binding proteins and their functions.  Mol Reprod Dev. 1993;  35 368-374; discussion 374 - 365
• 74 Andress D L, Loop S M, Zapf J, Kiefer M C. Carboxy-truncated insulin-like growth factor binding protein-5 stimulates mitogenesis in osteoblast-like cells.  Biochem Biophys Res Commun. 1993;  195 25-30
• 75 Shand J H, Beattie J, Song H, Phillips K, Kelly S M, Flint D J, Allan G J. Specific amino acid substitutions determine the differential contribution of the N- and C-terminal domains of insulin-like growth factor (IGF)-binding protein-5 in binding IGF-I.  J Biol Chem. 2003;  278 17 859-17 866
• 76 Firth S M, Baxter R C. Characterisation of recombinant glycosylation variants of insulin-like growth factor binding protein-3.  J Endocrinol. 1999;  160 379-387
• 77 Sommer A, Spratt S K, Tatsuno G P, Tressel T, Lee R, Maack C A. Properties of glycosylated and non-glycosylated human recombinant IGF binding protein-3 (IGFBP-3).  Growth Regul. 1993;  3 46-49
• 78 Schedlich L J, Nilsen T, John A P, Jans D A, Baxter R C. Phosphorylation of insulin-like growth factor binding protein-3 by deoxyribonucleic acid-dependent protein kinase reduces ligand binding and enhances nuclear accumulation.  Endocrinology. 2003;  144 1984-1993
• 79 Arai T, Parker A, Busby W Jr, Clemmons D R. Heparin, heparan sulfate, and dermatan sulfate regulate formation of the insulin-like growth factor-I and insulin-like growth factor-binding protein complexes.  J Biol Chem. 1994;  269 20 388-20 393
• 80 Hodgkinson S C, Napier J R, Spencer G S, Bass J J. Glycosaminoglycan binding characteristics of the insulin-like growth factor-binding proteins.  J Mol Endocrinol. 1994;  13 105-112
• 81 Booth B A, Boes M, Andress D L, Dake B L, Kiefer M C, Maack C, Linhardt R J, Bar K, Caldwell E E, Weiler J. et al . IGFBP-3 and IGFBP-5 association with endothelial cells: role of C-terminal heparin binding domain.  Growth Regul. 1995;  5 1-17
• 82 Arai T, Clarke J, Parker A, Busby W Jr, Nam T, Clemmons D R. Substitution of specific amino acids in insulin-like growth factor (IGF) binding protein 5 alters heparin binding and its change in affinity for IGF-I response to heparin.  J Biol Chem. 1996;  271 6099-6106
• 83 Perks C M, McCaig C, Clarke J B, Clemmons D R, Holly J M. A non-IGF binding mutant of IGFBP-3 modulates cell function in breast epithelial cells.  Biochem Biophys Res Commun. 2002;  294 988-994
• 84 Perks C M, McCaig C, Clarke J B, Clemmons D R, Holly J M. Effects of a non-IGF binding mutant of IGFBP-5 on cell death in human breast cancer cells.  Biochem Biophys Res Commun. 2002;  294 995-1000
• 85 Parker A, Clarke J B, Busby W H Jr, Clemmons D R. Identification of the extracellular matrix binding sites for insulin-like growth factor-binding protein 5.  J Biol Chem. 1996;  271 13 523-13 529
• 86 Parker A, Rees C, Clarke J, Busby W H Jr, Clemmons D R. Binding of insulin-like growth factor (IGF)-binding protein-5 to smooth-muscle cell extracellular matrix is a major determinant of the cellular response to IGF-I.  Mol Biol Cell. 1998;  9 2383-2392
• 87 Nam T, Moralez A, Clemmons D. Vitronectin binding to IGF binding protein-5 (IGFBP-5) alters IGFBP-5 modulation of IGF-I actions.  Endocrinology. 2002;  143 30-36
• 88 Twigg S M, Baxter R C. Insulin-like growth factor (IGF)-binding protein 5 forms an alternative ternary complex with IGFs and the acid-labile subunit.  J Biol Chem. 1998;  273 6074-6079
• 89 Twigg S M, Kiefer M C, Zapf J, Baxter R C. Insulin-like growth factor-binding protein 5 complexes with the acid-labile subunit. Role of the carboxyl-terminal domain.  J Biol Chem. 1998;  273 28 791-28 798
• 90 Twigg S M, Kiefer M C, Zapf J, Baxter R C. A central domain binding site in insulin-like growth factor binding protein-5 for the acid-labile subunit.  Endocrinology. 2000;  141 454-457
• 91 Nam T J, Busby W, Jr. , Clemmons D R. Insulin-like growth factor binding protein-5 binds to plasminogen activator inhibitor-I.  Endocrinology. 1997;  138 2972-2978
• 92 Campbell P G, Andress D L. Insulin-like growth factor (IGF)-binding protein-5-(201 - 218) region regulates hydroxyapatite and IGF-I binding.  Am J Physiol. 1997;  273 E1005-1013
• 93 Tonner E, Allan G J, Flint D J. Hormonal control of plasmin and tissue-type plasminogen activator activity in rat milk during involution of the mammary gland.  J Endocrinol. 2000;  167 265-273
• 94 Andress D L. Heparin modulates the binding of insulin-like growth factor (IGF) binding protein-5 to a membrane protein in osteoblastic cells.  J Biol Chem. 1995;  270 28 289-28 296
• 95 Radulescu R T. Nuclear localization signal in insulin-like growth factor-binding protein type 3.  Trends Biochem Sci. 1994;  19 278
• 96 Schedlich L J, Le Page S L, Firth S M, Briggs L J, Jans D A, Baxter R C. Nuclear import of insulin-like growth factor-binding protein-3 and -5 is mediated by the importin beta subunit.  J Biol Chem. 2000;  275 23 462-23 470
• 97 Butt A J, Fraley K A, Firth S M, Baxter R C. IGF-binding protein-3-induced growth inhibition and apoptosis do not require cell surface binding and nuclear translocation in human breast cancer cells.  Endocrinology. 2002;  143 2693-2699