1
|
Baxter RC. Nuclear actions of insulin-like growth factor binding protein-3. Gene 2015; 569:7-13. [PMID: 26074086 PMCID: PMC4496269 DOI: 10.1016/j.gene.2015.06.028] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Revised: 05/27/2015] [Accepted: 06/09/2015] [Indexed: 12/11/2022]
Abstract
In addition to its actions outside the cell, cellular uptake and nuclear import of insulin-like growth factor binding protein-3 (IGFBP-3) has been recognized for almost two decades, but knowledge of its nuclear actions has been slow to emerge. IGFBP-3 has a functional nuclear localization signal and interacts with the nuclear transport protein importin-β. Within the nucleus IGFBP-3 appears to have a role in transcriptional regulation. It can bind to the nuclear receptor, retinoid X receptor-α and several of its dimerization partners, including retinoic acid receptor, vitamin D receptor (VDR), and peroxisome proliferator-activated receptor-γ (PPARγ). These interactions modulate the functions of these receptors, for example inhibiting VDR-dependent transcription in osteoblasts and PPARγ-dependent transcription in adipocytes. Nuclear IGFBP-3 can be detected by immunohistochemistry in cancer and other tissues, and its presence in the nucleus has been shown in many cell culture studies to be necessary for its pro-apoptotic effect, which may also involve interaction with the nuclear receptor Nur77, and export from the nucleus. IGFBP-3 is p53-inducible and in response to DNA damage, forms a complex with the epidermal growth factor receptor (EGFR), translocating to the nucleus to interact with DNA-dependent protein kinase. Inhibition of EGFR kinase activity or downregulation of IGFBP-3 can inhibit DNA double strand-break repair by nonhomologous end joining. IGFBP-3 thus has the ability to influence many cell functions through its interactions with intranuclear pathways, but the importance of these interactions in vivo, and their potential to be targeted for therapeutic benefit, require further investigation.
Collapse
Affiliation(s)
- Robert C Baxter
- Kolling Institute of Medical Research, University of Sydney, Level 8, Kolling Building, Royal North Shore Hospital, St Leonards, NSW 2065, Australia.
| |
Collapse
|
2
|
Brahmkhatri VP, Prasanna C, Atreya HS. Insulin-like growth factor system in cancer: novel targeted therapies. BIOMED RESEARCH INTERNATIONAL 2015; 2015:538019. [PMID: 25866791 PMCID: PMC4383470 DOI: 10.1155/2015/538019] [Citation(s) in RCA: 172] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Revised: 10/13/2014] [Accepted: 10/20/2014] [Indexed: 12/15/2022]
Abstract
Insulin-like growth factors (IGFs) are essential for growth and survival that suppress apoptosis and promote cell cycle progression, angiogenesis, and metastatic activities in various cancers. The IGFs actions are mediated through the IGF-1 receptor that is involved in cell transformation induced by tumour. These effects depend on the bioavailability of IGFs, which is regulated by IGF binding proteins (IGFBPs). We describe here the role of the IGF system in cancer, proposing new strategies targeting this system. We have attempted to expand the general viewpoint on IGF-1R, its inhibitors, potential limitations of IGF-1R, antibodies and tyrosine kinase inhibitors, and IGFBP actions. This review discusses the emerging view that blocking IGF via IGFBP is a better option than blocking IGF receptors. This can lead to the development of novel cancer therapies.
Collapse
Affiliation(s)
| | - Chinmayi Prasanna
- NMR Research Centre, Indian Institute of Science, Bangalore 560012, India
| | - Hanudatta S. Atreya
- NMR Research Centre, Indian Institute of Science, Bangalore 560012, India
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India
| |
Collapse
|
3
|
Bikker FJ, Koop G, Leusink NB, Nazmi K, Kaman WE, Brand HS, Veerman ECI. Tailor made plasmin substrates as potential diagnostic tool to test for mastitis. Vet Res Commun 2014; 38:271-7. [DOI: 10.1007/s11259-014-9611-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/27/2014] [Indexed: 10/25/2022]
|
4
|
Shahjee H, Bhattacharyya N, Zappala G, Wiench M, Prakash S, Rechler MM. An N-terminal fragment of insulin-like growth factor binding protein-3 (IGFBP-3) induces apoptosis in human prostate cancer cells in an IGF-independent manner. Growth Horm IGF Res 2008; 18:188-197. [PMID: 17959403 DOI: 10.1016/j.ghir.2007.08.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/21/2007] [Accepted: 08/16/2007] [Indexed: 10/22/2022]
Abstract
OBJECTIVE IGF-binding protein-3 (IGFBP-3) can induce apoptosis in human prostate cancer cells by direct, IGF-independent mechanisms that are poorly understood. IGFBP-3 undergoes limited proteolysis by plasmin and other proteases to generate small N-terminal fragments (e.g., amino acids 1-97) that have lost their affinity for IGF-I and IGF-II yet still can inhibit mitogenesis. The present study examines whether the N-terminal 1-97-IGFBP-3 fragment can induce apoptosis in human prostate cancer cells in an IGF-independent manner. DESIGN N-terminal 1-97-IGFBP-3 with or without a signal prepeptide was fused to yellow fluorescent protein (YFP) and expressed in PC-3 human prostate cancer cells. In some cases, the N-terminal IGF-binding site was mutated. Subcellular localization was determined by confocal microscopy. Loss of cell viability was determined by Annexin V-APC staining in the presence and absence of a general caspase inhibitor, z-VAD-fmk. RESULTS All of the fusion proteins, including those synthesized with a signal peptide, were predominantly intracellular, suggesting that they had been internalized following secretion. YFP-1-97-IGFBP-3 is present at comparable concentrations in the nucleus and cytoplasm, indicating that it does not contain a nuclear localization signal. Cells transfected with YFP-1-97-IGFBP-3 lost viability. Cell death was blocked by incubation with a caspase inhibitor suggesting that it resulted from apoptosis. Similar results were obtained with YFP-1-97-IGFBP-3 mutants that do not bind IGFs. CONCLUSIONS The N-terminal 1-97-IGFBP-3 fragment induces apoptosis in human prostate cancer cells in an IGF-independent manner. Generation of the fragment might contribute to the proapoptotic activity of IGFBP-3 in vivo.
Collapse
Affiliation(s)
- H Shahjee
- Diabetes Branch, NIDDK, National Institutes of Health, Bldg 10-Room 8D12, 9000 Rockville Pike, MSC 1758, Bethesda, MD 20892, United States
| | | | | | | | | | | |
Collapse
|
5
|
Ghosh M, Shanker S, Siwanowicz I, Mann K, Machleidt W, Holak TA. Proteolysis of insulin-like growth factor binding proteins (IGFBPs) by calpain. Biol Chem 2005; 386:85-93. [PMID: 15843151 DOI: 10.1515/bc.2005.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Calpains are non-lysosomal, Ca 2+ -dependent cysteine proteases, which are ubiquitously distributed across cell types and vertebrate species. The rules that govern calpain specificity have not yet been determined. To elucidate the cleavage pattern of calpains, we carried out calpain-induced proteolytic studies on the insulin-like growth factor binding proteins IGFBP-4 and -5. Proteolysis of IGFBPs is well characterized in numerous reports. Our results show that calpain cleavage sites are in the non-conserved unstructured regions of the IGFBPs. Compilation of the calpain-induced proteolytic cleavage sites in several proteins reported in the literature, together with our present study, has not revealed clear preferences for amino acid sequences. We therefore conclude that calpains seem not to recognize amino acid sequences, but instead cleave with low sequence specificity at unstructured or solvent-exposed fragments that connect folded, stable domains of target proteins.
Collapse
Affiliation(s)
- Madhumita Ghosh
- Max Planck Institute for Biochemistry, D-82152 Martinsried, Germany
| | | | | | | | | | | |
Collapse
|
6
|
Mishra S, Murphy LJ. The effects of insulin-like growth factor binding protein-3 (IGFBP-3) on T47D breast cancer cells enriched for IGFBP-3 binding sites. Mol Cell Biochem 2005; 267:83-9. [PMID: 15663189 DOI: 10.1023/b:mcbi.0000049368.40558.0a] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
To investigate insulin-like growth factor (IGF)-independent effects of IGF binding protein-3 (IGFBP-3), T47D cells were enriched for a population of cells that expressed binding sites for biotinylated-IGFBP-3 by panning on streptavidin-coated plate. Proliferation of cell enriched for IGFBP-3 binding sites was significantly inhibited by IGFBP-3, whereas IGFBP-3 had no significant effect on the non-enriched cell population. Enriched and non-enriched cells were equally responsive to IGF-I, TGF-beta and EGF. Conditioned medium from enriched cells had less IGFBP-3 than that from non-enriched cells. Cross-linking of biotinylated IGFBP-3 to T47D cell membranes identified complexes with Mr of 32, 80 and 100 kDa. All of these complexes were more abundant in enriched cells compared with the non-enriched cell population. These data demonstrate that despite the anti-proliferative effects of IGFBP-3 it is possible to selectively enriched for cell populations with more abundant IGFBP-3 binding sites. These enriched cells are more responsive to IGFBP-3 and secrete less of this binding protein than non-enriched cells, supporting the concept that IGFBP-3 secretion by human breast cancer cells may function as an autocrine or paracrine modulator of cell proliferation.
Collapse
Affiliation(s)
- Suresh Mishra
- Departments of Internal Medicine & Physiology, University of Manitoba, Winnipeg R3E 0W3 Canada
| | | |
Collapse
|
7
|
Miyamoto S, Yano K, Sugimoto S, Ishii G, Hasebe T, Endoh Y, Kodama K, Goya M, Chiba T, Ochiai A. Matrix metalloproteinase-7 facilitates insulin-like growth factor bioavailability through its proteinase activity on insulin-like growth factor binding protein 3. Cancer Res 2004; 64:665-71. [PMID: 14744783 DOI: 10.1158/0008-5472.can-03-1916] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Matrix metalloproteinase-7 (MMP-7) secreted by cancer cells has been implicated classically in the basement membrane destruction associated with tumor cell invasion and metastasis. Recent epidemiologic studies have established a correlation between high levels of circulating insulin-like growth factor (IGF) and low levels of IGF binding protein 3 (IGFBP-3), and relative risk of developing colon, breast, prostate, and lung cancer, which are known to produce MMP-7. In this study, IGFBP-3 was assessed as a candidate for the physiologic substrate of MMP-7. MMP-7 proteolysis generated four major fragments (26 kDa, 17 kDa, 15.5 kDa, and 15.5 kDa), and two cleavage sites were identified: one at the site of hydrolysis of the K(144)-I(145) peptide bond and one at the R(95)-L(96) peptide bond. The former site is different from the previously reported site of cleavage of IGFBP-3 by other proteases. Addition of IGFBP-3 inhibited IGF-I-mediated IGF type 1 receptor (IGF-IR) phosphorylation and activation of the downstream molecule Akt in BALB/c 3T3 fibroblasts overexpressing human IGF-IR (3T3-IGF-IR) and in two human colon cancer cell lines (COLO201 and HT29). Coincubation of the IGF-I/IGFBP-3 complex with MMP-7 restored IGF-I-mediated IGF-IR phosphorylation and activation of Akt in these cell lines. The IGF-I signal recovered by MMP-7 protected against apoptosis induced by anoikis in 3T3-IGF-IR cells. These results indicate that MMP-7 proteolysis of IGFBP-3 plays a crucial role in regulating IGF-I bioavailability, thereby promoting cell survival. This mechanism may contribute to the tumorigenesis of MMP-7-producing IGF-IR-expressing tumors in the primary site and to organ-specific metastasis in a paracrine manner.
Collapse
Affiliation(s)
- Shin'ichi Miyamoto
- Pathology Division, National Cancer Center Research Institute East, Chiba, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
8
|
Mishra S, Murphy LJ. Phosphorylation of insulin-like growth factor (IGF) binding protein-3 by breast cancer cell membranes enhances IGF-I binding. Endocrinology 2003; 144:4042-50. [PMID: 12933678 DOI: 10.1210/en.2003-0089] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Cross-linking of nonglycosylated biotinylated IGF binding protein (IGFBP)-3 to T-47D cell membranes identifies complexes with Mr of 32, 50, 70, and 100 kDa. Nonbiotinylated glycosylated IGFBP-3 competed for binding to each of these sites. The 32-kDa band approximated the size of intact nonglycosylated IGFBP-3, but its abundance was enhanced by cross-linking, and it had a more acidic isoelectric point on isoelectric focusing, suggesting that it had undergone phosphorylation. Immobilized IGFBP-3 was phosphorylated in the presence of (32)P-gamma ATP by both T-47D cell membranes and by intact cells treated with phenylarsine oxide to inhibit internalization. MCF-7 and COS-1 cells were also able to bind and phosphorylated IGFBP-3. IGF-I inhibited both IGFBP-3 binding to membranes and phosphorylation. However, incubation of T-47D cells with IGFBP-3 enhanced binding of (125)I-IGF-I to the cell monolayer indicating that membrane bound IGFBP-3 was able to bind IGF-I. Immobilized IGFBP-3 when phosphorylated by T-47D membranes bound significantly more (125)I-IGF-I than nonphosphorylated IGFBP-3. Treatment with alkaline phosphatase significantly reduced (125)I-IGF-I binding to phosphorylated immobilized IGFBP-3 and also reduced (125)I-IGF-I to T-47D cell monolayers preincubated with IGFBP-3. Phosphorylation of IGFBP-3 by T-47D membranes was partially blocked by inhibitors of both protein kinase A and C. These data demonstrate that binding of IGFBP-3 to breast cancer membranes is accompanied by phosphorylation at the plasma membrane and that both processes are inhibited by IGF-I. However, once phosphorylated the ability of IGFBP-3 to bind IGF-I is enhanced, resulting in increased association of the IGF-I with the cell membrane.
Collapse
Affiliation(s)
- Suresh Mishra
- Departments of Internal Medicine and Physiology, University of Manitoba, Winnipeg, Canada, R3E 0W3
| | | |
Collapse
|
9
|
Abstract
In addition to their roles in IGF transport, the six IGF-binding proteins (IGFBPs) regulate cell activity in various ways. By sequestering IGFs away from the type I IGF receptor, they may inhibit mitogenesis, differentiation, survival, and other IGF-stimulated events. IGFBP proteolysis can reverse this inhibition or generate IGFBP fragments with novel bioactivity. Alternatively, IGFBP interaction with cell or matrix components may concentrate IGFs near their receptor, enhancing IGF activity. IGF receptor-independent IGFBP actions are also increasingly recognized. IGFBP-1 interacts with alpha(5)beta(1) integrin, influencing cell adhesion and migration. IGFBP-2, -3, -5, and -6 have heparin-binding domains and can bind glycosaminoglycans. IGFBP-3 and -5 have carboxyl-terminal basic motifs incorporating heparin-binding and additional basic residues that interact with the cell surface and matrix, the nuclear transporter importin-beta, and other proteins. Serine/threonine kinase receptors are proposed for IGFBP-3 and -5, but their signaling functions are poorly understood. Other cell surface IGFBP-interacting proteins are uncharacterized as functional receptors. However, IGFBP-3 binds and modulates the retinoid X receptor-alpha, interacts with TGFbeta signaling through Smad proteins, and influences other signaling pathways. These interactions can modulate cell cycle and apoptosis. Because IGFBPs regulate cell functions by diverse mechanisms, manipulation of IGFBP-regulated pathways is speculated to offer therapeutic opportunities in cancer and other diseases.
Collapse
Affiliation(s)
- Sue M Firth
- Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St Leonards, New South Wales 2065, Australia
| | | |
Collapse
|
10
|
Abstract
The IGF-binding proteins (IGFBPs) are multifunctional proteins that modulate IGF actions. To determine whether specific domains within these proteins account for specific functions, we and other laboratories have used in vitro mutagenesis. Prior experiments that used a variety of techniques had identified discrete regions within each protein that were proposed to account for specific functions. Alterations of these regions by substituting charged residues with neutral residues or hydrophobic residues with nonhydrophobic residues as well as domain swapping, i.e., substituting a domain from one specific form of IGFBP for the homologous domain in another form, has resulted in the elucidation of the functions of many of these specific sequences. Because the areas of protein sequence that are altered involve a limited number of amino acids, they generally do not alter the conformation of the entire protein; therefore, these specific substitutions can often be correlated with the functional changes that occur after mutagenesis. Mutants have been particularly useful for performing functional analyses in which the purified mutant protein is added to a biological test system. In some cases it has been possible to overexpress the mutagenized protein and determine whether the constitutively synthesized, mutant form of IGFBP has altered functional activity. These results have revealed that discrete regions of IGFBP sequence can mediate important and specific functional properties of these proteins.
Collapse
Affiliation(s)
- D R Clemmons
- Department of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7170, USA.
| |
Collapse
|
11
|
Ogueh O, Miell JP, Jones JC, Jones JS, Alaghband-Zadeh J, Johnson MR. Antenatal dexamethasone and the growth hormone-insulin-like growth factor axis. Hum Reprod 2000; 15:1403-6. [PMID: 10831578 DOI: 10.1093/humrep/15.6.1403] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Dexamethasone administration has marked effects on the growth hormone-insulin-like growth factor axis (GH-IGF) in animal and human studies. During pregnancy in the rat, it is associated with fetal growth restriction due to inhibition of IGF bioactivity. In the human only repeated dosages have been associated with fetal growth restriction. The aim of this study is to test the hypothesis that antenatal dexamethasone administration to pregnant women is associated with reduced activity of the GH-IGF axis. To achieve this blood samples were taken from 12 pregnant women pre- and at 24 h and 48 h after dexamethasone administration. In these samples GH, IGF-I, IGF bioactivity and IGF binding protein (IGFBP)-3 protease activity were measured. In view of the interaction between insulin and the GH-IGF axis, glucose and insulin concentrations were also measured. There were no significant differences between the concentrations of GH, IGF-I, IGF bioactivity and IGFBP-3 protease activity before and after dexamethasone. The concentrations of glucose and insulin were significantly higher at 24 h, but not 48 h post-dexamethasone. It is concluded that a single antenatal course of dexamethasone does not alter the GH-IGF-I axis in pregnant women at the time points studied.
Collapse
Affiliation(s)
- O Ogueh
- Section of Obstetrics and Gynaecology, Imperial College School of Medicine, Chelsea and Westminster Hospital, London, UK
| | | | | | | | | | | |
Collapse
|
12
|
Abstract
Over the last decade, the concept of an IGFBP family has been well accepted, based on structural similarities and on functional abilities to bind IGFs with high affinities. The existence of other potential IGFBPs was left open. The discovery of proteins with N-terminal domains bearing striking structural similarities to the N terminus of the IGFBPs, and with reduced, but demonstrable, affinity for IGFs, raised the question of whether these proteins were "new" IGFBPs (22, 23, 217). The N-terminal domain had been uniquely associated with the IGFBPs and has long been considered to be critical for IGF binding. No other function has been confirmed for this domain to date. Thus, the presence of this important IGFBP domain in the N terminus of other proteins must be considered significant. Although these other proteins appear capable of binding IGF, their relatively low affinity and the fact that their major biological actions are likely to not directly involve the IGF peptides suggest that they probably should not be classified within the IGFBP family as provisionally proposed (22, 23). The conservation of this single domain, so critical to high-affinity binding of IGF by the six IGFBPs, in all of the IGFBP-rPs, as well, speaks to its biological importance. Historically, and perhaps, functionally, this has led to the designation of an "IGFBP superfamily". The classification and nomenclature for the IGFBP superfamily, are, of course, arbitrary; what is ultimately relevant is the underlying biology, much of which still remains to be deciphered. The nomenclature for the IGFBP related proteins was derived from a consensus of researchers working in the IGFBP field (52). Obviously, a more general consensus on nomenclature, involving all groups working on each IGFBP-rP, has yet to be reached. Further understanding of the biological functions of each protein should help resolve the nomenclature dilemma. For the present, redesignating these proteins IGFBP-rPs simplifies the multiple names already associated with each IGFBP related protein, and reinforces the concept of a relationship with the IGFBPs. Beyond the N-terminal domain, there is a lack of structural similarity between the IGFBP-rPs and IGFBPs. The C-terminal domains do share similarities to other internal domains found in numerous other proteins. For example, the similarity of the IGFBP C terminus to the thyroglobulin type-I domain shows that the IGFBPs are also structurally related to numerous other proteins carrying the same domain (87). Interestingly, the functions of the different C-terminal domains in members of the IGFBP superfamily include interactions with the cell surface or ECM, suggesting that, even if they share little sequence similarities, the C-terminal domains may be functionally related. The evolutionary conservation of the N-terminal domain and functional studies support the notion that IGFBPs and IGFBP-rPs together form an IGFBP superfamily. A superfamily delineates between closely related (classified as a family) and distantly related proteins. The IGFBP superfamily is therefore composed of distantly related families. The modular nature of the constituents of the IGFBP superfamily, particularly their preservation of an highly conserved N-terminal domain, seems best explained by the process of exon shuffling of an ancestral gene encoding this domain. Over the course of evolution, some members evolved into high-affinity IGF binders and others into low-affinity IGF binders, thereby conferring on the IGFBP superfamily the ability to influence cell growth by both IGF-dependent and IGF-independent means (Fig. 10). A final word, from Stephen Jay Gould (218): "But classifications are not passive ordering devices in a world objectively divided into obvious categories. Taxonomies are human decisions imposed upon nature--theories about the causes of nature's order. The chronicle of historical changes in classification provides our finest insight into conceptual revolutions
Collapse
Affiliation(s)
- V Hwa
- Department of Pediatrics, Oregon Health Sciences University, Portland 97201, USA
| | | | | |
Collapse
|
13
|
Maile LA, Gill ZP, Perks CM, Holly JM. The role of cell surface attachment and proteolysis in the insulin-like growth factor (IGF)-independent effects of IGF-binding protein-3 on apoptosis in breast epithelial cells. Endocrinology 1999; 140:4040-5. [PMID: 10465274 DOI: 10.1210/endo.140.9.6984] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We have recently reported that insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) can significantly increase ceramide-induced apoptosis in an Hs578T breast carcinoma cell line in an IGF-independent manner. It was observed in that study that IGFBP-3 added to the cultures was proteolytically modified, generating a specific pattern of fragmentation. We have also previously reported that almost all of the IGFBP-3 outside the circulation in extravascular fluids is in a fragmented form, apparently due to the activity of a cation-dependent serine protease. The aim of this study was to investigate the role of proteolysis in the IGFBP-3 enhancement of C2-induced apoptosis. In this study we confirmed that preincubation of Hs578T cells with IGFBP-3 enhances the apoptotic effect of the ceramide analog C2. The presence of IGF-I completely inhibited the enhancement effect, apparently by inhibiting cell surface association and proteolytic modification. The presence of a serine protease inhibitor [4-(2-aminoethyl)benesulfonyl fluoride] completely inhibited the enhancement effect of IGFBP-3, and Western immunoblotting of conditioned medium and cell surface-associated IGFBP-3 revealed that proteolytic fragmentation of the IGFBP-3 was reduced. In addition, fragments from the incubation of IGFBP-3 with plasmin were able to enhance the susceptibility of Hs578T cells to C2. The effect of these fragments could, however, also be reduced by 4-(2-aminoethyl)benesulfonyl fluoride despite the fact that IGFBP-3 was already fragmented. This suggests additional roles for serine proteases in the IGFBP-3 effect on C2-induced apoptosis in addition to the cleavage of the binding protein.
Collapse
Affiliation(s)
- L A Maile
- Department of Surgery, University of Bristol, Bristol Royal Infirmary, United Kingdom
| | | | | | | |
Collapse
|
14
|
Perbal B. Nuclear localisation of NOVH protein: a potential role for NOV in the regulation of gene expression. Mol Pathol 1999; 52:84-91. [PMID: 10474687 PMCID: PMC395679 DOI: 10.1136/mp.52.2.84] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
AIMS To identify the NOV protein detected by immunofluorescence in the nucleus of human cancer cell lines to establish whether targeting to the nucleus reflects dual paracrine and intracrine biological functions of NOV, as has been reported previously for several signalling peptides and proteins. METHODS Nuclear and cytoplasmic fractions were prepared from 143 and HeLa cells in which nuclear NOV protein was detected. Western blotting analysis of NOV proteins in both types of fractions was performed using two NOV specific antibodies. Confocal microscopy was used to visualise the nuclear NOV protein in HeLa and 143 cells. A yeast two hybrid screening system was used to isolate cDNAs encoding proteins able to interact with the human NOV protein. RESULTS A 31/32 kDa doublet of NOV protein was identified in the nuclear fraction of 143 and HeLa cells. Because the antibodies were directed against the C-terminus of NOV, the 31/32 kDa NOV isoform is probably truncated at the N-terminus and might correspond to the secreted 32 kDa NOV isoform detected in cell culture medium. Confocal microscopy indicated that in addition to the cytoplasmic NOV protein already identified, a nuclear NOV protein was present in both the nucleoplasm and nucleoli of Hela and 143 cells. Screening of cDNA libraries prepared from HeLa cells, Epstein-Barr virus transformed lymphocytes, and normal human brain showed that the NOV protein interacts with the rpb7 subunit of RNA polymerase in a yeast two hybrid system. CONCLUSIONS The NOV protein detected in the nucleus of 143 and HeLa cells is probably an N-terminus truncated isoform of the secreted 48 kDa NOV protein. A growing body of evidence suggests that novH expression is closely associated with differentiation in normal human tissues and that the nov gene encodes a signalling protein that belongs to an emerging family of cell growth regulators. The nuclear localisation of a NOV isoform potentially provides an additional degree of signalling specificity. The interaction of the NOV protein and the rpb7 subunit of RNA polymerase II in the two hybrid system suggests that NOV might be involved in regulating gene expression at the transcriptional level. As has already been suggested for several other nuclearly located cytokines, the NOV protein does not contain a typical nuclear localisation signal. Therefore, it is possible that it combines with either a receptor or a chaperone during its translocation. Disruption of the balance between the secreted and nuclear NOV isoforms might affect the putative autocrine and paracrine functions of NOV and might be of considerable importance in the development of cancers in which the expression of novH has been shown to be impaired.
Collapse
Affiliation(s)
- B Perbal
- UFR de Biochimie, Université, Paris, France.
| |
Collapse
|
15
|
Abstract
The six insulin-like growth factor-binding proteins (IGFBPs) are important regulators of insulin-like growth factor (IGF) action. Circulating high molecular weight complexes that contain IGF and IGFBP-3 restrict IGF bioavailability, and excess IGFBPs inhibit IGF action by forming biologically inactive complexes. IGFs can be released from these complexes by proteolysis. Potentiation of IGF activity might occur under specific circumstances, and involves the slow dissociation of IGFs from IGFBP complexes localized in the pericellular space, whose affinity has been reduced by dephosphorylation or association with the cell surface or extracellular matrix. Several IGFBPs or IGFBP fragments also have activities that do not involve IGFs or IGF receptors. The mechanisms by which IGFBPs regulate IGF action and exert their independent actions will be examined.
Collapse
Affiliation(s)
- M M Rechler
- Growth and Development Section, Molecular and Cellular Endocrinology Branch, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA
| | | |
Collapse
|