Demonstration of insulin-like growth factor (IGF-I and -II) receptors and binding protein in human breast cancer cell lines

IGFBP-2 and -5: important regulators of normal and neoplastic mammary gland physiology

The insulin-like growth factor (IGF) axis plays an important role in mammary gland physiology. In addition, dysregulation of this molecular axis may have a causal role in the aetiology and development of breast cancer (BC). This report discusses the IGF axis in normal and neoplastic mammary gland with special reference to IGF binding proteins (IGFBPs) -2 and -5. We describe how these high affinity binders of IGF-1 and IGF-2 may regulate local actions of growth factors in an autocrine and/or paracrine manner and how they also have IGF-independent effects in mammary gland. We discuss clinical studies which investigate both the prognostic value of IGFBP-2 and -5 expression in BC and possible involvement of these genes in the development of resistance to adjuvant endocrine therapies.

Insulin-like growth factor - oestradiol crosstalk and mammary gland tumourigenesis

Development and differentiation of the mammary gland are dependent on the appropriate temporal expression of both systemically acting hormones and locally produced growth factors. A large body of evidence suggests that molecular crosstalk between these hormonal and growth factor axes is crucial for appropriate cell and tissue function. Two of the most important trophic factors involved in this process are the oestrogen (E) and insulin-like growth factor (IGF) molecular axes. The reciprocal crosstalk that exists between these pathways occurs at transcriptional/post-transcriptional and translational/post-translational levels regulate the expression and activity of genes involved in this process. In a clinical context an important consequence of such crosstalk in the mammary gland is the role which it may play in the aetiology, maintenance and development of breast tumours. Although oestradiol (E2) acting through oestrogen receptors α and β (ERα/β) is important for normal mammary gland function it can also provide a mitogenic drive to ER+ breast tumours. Therefore over several years anti-oestrogen therapeutic regimens in the form of selective oestrogen receptor modulators (SERMs - e.g. tamoxifen), aromatase inhibitors (AI e.g. anastrozole) or selective oestrogen receptor down regulators (SERDs - e.g. fulvestrant) have been used in an adjuvant setting to control tumour growth. Although initial response is usually encouraging, large cohorts of patients eventually develop resistance to these treatments leading to tumour recurrence and poor prognosis. There are potentially many routes by which breast cancer (BC) cells could escape anti-oestrogen based therapeutic strategies and one of the most studied is the possible growth factor mediated activation of ER(s). Because of this, growth factor modulation of ER activity has been an intensively studied route of molecular crosstalk in the mammary gland. The insulin-like growth factors (IGF-1 and -2) are amongst the most potent mitogens for mammary epithelial cells and there is accumulating evidence that they interact with the E2 axis to regulate mitogenesis, apoptosis, adhesion, migration and differentiation of mammary epithelial cells. Such interactions are bi-directional and E2 has been shown to regulate the expression and activity of IGF axis genes with the general effect of sensitising breast epithelial cells to the actions of IGFs and insulin. In this short review we discuss the evidence for the involvement of crosstalk between the insulin-like growth factor (IGF) and oestrogen axes in the mammary gland and comment on the relevance of such studies in the aetiology and treatment of BC.

Insulin-like growth factor-2 (IGF-2) activates estrogen receptor-α and -β via the IGF-1 and the insulin receptors in breast cancer cells

The estrogen receptor (ER) is a primary target for breast cancer (BC) treatment. As BC progresses to estrogen-independent growth, the insulin-like growth factor-1 receptor (IGF-1R) and the ER interact in synergistic cross-talk mechanisms, which result in enhanced activation of both receptors' signaling cascades. Insulin-like growth factor-2 (IGF-2) is critical in BC progression and its actions are mediated by the IGF-1R. Our previous studies showed that IGF-2 regulates survival genes that protect the mitochondria and promote chemoresistance. In this study, we analyzed BC cells by subcellular fractionation, Western-Blot, qRT-PCR, and siRNA analysis. Our results demonstrate that IGF-2 activates ER-α and ER-β, and modulates their translocation to the nucleus, membrane organelles, and the mitochondria. IGF-2 actions are mediated by the IGF-1R and the insulin receptor. This novel mechanism of IGF-2 synergistic cross-talk signaling with ER-α and ER-β can promote estrogen-independent BC progression and provide new therapeutic targets for the treatment of BC patients.

Effects of endogenous insulin-like growth factor binding protein-3 on cell cycle regulation in breast cancer cells

High tissue insulin-like growth factor binding protein-3 (IGFBP-3) expression in breast cancers is associated in some studies with rapid growth and poor outcome. This study examined the effects of endogenous IGFBP-3 in Hs578T breast cancer cells, which are IGF-unresponsive and grow aggressively despite relatively high IGFBP-3 expression. IGFBP-3 downregulation using siRNA was associated with increases in DNA synthesis, the percentage of cells in S phase and viable cell numbers, accompanied by increases in cyclins A and D1, a decrease in p27 expression, and increased phosphorylation of retinoblastoma (Rb) on Ser795. Downregulation of IGFBP-3 inhibited extracellular signal-regulated kinase (ERK) activation and cell migration in a monolayer wound healing assay. These results indicate that endogenous IGFBP-3 is anti-proliferative and pro-migratory in Hs578T cells and that these effects are IGF-independent. Poor outcome in breast tumours expressing high levels of IGFBP-3 may be due to the effects of IGFBP-3 on cell migration rather than cell growth.

Resveratrol regulates insulin-like growth factor-II in breast cancer cells

IGF-II is a potent mitogen and inhibitor of apoptosis in breast cancer. Regulation of IGF-II is complex and includes inhibition by tumor suppressors, stimulation by oncogenes, and imprinting and hormonal regulation by estrogens. Resveratrol (RSV) is a phytoestrogen that displays estrogen-like agonistic and antagonistic activity. Recent studies have shown that RSV inhibits the growth of breast cancer cells and may represent a potent agent in chemopreventive therapy. Because 17beta-estradiol regulates IGF-II, we hypothesized that RSV may have a similar effect on IGF-II. The present study was designed to examine whether: 1) RSV modulates IGF-II in breast cancer cells; 2) regulation of IGF-II by RSV is dependent on the ER status; and 3) IGF-II (not IGF-I) mediates RSV effects on breast cancer cells. Treatment of MCF-7 and T47D cells with RSV (10(-6) M) caused stimulation of precursor IGF-II mRNA and protein; this effect was blocked by coincubation with 17beta-estradiol (10(-9) M). Cell growth stimulated by RSV (10(-6) M) was blocked by addition of a blocking IGF-I receptor antibody, or the antiestrogen tamoxifen (10(-7) M). In contrast, RSV treatment (10(-4) M) inhibited IGF-II secretion and cell growth in MCF-7 and T47D cells. No increase in IGF-II levels is seen in estrogen receptor (-) MCF-10 cells, even though cell growth was inhibited by RSV 10(-4) M and precursor IGF-II blocked the inhibitory effect of resveratrol. No change in IGF-I was observed with RSV treatment (10(-6) to 10(-4) M). Our study demonstrates that RSV regulates IGF-II and that IGF-II mediates RSV effect on cell survival and growth in breast cancer cells.

Insulin-Like Growth Factor-I and Breast Cancer Therapy

Targeting hormonal and growth factor signaling pathways has proven to be useful in the treatment of breast cancer. In vitro, animal, and epidemiologic evidence provide a rationale for the relevance of the insulin-like growth factor (IGF) system to breast cancer biology. The IGF system has been implicated in promoting mitogenic, metastatic, and antiapoptotic phenotypes in breast cancer. As a consequence of the ability of IGF to promote tumorigenesis, pharmacologic interventions targeting the IGF system are being devised. Such strategies include decreasing ligand production, ligand binding, or receptor activation. In this article, directed anti-IGF strategies and the possible clinical impact of using such therapies for treating breast cancer are discussed.

The insulin-like growth factor system in advanced breast cancer

Despite improvements in therapy, the prognosis for advanced breast cancer is poor and a search for new treatment targets and key regulators of tumour growth is warranted. Extensive data are available on the importance of the insulin-like growth factor (IGF) system in growth regulation of breast cancer cell lines in vitro, indicating that the IGF-I receptor (IGF-IR), IGF-I (and IGF-II) function as survival factors, while IGF binding protein (IGFBP)-3 may act as a growth inhibitor. There is a tight link between the growth regulatory pathways of IGFs and oestrogens in oestrogen-receptor(OR)-positive breast cancer cells. In vivo studies indicate a role of IGF-I and IGF-IR in breast cancer development. However, the importance of the IGF system in metastatic and highly aggressive breast tumours in vivo is not clear, and therapeutic strategies designed to interrupt IGF signalling have not yet proved to be an effective treatment modality in patients with metastatic breast cancer.

Cytokines facilitate chemotactic motility of breast carcinoma cells

BACKGROUND

Both growth and motility of various tumor cells have been shown to be influenced by surrounding cells such as lymphocytes, histiocytes and fibroblasts through various cytokines, growth factors and extracellular matrices. The role of cytokines and extracellular matrices produced by lymphocytes, histiocytes and fibroblasts on migration and invasion of breast carcinoma cells has not been fully investigated

METHODS

We investigated the effect of hepatocyte growth factor (HGF), interleukin (IL)-6, IL-8, IL-11, soluble type IV collagen and soluble laminin on the migration of 3 human breast carcinoma cell lines, MDA-MB-231, MCF-7 and T-47D, using a cell culture insert and a biocoat matrigel invasion chamber to assess migration across a matrigel-coated polyethylene telephtalate membrane.

RESULTS

HGF, IL-6, IL-11 and IL-8 induced significant migration of MDA-MB-231 cells depending on the dose of each cytokine. However, type IV collagen and laminin inhibited migration of MDA-MB-231 cells. In contrast, IL-8 inhibited migration of MCF-7 cells and IL-6 induced significant migration of T-47D cells, while no other cytokine or extracellular matrix induced significant migration of MCF-7 and T-47D cells. Only HGF induced significant invasion of MDA-MB-231 cells depending on the dose. MCF-7 and T-47D cells did not invade in response to any of the cytokines and extracellular matrices tested.

CONCLUSIONS

These results suggest the possibility that the potency of chemotaxis or chemoinvasion differs according to the breast carcinoma cell line and that various cytokines and extracellular matrices secreted by lymphocytes, histiocytes and fibroblasts in the stroma of breast carcinoma can affect the invasion of breast carcinoma cells.

The effects of insulin-like growth factors on tumorigenesis and neoplastic growth

Several decades of basic and clinical research have demonstrated that there is an association between the insulin-like growth factors (IGFs) and neoplasia. We begin with a brief discussion of the function and regulation of expression of the IGFs, their receptors and the IGF-binding proteins (IGFBPs). A number of investigational interventional strategies targeting the GH or IGFs are then reviewed. Finally, we have assembled the available scientific knowledge about this relationship for each of the major tumor types. The tumors have been grouped together by organ system and for each of the major tumors, various key elements of the relationship between IGFs and tumor growth are discussed. Specifically these include the presence or absence of autocrine IGF-I and IGF-II production; presence or absence of IGF-I and IGF-II receptor expression; the expression and functions of the IGFBPs; in vitro and in vivo experiments involving therapeutic interventions; and available results from clinical trials evaluating the effect of GH/IGF axis down-regulation in various malignancies.

The haematopoietic effects of growth hormone and insulin-like growth factor-I

The process of haemopoiesis, occurring primarily within the bone marrow, involves the proliferation and differentiation of pluripotent haemopoietic stem cells into committed, or pathway-restricted progenitors /1/. The latter further proliferate and undergo a process of maturation into circulating blood cells of myeloid and erythroid lineages /2/. Haemopoietic cell growth and differentiation is primarily regulated by the local production of various cytokines within the bone marrow micro-environment /3/, as well as by the circulating hormone, erythropoietin (EPO). The formation as well as functional activation of mature blood cells, are also modulated by a variety of hormones and growth peptides, including growth hormone (GH) and insulin-like growth factor-I (IGF-I) /4,5/. Early evidence for the role of GH in modulating haemopoiesis was provided in classical studies in rodents, which showed that removal of the pituitary gland affects blood cell formation and function /6/ and that impairment of the latter can be restored by GH administration /7/. GH exerts its effects on target cells by binding to its own receptor, which belongs to the class I cytokine receptor superfamily /8/. In humans, GH can also bind to and activate the prolactin receptor /9/. Based on the somatomedin hypothesis of Salmon and Daughaday /10/, it is now generally accepted that, in addition to the above, GH exerts many of its effects via autocrine or paracrine IGF-I, as well as via endocrine IGF-I produced in the liver. IGF-I, a small single-chain polypeptide, is one of two highly homologous peptides (IGF-I and IGF-II), that stimulate the proliferation and differentiation of a wide variety of cell types, including bone marrow cells /5,11/. Both IGF-I and IGF-II play an important role in prenatal growth and IGF-I is also essential for postnatal growth and development /12/. Two types of IGF receptors have been described. The type I IGF receptor, a tyrosine kinase receptor highly homologous to the insulin receptor, binds IGF-I and IGF-II with a high affinity. The type II/mannose 6-phosphate receptor which lacks intrinsic kinase activity, binds IGF-II with a high affinity and IGF-I with a low affinity /13,14/. Haemopoietic progenitors and mature blood cells have been shown to produce GH and IGF-I and to express receptors for these peptides. GH and IGF-I may act independently on these cells or, as more commonly observed, in a synergistic manner with primary haemopoietic cytokines. GH and IGF-I receptors are also present on freshly explanted leukemic cells and leukemic cell lines. Thus, their possible contribution to the development of leukemia should also be considered. This review summarizes our current understanding of the role of GH and IGF-I in normal and malignant haemopoiesis.

Hormonal breast augmentation: prognostic relevance of insulin-like growth factor-I

Many women would like to after their breasts but are deterred by the risks involved. Silicone breast implants have been linked to a variety of illnesses, the most controversial of which are connective-tissue diseases. These circumstances urged us to perform this pilot study using a non-invasive method that involved the application of 17 beta-estradiol as it is known that estradiol enhances expression of insulin-like growth factor-I (IGF-I) which can promote growth in breast tissue. Forty-five women were included in the study. Their breast volume, IGF-I, prolactin (PRL) and estradiol levels were measured before treatment and between each application of 80 mg estradiol polyphosphate. The women's satisfaction with the results obtained was also subsequently evaluated. In 21 women (46.7%), breast size increased from 824.3 +/- 13.7 mm to 898.5 +/- 12.5 mm after 6 months. In these women a significant increase in IGF-I values was noted after 4 weeks of treatment. The increase in IGF-I values was not statistically significant in the remaining women. In addition, treatment was not successful in these women. IGF-I concentration seems to be of prognostic value as far as the response of breast tissue to estrogen stimulation is concerned. If IGF-I levels do not increase within 1 month, treatment should be discontinued. If IGF-I values do increase, this indicates that treatment is likely to be successful and can therefore be continued.

IGF-independent regulation of breast cancer growth by IGF binding proteins

The human IGFBP family consists of at least seven proteins, designated as IGFBP-1, -2, -3, -4, -5, -6, and-7. IGFBPs 1-6 bind IGF-I and IGF-II with high affinity whereas IGFBP-7, a newly identified IGFBP, binds IGFs with lower affinity and constitutes a low-affinity member of the IGFBP family. IGFBPs serve to transport the IGFs, prolong their half-lives, and modulate their biological action. At the cellular level, IGFBPs can either potentiate or inhibit the mitogenic effects of IGFs, depending upon cell types and IGFBP species (IGF-dependent action of IGFBPs). However, recent studies have indicated that IGFBPs, especially IGFBP-3, potently inhibit breast cancer cell growth in an IGF-independent manner. The IGF-independent action of IGFBP-3 requires interaction with cell-surface association proteins, presumably putative IGFBP-3 specific receptors, and is responsible for growth inhibitory action of the known growth suppressing factors such as TGF-beta, retinoic acid, and antiestrogens in breast cancer cells. Thus, IGFBP-3 appears to be a major factor in a negative control system involved in regulating human breast cancer cell growth in vitro. IGFBP-7, representing a low affinity IGFBP, appears to function as an IGF-independent cell growth regulator in breast cancer cells. Overall structural similarity between IGFBP-7 and classical high affinity IGFBPs 1-6 suggests that the mechanisms of action and signaling pathways used by IGFBP-7 may provide insight into the IGF-independent actions of the high affinity IGFBPs. A fuller understanding of the IGF-independent action of IGFBPs will allow us to understand how the growth of neoplastic cells can be modulated by the IGF/IGFBP system, and how other growth factors or pharmacological agents can interface with this system.

Loss of heterozygosity at the mannose 6-phosphate insulin-like growth factor 2 receptor gene correlates with poor differentiation in early breast carcinomas

Chromosome 6q has been shown to be one of the most frequent sites for allelic loss in human breast cancer. The mannose 6-phosphate/insulin-like growth factor 2 receptor (IGF2R) gene, which maps to chromosome 6q26-27, functions in the activation of TGF-beta1, a potent growth inhibitor for most cell types, the degradation of the mitogen IGF2 and the intracellular trafficking of lysosomal enzymes. Loss of heterozygosity (LOH) at the IGF2R locus with mutations in the remaining allele have been reported in liver cancers and recently in two high-grade cases of ductal carcinoma in situ of the breast. We have sought to confirm that allelic loss of IGF2R is an early event in the aetiology of breast cancer by screening a group of 'early' lesions for LOH at a polymorphic microsatellite marker within the IGF2R gene using polymerase chain reaction (PCR). Several microdissected tumour foci were analysed for each of 40 mammographically detected invasive carcinomas and 22 cases of pure ductal carcinoma in situ (DCIS). None of 25 (62.5%) informative early invasive carcinomas showed any evidence of LOH. This group comprised predominantly of well- to moderately differentiated cases (95%). However, 4 out of 18 informative DCIS cases (22%) showed clear evidence of LOH. Three of these were poorly differentiated (high-grade) lesions. These data suggest that loss of heterozygosity at the IGF2R gene is associated with poor differentiation at this early stage of breast cancer development and progression.

Mechanisms of action of endocrine treatment in breast cancer

Endocrine treatment plays an important role in the therapy of breast cancer. While the basic mechanisms are understood, additional mechanisms may be of importance to their action and they may also contribute to the mechanism(s) of acquired resistance. Currently, several novel drugs are entering into clinical trials. Observations of the absence or presence of cross resistance to novel 'pure' steroidal antiestrogens and the non-steroidal tamoxifen may add important information to our understanding of the mechanisms of action of both classes of drugs. Similarly, exploration of different aromatase inhibitors in sequence or concert, as well as the combining of different endocrine treatment options may be warranted. Additionally, alterations in different biochemical parameters such as growth factors should not only be carefully explored in relation to treatment options but should also be followed during the course of treatment to asess alterations over time and in relation to the development of drug resistance.

Components of the IGF system mediate the opposing effects of tamoxifen on endometrial and breast cancer cell growth

The involvement of the IGF system in the growth regulation of hormone-dependent (e.g. endometrial and breast) cancer cells was studied. We chose two opposing effects of tamoxifen: the paradoxical stimulation of Ishikawa endometrial cancer cells growth and its inhibitory effect on MCF-7 mammary cancer cells. The results clearly confirm our working hypothesis that the IGF system is involved in growth regulation of these cancer cells irrespective of the direction of the drug effect. The following parameters of the IGFs system were studied: IGF-I receptors, IGF-I stimulated protein tyrosine phosphorylation, and membrane-associated and secreted IGF-binding proteins (IGFBPs). In Ishikawa cells, tamoxifen, similar to estradiol, increased IGF-I stimulated tyrosine phosphorylation of cellular substrates in accordance with its effect on cell growth. This effect of tamoxifen was inverted in MCF-7 cells. Tamoxifen did not affect the number or affinity of IGF-I receptors in both Ishikawa and MCF-7 cells, however, it caused a three-fold decrease in membrane-associated IGFBPs in the endometrial cells but an increase in these proteins in breast cancer cells. Similar but much less pronounced changes in soluble IGFBPs were observed. Our results indicate that the opposing growth effects of tamoxifen an endometrial and mammary cancer cells are associated with modulation of the IGF system components, mainly with reciprocal changes in membrane-associated IGFBPs.

Antiproliferative actions of insulin-like growth factor binding protein (IGFBP)-3 in human breast cancer cells

A number of lines of evidence suggest that IGFs are important mitogens in human breast cancer: (1) IGFs are the most potent growth factor in human breast cancer cells; (2) estrogen stimulates expression of IGF-II and the type 1 IGF receptor; and (3) stromal cells express IGFs, which may act in a paracrine manner. Numerous studies have demonstrated that IGFBPs modulate the mitogenic effects of IGFs in the local environment. In particular, we have recently demonstrated that IGFBP-3 inhibits the growth of Hs578T and MDA-MB-231 human breast cancer cells in an IGF-independent manner. Further studies revealed the existence of cell surface-associated IGFBP-3 receptors. Receptor binding and the subsequent antiproliferative action of IGFBP-3 was inhibited by IGFs, owing to the formation of an IGF-IGFBP-3 complex that prevents the binding of IGFBP-3 to its receptors. In addition, exogeneously added soluble heparin or heparan sulfate inhibited the binding of IGFBP-3 to the cell surface in a dose-dependent manner. However, when heparin and heparan sulfate linkages of glycosaminoglycans on the cell surface were enzymatically remove, IGFBP-3 binding was only minimally affected. These data suggest that soluble heparin or heparan sulfate forms a complex with IGFBP-3, thereby inhibiting receptor binding of IGFBP-3, rather than competing with cell-surface glycosaminoglycans for binding of IGFBP-3. Additionally, the role of IGFBP-3 in the antiproliferative effects of transforming growth factor (TGF)-beta and retinoic acid (RA) is supported by our observations that: (1) inhibition of IGFBP-3 gene expression using an IGFNBP-3 antisense oligodeoxynucleotide not only blocks TGF-beta and RA simulation of IGFBP-3 production by up to 90%m but also inhibits their antiproliferative effects by 40-60%; and (2) treatment with IGF-II and IGF-II analogs diminish TGF-beta effects by blocking TGF-beta induced binding of IGFBP-3 to the cell surface. Taken together, our results support the hypothesis that IGFBP-3 is an important antiproliferative factor in human breast cancer, acting in an IGF-independent manner in addition to its ability to modulate the binding of IGF peptides to IGF receptors.

Insulin-like growth factors and breast cancer

Several years of research have indicated that the insulin-like growth factor (IGF) family of ligands, receptors and binding proteins are expressed in human breast cancer. The ligands are potent mitogens for breast cancer cell lines, and blockade of IGF signaling inhibits tumor growth. The IGFs can be regulated in normal and neoplastic tissue, indicating their important role in proliferation. For example, estrogen, a hormone important in the growth and progression of breast cancer is able to alter expression of IGF ligands, receptors and binding proteins. In addition, recent data now indicate that IGF ligands can also activate estrogen receptor (ER) in a ligand-independent manner. The apparent cross-talk between IGF and ER signaling is especially important to consider since anti-estrogens, such as tamoxifen, are a major modality for the treatment of breast cancer. Recent data suggest that IGFs may also be involved in tamoxifen resistance, through upregulation of the IGF-I receptor. Thus blockade of IGF signaling in combination with tamoxifen may prove to be a beneficial treatment for breast cancer patients.

Pharmacokinetic and pharmacodynamic properties of a long-acting formulation of the new somatostatin analogue, lanreotide, in normal healthy volunteers

1. The aims of the study were to assess the pharmacokinetic parameters and the hormonal effects of the slow-release formulation of the somatostatin analogue (SR-L) in normal male volunteers. 2. Eight healthy males were studied. For the determination of basal values blood was sampled before the injection of vehicle and then every other hour for 8 h in order to measure plasma GH, prolactin (PRL), TSH, free thyroxin (fT4), insulin and glucagon levels. Plasma insulin-like growth factor 1 (IGF-1) levels were measured on a single sample. On day 1 of the study, 30 mg SR-L was administered intramuscularly. Blood was drawn just before injection and then every other hour for a period of 8 h. Thereafter, blood was sampled three times a week for 3 weeks in order to measure lanreotide, IGF-1, TSH, fT4 and PRL concentrations. Plasma GH was determined on days 6 and 11 of the study. 3. Plasma lanreotide concentrations rose to 38.3 +/- 4.1 ng ml-1 2 h following injection. The levels then progressively decreased, remaining above 1.5 ng ml-1 until day 11 and reaching 0.92 +/- 0.28 ng ml-1 2 weeks after injection. The apparent plasma half-life and mean residence time were 4.52 +/- 0.50 and 5.48 +/- 0.51 days respectively. 4. By comparison with the control day, plasma insulin concentrations only decreased 2 h following injection, whereas plasma glucagon did not change at any time. 5. Plasma TSH concentrations were significantly (P < 0.01) reduced from 2 h to day 4 following SR-L injection.2+ '

Regulation of insulin-like growth factor 1 binding protein 3 levels by epidermal growth factor and retinoic acid in cervical epithelial cells

Insulin-like growth factors (IGFs) are important regulators of epithelial cell growth. The mitogenic activity of these factors is influenced by the levels of extracellular IGF binding proteins, including insulin-like growth factor binding protein 3 (IGFBP-3). In the present report we study the effects of epidermal growth factor (EGF) and all-trans-retinoic acid (RA) on IGFBP-3 RNA and protein levels in human papillomavirus-immortalized cervical epithelial cells. Treatment of ECE16-1 cells with 3-20 ng/ml EGF causes a marked reduction in IGFBP-3 levels. In contrast, 1 microM RA increases IGFBP-3 mRNA and protein levels in the presence or absence of 20 ng/ml EGF. The response is concentration dependent with a half-maximal increase observed at 1 nM RA. RA is able to reverse the EGF suppression when added simultaneously or 3 days after initiation of EGF treatment. Conversely, when cells are treated with RA, IGFBP-3 levels increase within 24 h and subsequent addition of EGF is without effect. Thus, the RA-dependent increase in IGFBP-3 levels is dominant over the EGF suppression. The increased IGFBP-3 levels are correlated with RA suppression of proliferation. Similar RA effects on IGFBP-3 mRNA levels were observed in other cervical epithelial cell lines (i.e., ECE16-D1, ECE16-D2, and CaSki). These results suggest that RA may act to inhibit cervical cell growth by increasing IGFBP-3 levels and reducing the extracellular concentration of free insulin-like growth factor I (IGFI) and/or alternatively, IGFBP-3 may inhibit cell growth by direct effects on the cell, independent of IGFI.

Analysis of the IGF-II receptor gene copy number in breast carcinoma

Insulin and the insulin-like growth factors (IGFs) may be important regulators of breast cancer growth. The IGF-II receptor is identical to the mannose 6-phosphate (Man-6-P) receptor, which is involved in lysosomal enzyme pathways. In order to determine whether the Man-6-P/IGF-II receptor gene copy number is altered in breast cancer we analysed specimens of invasive breast carcinoma from 51 patients by Southern blotting. No amplification of the receptor gene was observed whatever the clinical presentation of the tumour and irrespective of a concomitant amplification of c-erbB2 or int-2 genes in several tumours. As indicated by Northern blotting, the gene is transcribed in breast tumour tissues and non-tumour breast tissue. These results suggest that the receptor gene is stable in breast carcinoma and that, if anything, the receptor involvement in breast cancer progression may be the result of a disregulation of its expression at a post-transcriptional or post-translational level.

Expression of insulin-like growth factor binding proteins by T-47D human breast cancer cells: regulation by progestins and antiestrogens

We have used ligand blotting and Northern blotting techniques to examine the effects of progestins and antiestrogens on expression of insulin-like growth factor binding proteins (IGFBPs) by T-47D human breast cancer cells under conditions where these agents are growth inhibitory. Under basal conditions, conditioned medium from T-47D cells was found to contain IGFBPs of 39, 33, and 27 kDa. Northern blot and/or Western blot analysis have identified these as IGFBP 2, 5, and 4, respectively. Medroxyprogesterone acetate (MPA) treatment resulted in a time- and dose-dependent decrease in IGFBP 4 and 5 mRNA abundance and secretion of these proteins, while little if any effect was observed on IGFBP 2 expression. A decrease in the steady state mRNA levels for IGFBP 4 and 5 was observed with as little as 0.1 nM MPA. Using 10 nM MPA a maximum decrease in IGFBP 4 and 5 mRNA levels was observed between 12 and 24 hours. While RU 486 alone had little or no effect on IGFBP 4 expression, it inhibited the effect of MPA. However, in the same samples, IGFBP 5 expression was inhibited by RU 486, and RU 486 was unable to reverse the effects of progestins on the expression of IGFBP 5. Furthermore, another synthetic progestin, Org 2058, but not dexamethasone, inhibited IGFBP 4 and IGFBP 5 expression. The antiestrogen ICI 164384 also transiently decreased the steady state mRNA levels of both IGFBP 4 and IGFBP 5. Regulation of expression of the IGFBPs by these agents suggests a potential role for the IGFBPs in the growth response of T-47D cells to these agents.

Pharmacokinetic study and effects on growth hormone secretion in healthy volunteers of the new somatostatin analogue BIM 23014

We have studied the pharmacokinetics and the effects of BIM 23,014 (BIM), a new, long-acting octapeptide somatostatin analogue, on basal and stimulated GH secretion in normal men. BIM 250 micrograms sc significantly reduced a GHRH-induced increase in plasma GH. The continuous sc administration of BIM for 24 h dramatically blunted spontaneous GH secretion; 2000 and 3000 micrograms daily reduced GH secretion to a greater extent than 1000 micrograms daily. During these experiments a significant negative correlation (r - 0.66) was found between plasma GH and BIM levels. Acute sc administration of 1000 micrograms BIM significantly reduced the rise in plasma GH observed in the second part of the oral glucose tolerance test. Plasma BIM levels peaked around 30 min, and the elimination half life was 90 min. Plasma BIM levels were below 1 ng/ml 6 h after the injection of 1000 micrograms BIM, and at that time GH started to rise again. We conclude that BIM 23,014 250 to 1000 micrograms sc is able to reduce the plasma GH response to GHRH or to the fall in glucose following an oral glucose tolerance test; a constant infusion of BIM, in doses 1000 micrograms daily, dramatically suppresses spontaneous GH secretion; 2000 micrograms/day by chronic subcutaneous infusion was the most effective dose of BIM in the suppression of GH secretion, and was associated only with minor adverse effects.

Insulin-like growth factor I activates the invasion suppressor function of E-cadherin in MCF-7 human mammary carcinoma cells in vitro

The calcium-dependent cell-cell adhesion molecule E-cadherin has been shown to counteract invasion of epithelial neoplastic cells. Using three monoclonal antibodies, we have demonstrated the presence of E-cadherin at the surface of human MCF-7/6 mammary carcinoma cells by indirect immunofluorescence coupled to flow cytometry and by immunocytochemistry. Nevertheless, MCF-7/6 cells failed to aggregate in a medium containing 1.25 mM CaCl2, and they were invasive after confrontation with embryonic chick heart fragments in organ culture. Treatment of MCF-7/6 cells with 0.5 microgram ml-1 insulin-like growth factor I (IGF-I) led to homotypic aggregation within 5 to 10 min and inhibited invasion in vitro during at least 8 days. The effect of IGF-I on cellular aggregation was insensitive to cycloheximide. However, monoclonal antibodies that interfered with the function of either the IGF-I receptor (alpha IR3) or E-cadherin (HECD-1, MB2) blocked the effect of IGF-I on aggregation. The effects of IGF-I on aggregation and on invasion could be mimicked by 1 microgram ml-1 insulin, but not by 0.5 microgram ml-1 IGF-II. The insulin effects were presumably not mediated by the IGF-I receptor, since they could not be blocked by an antibody against this receptor (alpha IR3). Our results indicate that IGF-I activates the invasion suppressor role of E-cadherin in MCF-7/6 cells.

Plasma insulin-like growth factor-1 (IGF-1) concentrations in human breast cancer

Insulin-like growth factor-1 (IGF-1) is capable of stimulating breast cancer cell growth in vitro and the presence of IGF-1 receptors has been demonstrated in primary breast cancers. We determined plasma IGF-1 in a primary breast cancer population and in a control population. Radioimmunoassays were performed either directly on plasma, IGF-1 (NE), or after an acid-ethanol extraction of the plasma, IGF-1 (E). We demonstrated an inverse correlation between age and IGF-1: for this reason, only results obtained in females of the same age range (> 35 years) were compared. Median concentrations of IGF-1 were significantly higher in primary breast cancers [IGF-1 (E) = 152 ng/ml, IGF-1 (NE) = 26 ng/ml, n = 44] than in controls [IGF-1 (E) = 115 ng/ml, IGF-1 (NE) = 20 ng/ml, n = 92]. To our knowledge such a growth factor increase has never been described in breast cancer. We conclude that IGF-1 could be an important factor involved in the development of breast cancer and that treatment reducing IGF-1 levels could be beneficial for patients.

Effect of endocrine therapy on growth of T61 human breast cancer xenografts is directly correlated to a specific down-regulation of insulin-like growth factor II (IGF-II)

Insulin-like growth factors I and II (IGF-I and IGF-II) are potent mitogens for some human breast cancer cell lines, and expression of IGF-II mRNA in the oestrogen receptor-positive (ER+) and oestradiol (E2) stimulated human breast cancer cell line T47D is increased by E2, suggesting a role for IGF-II in the mitogenic response to E2. Very little information is available from the literature on the relation between growth inhibition by endocrine therapy and cellular production of IGF-II. Here we report on the effect of E2 and tamoxifen (TAM) on IGF-II mRNA and protein expression in the ER+T61 human breast cancer xenograft. Growth of the T61 tumour is inhibited by treatment with E2 and TAM. Ribonuclease (RNAse) protection assays with human- and mouse-specific IGF-II antisense probes were used to study the regulation of IGF-II mRNA by E2 and TAM in the tumour. IGF-II protein expression was studied by radioimmunoassay. Untreated T61 tumours have a high baseline expression of IGF-II mRNA. TAM treatment of T61 tumours, which results in inhibition of tumour growth without tumour regression, reduced IGF-II mRNA expression approximately 10-fold after 48 h of treatment. E2 treatment of T61 tumours, which results in tumour regression, was accompanied by a more pronounced decrease in IGF-II mRNA expression in the tumour cells; 96 h after initiation of E2 treatment, there was almost no detectable IGF-II mRNA. Analyses of IGF-II protein showed that both treatments significantly reduced the concentration of IGF-II protein in the tumours. This down-regulation was found to be specific for IGF-II, since analyses of the effect of E2 on the expression of IGF-I mRNA, 36B4 mRNA, transforming growth factor alpha(TGF-alpha) mRNA, and epidermal growth factor (EGF) receptor mRNA in T61 tumours did not reveal any down-regulation. To further study the relation between inhibition of tumour growth and down-regulation of IGF-II, we exposed T61 tumours to a monoclonal antibody, alpha-IR3, which abolishes the physiological effect of IGF-I and IGF-II by blocking the binding of both growth factors to the type I IGF receptor. Treatment with alpha-IR3 resulted in inhibition of tumour growth during treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin-like growth factor binding protein-5 gene expression is differentially regulated at a post-transcriptional level in retinoic acid-sensitive and resistant MCF-7 human breast carcinoma cells

Insulin-like growth factor binding protein (IGFBP) gene expression and IGFBP secretion were investigated in a retinoic acid (RA)-resistant subline (RROI) of MCF-7 human breast carcinoma cells. Our results demonstrate that RRO-I cells constitutively secrete higher levels of IGFBP-3 and IGFBP-5. In addition, we found that a 5-fold increase in IGFBP-5 mRNA levels observed in RRO-I cells, which eventually leads to a similar increase in the secreted levels of IGFBP-5, was partly due to an increase in the stability of IGFBP-5 mRNA. Actinomycin D and cycloheximide differentially stabilized IGFBP-5 mRNA in MCF-7 cells but not in RRO-I cells, indicating a difference in the control of IGFBP-5 gene regulation at the level of mRNA stability in these cell lines.

Insulin-like growth factor 1 receptors in human breast tumour: localisation and quantification by histo-autoradiographic analysis

To assess the precise role of IGF1 in benign and malignant breast diseases, we analysed the tissular localisation, characterised, and quantified specific insulin-like growth factor 1 (IGF1) binding sites in these heterogenous tissues, using histo-autoradiographic analysis (HAA). The 125I-IGF1 binding was performed on frozen tissue sections and analysed using 3H Ultrofilm autoradiography coupled to computerised image analysis. Competitive binding experiments using unlabelled IGF1, IGF2 and insulin showed that the tissues exhibited typical type I IGF binding sites. This specificity was confirmed by the use of alpha IR-3 monoclonal antibody, as inhibitor of 125I-IGF1 binding. IGF1 binding sites were detected in 18 human primary breast cancers, 12 benign breast tumours and two normal breast tissues. Using HAA we found that the human breast carcinomas studied exhibit a specific and high binding capacity for 125I-IGF1 exclusively localised on the proliferative epithelial component. The 125I-IGF1 binding activity of benign breast tumours or normal breast tissue was significantly lower than in cancerous tissues. There was a significant correlation between IGF1-R concentrations detected with HAA and those detected with a classical biochemical method. Moreover, HAA could be useful in further detailing whether a tumour is IGF1-R positive or negative HAA appears to be a useful method for the detection of growth factor receptors, specially in small biopsy specimens.

Identification of the insulin-like growth factor binding proteins 5 and 6 (IGFBP-5 and 6) in human breast cancer cells

Four estrogen receptor-positive (ER+) [MCF-7, T47D, ZR75 and BT474] and 3 ER- [Hs578T, MDA-MB-468 and MDA-MB-231] human breast cancer cell lines were examined for expression of the IGFBP-5 and IGFBP-6 genes. Northern blot analysis revealed that all cell lines, except MDA-MB-231, expressed IGFBP-5 mRNA. IGFBP-6 mRNA, however, was expressed only by the ER- cell lines. Western immunoblotting indicated that the previously unidentified 31-kDa and 32-kDa IGF binding species secreted by these cell lines are IGFBP-5. The levels of IGFBP-4 and IGFBP-5 were increased in MCF-7 cells by estradiol and IGF-I, respectively, indicating that these BPs may contribute to the growth stimulatory response to these mitogens.

IGF-I and IGF-II expression in human breast cancer xenografts: relationship to hormone independence

Although the growth of some estrogen receptor (ER) positive breast cancers can initially be hormonally manipulated, all will eventually escape hormonal control. It is possible that the expression of polypeptide growth factors is initially under the control of steroid hormones, while the hormone unresponsive state is characterized by constitutive expression of growth factors. We studied the relationship between hormone responsiveness and IGF expression in xenograft models. The ER+ T61 xenograft was established from a primary breast cancer and has been continually passaged in athymic mice. ER+ MCF-7 cells and ER-MDA-MB-231 cells were grown in tissue culture and then inoculated into athymic mice. ER+ xenograft growth was regulated by estrogen, but with opposite results--T61 xenografts are inhibited by estrogen, while MCF-7 xenografts require estrogen for tumor formation. All xenografts expressed type I and II IGF receptors. Although T61 xenografts also express an alternatively spliced IGF-I mRNA, its expression was not regulated by estrogen. Both xenografts expressed IGF-II in a hormonally regulated manner--T61 levels were depressed by estrogen, while MCF-7 levels were increased. Thus, in these model systems, xenograft regulation of tumor growth is accompanied by parallel changes in IGF-II expression. In the estrogen independent MDA-MB-231 cells, IGF-II was constitutively expressed. These data show that IGF-II expression correlates with estrogen treatment, suggesting that autocrine expression of IGF-II may mediate estrogen-regulated cell growth.

Tamoxifen reduces serum insulin-like growth factor I (IGF-I)

Antiestrogens are widely used in the management of hormonally responsive breast cancer in both adjuvant and palliative settings, and are currently being evaluated as chemopreventive agents. The classical mechanism of action of these drugs involves inhibition of estrogen-stimulated neoplastic cell proliferation by blockade of estrogen receptors present on breast cancer cells. This paper reviews recent clinical and laboratory data that suggest that the commonly used antiestrogen tamoxifen also acts to reduce serum IGF-I levels. Estrogens appear to play a permissive role in growth hormone (GH) release by the pituitary gland and GH is known to stimulate IGF-I expression by hepatocytes. It is therefore possible that blockade of estrogen receptors in the hypothalamic-pituitary axis by tamoxifen interferes with GH release, leading to reduced hepatic IGF-I expression. In view of results suggesting that IGF-I is a more potent mitogen than estradiol for breast cancer cells and data demonstrating a positive correlation between estrogen receptor level and IGF-I receptor level of breast cancer cells, the IGF-I lowering effect of tamoxifen may contribute to the cytostatic activity of the drug. The interrelationships between steroid hormone physiology and IGF-I physiology may have relevance to a variety of commonly used treatments for hormonally responsive cancers.

Interactions of pro-cathepsin D and IGF-II on the mannose-6-phosphate/IGF-II receptor

The mannose-6-phosphate (Man-6P)/IGF-II receptor is a multifunctional receptor which binds with a high affinity on distinct sites two strikingly different classes of ligands: IGF-II, and Man-6P bearing molecules such as lysosomal enzymes or other biologically relevant ligands (TGF beta precursor, EGF receptor, proliferin...). Binding of each ligand on its cognate site is severely decreased in the presence of the other type of ligand, thus revealing that the two distinct sites are strongly interacting (steric hindrance, conformational change). Any imbalance in ligands and receptor concentration in various pathological situations (transformation, tumor, altered hormonal levels...) is thus likely to perturb their associated biological functions in the targeting and routing of lysosomal enzymes or Man-6P ligands or in the autocrine/paracrine IGF-II--induced cellular responses.

Type 1 IGF receptor in human breast diseases

The first step of the action of IGF1 and IGF2 (IGFs) is their binding to membrane receptors. IGF binding sites have been characterized by competitive binding and cross-linking techniques in human breast cancer cell lines as well as in human breast cancers and in human benign breast diseases. IGF2 is a good competitor of 125I-IGF1 binding to IGF1-R; insulin competes but with a potency 1/100 lower than the IGF1 potency. Chemical cross-linking experiments revealed that the apparent molecular weight of the IGF1-binding sites is 130,000. Alpha IR-3, a murine monoclonal antibody against the IGF1-R, blocks IGF1-binding to this receptor. This antibody inhibits the IGF1-stimulated growth of breast cancer cells. Therefore, the IGF1 specific binding sites correspond to the previously described type 1 IGF receptors (IGF1-R) in normal tissues. Cross-linking experiments with labeled IGF2 resulted in a major band of apparent Mr 260,000-270,000 that was inhibited by unlabeled IGF2 but not by insulin, and corresponds to the type 2 IGF receptor; a second band of apparent Mr 130,000 was inhibited by excess IGFs and insulin (Type I receptor). The alpha-IR3 inhibition of the IGF2 mitogenic activity suggest that IGF1-R partially mediates the growth effect of IGF2 in these cells. We and others have demonstrated that most breast cancer cell lines contain IGF1-R.(ABSTRACT TRUNCATED AT 250 WORDS)

The insulin-like growth factor binding proteins (IGFBPs) in human breast cancer

Several lines of evidence suggest that IGFs are important regulators of breast cancer cell growth. Unlike other growth factors, the IGFs interact with specific binding proteins in all extracellular fluids. To date, six different IGFBPs have been cloned, although their exact physiological function is not understood. Experimental evidence accumulated over the past few years suggests that IGFBPs could function as modulators of IGF actions in a variety of systems. This includes breast cancer, since several groups have demonstrated the production of IGFBPs by human breast cancer cells. We have found that the pattern of expression of these binding proteins is heterogeneous and varies depending on the breast cancer cell ER status. We have also shown that estrogen is capable of regulating the expression of certain IGFBPs in MCF-7 cells. Specifically, estradiol enhanced the expression of IGFBP 2, 4, and 5, and decreased that of IGFBP-3 in this cell line. Since the IGFBPs can modulate IGF actions in different experimental systems, we and others have studied their potential role as inhibitors of IGF-induced mitogenesis in breast cancer cells. We have demonstrated that purified IGFBP-1 neutralized IGF-dependent growth of MCF-7 cells in a reversible manner. These results suggest that the IGFBPs might be used to inhibit IGF-mediated breast cancer proliferation.

Effects of insulin-like growth factors (IGFs) and IGF receptor antibodies on the proliferation of human breast cancer cells

It has been shown previously that MCF-7 cells proliferate in response to nanomolar concentrations of IGF-I and IGF-II. It has also been reported that the actions of both peptides are mediated through the IGF-I receptor. To further characterize these observations, we used MCF-7 and Hs578T cell lines in the serum-free/phenol red-free system developed by Ogasawara and Sibarsku, 1988. Cell proliferation was studied in the presence of insulin, IGF-I and -II and a series of growth factor receptor antibodies. No effect was observed on Hs578T cell proliferation with any of the growth factors. However, MCF-7 cells were stimulated 4-5 fold with IGF-I and insulin, while IGF-II was only slightly less potent. alpha IR3, a monoclonal antibody directed against the IGF-I receptor, was stimulatory when added alone. However, alpha IR3 blocked approximately 50% of the IGF-I response, only 5% of the insulin response, and did not block the IGF-II effect on cell proliferation. These data suggest that alpha IR3 and IGF-I are acting as agonists through the IGF-I receptor, but that insulin and IGF-II are acting through other receptors. Two different IGF-II/M-6-P receptor antibodies and an insulin receptor antibody failed to significantly block IGF-II actions. All three antibodies were stimulatory when added alone. beta-gal inhibited 27% of the IGF-II response and had no effect when added alone. Since beta-gal decreases the binding affinity of the IGF-II/M-6-P receptor for IGF-II and does not bind to the IGF-I or insulin receptor, these data suggest the possibility that IGF-II mitogenic action is mediated through the IGF-II/M-6-P receptor. In summary, these data indicate that nanomolar concentration of insulin, IGF-I and IGF-II are potent mitogens in MCF-7 cells and can potentially stimulate cell proliferation through all three receptors.

Growth factor involvement in the multihormonal regulation of MCF-7 breast cancer cell growth in soft agar

The hormone dependency of the MCF-7 breast cancer cell line, while extensively tested in liquid culture, has not been previously evaluated under conditions of anchorage-independent growth in serum-free media. Using the soft agar clonogenic assay, we demonstrate that physiologically relevant concentrations of estradiol (E2), progesterone (Pg), and prolactin (PRL) similarly stimulated MCF-7 cell colony formation in the absence of serum. Addition of an anti-insulin-like growth factor-I (IGF-I) antibody inhibited E2- and Pg-stimulated growth, while PRL action was not affected. Similar results were obtained with an anti-IGF-I receptor antibody, except that its inhibitory effect on Pg-induced colony formation was modest and not statistically significant. Administration of either an anti-transforming growth factor-alpha (TGF-alpha) antibody or an anti-epidermal growth factor (EGF) receptor antibody similarly inhibited E2-stimulated MCF-7 cell growth in soft agar, while neither antibody influenced Pg or PRL effects. Addition of TGF-beta 1, -beta 2, -beta 3 similarly suppressed MCF-7 cell colony formation in a dose dependent manner to a degree comparable to that observed with 4-OH-tamoxifen (4-OH-T). Furthermore, the growth inhibitory effect of 4-OH-T was completely reversed by an anti-TGF-beta antibody. We conclude that IGFs and TGF-alpha are important mediators of E2-stimulated MCF-7 cell growth in soft agar. IGFs may also be playing a role in Pg action, while neither growth factor is involved in PRL-stimulated colony formation. Finally, TGF-beta appears to be an important mediator of antiestrogen-induced inhibition of tumor growth.

The mammary gland

In vivo studies have shown that the growth of the mammary gland is regulated by a complex synergistic interaction of protein, steroid and thyroid hormones, but it has proved difficult to fully reproduce these effects in vitro. It is becoming apparent that the hormones classically recognized as involved in mammary growth (oestrogen, progesterone, prolactin, GH, adrenal corticoids, triiodothyronine) bring about effects on epithelial cell proliferation at least in part through growth factors produced at distant sites (such as the liver) and also locally by mammary tissue, both parenchyma and stroma. Growth factor receptors can be demonstrated in mammary tissue. Receptor occupancy generates intracellular signals which enable cells to progress through the cell cycle, leading in ways still not understood to DNA synthesis and cell division. Within the mammary gland there probably exists a balance of stimulatory factors (such as IGFs and EGF/TGF-alpha) and inhibitory factors (such as TGF-beta). Interactions between epithelial and stromal cells, involving growth factors and the extracellular matrix, bring about pattern formation. Growth factors may also play some part in mammary differentiation and function, although the evidence here is less clear. Growth factors are also implemented in the failure of growth regulation which neoplastic transformation represents. Breast cancer cells can synthesize and secrete a variety of growth factors which may stimulate tumour growth through local autocrine/paracrine mechanisms. The oestrogen dependence of some breast cancers may involve oestrogen regulation of and interaction with growth factors, progression to hormone independence involving loss of this control. It is significant that the proteins which protooncogenes encode include growth factors and growth factor receptors. Much remains to be learnt about the nature and control of growth factors produced by and acting on the mammary gland. In breast cancer, this research offers the possibility of new methods of diagnosis and treatment.

Expression of the insulin like growth factor-binding protein 3 (IGFBP-3) gene is increased in human renal carcinomas

After we had established that the IGFBP-3 gene is expressed in normal human kidney we examined renal adenocarcinoma tissue for alterations of the expression of this gene. For this purpose we prepared poly(A)+ RNA from normal kidney tissue and adjacent renal adenocarcinoma of 18 adult patients and compared the levels of IGFBP-3 mRNA by Northern analysis in both samples. The mean content by densitometry was markedly increased in the carcinoma tissues; in 17 of 18 patients the carcinoma contained significantly more IGFBP-3 mRNA than the normal kidney sample. The highest mRNA levels were found in patients with N2 and N3 lymph node extensions. Comparative Southern analysis of paired samples of four of these patients did not reveal amplification of the gene as the cause of these increased mRNA levels. In one patient, however, we identified a restriction fragment length polymorphism (RFLP) present in normal and malignant cellular DNA. This suggests a participation of the IGFBP-3 gene in the development of human renal cell cancer.

Secretion and biological actions of insulin-like growth factor binding proteins in two human tumor-derived cell lines in vitro

The insulin-like growth factors (IGFs) I and II are present in extracellular fluids associated with specific binding proteins (IGFBPs) that can modify their biologic actions. These studies were undertaken to determine which forms of IGFBP are secreted by endometrial carcinoma (HEC-1B) and breast carcinoma (MDA-231) cells, to characterize variables that control IGFBP secretion, and to study the effect of IGFBP-1 and IGFBP-2 on IGF-I stimulated cell proliferation. Secreted IGFBPs were identified by ligand blotting and IGFBP-1 was quantified using a specific radioimmunoassay (RIA). MDA-231 cell conditioned media (CM) contained four (43,000, 39,000, 30,000 and 24,000 Mr) forms of IGFBP, and HEC-1B cell CM contained three forms (39,000, 34,000 and 30,000 Mr). Immunoblotting showed that the 30,000 Mr form secreted by both cell types was IGFBP-1. Likewise the 34,000 Mr band in HEC-1B media reacted with IGFBP-2 antiserum and the 39,000 and 43,000 Mr bands reacted with IGFBP-3 antiserum. IGF-I stimulated the secretion of IGFBP-3 from both cell types and IGFBP-2 from HEC-1B cells but either decreased or caused no change in secretion of IGFBP-1 and a 24,000 Mr form. In contrast, insulin inhibited the secretion of IGFBP-1 but increased the secretion of the 24,000 Mr form. Compounds that elevate intracellular cAMP levels increased the secretion of IGFBP-3, IGFBP-1, and the 24,000 Mr form from both MDA-231 and HEC-1B cells. When sparse cultures of MDA-231 cells were used, addition of IGF-I caused a 24% increase in cell number after 48 hr. This mitogenic response was enhanced by the presence of recombinant human IGFBP-1 (45% increase in cell number, P less than 0.001). Bovine IGFBP-2 did not potentiate IGF-I stimulated cell proliferation. These findings show that two tumor cell lines secrete distinct forms of IGFBPs and that there is differential regulation of IGFBP secretion. At least one form secreted by both tumors may act as a positive autocrine modulator of IGF-I's growth stimulating actions.

Identification and regulation of insulin-like growth factor binding proteins produced by hormone-dependent and -independent human breast cancer cell lines

Using molecular hybridization, ligand blotting and immunoprecipitation, our studies were designed to identify the insulin-like growth factor binding proteins (IGFBPs) produced by human breast cancer cells in culture and evaluate their regulation by estradiol (E2) and polyamines (PA). We demonstrate that the hormone-dependent MCF-7 and -independent BT-20 cell lines express the mRNA for IGFBP-2 (1.7 kb) and secrete this BP (31 kDa) in the conditioned medium. In contrast, the hormone-independent MDA-MB-231 cell line does not express the IGFBP-2 gene, while synthesizing and secreting IGFBP-1. E2 administration (10(-9) M) did not significantly influence IGFBPs secretion in MCF-7 cells. Addition of alpha-difluoromethylornithine (DFMO, 4 mM), an inhibitor of PA biosynthesis, consistently lowered IGFBP-2 mRNA in the MCF-7 and BT-20 cell lines and IGFBP-1 mRNA in MDA-MB-231 cells. Surprisingly, however, this compound either did not influence IGFBPs secretion in MCF-7 cells or actually increased their secretion in the BT-20 and MDA-MB-231 cell lines. PA involvement in IGFBPs production by breast cancer cells is complex and may involve differential regulation of transcriptional and post-translational events.

Insulin-like growth factors in human breast cancer

Several protooncogenes and suppressor genes and a variety of growth factors and their receptors have been shown to be mutated, deleted, or activated in human breast cancer. These changes may account for the unregulated growth of breast carcinoma cells. Insulin-like growth factors I and II (IGF-I, IGF-II) belong to a family of polypeptides with growth promoting properties and structural homology to insulin. They exert their mitogenic effects by binding to the IGF-I receptor and activating its tyrosine protein kinase. Other proteins that specifically bind the IGFs include the plasma membrane IGF-II receptor, which also binds lysosomal hydrolases, and several IGF-binding proteins which may serve to modulate IGF interactions with receptors. Breast cancer cell lines express IGF-I and IGF-II receptors and different patterns of binding proteins. IGF-I and IGF-II are each mitogenic for subsets of breast cancer cell lines. This effect is inhibited by antibodies directed against the IGF-I receptor. In breast tumors, IGF-I is expressed by stromal cells, but not carcinoma cells; it is not expressed by breast cancer cell lines. IGF-I is therefore a potential paracrine regulator of breast cancer cell growth. Similarly, IGF-II is expressed in breast tumors, predominantly in stromal cells, but sometimes also in carcinoma cells and in a subset of cell lines. Thus, IGF-II is also a potential paracrine regulator of breast cancer cell growth; in addition, it can be an autocrine regulator in some breast cancer cells.