The expression of IGFBP-5 in the reproductive axis and effect on the onset of puberty in female rats

Insulin-like growth factor-binding protein-5 (IGFBP-5) has recently been shown to alter the reproductive capacity by regulating insulin-like growth factor (IGF) bioavailability or IGF-independent effects. The present study aimed to investigate the effect and mechanism of IGFBP-5 on the onset of puberty in female rats. Immunofluorescence and real-time quantitative PCR were used to determine the expression and location of IGFBP-5 mRNA and protein distribution in the infant's hypothalamus-pituitary-ovary (HPO) axis prepuberty, peripuberty, puberty and adult female rats. Prepubertal rats with IGFBP-5 intracerebroventricular (ICV) were injected to determine the puberty-related genes expression and the concentrations of reproductive hormones. Primary hypothalamic cells were treated with IGFBP-5 to determine the expression of puberty-related genes and the Akt and mTOR proteins. Results showed that Igfbp-5 mRNA and protein were present on the HPO axis. The addition of IGFBP-5 to primary hypothalamic cells inhibited the expression of Gnrh and Igf-1 mRNAs (P < 0.05) and increased the expression of AKT and mTOR protein (P < 0.01). IGFBP-5 ICV-injection delayed the onset of puberty, reduced Gnrh, Igf-1, and Fshβ mRNAs, and decreased the concentrations of E2, P4, FSH,serum LH levels and the ovaries weight (P < 0.05). More corpus luteum and fewer primary follicles were found after IGFBP-5 injection (P < 0.05).

Bald thigh syndrome in sighthounds-Revisiting the cause of a well-known disease

Bald thigh syndrome is a common hair loss disorder in sighthounds. Numerous possible causes, including environmental conditions, trauma, stress, endocrinopathies and genetic components have been proposed, but only endocrinopathies have been ruled out scientifically. The overall goal of our study was to identify the cause of bald thigh syndrome and the pathological changes associated with it. We approached this aim by comparing skin biopsies and hair shafts of affected and control dogs microscopically as well as by applying high-throughput technologies such as genomics, transcriptomics and proteomics. While the histology is rather unspecific in most cases, trichogram analysis and scanning electron microscopy revealed severe structural abnormalities in hair shafts of affected dogs. This finding is supported by the results of the transcriptomic and proteomic profiling where genes and proteins important for differentiation of the inner root sheath and the assembly of a proper hair shaft were downregulated. Transcriptome profiling revealed a downregulation of genes encoding 23 hair shaft keratins and 51 keratin associated proteins, as well as desmosomal cadherins and several actors of the BMP signaling pathway which is important for hair shaft differentiation. The lower expression of keratin 71 and desmocollin 2 on the mRNA level in skin biopsies corresponded with a decreased protein expression in the hair shafts of affected dogs. The genetic analysis revealed a missense variant in the IGFBP5 gene homozygous in all available Greyhounds and other sighthounds. Further research is required to clarify whether the IGFBP5 variant represents a predisposing genetic risk factor. We conclude from our results that structural defects in the hair shafts are the cause for this well-known disease and these defects are associated with a downregulation of genes and proteins essential for hair shaft formation. Our data add important knowledge to further understand the molecular mechanisms of HF morphogenesis and alopecia in dogs.

Orthodontic forces modulate insulin-like growth factor binding protein-5 changes in gingival crevicular fluid

Orthodontic tooth movement results from the response of the periodontal tissue to orthodontic force, which leads to modeling and remodeling of the surrounding alveolar bone. The response is considered to occur through the activation of specific signaling pathways, many of which are known, all acting to ultimately result in tooth movement. Much is known about the actions of these two cells, and the signaling pathways that affect them, both in bone and orthodontic literature, however, to date, little work has been carried out to examine the effect of the insulin-like growth factor binding proteins (IGFBP) in orthodontics. Therefore, we investigated the presence of IGFBP-5 in the gingival crevicular fluid (GCF) of 6 healthy subjects, and assessed the effects of orthodontic treatment on the levels and molecular state of this protein.

Overexpression of IGFBP5, but not IGFBP3, Correlates with the Histologic Grade of Human Diffuse Glioma: A Tissue Microarray and Immunohistochemical Study

Insulin-like growth factor binding proteins (IGFBPs) comprise a family of proteins that bind and regulate the functions of IGFs. One of the IGFBPs, IGFBP2, has recently been shown to be overexpressed in glioblastoma. Overexpression of IGFBP2 contributes to the invasiveness of glioblastoma and correlates with histologic grade and survival in patients with diffuse gliomas, suggesting that IGFBP2 expression may contribute to the glioma formation and/or progression. The expression of other IGFBP family members in gliomas has, however, not been examined in detail. This study was designed to evaluate the expression of IGFBP3 and IGFBP5 in diffuse gliomas using immunohistochemistry applied to a tissue array constructed from 259 gliomas, including ten gliosarcomas. Expression of IGFBP5 correlated significantly with glioma histologic grade. 83% (58/70) of glioblastomas (WHO Grade IV) were positive for IGFBP5, which was significantly higher than WHO Grade III gliomas (41%, 41/101) or WHO Grade II gliomas (18%, 13/72) (p<0.001). In contrast, IGFBP3 was expressed in 17%, 23%, and 17% of WHO Grade IV, Grade III, and Grade II gliomas, respectively (p>0.05). There was no significant difference in IGFBP3 expression among different grades of glioma. Our study thus demonstrates that the expression of IGFBP5, but not IGFBP3, increases with glioma anaplastic progression. The strong correlation between overexpression of IGFBP5 and histologic grade suggests that, in addition to IGFBP2, IGFBP5 may also play a role in glioma progression.

IGFBP-4 and -5 are expressed in first-trimester villi and differentially regulate the migration of HTR-8/SVneo cells

BACKGROUND

Adverse gestational outcomes such as preeclampsia (PE) and intrauterine growth restriction (IUGR) are associated with placental insufficiency. Normal placental development relies on the insulin-like growth factors -I and -II (IGF-I and -II), in part to stimulate trophoblast proliferation and extravillous trophoblast (EVT) migration. The insulin-like growth factor binding proteins (IGFBPs) modulate the bioavailability of IGFs in various ways, including sequestration, potentiation, and/or increase in half-life. The roles of IGFBP-4 and -5 in the placenta are unknown, despite consistent associations between pregnancy complications and the levels of two IGFBP-4 and/or -5 proteases, pregnancy-associated plasma protein -A and -A2 (PAPP-A and PAPP-A2). The primary objective of this study was to elucidate the effects of IGFBP-4 and -5 on IGF-I and IGF-II in a model of EVT migration. A related objective was to determine the timing and location of IGFBP-4 and -5 expression in the placental villi.

METHODS

We used wound healing assays to examine the effects of IGFBP-4 and -5 on the migration of HTR-8/SVneo cells following 4 hours of serum starvation and 24 hours of treatment. Localization of IGFBP-4, -5 and PAPP-A2 was assessed by immunohistochemical staining of first trimester placental sections.

RESULTS

2 nM IGF-I and -II each increased HTR-8/SVneo cell migration with IGF-I increasing migration significantly more than IGF-II. IGFBP-4 and -5 showed different levels of inhibition against IGF-I. 20 nM IGFBP-4 completely blocked the effects of 2 nM IGF-I, while 20 nM IGFBP-5 significantly reduced the effects of 2 nM IGF-I, but not to control levels. Either 20 nM IGFBP-4 or 20 nM IGFBP-5 completely blocked the effects of 2 nM IGF-II. Immunohistochemistry revealed co-localization of IGFBP-4, IGFBP-5 and PAPP-A2 in the syncytiotrophoblast layer of first trimester placental villi as early as 5 weeks of gestational age.

CONCLUSIONS

IGFBP-4 and -5 show different levels of inhibition on the migration-stimulating effects of IGF-I and IGF-II, suggesting different roles for PAPP-A and PAPP-A2. Moreover, co-localization of the pappalysins and their substrates within placental villi suggests undescribed roles of these molecules in early placental development.

Down-regulation of insulin-like growth factor binding protein-5 (IGFBP-5): novel marker for cervical carcinogenesis

To better understand the underlying pathways of cervical carcinogenesis, cDNA microarray analysis was performed on 2 sets of squamous cell carcinomas (SCCs) and their adjacent normal squamous epithelia. Consistently altered expression was detected for 32 genes. Real-time RT-PCR analysis was conducted on a selected subset of these genes (S100A2, GPC4, p72, IGFBP-5, TRIM2 and NAB2) for 14 additional SCCs and 10 normal epithelia. This found that, of the 6 candidate genes, only the insulin-like growth factor binding protein-5 (IGFBP-5) mRNA was generally and significantly under-expressed in SCCs (p < 0.001). All normal cervical epithelia (30 of 30) stained positively for IGFBP-5 protein, with 70% showing strong staining, whereas 65% (17/26) of SCC had complete loss of IGFBP-5, and only 8% (2/26) SCC retained strong expression (p < 0.001). Immunohistochemistry of premalignant cervical intraepithelial neoplasia (CIN) lesions shows a significantly weaker or negative staining in advanced CIN3 lesions compared with normal squamous epithelia (p = 0.001). This is the first study to show that down-regulation of IGFBP-5 protein correlates with cervical carcinogenesis and does so at a preneoplastic stage.

Insulin-like growth factor binding proteins IGFBP3, IGFBP4, and IGFBP5 predict endocrine responsiveness in patients with ovarian cancer

PURPOSE

This study sought to explore the predictive value of the insulin-like growth factor (IGF) binding proteins (IGFBP) as markers of response in ovarian cancer patients treated with the aromatase inhibitor letrozole.

EXPERIMENTAL DESIGN

IGFBP mRNA expression in cell lines was measured by quantitative reverse transcription-PCR and IGFBP protein expression measured in sections from primary tumors of patients treated with letrozole by semiquantitative immunohistochemistry.

RESULTS

Quantitative reverse transcription-PCR analysis showed that IGFBP3 and IGFBP5 were down-regulated and IGFBP4 was up-regulated by 17beta-estradiol (E(2)) in an estrogen receptor (ER)-positive ovarian cancer cell line. Expressions of IGFBP1, IGFBP2, and IGFBP6 were unaffected by E(2). The E(2) modulation of these genes was reversed by tamoxifen. Using ERalpha-specific (propyl pyrazole triol) and ERbeta-specific (diarylpropionitrile) agonists, the gene expression modulations produced by E(2) could be replicated by propyl pyrazole triol but not by diarylpropionitrile. For ovarian cancer patients being treated with letrozole, we tested the predictive value of the IGFBPs in paraffin-fixed sections from their primary tumors by semiquantitative immunohistochemistry. Using serum CA125 as an indicator of progression/response, significant differences in expression levels of IGFBPs were observed between tumors from CA125 responding/stable patients compared with tumors from progressing patients. Mean immunoscores for IGFBP3 and IGFBP5 were significantly lower, and mean expression of IGFBP4 was significantly higher in tumors from patients demonstrating CA125 response or stabilization compared with CA125 progression.

CONCLUSION

These results indicate that expression levels of certain IGFBP family members in ovarian cancers are estrogen regulated and can, thus, help identify patients who could benefit from endocrine therapy.

The MN1 oncoprotein activates transcription of the IGFBP5 promoter through a CACCC-rich consensus sequence

The IGF-binding protein (IGFBP) family consists of six proteins that are expressed and secreted in different tissues. The proteins are regulators of physiological processes throughout the body by modulating the activity of IGF-I and IGF-II. In this article, we describe the coordinated expression of IGFBP5 and MN1 in meningiomas. MN1 is a transcriptional co-activator and we show that MN1 stimulates the IGFBP5 promoter in Hep3B cells. A CACCC-containing sequence, located 140 bp upstream of the transcription start site of the promoter, is required for MN1 action. This sequence matches with the CACCCAC consensus sequence that was selected in an oligonucleotide selection assay performed for MN1. The CACCC element has also been shown to be important for induction of the IGFBP5 promoter by retinoic acid (RA) and progesterone (Pg). We were unable to confirm the effect of Pg on the promoter in Hep3B and U2-osteosarcoma cells regardless of the presence of MN1. On the other hand, we show that induction of the promoter by RA depends on co-expressed MN1 in Hep3B cells. MN1TEL, a leukemia-related fusion protein containing parts of the MN1 and TEL (ETV6) genes, is capable of stimulating the IGFBP5 promoter but is unable to cooperate with RA in Hep3B cells. This suggests that the effects of RA can be negatively affected in leukemias caused by MN1TEL.

Comparison of Estrogen Responsive Genes in the Mouse Uterus, Vagina and Mammary Gland

Female reproductive organs are mainly regulated by estrogen and progesterone. Specifically, the uterus, vagina and mammary gland show organ-specific mitosis and morphological changes during proliferative events, such as estrous cycle, gestation and lactation. The mechanism underlying these organ-specific estrogen-dependent events is still unknown. We examined, therefore, global gene expression in the mature uterus, vagina and mammary gland of ovariectomized adult mice 6 hr after an injection of 5 microg/kg 17beta-estradiol (E2) using a microarray method in order to identify primary E2-responsive genes. Half of the E2 up-regulated genes in the uterus were similar to those in the vagina. E2 up-regulated the expression of Insulin-like growth factor 1 (Igf-1) genes in the uterus and vagina. In the vagina, E2 up-regulated the expression of IGF binding proteins (Igfbp2 and Igfbp5). In the mammary gland, unlike the uterus and vagina, no gene showed altered expression 6 hr after the E2 exposure. These results suggest that expression of Igf-1 and morphogenesis genes is regulated by E2 in an organ-specific manner, and it is supported by the results of BrdU labeling showing E2-induced mitosis in the uterus and vagina except the mammary gland. The differences in organ specificity in response to E2 may be attributed by differences in gene expression regulated by E2 in female reproductive organs. The candidate estrogen-responsive genes in the uterus and vagina identified by profiling provide an important foundation understanding functional mechanisms of estrogen regulating morphogenesis and maintenance of each reproductive organ.

Expression of insulin like growth factor binding protein-5 in drug induced human gingival overgrowth

BACKGROUND & OBJECTIVE

Insulin like growth factor binding proteins (IGFBPs) control the distribution, function and activity of insulin like growth factors (IGFs) in various cells, tissues and body fluids, thereby modulating their metabolic and mitogenic effects. IGFBP-5, the most conserved IGFBP, can function through IGF or directly play a role in fibrosis. Cyclosporine A (CsA) widely used in organ transplant patients, often causes various side effects including gingival fibrotic overgrowth. This study was carried out to assess the mRNA expression of IGFBP-5 in healthy human gingival, chronic periodontitis and CsA induced gingival overgrowth tissues.

METHODS

Total RNA was isolated from gingival tissues collected from eight patients with chronic periodontitis, eight patients with CsA induced gingival outgrowth and an equal number of healthy individuals, and subjected to reverse transcription (RT)-PCR for IGFBP-5 gene expression.

RESULTS

CsA induced gingival overgrowth tissues expressed increased IGFBP-5 mRNA compared to control and chronic periodontitis.

INTERPRETATION & CONCLUSION

Increased mRNA expression of IGFBP-5 in CsA induced gingival outgrowth tissues may be associated with increased collagen synthesis, thereby promoting fibrogenesis.

Involvement of ligand occupancy in Insulin-like growth factor-I (IGF-I) induced cell growth in osteoblast like MC3T3-E1 cells

Growth factors and matrix proteins regulate the proliferation and differentiation of osteoblasts. The insulin-like growth factor (IGF) system comprises IGF-I, IGF-II, and six high-affinity IGF-binding proteins (IGFBPs). IGFs stimulate cell growth in many types of tissue; IGF-binding proteins regulate cellular actions and can affect cell growth. IGF-I is involved in differentiation, proliferation, and matrix formation in osteoblasts; IGFBP-5 is associated with the extracellular matrix (ECM) and can potentiate the actions of IGF-I. We investigated the effect of ECM proteins on the responses of MC3T3-E1 osteoblast cells to IGF-I and IGFBP-5. In addition, because extracellular signal-regulated kinases 1 and 2 (Erk 1/2) affect cell growth, we evaluated the effects of IGFBP-5 on Erk 1/2 phosphorylation in MC3T3-E1 cells. IGF-I caused an increase in IGFBP-5 expression in cultured MC3T3-E1 cells, and IGF-I plus IGFBP-5 significantly increased cell growth. Likewise, the addition of IGF-I and IGFBP-5 to cultured MC3T3-E1 cells increased the synthesis of the ECM proteins osteopontin (OPN) and thrombospondin-1 (TSP-1), which can bind to alphaVbeta3 integrin receptors on the cell surface. By contrast, the addition of an antibody against ECM proteins inhibited the effects of OPN and TSP-1 on IGFBP-5 expression. The stimulatory effect of IGFBP-5 was mediated via Erk 1/2 activation. These data suggest that IGFBP-5 regulates Erk 1/2 phosphorylation in cultured MC3T3-E1 cells via ECM proteins that may ultimately stimulate the growth of osteoblasts. We determined whether occupation of the alphaVbeta3 integrin receptor affects IGF-I receptor (IGF-IR)-mediated signaling and function in MC3T3-E1 osteoblast cells. Occupation of the alphaVbeta3 integrin receptor with ECM proteins induced IGF-I-stimulated IGF-IR phosphorylation. Conversely, in the presence of the alphaVbeta3-specific disintegrin echistatin, IGF-I-stimulated IGF-IR activation was inhibited. IGF-I-stimulated IGF-IR phosphorylation was accompanied by IRS-1 phosphorylation and MAPK activation. However, these effects were attenuated by echistatin. Thus, occupancy of the alphaVbeta3 disintegrin receptor modulates IGF-I-induced IGF-IR activation and IGF-IR-mediated function in MC 3T3-E1 osteoblasts.

IGF binding protein-5 synthesis is regulated by testosterone through transcriptional mechanisms in androgen responsive cells

We found that androgen and IGF-I up-regulated IGFBP-5 mRNA in androgen-responsive normal human fibroblast, which was blocked by co-treatment with 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole, but not cycloheximide. IGFBP-5 promoter activity was stimulated by androgen. Nuclear run-on assay revealed that IGFBP-5 transcripts were increased in response to androgen, which was not enhanced by co-addition of IGF-I. These results collectively indicate that IGFBP-5 synthesis is regulated by androgen through transcriptional mechanisms in androgen responsive cells.

Bim-dependent apoptosis follows IGFBP-5 down-regulation in neuroblastoma cells

The insulin-like growth factor (IGF) axis is frequently activated in neuroblastoma (NB) tumors and cell lines. We show that silencing endogenous expression of IGF Binding Protein-5 (IGFBP-5) in NB cells by using microRNA and siRNA causes mitochondrial apoptosis that is characterized by: (a) release of cytochrome C in the cytoplasm and activation of caspase 9; (b) Erk1 and Erk2 inhibition; and (c) upregulation of pro-apoptotic proteins Bim and Bax. Bim upregulation is caused, at least in part, by protein stabilization that may depend on inhibition of Erk1 and Erk2. Of interest, Bim knock-down by siRNA decreases apoptosis in IGFBP-5-interfered cells. Thus, inhibition of endogenously produced IGFBP-5 is associated with Bim-dependent apoptosis in NB cells.

Osteoblast differentiation of NIH3T3 fibroblasts is associated with changes in the IGF-I/IGFBP expression pattern

Insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) are essential regulators for osteoblast proliferation and differentiation. It has been reported that Dexamethasone (Dex), an active glucocorticoid (GC) analogue, synergizes the stimulatory effect of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) on osteoblast differentiation in the mouse fibroblastic cell line NIH3T3. I investigated whether this stimulatory effect is associated with changes in the expression pattern of the IGF/IGFBP system. Quantitative real-time PCR technology was used to quantify the gene expression levels of the IGF-system during osteoblast differentiation and in response to 1,25(OH)₂D₃ or Dex alone under serum-containing and serum-free culture conditions. Interestingly, NIH3T3 was shown to express high mRNA levels of IGF-I, IGF-II and IGFBP-5, and low levels of both IGFBP-2 and-6. During osteoblast differentiation (days 6-12), IGF-I mRNA was repressed by more than 60%, while the transcript of IGFBP-5 was markedly up-regulated, by more than 50-fold. Similarly, treatment with Dex alone resulted in a dose-and time-dependent increase in the expression of IGFBP-5 and a decrease in IGF-I mRNA. Treatment with 1,25(OH)₂D₃ alone increased the mRNA levels of IGF-I and IGFBP-6 by around 4-and 7-fold, respectively, in a dose-and time-dependent manner. In conclusion, my data demonstrated that osteoblast differentiation of NIH3T3 is associated with changes in the expression pattern of IGFs/IGFBPs, which are regulated by glucocorticoid in the presence of 1,25(OH)₂D₃. Modulation of the IGF/IGFBP levels by glucocorticoid might suggest important roles for the IGF-system in mediating the osteoblast differentiation of the NIH3T3 cell line.

Insulin-like growth factor-binding protein (IGFBP)-1, -2, -3, -4, -5, and -6 and IGFBP-related protein 1 during rainbow trout postvitellogenesis and oocyte maturation: molecular characterization, expression profiles, and hormonal regulation

In the present study we report the full coding sequence of rainbow trout IGF-binding protein-1 (IGFBP1), -2, -3, -5, and -6 and IGFBP-related protein-1 (IGFBP-rP1) mRNAs as well as the partial coding sequence of IGFBP-4 mRNA. To our knowledge, this is the first report of IGFBP4, IGFBP6, and IGFBP-rP1 in a nonmammalian species. The tissue distribution of all mRNAs was studied, and the ovarian expression profiles of IGFBP2 to -6 and IGFBP-rP1 between late vitellogenesis and oocyte maturation were characterized. In addition, in vitro hormonal regulation by the maturation-inducing steroid 17,20beta-dihydroxy-4-pregnen-3-one (17,20betaP), gonadotropin, and estradiol were studied. We observed that besides IGFBP1, which was only found in liver, IGFBP2 to -6 and IGFPB-rP1 were expressed in the preovulatory ovary. IGFBP3 was also detected in liver, trunk, kidney, skin, and gills, whereas IGFBP2 to -6 and IGFBP-rP1 exhibited a wider tissue distribution. In the preovulatory ovary, IGFBP3 was strongly down-regulated during the postvitellogenesis period, whereas IGFBP5 exhibited a limited up-regulation. In addition, IGFBP6 and IGFBP-rP1 were up-regulated during oocyte maturation. Hormonal regulation data indicated that all ovarian IGFBPs and IGFBP-rP1 transcripts are regulated under gonadotropic stimulation at a concentration that induced 100% oocyte maturation. In addition, IGFBP2 to -5 transcripts are regulated by 17,20betaP and estradiol. Together, our observations strongly suggest that during final oocyte maturation, a down-regulation of IGFBP3, -4, and -5 occurs in the oocyte in response to gonadotropic and 17,20betaP (IGFBP3 and -5) stimulation, whereas an up-regulation of IGFBP2 and -6 occurs in follicular layers or extrafollicular tissue in response to gonadotropic stimulation.

Neuromuscular stimulation causes muscle phenotype-dependent changes in the expression of the IGFs and their binding proteins in developing slow and fast muscle of chick embryos

Insulin-like growth factor (IGF) -1 and -2 and binding protein (IGFBP-2, -4, and -5) expression can be affected by several environmental factors, but the impact of movement on the IGF axis during late embryogenesis has yet to be fully characterized. Movement was promoted in chick embryos during mid-embryogenesis using 4-aminopyridine (4-AP). The results indicate an increase in IGF-1 (P < 0.01) and a decrease in IGFBP-2 (P < 0.05) mRNA expression in slow muscle of the stimulated group compared with the control group. In fast muscle, there was a decrease in IGF-2 (P < 0.01) on embryonic day (ED) 16 and an increase in IGFBP-2 (P < 0.01) and IGFBP-4 (P < 0.05) and in IGFBP-5 (P < 0.05) expression on ED18 in the stimulated group compared with the control group. These results indicate that neuromuscular stimulation with 4-AP influences IGF axis gene expression in a muscle fiber type-dependent manner. Consequences of the changes in the IGF system for each muscle are discussed.

Interleukin-11 inhibits expression of insulin-like growth factor binding protein-5 mRNA in decidualizing human endometrial stromal cells

Differentiation of endometrial stromal cells into decidual cells is essential for successful embryo implantation. Interleukin (IL)-11 signalling is critical for normal decidualization in the mouse. The expression of IL-11 and its receptors during the menstrual cycle, and the effect of exogenous IL-11 on the decidualization of human endometrial stromal cells in vitro, suggests a role for this cytokine in human decidualization. As the downstream target genes of IL-11 are also likely to be critical mediators of this process, this study aimed to identify genes regulated by IL-11 in decidualizing human endometrial stromal cells in vitro. Stromal cells isolated from endometrial biopsies were decidualized with 17beta estradiol (E) and medroxyprogesterone acetate (EP) in the presence or absence of exogenous IL-11, and total RNA used for cDNA microarray analysis and real-time RT-PCR. Microarray analysis revealed 16 up-regulated and 11 down-regulated cDNAs in EP + IL-11-treated compared with EP-treated cells. The most down-regulated gene was insulin-like growth factor binding protein-5 (IGFBP-5) (3.6-fold). Using real-time RT-PCR, IL-11 was confirmed to decrease IGFBP-5 transcript abundance 102-fold (P = 0.016; n = 6). No difference in IGFBP-5 immunostaining intensity was detected in stromal cells decidualized in the presence or absence of IL-11, and there was no effect of exogenous IGFBP-5 on the progression of steroid-induced in vitro decidualization. Interactions between IL-11 and its target genes, including IGFBP-5, may contribute to the regulation of decidualization and/or mediate communication between the decidua and invading trophoblast at implantation.

Expression of genes involved in regulation of cell turnover during milk stasis and lactation rescue in sow mammary glands1

We studied the transcription of selected genes involved in the regulation of cell turnover during milk stasis and lactation rescue in individual mammary glands of sows and evaluated the timeframe for lactation rescue and the subsequent productivity of rescued glands. Suckling was prevented in two glands from each of five sows by taping them the day after farrowing for 1 or 3 d (Closed 24 h and Closed 72 h glands, respectively). After removing the tape, Closed 24 h glands were suckled until weaning. Closed 72 h glands were refused by the piglets and therefore remained unsuckled. Mammary gland biopsies were collected to quantify the transcription of genes involved in cell turnover and the percentage of proliferating and apoptotic cells. Transcriptional data were analyzed with a gamma-distributed generalized linear mixed model. Mammary transcription of alpha-lactalbumin was high in suckled glands the day after farrowing, indicating onset of lactation, but was downregulated after 1 d of milk stasis. The prolactin receptor mRNA was downregulated and IGFBP-5 mRNA was upregulated within 1 d of milk stasis. The downregulation of alpha-lactalbumin and prolactin receptor and upregulation of IGFBP-5 mRNA noted after 1 d of milk stasis was maintained in Closed 72 h glands (those glands regressed) but reversed on d 4 and 6 of lactation in Closed 24 h glands. Mammary IGF-I mRNA was not regulated in response to milk stasis or lactation rescue. The percentage of proliferating cells in mammary glands was high prepartum (13.1%) and intermediate (7.8%) the day after farrowing. By d 6 of lactation, the percentage of proliferating cells was increased to 10.1% (P < 0.01) in glands suckled regularly but decreased to 5.9% (P < 0.05) in regressing glands (Closed 72 h glands). Glands rescued after 1 d of milk stasis had lower productivity throughout lactation than glands suckled regularly, as indicated by the BW of piglets suckling these glands (242 vs. 315 g/d, respectively; P < 0.05). In conclusion, regularly suckled glands had a greater cell proliferation, greater transcriptions of alpha-lactalbumin and prolactin receptor genes, and less IGFBP-5 transcription compared with rescued (Closed 24 h) and regressing (Closed 72 h) glands. Glands that were not suckled for 1 d could be rescued, although their subsequent productivity was lower, whereas glands not suckled for 3 d could not be rescued.

Regulation of multiple insulin-like growth factor binding protein genes by 1alpha,25-dihydroxyvitamin D3

Recently, insulin-like growth factor binding proteins (IGFBPs) have been found to be primary mediators of the anti-proliferative actions of the nuclear hormone 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3], but dependent on cellular context IGFBPs can also have a mitogenic effect. In this study, we performed expression profiling of all six human IGFBP genes in prostate and bone cancer cells and demonstrated that IGFBP1, 3 and 5 are primary 1alpha,25(OH)2D3 target genes. In silico screening of the 174 kb of genomic sequence surrounding all six IGFBP genes identified 15 candidate vitamin D response elements (VDREs) close to or in IGFBP1, 2, 3 and 5 but not in the IGFBP4 and 6 genes. The putative VDREs were evaluated in vitro by gelshift assays and in living cells by reporter gene and chromatin immuno-precipitation (ChIP) assays. Of these 10 VDREs appear to be functional. ChIP assays demonstrated for each of these an individual, stimulation time-dependent association profile not only with the vitamin D receptor, but also with first heterodimeric partner the retinoid X receptor, other regulatory complex components and phosphorylated RNA polymerase II. Some of the VDREs are located distantly from the transcription start sites of IGFBP1, 3 and 5, but all 10 VDREs seem to contribute to the regulation of the genes by 1alpha,25(OH)2D3. In conclusion, IGFBP1, 3 and 5 are primary 1alpha,25(OH)2D3 target genes that in intact cells are each under the control of multiple VDREs.

Insulin-like growth factor (IGF)-I stimulates cell proliferation and induces IGF binding protein (IGFBP)-3 and IGFBP-5 gene expression in cultured growth plate chondrocytes via distinct signaling pathways

The bioactivity of IGF-I in the cellular microenvironment is modulated by both inhibitory and stimulatory IGF binding proteins (IGFBPs), whose production is partially under control of IGF-I. However, little is known on the IGF-mediated regulation of these IGFBPs in the growth plate. We therefore studied the effect of IGF-I on IGFBP synthesis and the involved intracellular signaling pathways in two cell culture models of rat growth plate chondrocytes. In growth plate chondrocytes in primary culture, incubation with IGF-I increased the concentrations of IGFBP-3 and IGFBP-5 in conditioned cell culture medium in a dose- and time-dependent manner. Coincubation of IGF-I with specific inhibitors of the p42/44 MAPK pathway (PD098059 or U0126) completely abolished the stimulatory effect of IGF-I on IGFBP-3 mRNA expression but did not affect increased IGFBP-5 mRNA levels. In contrast, inhibition of the phosphatidylinositol-3 kinase signaling pathway by LY294002 abrogated both IGF-I-stimulated IGFBP-3 and -5 mRNA expression. Comparable results regarding IGFBP-5 were obtained in the mesenchymal chondrogenic cell line RCJ3.1C5.18, which does not express IGFBP-3. The IGF-I-induced IGFBP-5 gene expression required de novo mRNA transcription and de novo protein synthesis. These data suggest that IGF-I modulates its activity in cultured rat growth plate chondrocytes by the synthesis of both inhibitory (IGFBP-3) and stimulatory (IGFBP-5) binding proteins. The finding that IGF-I uses different and only partially overlapping intracellular signaling pathways for the regulation of two IGFBPs with opposing biological functions might be important for the modulation of IGF bioactivity in the cellular microenvironment.

Altered expression of members of the IGF-axis in clear cell renal cell carcinoma

Renal cell carcinoma (RCC) is a heterogeneous disease and its biology is poorly understood. The commonest subtype identified is clear cell RCC. The insulin-like growth factor axis is intimately involved with many cellular roles including that of renal development. Dysregulation of this axis has frequently been demonstrated in cancer. In this study, we examine the expression of several IGF-axis components, including receptors, ligands, and binding proteins in clear cell renal cell carcinoma. A series of clear cell RCCs with matched normal kidney from the same individuals were obtained. Total RNA was extracted and expression levels of genes examined using RNase protection analysis. We confirm the dysregulation of the IGF-axis within clear cell renal cell carcinoma including the upregulation of IGFBP-3, which is further validated by immunohistochemical staining on a tissue array containing 50 RCC: positive staining in 29/30 clear cell; 1/10 papillary and 0/10 chromophobe. In addition, we demonstrate that the expression of the A isoform of the insulin receptor is significantly upregulated, while that of IGFBP-5 are significantly downregulated in this tumour subtype.

Insulin-like growth factor binding proteins 3 and 5 are overexpressed in idiopathic pulmonary fibrosis and contribute to extracellular matrix deposition

Idiopathic pulmonary fibrosis (IPF) is a fibrotic disease of unknown etiology that results in significant morbidity and mortality. The pathogenesis of IPF is not completely understood. Because recent studies have implicated insulin-like growth factor-I (IGF-I) in the pathogenesis of fibrosis, we examined the expression and function of insulin-like growth factor binding proteins (IGFBP)-3 and -5 in IPF. IGFBP-3 and -5 levels were increased in vivo in IPF lung tissues and in vitro in fibroblasts cultured from IPF lung. The IGFBPs secreted by IPF fibroblasts are functionally active and can bind IGF-I, and IGFBPs secreted by primary fibroblasts bind extracellular matrix components. Our results also suggest that IGFBPs may be involved in the initiation and/or perpetuation of fibrosis by virtue of their ability to induce the production of extracellular matrix components such as collagen type I and fibronectin in normal primary adult lung fibroblasts. Although transforming growth factor-beta increased IGFBP-3 production by primary fibroblasts in a time-dependent manner, IGFBP-5 levels were not increased by transforming growth factor-beta. Taken together, our results suggest that IGFBPs play an important role in the development of fibrosis in IPF.

Osteoblast-specific expression of insulin-like growth factor-1 in bone of transgenic mice induces insulin-like growth factor binding protein-5

The activities of insulin-like growth factors (IGFs) in bone are modulated by a family of binding proteins (IGFBPs) whose physiological roles remain poorly understood. We have previously shown that targeted overexpression of IGF-I in osteoblasts of transgenic (OC-IGF-I) mice stimulates bone formation. In this model, bone formation is markedly but transiently increased in an age-dependent manner, raising the possibility that IGF-I may be influencing IGFBPs to in turn modulate its paracrine actions within bone. We sought to characterize the IGFBPs in normal mouse bone during development and to determine whether osteoblast-targeted overexpression of IGF-I influenced bone IGFBP abundance in vivo. Femoral bone IGFBP content was assessed in control nontransgenic and OC-IGF-I mice by I125-IGF-I ligand and immunoblotting. Bone IGFBP-5 and IGF-I mRNA abundance was determined using real-time reverse transcription (RT)-PCR. Ligand blot of bone extract showed a 30-kDa band, identified as IGFBP-5 by immunoblot, predominated. The abundance of IGFBP-5 declined with age in both control and transgenic bone. Ligand and immunoblot analysis revealed a 5-fold increase in IGFBP-5 protein levels at 3 weeks in transgenic bone (P<0.0001). The elevated IGFBP-5 protein levels were associated with a similar increase in IGF-I mRNA abundance (4-fold, P<0.01) and a significant increase in IGFBP-5 mRNA abundance (1.5-fold). Despite the age-related decline at 6 weeks, IGFBP-5 remained significantly (P<0.01) more abundant in transgenic bone compared to controls. In contrast, bone IGFBP-4 abundance was relatively unchanged by either age or IGF-I overexpression. These studies demonstrate a distinctive developmental pattern of IGFBP-5 content in mouse bone and show that osteoblast-derived IGF-I determines skeletal IGFBP-5 abundance, at least in part by inducing its synthesis. In that IGFBP-5 is thought to stimulate bone formation, directly or via IGF-I action, such changes in bone IGFBP-5 may be important to ensure robust bone acquisition in the early postnatal period.

Overexpression of insulin-like growth factor binding protein-5 decreases osteoblastic function in vitro

Skeletal cells synthesize insulin-like growth factors (IGF) and their binding proteins (IGFBP). The effects of IGFBP-5 on bone cell growth and osteoblastic function are controversial, and transgenic mice overexpressing IGFBP-5 exhibit osteopenia. The mechanisms were not explored, and in this study, we investigated the effects of IGFBP-5 overexpression in MC3T3 cells in vitro. MC3T3 cells were transduced with a retroviral vector (pLPCX) or a vector directing IGFBP-5 transcription under the control of a constitutive promoter. Untreated MC3T3 cells expressed alkaline phosphatase, and osteocalcin mRNA 1 week after confluence and at 4 weeks of culture they formed mineralized nodules. IGFBP-5 overexpression delayed the appearance of alkaline phosphatase and osteocalcin mRNA, decreased type I collagen and osteopontin mRNA and alkaline phosphatase activity (APA), and inhibited the formation of mineralized nodules. IGFBP-5 caused a modest stimulation of DNA synthesis. In conclusion, overexpression of IGFBP-5 decreases osteoblastic function possibly by binding IGFs in the bone microenvironment.

Insulin-like growth factor binding protein-1-6 expression in activated microglia

In the CNS insulin-like growth factor-1 (IGF-1) enhances survival of neurons, promotes myelin synthesis and acts as a mitogen for microglia. The effects of IGF-1 are regulated by a family of 6 IGF binding proteins (IGFBPs). We investigated mRNA expression patterns of IGFBPs in primary rat microglia under basal conditions and after activation with lipopolysaccharide (LPS). Under basal conditions, microglia expressed IGFBP-2 to -6, whereas, IGFBP-1 could not be detected. Following 2 h treatment with LPS mRNA levels for IGFBP-4 and -6 displayed a down regulation, and IGFBP-5 became undetectable. Levels of IGFBP-2 and -3 remained unaltered. Expression patterns of IGFBPs might play an important role in regulating the autocrine/paracrine IGF-1 actions on microglia under inflammatory conditions.

Molecular pathways executing the "trophic sentinel" response in HPV-16 E7-expressing normal human diploid fibroblasts upon growth factor deprivation

In response to oncogenic insults, normal human cells execute a defense response that culminates in cellular suicide, apoptosis. Normal human diploid fibroblasts expressing the human papillomavirus type 16 (HPV-16) E7 oncoprotein are predisposed to apoptosis when they are deprived of growth factors. Even though a dominant negative p53 mutant abrogates the cell death response, it is not accompanied by p53 phosphorylation, the DNA binding capacity of p53 remains unaltered, and no activation of common p53-dependent transcriptional targets is observed. Expression of two insulin-like growth factor-1 binding proteins, IGFBP-2 and -5, is increased presumably in response to enhanced NF-kappaB activity in HPV-16 E7-expressing serum-starved cells. Phosphorylation of AKT, an important modulator of IGF-1 survival signaling, is lower in serum-starved E7-expressing cells, and exogenously added IGF-1 can partially inhibit the cell death response. This suggests that IGFBP-2 and -5 may limit IGF-1 availability thus decreasing survival signaling. Caspase 3 but not caspase 8 is activated in serum-starved HPV-16 E7-expressing cells. Caspase inhibition affects nuclear DNA fragmentation, but cell death is not inhibited. Although mitochondria play important roles in caspase-dependent as well as -independent forms of cell death, there is no evidence for cytochrome c release and thus for mitochondrial permeabilization in growth factor deprived HPV-16 E7-expressing cells.

Evidence That IGF Binding Protein-5 Functions as a Ligand-Independent Transcriptional Regulator in Vascular Smooth Muscle Cells

Insulin-like growth factor binding protein (IGFBP)-5 is a conserved protein synthesized and secreted by vascular smooth muscle cells (VSMCs). IGFBP-5 binds to extracellular IGFs and modulates IGF actions in regulating VSMC proliferation, migration, and survival. IGFBP-5 also stimulates VSMC migration through an IGF-independent mechanism, but the molecular basis underlying this ligand-independent action is unknown. In this study, we show that endogenous IGFBP-5 or transiently expressed IGFBP-5-EGFP, but not IGFBP-4-EGFP, is localized in the nuclei of VSMCs. Using a series of IGFBP-4/5 chimeras and IGFBP-5 points mutants, we demonstrated that the IGFBP-5 C-domain is necessary and sufficient for its nuclear localization, and residues K206, K208, K217, and K218 are particularly critical. Intriguingly, inhibition of protein secretion abolishes IGFBP-5 nuclear localization, suggesting the nuclear IGFBP-5 is derived from the secreted protein. When added exogenously, 125 I- or Cy3-labeled IGFBP-5 is capable of cellular entry and nuclear translocation. To identify potential transcriptional factor(s) that interact with IGFBP-5, a human aorta cDNA library was screened by a yeast two-hybrid screening strategy. Although this screen identified many extracellular and cytosolic proteins that are known to interact with IGFBP-5, no known transcription factors were found. Further motif analysis revealed that the IGFBP-5 N-domain contains a putative transactivation domain. When fused to GAL-4 DNA dinging domain and tested, the IGFBP-5 N-domain has strong transactivation activity. Mutation of the IGF binding domain or treatment of cells with IGF-I has little effect on transactivation activity. These results suggest that IGFBP-5 is localized in VSMC nucleus and possesses transcription-regulatory activity that is IGF independent. The full text of this article is available online at http://circres.ahajournals.org.

Role of Insulin-Like Growth Factor-1 Signaling in Dental Fibroblast Apoptosis

BACKGROUND

Studies have shown that periodontal ligament fibroblasts (PDLF) and gingival fibroblasts (GF) respond differently to growth factors in the repair and regeneration of periodontal tissues. The goal of this study was to determine the effects of insulin-like growth factor-1 (IGF-1) signaling on cell apoptosis in PDLF compared to GF.

METHODS

The levels of apoptosis were compared between cultured PDLF and GF by DNA fragmentation assay and trypan blue exclusion assay, either in the presence or absence of IGF-1. The transcript level of upstream signaling molecules, such as IGF binding protein-5 (IGFBP-5), IGF-1 receptor (IGF-1R), and phosphoinositide 3-kinase (PI3K), was studied using reverse transcription-polymerase chain reaction (RT-PCR). Furthermore, the role of IGFBP-5 in IGF-1 signaling was verified by annexin-V staining using flow cytometric analysis.

RESULTS

IGF-1 significantly inhibited the level of DNA fragmentation and decreased trypan blue-positive cells in PDLF compared to GF during serum deprivation. The mRNA expression of IGFBP-5, IGF-1R, and PI3K was constitutively upregulated in PDLF compared to GF. In the presence of exogenous IGFBP-5, the annexin-V-positive cells were significantly decreased in GF after IGF-1 stimulation.

CONCLUSIONS

The present study provides evidence that IGF-1 reduces apoptosis in cultured PDLF compared to GF. Upregulation of IGF-1R and PI3K in PDLF further suggests the activation of IGF signaling in PDLF. In addition, the anti-apoptotic effect of IGF-1 may be facilitated by the upregulation of IGFBP-5 in PDLF.

Effect of follicle size on in vitro production of steroids and insulin-like growth factor (IGF)-I, IGF-II, and the IGF-binding proteins by equine ovarian granulosa cells

Little is known regarding the hormonal regulation of granulosa cell steroidogenesis and the ovarian insulin-like growth factor (IGF) system in the mare. The objectives of this study were to determine, first, if estradiol, insulin, and/or FSH affect steroid production by equine granulosa cells (experiment 1) and, second, if the components of the IGF system are produced by equine granulosa cells in culture as well as whether estradiol, insulin, and/or FSH affects IGF and/or IGF-binding protein (IGFBP) production by equine granulosa cells (experiment 2). Granulosa cells from small (6-15 mm), medium (16-25 mm), and large (25-48 mm) follicles were collected from cyclic mares (n = 14), cultured for 2 days in medium containing 10% fetal calf serum, washed, and then treated for an additional 2 days in serum-free medium with or without added hormones. In experiment 1, large-follicle granulosa cells produced less progesterone and more estradiol than did medium- and/or small-follicle granulosa cells (P < 0.05). Progesterone production was inhibited (P < 0.05) by FSH and insulin in small- and medium- but not in large-follicle granulosa cells; estradiol was without effect. Insulin increased (P < 0.05) estradiol production in small- and medium-follicle granulosa cells but had no effect in large-follicle granulosa cells. In experiment 2, IGF-I production was inhibited (P < 0.05) by insulin across all follicle sizes but was not affected by estradiol or FSH. Granulosa cells of medium and large follicles produced more IGF-II than did granulosa cells of small follicles (P < 0.05). Insulin and FSH inhibited (P < 0.05) IGF-II production by granulosa cells of large and medium but not of small follicles; estradiol was without effect. Only IGFBP-2 and -5 were produced by equine granulosa cells. Production of IGFBP-2 was less (P < 0.10) in granulosa cells of large versus those of small and medium follicles, whereas medium-follicle granulosa cells produced more (P < 0.05) IGFBP-5 than did small- or large-follicle granulosa cells. Averaged across follicle sizes, estradiol increased (P < 0.05) IGFBP-2 production, FSH increased (P < 0.10) IGFBP-2 and -5 production, and insulin was without effect. These results indicate that IGF-I, IGF-II, IGFBP-2, and IGFBP-5 are produced by equine granulosa cells and that insulin, FSH, and estradiol play a role in the regulation of steroidogenesis and the IGF system of equine granulosa cells.

Expression of insulin-like growth factor (IGF), IGF receptor, and IGF-binding protein messenger ribonucleic acids in luteinized granulosa cells from different size follicles after controlled ovarian hyperstimulation

PURPOSE

This study was conducted to determine the gene expression of insulin-like growth factors (IGFs), their receptors, and binding proteins (IGFBPs) in human luteinized granulosa cells collected during ovum retrieval.

METHODS

cDNA probes were used to analyze the gene expression of IGF-I, IGF-II, IGF type 1 receptor (IGFR-1), IGF type 2 receptor (IGFR-2), and IGFBP-1 to -6 in luteinized granulosa cells.

RESULTS

The levels of IGFBP-5 transcripts of the luteinized granulosa cells increased with increasing follicular fluid (FF) volume when follicles were grouped into 3 volume catagories of < or = 1.5 mL: > 1.5 mL but < or = 4.5 mL; and > 4.5 mL (0.28 +/- 0.64 vs. 0.41 +/- 0.76 vs. 0.46 +/- 0.92, p = 0.037).

CONCLUSIONS

The increased levels of IGFBP-5 transcripts in luteinized granulosa cells found with increased follicular fluid volume after COH may favor a shift toward diminished action of IGFs in larger follicles immediately prior to ovulation.

Transforming growth factor-beta inhibition of insulin-like growth factor-binding protein-5 synthesis in skeletal muscle cells involves a c-Jun N-terminal kinase-dependent pathway

Transforming growth factor-beta (TGF-beta) and insulin-like growth factors (IGFs) play critical roles in the control of myogenesis. Insulin-like growth factor-binding protein-5 (IGFBP-5), by regulating the bioavailability of IGFs, is involved in controlling IGF-dependent differentiation. We investigated the effects of TGF-beta on the IGFBP-5 production induced by IGFs in mouse myoblasts. TGF-beta leads to a decrease in IGFBP-5 synthesis at both transcript and protein levels, and blocked muscle differentiation. The Smad proteins and the c-Jun N-terminal kinase (JNK) have been shown to be involved in TGF-beta signaling pathways. We provide evidence that the JNK pathway, rather than Smad proteins, is involved in the response of muscle cells to TGF-beta. This factor failed to stimulate the GAL4-Smad 2/3 transcriptional activities of the constructs used to transfect myoblasts. Moreover, stable expression of the antagonistic Smad7 did not abolish the inhibitory effect of TGF-beta on IGFBP-5 production whereas expression of a dominant-negative version of MKK4, an upstream activator of JNK, did. We also showed, using a specific inhibitor, that the p38 mitogen-activated protein kinase (p38 MAPK) was not involved in the inhibition of IGFBP-5 production. Thus, TGF-beta-mediated IGFBP-5 inhibition is independent of Smads and requires activation of the JNK signaling pathway.

In vivo progression of LAPC-9 and LNCaP prostate cancer models to androgen independence is associated with increased expression of insulin-like growth factor I (IGF-I) and IGF-I receptor (IGF-IR)

Androgen deprivation therapies for metastatic prostate cancer are useful initially, but progression to androgen independence usually results in relapse within 2 years. The molecular mechanisms underlying the clinically important transition from androgen dependence to androgen independence are poorly described. Several lines of investigation have suggested that insulin-like growth factors (IGFs) are involved in the biology of prostate cancer, but little is known about their relevance to progression to androgen independence. We used three in vivo models of androgen-dependent (AD) human prostate cancer to study this issue. Progression to androgen-independent (AI) growth was associated with a 60-fold increase in expression of IGF-I mRNA in LAPC-9 xenografts and a 28-fold increase in IGF-I expression in LNCAP xenografts, relative to the initial AD neoplasms. IGF type I receptor (IGF-IR) mRNA levels were approximately 2.5-fold and approximately 5-fold higher, respectively, in AI LAPC-9 and LNCaP tumors compared with the original AD neoplasms. AI growth of these xenografts was also associated with significant reductions in IGF binding protein-3 expression. LAPC-4 xenografts, which previously have been shown to exhibit molecular pathology related to HER-2/neu expression with progression to AI, showed relatively minor changes in expression of the genes investigated, but we nevertheless found evidence of increased IGF-IR phosphorylation with progression to androgen independence in this model. Taken together with prior observations, our results suggest that deregulation of expression of genes related to any one of several critical receptor tyrosine kinase regulatory systems, including IGF signaling, may confer androgen independence.

Differential regulation of IGFBP-2 and IGFBP-5 gene expression by vitamin A status in Japanese quail

To investigate the involvement of the insulin-like growth factor (IGF) system in vitamin A (VA)-supported growth, we examined the effects of VA status on IGF binding protein (IGFBP)-2 and -5 gene expression in Japanese quail. VA deficiency caused a reduction in IGFBP-2 mRNA only in lung, without effect in other tissues. However, the expression of IGFBP-5 mRNA was more sensitive to the change of VA status. IGFBP-5 mRNA levels were significantly reduced by VA depletion in a tissue-specific manner, which preceded the decrease in body weight. A single injection of retinoic acid or retinol to VA-deficient quail did not affect the levels of IGFBP-2 mRNA, but it rapidly induced the expression of IGFBP-5 mRNAs in some tissues. These results are the first to show that gene expression of some IGFBPs in vivo are under the control of VA status and suggest a possible involvement of the IGF system in mediating the physiological actions of VA in the growth of Japanese quail.

Expression and localisation of IGF-binding protein mRNAs in regenerating rat skeletal muscle

The expression of the insulin-like growth factor-binding proteins (IGFBP) -3, -4, -5 and -6 was investigated in neonatal, in normal adult and in regenerating rat skeletal muscle. Semi-quantification was done by densitometric scannings of Northern blots. The expression of all investigated IGFBPs, with the exception of IGFBP-5, was higher in neonatal than in adult muscle. During postischaemic regeneration the expression of all IGFBPs increased, but with different time schedules. IGFBP-3 increased transiently during the early phase of regeneration, while IGFBP-4, -5 and -6 increased during the later phase of regeneration. In situ hybridisation on regenerating muscle showed that the expression of the various IGFBPs was cell specific; thus, IGFBP 3 was mainly expressed in macrophages, IGFBP-4 in connective tissue, IGFBP-5 in regenerating muscle cells, and IGFBP-6 in muscle cells, connective tissue and endothelium. Ligand blotting, using 125I-IGF-I as the ligand, showed a number of bands ranging between 24 and 44 kDa. Samples from neonatal and regenerating muscle contained much higher levels of all IGFBPs than those from normal adult muscle. An ordered and cell-specific expression of IGFBPs, allowing a strict regulation of IGF actions, is probably necessary to ensure an optimal regeneration process.

Increased expression of IGF-binding protein-5 in Duchenne muscular dystrophy (DMD) fibroblasts correlates with the fibroblast-induced downregulation of DMD myoblast growth: an in vitro analysis

In DMD the progressive loss of muscle ability and concomitant increasing fibrosis might originate from, besides other causes, the fibroblast paracrine inhibition of satellite cell "growth." In this study we report that in myoblast/fibroblast coculture experiments, the presence of DMD fibroblasts negatively interfered with DMD myoblast growth to an extent directly proportional to the percentage of DMD fibroblasts present in the mixed-cell cultures. Moreover, the observation that media conditioned with proliferating DMD fibroblasts inhibited the growth of DMD myoblasts more seriously than did control fibroblast-conditioned media suggested a paracrine effect by diffusible factors. IGF-binding proteins could act as such diffusible factors; in fact, IGFBP-5 transcript increased threefold in DMD fibroblasts proliferating in DMD muscle extracts, whereas IGFBP-3 mRNA decreased. In addition, high levels of IGFBP-5 protein were detected in DMD fibroblast-conditioned media. In neutralizing IGFBP-5 in DMD fibroblast-conditioned media by means of specific antibodies, or inhibiting IGFBP-5 gene expression in DMD fibroblasts by means of oligo antisense, the fibroblast-conditioned media lost inhibitory power over DMD myoblast proliferation.

Enterotrophic effect of insulin-like growth factor-I but not growth hormone and localized expression of insulin-like growth factor-I, insulin-like growth factor binding protein-3 and -5 mRNAs in jejunum of parenterally fed rats

BACKGROUND

Administration of insulin-like growth factor (IGF)-I, but not growth hormone (GH), stimulates mucosal hyperplasia in surgically stressed rats with intestinal atrophy induced by hypocaloric total parenteral nutrition (TPN). Our aim was to characterize the basis for this disparity in enterotrophic action by assessing the relationships between stimulation of intestinal growth, nutritional adequacy, and localization of expression of IGF-I, insulin-like growth factor binding protein (IGFBP)-3 and IGFBP-5 mRNAs in jejunum.

METHODS

Rats were maintained with TPN for 8 days and treated with IGF-I or GH and adequate nutrition for 5 days after recovery from surgery. Jejunal mass, morphology, and sucrase activity were assessed. Localization of expression of IGF-I, IGFBP-3, and IGFBP-5 mRNAs in jejunum was accomplished by in situ hybridization.

RESULTS

Serum IGF-I and body weight gain were significantly increased by IGF-I or GH. Jejunal mucosal dry mass, morphology, and sucrase activity were improved with IGF-I but not GH. There were no differences in IGF-I mRNA. IGFBP-3 mRNA was localized in the lamina propria of the villi. IGF-I or GH stimulated IGFBP-3 expression. IGF-I strongly stimulated IGFBP-5 expression in the lamina propria and the muscularis and induced a twofold increase in IGFBP-5 mRNA based on RNase protection assay of intact jejunum total RNA. GH induced a modest increase in IGFBP-5 expression in the muscularis with no effect on intact jejunum total RNA.

CONCLUSIONS

The GH resistance observed in the jejunal mucosa of TPN rats cannot be fully explained by inadequate nutrition. The expression of IGFBP-5 in the lamina propria suggests it may modulate the enterotrophic action of exogeneous IGF-I.

Altered expression of insulin-like growth factor-1 and insulin like growth factor binding proteins-2 and 5 in the mouse mutant Hypodactyly (Hd) correlates with sites of apoptotic activity

Insulin-like growth factor-I (IGF-I) mediated signalling has been implicated to be of significant importance during vertebrate embryonic development. IGF-I signalling has also been shown to be modulated by a number of IGF binding proteins that are thought to act as either agonists or antagonists of IGF activity. IGF-I has been implicated in a number of cellular processes, including cell division and programmed cell death (apoptosis). We have used the mouse mutant Hypodactyly (Hd) as a tool to determine the role of IGF-I and two key IGF binding proteins (IGFBP-2 and IGFBP-5) during embryonic development. The Hd mutant is a good model with which to study developmental cascades, since it has a distinct phenotype in the limb where cellular and molecular circuits have been thoroughly investigated. The distinctive pointed limb buds observed in Hd mutant embryos have been shown to be the result of a massive increase in apoptosis. We show that all three genes, IGF-1, IGFBP-2 and IGFBP-5, display restricted expression patterns during limb development. Indeed, IGFBP-5 shows a remarkable similarity to the expression of Engrailed-1, which is the vertebrate homologue of the Drosophila selector gene Engrailed. We show that there is downregulation in the expression of IGFBP-2 in the entire apical ectodermal ridge (AER) in homozygous Hd/Hd limb buds, whereas IGFBP-5 is downregulated in specific regions in the mutant AER. IGF-I expression is downregulated in Hd limb buds in regions undergoing high levels of cell death, consistent with its proposed role as an anti-apoptotic factor, while IGFBP-5 is found at higher levels in regions of cell death, consistent with reports of its association with apoptosis in adult tissues. We propose that these three components of the IGF axis could be involved in the manifestation of the mutant phenotype in Hypodactyly, and that this is probably a result of their ability to regulate cell survival and cell death.

Tumor necrosis factor-alpha-induced apoptosis is associated with suppression of insulin-like growth factor binding protein-5 secretion in differentiating murine skeletal myoblasts

Wasting of muscle and fat during cachexia exceeds that explained by reduced food intake alone. This wasting may result from an imbalanced cytokine environment, which could lead to increased protein catabolism. Supporting this, tumor necrosis factor-alpha (TNF-alpha) is raised in several animal models of cachectic muscle wasting. Therefore, we assessed the effects of TNF-alpha and its second messenger, ceramide, on the proliferation, differentiation, and survival of murine C2 skeletal myoblasts. Because insulin-like growth factor binding protein-5 (IGFBP-5) and insulin-like growth factor-II (IGF-II) are potent regulators of myoblast proliferation and differentiation, we monitored the ability of exogenous TNF-alpha to manipulate this system. Fibroblast growth factor (FGF) ceramide, or TNF-alpha suppressed differentiation of C2 cells compared with controls. All treatments suppressed IGF-II production but only TNF-alpha blocked IGFBP-5 secretion. TNF-alpha increased apoptotic cell death, which otherwise remained basal (low serum differentiation medium (LSM), FGF) or low (ceramide). Suppression of both IGFBP-5 and IGF-II secretion may explain why of all triggers tested, only TNF-alpha not only blocked differentiation, but also promoted cell death. This suggests a fundamental role of IGFBP-5 for maintaining muscle survival. Supporting this hypothesis, no increase in apoptosis was seen in IGFBP-5 cDNA tranfected C2 cells after TNF-alpha treatment. In summary, the IGF system is essential for maintaining skeletal muscle cell survival and differentiation, and its suppression by TNF-alpha is fundamental regarding muscle wasting, and may be associated in vivo with cancer cachexia.

Endogenous IGF-I regulates IGF binding protein production in human intestinal smooth muscle cells

Human intestinal smooth muscle in culture produces insulin-like growth factor (IGF)-I and IGF binding protein (IGFBP)-3, IGFBP-4, and IGFBP-5, which modulate the effects of IGF-I. This study examined the regulation of IGFBP production by endogenous IGF-I. R3-IGF-I, an agonist unaffected by IGFBPs, elicited concentration-dependent increase in growth, measured by [(3)H]thymidine incorporation, and production of IGFBP-3, IGFBP-4, and IGFBP-5, measured by Western blot. Antagonists of the IGF-I receptor, IGF-I Analog or monoclonal antibody 1H7, elicited concentration-dependent inhibition of growth and decrease in IGFBP-3, IGFBP-4, and IGFBP-5 production, implying that endogenous IGF-I stimulated growth and IGFBP production. R3-IGF-I-induced increase in IGFBP-3, IGFBP-4, and IGFBP-5 production was partially inhibited by a mitogen-activated protein (MAP) kinase or a phosphatidylinositol-3-kinase (PI 3-kinase) inhibitor and abolished by the combination. We conclude that endogenous IGF-I stimulates growth and IGFBP-3, IGFBP-4, and IGFBP-5 production in human intestinal smooth muscle cells. Regulation of IGFBP production by IGF-I is mediated by activation of distinct MAP kinase and PI 3-kinase pathways, the same pathways through which IGF-I stimulates growth.

Testosterone and insulin-like growth factor (IGF) I interact in controlling IGF-binding protein production in androgen-responsive foreskin fibroblasts

The growth of the male external genitalia is primarily regulated by androgens. However, human genital fibroblast growth is also stimulated by insulin-like growth factor (IGF) I. In this study, we report that IGF-binding protein (IGFBP) production in human foreskin fibroblasts is regulated by androgens and IGF-I. Human foreskin fibroblasts secrete IGFBP-3, IGFBP-4, and IGFBP-5. IGF-I increased the abundance of both intact IGFBP-3 and -5 in the culture medium. Testosterone increased IGFBP-3, and the combination of IGF-I and testosterone had an additive effect. Following its secretion, IGFBP-5 was degraded, but the effect of IGF-I on IGFBP-5 peptide abundance in conditioned media did not seem to be due to inhibition of proteolysis. Testosterone had no effect on IGFBP-5 degradation. Intact IGFBP-4 was decreased by IGF-I, and the combination resulted in a similar reduction. The mechanism seemed to be decreased synthesis, since IGFBP-4 messenger RNA was also decreased. The increase in IGFBP-5 synthesis was associated with an increase in the abundance of intact IGFBP-5 in the extracellular matrix. The combination of testosterone and IGF-I resulted in a synergistic stimulation of total protein synthesis by the fibroblast cultures, suggesting that a maximum anabolic response requires both hormones. These observations suggest that combined exposure to androgen and IGF-I altered the abundance of some forms of IGFBPs and that the IGFBPs that are regulated may play a role in modulating the effects of IGF-I on the anabolic response.

Reduction in atherosclerotic lesion size in pigs by alphaVbeta3 inhibitors is associated with inhibition of insulin-like growth factor-I-mediated signaling

Insulin-like growth factor-I (IGF-I) is a potent stimulant of smooth muscle cell (SMC) migration and proliferation and has been implicated in the development of experimental atherosclerotic lesions. Because optimal stimulation of SMC in vitro by IGF-I requires ligand occupancy of alphaVbeta3, these studies were conducted to determine whether alphaVbeta3 antagonists would result in a change in lesion size and whether they could alter IGF-I-mediated actions. Clamps were placed on the carotid and femoral arteries of normal pigs that had been fed a high-cholesterol diet for 4 weeks. alphaVbeta3 inhibitors (SC-69000, SC-65811) (10(-6) mol/L) or saline were infused for 2 weeks into the peristenotic area. Lesion area, the number of SMC layers, and proliferating cell nuclear antigen positive cells were determined in a 1.2-mm segment of each artery. Lesion areas were 304 788+/-113 453 micron(2) (saline), compared with 149 799+/-35 456 micron(2) (SC-69000) (P<0.01). Lesion areas in arteries treated with SC-64258, a compound that does not bind to alphaVbeta3, were 310 284+/-160 467 micron(2), P=not significant. In a second experiment, lesion areas were 110 391+/-17 347 micron(2) (saline) and 59 533+/-17 568 micron(2) (SC-65811, P<0.001). Neointimal SMC layers were reduced by SC-65811 from 7.4+/-4.5 to 3.0+/-0.4 (P<0.001). To determine whether IGF-I action was altered, IGF binding protein-5, which is synthesized in response to IGF-I, was analyzed. IGF-I binding protein-5 mRNA abundance was reduced by 67+/-8% in the 6 lesions treated with SRL-69000 compared with saline controls (P<0.001). We conclude that alphaVbeta3 antagonists block the development of lesions in pigs that have been induced by a high-cholesterol diet and stenosis, and the effect of these compounds is associated with their ability to inhibit IGF-I-mediated signaling.

Regulation of IGF-I, IGFBP-4 and IGFBP-5 gene expression by loading in mouse skeletal muscle

Gene expression of IGF-I, IGFBP-4 and IGFBP-5 was studied in hindhimb skeletal muscle of mice, which were either overloaded or unloaded for 8 days. Overloading induced a 15% hypertrophy in soleus muscle associated with a 60% increase of IGF-I transcript levels and a doubling of IGFBP-4 mRNA levels. IGFBP-5 mRNA levels were decreased to one third of the control value. Changes in IGFBPs mRNA always preceded changes in IGF-I gene expression. Unloading by hindlimb suspension resulted in atrophy of soleus muscle (20%) and phenotype change towards the fast type associated with a transient decrease of IGF-I mRNA (30%) and a sustained increase (x2) of IGFBP-5 transcript. These alterations in IGFBPs expression, in unloaded or overloaded soleus, suggest that they may play a role in skeletal muscle adaptation to changes in loading.

Influence of microenvironment on mammary epithelial cell survival in primary culture

Mammary epithelial cells cultured on Engelbreth-Holm-Swarm (EHS) matrix form multicellular structures termed mammospheres, in which cells and matrix become arranged around a central luminal space. In the presence of lactogenic hormones, cells within mammospheres become polarized, form tight intercellular junctions, and secrete milk proteins vectorially into the luminal space. This study examined the mechanism of lumen formation. Histological examination of developing mammospheres showed that cavitation was associated spatially and temporally with the appearance of fragmented nuclear material in apoptotic bodies, and with the presence of cells positively labeled by terminal deoxynucleotide transferase-mediated deoxyuridine nick end-labeling (TUNEL). Analysis of [(32)P]-deoxynucleotide end-labeled genomic DNA by electrophoresis and autoradiography showed DNA laddering indicative of apoptosis. A transient increase in laddering coincided with both lumen formation and the presence of TUNEL-positive cells. Lumen formation, DNA laddering, and detection of TUNEL-positive cells were all accelerated when matrix composition was altered. They were also impaired coordinately when caspase inhibitor was present during the first two days of culture. Therefore, lumen formation in mammosphere cultures is due to selective apoptosis of centrally located cells. Mammosphere cavitation was accompanied by redistribution of matrix constituents to the mammosphere periphery. Western blotting and Western ligand blotting of culture medium showed that lumen formation was also associated with a transient increase in insulin-like growth factor binding protein-5 (IGFBP5), a factor implicated in mammary apoptosis in vivo. We propose that epithelial cell survival during mammosphere development is induced selectively through stabilization by basement membrane constituents, which may act directly on the epithelial cell or confer protection against autocrine apoptotic factors.

Synthetic alphaVbeta3 antagonists inhibit insulin-like growth factor-I-stimulated smooth muscle cell migration and replication

Porcine aortic smooth cells respond to insulin-like growth factor-I (IGF-I) with increases in DNA synthesis and cell migration. Because ligand occupancy of the alphaVbeta3 integrin has been shown to be necessary for IGF-I to stimulate maximal increases in both processes, we determined whether synthetic alphaVbeta3 antagonists could inhibit IGF-I-stimulated actions on this cell type. Low-molecular-weight compounds that had been selected based on their ability to compete with vitronectin for binding to purified human alphaVbeta3 in vitro were analyzed for their ability to compete with 125I-kistrin (a known ligand for porcine alphaVbeta3) for binding to porcine alphaVbeta3. Nine compounds were screened, and five were found to be potent competitive inhibitors. The most potent compound, SC-69000, resulted in 88% competition at 10(-7) M and was nearly equipotent with echistatin. The compounds that were the most potent inhibitors of kistrin binding were tested for their capacity to inhibit the cell migration response to IGF-I. Three compounds caused between 81-88% inhibition of IGF-I-stimulated migration at 10(-7) M. To determine whether these compounds could inhibit other IGF-I-stimulated actions, their ability to inhibit IGF-I-stimulated [3H]-thymidine incorporation into DNA was analyzed. The four compounds that were the most potent inhibitors of cell migration also inhibited IGF-I-stimulated DNA replication. IGF-I stimulates the synthesis of IGF binding protein-5 by these cells. Preincubation with the four most active compounds also resulted in significant inhibition of the ability of IGF-I to stimulate IGF binding protein-5 synthesis. AlphaVbeta3 occupancy by the ligand vitronectin has been shown to enhance the capacity of IGF-I to activate its receptor tyrosine kinase. The four most active compounds were shown to inhibit IGF-I-stimulated IGF-I receptor autophosphorylation. These findings suggest that blockade of ligand occupancy of the alphaVbeta3 integrin globally inhibits several IGF-I-stimulated biologic actions and that synthetic inhibitors are very active in this regard. Because these compounds can be administered to whole animals, they should be very useful in determining whether blocking alphaVbeta3 occupancy in vivo results in alteration in responsiveness to IGF-I.

Castration-induced apoptosis of androgen-dependent shionogi carcinoma is associated with increased expression of genes encoding insulin-like growth factor-binding proteins

Insulin-like growth factor (IGF)-I has well-characterized mitogenic and antiapoptotic effects that are essential for maintenance of the normal prostate and may be important during regression of the normal prostate and/or prostate tumors induced by androgen-targeting therapies for prostate cancer. IGF-I activity is modulated by IGF-binding proteins (IGFBPs). Here we examine IGFBP expression during regression of androgen-dependent Shionogi carcinoma tumors after castration. In this model, we observe a 90% reduction in Shionogi tumors by 10 days postcastration. Northern blotting of RNA from tumors collected at various times after castration indicates a rapid induction of IGFBP-5 concomitant with apoptotic regression of tumors, as detected by Apoptag staining of tumor sections after castration. IGFBP-5 mRNA was not detectable in tumors from control animals, but levels increased 120-fold in tumors 3 days after castration. The mRNAs for IGFBP-3 and 4 were abundant in Shionogi tumors from intact mice and decreased to -33% and -20% of control, respectively. Castration had no significant effect on IGFBP-2 expression. Treatment with calcium channel blockers inhibited castration-induced apoptosis and tumor regression and also significantly inhibited up-regulation of IGFBP-5 after castration. These data provide strong evidence for a functional role of IGFBP-5 expression in mediating the apoptosis induced by androgen deprivation in androgen-dependent neoplasia.

Expression and location of IGF binding proteins-2, -4, and -5 in developing fetal tissues

Insulin-like growth factors are associated with myogenesis in vivo, and their actions are mediated by IGF binding proteins (IGFBP). Sites of IGFBP production and their location during early development are not clear. The objective of this research was to examine the developmental expression and location of IGFBP-2, -4, and -5 mRNA and peptides in developing porcine skeletal muscle and liver. Pregnant pigs were euthanatized at various times postconception (pc). Developmental expression of IGFBP was evaluated using total RNA extracted from skeletal muscle and liver of 30-, 44-, 59-, 68-, 75-, 89-, and 109-d pc fetuses and from adult and neonatal pigs. Localization of IGFBP-2, -4, and -5 mRNA and peptides was examined by in situ hybridization and immunocytochemistry of muscle samples from contralateral pelvic limbs of each pig. Overall muscle IGFBP gene expression decreased (P < .05) with increasing age. Moreover, expression of liver IGFBP-2 and -5, but not of IGFBP-4, was greater (P < .05) during prenatal than during postnatal periods. The majority of immunoreactive IGFBP was located in developing muscle cells, with little localized to connective tissue, except at later stages of development. These data show that IGFBP-2, -4, and -5 expression is time- and tissue-dependent in fetal liver and muscle.

Maturation of the myogenic program is induced by postmitotic expression of insulin-like growth factor I

The molecular mechanisms underlying myogenic induction by insulin-like growth factor I (IGF-I) are distinct from its proliferative effects on myoblasts. To determine the postmitotic role of IGF-I on muscle cell differentiation, we derived L6E9 muscle cell lines carrying a stably transfected rat IGF-I gene under the control of a myosin light chain (MLC) promoter-enhancer cassette. Expression of MLC-IGF-I exclusively in differentiated L6E9 myotubes, which express the embryonic form of myosin heavy chain (MyHC) and no endogenous IGF-I, resulted in pronounced myotube hypertrophy, accompanied by activation of the neonatal MyHC isoform. The hypertrophic myotubes dramatically increased expression of myogenin, muscle creatine kinase, beta-enolase, and IGF binding protein 5 and activated the myocyte enhancer factor 2C gene which is normally silent in this cell line. MLC-IGF-I induction in differentiated L6E9 cells also increased the expression of a transiently transfected LacZ reporter driven by the myogenin promoter, demonstrating activation of the differentiation program at the transcriptional level. Nuclear reorganization, accumulation of skeletal actin protein, and an increased expression of beta1D integrin were also observed. Inhibition of the phosphatidyl inositol (PI) 3-kinase intermediate in IGF-I-mediated signal transduction confirmed that the PI 3-kinase pathway is required only at early stages for IGF-I-mediated hypertrophy and neonatal MyHC induction in these cells. Expression of IGF-I in postmitotic muscle may therefore play an important role in the maturation of the myogenic program.

IGFBP-3 and IGFBP-5 production by human intestinal muscle: reciprocal regulation by endogenous TGF-beta1

Insulin-like growth factor-I (IGF-I)-mediated growth of cells can be modulated by specific IGF binding proteins (IGFBPs) that inhibit or augment IGF-I ligand-receptor interaction. IGFBP expression and production by human intestinal muscle cells in culture was characterized in rapidly growing cells (day 3 of culture), in confluent cells (day 7), and in postconfluent cells (day 14). RT-PCR analysis identified IGFBP-3, IGFBP-4, and IGFBP-5 mRNA during all three phases of growth. The production of IGFBP-3 and IGFBP-5 was regulated in reciprocal fashion. IGFBP-5 production was high on day 3 and decreased two- to fivefold by day 14, and IGFBP-3 production was low on day 3 and increased five- to eightfold by day 14. IGFBP-4 production remained constant. IGFBP-3 inhibited and IGFBP-5 augmented IGF-I-induced proliferation. IGFBP-3 and IGFBP-5 production was regulated in reciprocal fashion by transforming growth factor-beta1 (TGF-beta1). Immunoneutralization of endogenous TGF-beta1 decreased the production of IGFBP-3 and increased the production of IGFBP-5. Addition of exogenous recombinant human TGF-beta1 had the opposite effect. We conclude that the expression and time-dependent production of IGFBP-3, IGFBP-4, and IGFBP-5 and their regulation by endogenous TGF-beta1 represent mechanisms by which human intestinal muscle cells regulate autocrine IGF-I-mediated growth.

In vivo regulation of the insulin-like growth factor system of mitogens by human chorionic gonadotropin

Human chorionic gonadotropin (hCG) is a differentiating agent and chemopreventive in rat DMBA-induced breast carcinogenesis. Insulin-like growth factors (IGFs) are potent mitogens for breast cancer cells. We report that the administration of hCG to female rats resulted in a significant increase in serum IGFBP-3 levels at doses greater than 10 UI and a significant decrease in serum IGF-I levels. Northern blot analysis revealed that hCG inhibited hepatic and mammary IGF-I gene expression at doses greater than 10 UI. Mammary IGFBP-5 and IGFBP-2 gene expression significantly increased at high doses of hCG while IGFBP-4 slightly decreased. Treatments greater than 10 UI of hCG resulted in a significant suppression of mammary IGFBP-3 and IGF-I receptor expression. Since IGFs are potent mitogens and antiapoptotic agents for breast cancer, this newly described activity of hCG may contribute to its antiproliferative properties, particularly with regard to the differentiation and inhibition of mammary tumours seen in animal models.