Insulin-like growth factor binding protein-3: insulin-like growth factor independence comes of age

IGF-Binding Proteins, Adiponectin, and Survival in Metastatic Colorectal Cancer: Results From CALGB (Alliance)/SWOG 80405

Background

Energy balance-related biomarkers are associated with risk and prognosis of various malignancies. Their relationship to survival in metastatic colorectal cancer (mCRC) requires further study.

Methods

Baseline plasma insulin-like growth factor (IGF)-1, IGF-binding protein (IGFBP)-3, IGFBP-7, C-peptide, and adiponectin were measured at time of trial registration in a prospective cohort of patients with mCRC participating in a National Cancer Institute–sponsored trial of first-line systemic therapy. We used Cox proportional hazards regression to adjust for confounders and examine associations of each biomarker with overall survival (OS) and progression-free survival (PFS). P values are 2-sided.

Results

Median follow-up for 1086 patients was 6.2 years. Compared with patients in the lowest IGFBP-3 quintile, patients in the highest IGFBP-3 quintile experienced an adjusted hazard ratio (HR) for OS of 0.57 (95% confidence interval [CI] = 0.42 to 0.78; P_nonlinearity < .001) and for PFS of 0.61 (95% CI = 0.45 to 0.82; P_trend = .003). Compared with patients in the lowest IGFBP-7 quintile, patients in the highest IGFBP-7 quintile experienced an adjusted hazard ratio for OS of 1.60 (95% CI = 1.30 to 1.97; P_trend < .001) and for PFS of 1.38 (95% CI = 1.13 to 1.69; P_trend < .001). Plasma C-peptide and IGF-1 were not associated with patient outcomes. Adiponectin was not associated with OS; there was a nonlinear U-shaped association between adiponectin and PFS (P_nonlinearity = .03).

Conclusions

Among patients with mCRC, high plasma IGFBP-3 and low IGFBP-7 were associated with longer OS and PFS. Extreme levels of adiponectin were associated with shorter PFS. These findings suggest potential avenues for prognostic and therapeutic innovation.

Structural and functional analysis of the amphioxus IGFBP gene uncovers ancient origin of IGF-independent functions

IGFs play key roles in regulating vertebrate development, growth, reproduction, and aging. In extracellular fluids, IGFs are bound and regulated by a family of IGF-binding proteins (IGFBPs). Although all known IGFBPs are secreted proteins, some are also found in the nucleus and possess IGF-independent activities. When and how these distinct modes of biological actions have evolved is unknown. In this study, we identified and analyzed an IGFBP gene from amphioxus. Amphioxus shares a common ancestor with the modern vertebrate lineage that dates back to more than 520 million years ago. The amphioxus IGFBP shares all major structural characteristics of vertebrate IGFBPs. Phylogenetic analyses place it in a basal position in the IGFBP lineage. Ligand blot analysis reveals that amphioxus IGFBP does not bind to IGF-I or -II. Changing its Phe70 into Leu, however, is sufficient to convert it into a functional IGF binder. When tested in cultured cells, amphioxus IGFBP is localized in the nucleus, and this is attributed to 2 redundant nuclear localization sequences in its L domain. Furthermore, the amphioxus IGFBP N-terminal domain has strong transcriptional activation activity. Forced expression of amphioxus IGFBP in zebrafish embryos results in dorsalized phenotypes. This action requires nuclear localization. These results suggest that the nuclear localization and transcription activation activity of IGFBPs are ancient functions and the IGF-binding function may have been acquired by opportunistic gain-of-functional mutations later in evolution.

IGF binding protein-3 mediates stress-induced apoptosis in non-transformed mammary epithelial cells

Mammary epithelial cell (MEC) number is an important determinant of milk production in lactating dairy cows. IGF-I increases IGF binding protein-3 (IGFBP-3) production in these cells, which plays a role in its ability to enhance proliferation. In the present study, we show that the apoptotic factor anisomycin (ANS) also increases IGFBP-3 mRNA and protein in a dose- and concentration-dependent manner that mirrors activation of caspase-3 and -7, with significant increases in both IGFBP-3 protein and caspase activation observed by 3 h. Knock-down of IGFBP-3 with small interfering (si) RNA attenuated the ability of ANS to induce apoptosis, while knock-down of IGFBP-2, the other major IGFBP made by bovine MEC, had no effect. Reducing IGFBP-3 also decreased the ability of ANS to induce mitochondrial cytochrome c release, indicating its involvement in the intrinsic apoptotic pathway. In contrast, transfection with IGFBP-3 in the absence of ANS failed to induce apoptosis. Since both the mitogen IGF-I and the apoptotic inducer ANS increase IGFBP-3 production in MEC, we proposed that cellular localization might determine IGFBP-3 action. While both IGF-I and ANS stimulated the release of IGFBP-3 into conditioned media, only ANS induced nuclear localization of IGFBP-3. A pan-caspase inhibitor had no effect on ANS-induced nuclear localization of IGFBP-3, indicating that nuclear entry of IGFBP-3 precedes caspase activation. Treatment with IGF-I had no effect on ANS-induced nuclear localization, but did block ANS-induced apoptosis. In summary, our data indicate that IGFBP-3 plays a role in stress-induced apoptosis that may require nuclear localization in non-transformed MEC.

Somatotropic signaling: trade-offs between growth, reproductive development, and longevity

Growth hormone (GH) is a key determinant of postnatal growth and plays an important role in the control of metabolism and body composition. Surprisingly, deficiency in GH signaling delays aging and remarkably extends longevity in laboratory mice. In GH-deficient and GH-resistant animals, the "healthspan" is also extended with delays in cognitive decline and in the onset of age-related disease. The role of hormones homologous to insulin-like growth factor (IGF, an important mediator of GH actions) in the control of aging and lifespan is evolutionarily conserved from worms to mammals with some homologies extending to unicellular yeast. The combination of reduced GH, IGF-I, and insulin signaling likely contributes to extended longevity in GH or GH receptor-deficient organisms. Diminutive body size and reduced fecundity of GH-deficient and GH-resistant mice can be viewed as trade-offs for extended longevity. Mechanisms responsible for delayed aging of GH-related mutants include enhanced stress resistance and xenobiotic metabolism, reduced inflammation, improved insulin signaling, and various metabolic adjustments. Pathological excess of GH reduces life expectancy in men as well as in mice, and GH resistance or deficiency provides protection from major age-related diseases, including diabetes and cancer, in both species. However, there is yet no evidence of increased longevity in GH-resistant or GH-deficient humans, possibly due to non-age-related deaths. Results obtained in GH-related mutant mice provide striking examples of mutations of a single gene delaying aging, reducing age-related disease, and extending lifespan in a mammal and providing novel experimental systems for the study of mechanisms of aging.

IGFBP-3 nuclear localization predicts human prostate cancer recurrence

Insulin-like growth factor binding protein-3 (IGFBP-3) is a pro-apoptotic, anti-metastasic, and anti-angiogenic protein. Low serum IGFBP-3 has been associated with risk of more aggressive prostate cancer (PCa). We investigated the impact of nuclear and cytoplasmic IGFBP-3 protein expression levels in PCa by examining their in situ expression across a wide spectrum of primary tumors by immunohistochemical analysis of tissue microarrays. Immunohistochemistry was performed on PCa microarrays constructed from 226 hormone naïve patients who underwent radical prostatectomy. Both cytoplasmic and nuclear IGFBP-3 expressions were scored in a semi-quantitative fashion using an integrated measure of intensity and positivity. The distribution of IGFBP-3 protein expression was examined across the spectrum of epithelial tissues, and its association with standard clinicopathological covariates and tumor recurrence was examined. There was a broad range of IGFBP-3 staining across all histologies examined. Tumor had higher IGFBP-3 cytoplasmic and nuclear staining than benign histologies. For IGFBP-3 nuclear staining, PCa was significantly different than benign prostatic hyperplasia, normal prostate, and prostate intraepithelial neoplasia. As both a continuous and dichotomized variable, higher nuclear IGFBP-3 expression had statistically significant associations with PCa recurrence. The cytoplasmic staining had no significance in any patient subgroup. In patients with low-grade cancer, IGFBP-3 nuclear positivity was a better predictor of recurrence than baseline PSA, tumor margin status, TNM tumor stage, or presence of capsular invasion. High nuclear IGFBP-3 is amongst the strongest predictors of cancer recurrence in patients with low-grade prostate cancers and may therefore play an important role in risk stratification.

Analysis of the cellular uptake and nuclear delivery of insulin-like growth factor binding protein-3 in human osteosarcoma cells

Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) regulates cell proliferation and survival by extracellular interaction and inactivation of the growth factor IGF-I. Beyond that, IGF-independent actions mediated by intracellular IGFBP-3 including nuclear-IGFBP-3, have also been described. We here show, using both confocal and electron microscopy and cell fractionation, that the extracellular addition of IGFBP-3 to living cells results in rapid uptake and nuclear delivery of IGFBP-3, by yet partly unknown mechanisms. IGFBP-3 is internalized through a dynamin-dependent pathway, traffics through endocytic compartments and is finally delivered into the nucleus. We observed docking of IGFBP-3 containing structures to the nuclear envelope and found IGFBP-3 containing dot-like structures to permeate the nuclear envelope. In summary, our findings establish the pathway by which this tumor suppressor protein is delivered from extracellular space to the nucleus.

Insulin-like growth factor I and the pathogenesis of delirium: a review of current evidence

Delirium is a frequent complication in medically ill elderly patients that is associated with serious adverse outcomes including increased mortality. Delirium risk is linked to older age, dementia, and illness that involves activation of inflammatory responses. IGF-I is increasingly postulated as a key link between environmental influences on body metabolism with a range of neuronal activities and has been described as the master regulator of the connection between brain and bodily well-being. The relationships between IGF-I and ageing, cognitive impairment and inflammatory illness further support a possible role in delirium pathogenesis. Five studies of IGF-I in delirium were identified by a systematic review. These conflicting findings, with three of the five studies indicating an association between IGF-1 and delirium occurrence, may relate to the considerable methodological differences in these studies. The relevance of IGF-I and related factors to delirium pathogenesis can be clarified by future studies which account for these issues and other confounding factors. Such work can inform therapeutic trials of IGF-I and/or growth hormone administration.

Humanin preserves endothelial function and prevents atherosclerotic plaque progression in hypercholesterolemic ApoE deficient mice

OBJECTIVE

Humanin (HN) is a cytoprotective peptide derived from endogenous mitochondria, expressed in the endothelial layer of human vessels, but its role in atherogenesis in vivo is not known. In vitro study, however, HN reduced oxidized low-density lipoprotein induced formation of reactive oxygen species and apoptosis. The present study tested the hypothesis that long term treatment with HN will have a protective role against endothelial dysfunction and progression of atherosclerosis in vivo.

METHODS AND RESULTS

Daily intraperitonial injection of the HN analogue HNGF6A for 16 weeks prevented endothelial dysfunction and decreased atherosclerotic plaque size in the proximal aorta of ApoE-deficient mice fed on a high cholesterol diet, without showing direct vasoactive effects or cholesterol-reducing effects. HN was expressed in the endothelial layer on the aortic plaques. HNGF6A treatment reduced apoptosis and nitrotyrosine immunoreactivity in the aortic plaques without affecting the systemic cytokine profile. HNGF6A also preserved expression of endothelial nitric oxide synthase in aorta.

CONCLUSIONS

HN may have a protective effect on endothelial function and progression of atherosclerosis by modulating oxidative stress and apoptosis in the developing plaque.

IGFBP-3 is a metastasis suppression gene in prostate cancer

The insulin-like growth factor binding protein IGFBP-3 is a proapoptotic and antiangiogenic protein in prostate cancer (CaP). Epidemiologic studies suggest that low IGFBP-3 is associated with greater risk of aggressive, metastatic prostate cancers, but in vivo functional data are lacking. Here we show that mice that are genetically deficient in IGFBP-3 exhibit weaker growth of primary prostate tumors but higher incidence of metastatic disease. Prostates in IGFBP-3 knockout mice (IGFBP-3KO mice) failed to undergo apoptosis after castration. Spontaneous prostate tumors did not develop in IGFBP-3KO mice, but splenic lymphomas occurred in 23% of female IGFBP-3KO mice by 80 weeks of age. To assess the effects of IGFBP-3 deficiency on prostate cancer development, we crossed IGFBP-3KO mice with a c-Myc-driven model of CaP that develops slow-growing, nonmetastatic tumors. By 24 weeks of age, well-differentiated prostate cancers were observed in all mice regardless of IGFBP-3 status. However, by 80 weeks of age IGFBP-3KO mice tended to exhibit larger prostate tumors than control mice. More strikingly, lung metastases were observed at this time in 55% of the IGFBP-3KO mice but none in the control animals. Cell lines established from IGFBP-3KO:Myc tumors displayed more aggressive phenotypes in proliferation, invasion, and colony formation assays, relative to control Myc tumor cell lines. In addition, Myc:IGFBP-3KO cells exhibited evidence of epithelial-mesenchymal transition. Our findings established a function for IGFBP-3 in suppressing metastasis in prostate cancer, and they also offered the first reported transgenic model of spontaneous metastatic prostate cancer for studies of this advanced stage of disease.

Host genetic variants in the IGF binding protein-3 impact on survival of patients with advanced gastric cancer treated with palliative chemotherapy

AIM

IGF binding protein-3 (IGFBP-3) displays growth inhibitory/proapoptotic action and counteracts the IGF-1 tumor-promoting effects by downregulating its bioavailability. We investigated whether IGFBP-3 SNPs determining high IGFBP-3 circulating levels are associated with improved survival of patients with advanced gastric cancer treated with palliative chemotherapy.

MATERIALS & METHODS

A total of 185 patients undergoing combination chemotherapy for relapsed/metastatic disease were considered eligible for the present clinical investigation. Four functional IGFBP-3 SNPs (rs3110697, rs2854746, rs2864744 and rs2960436) were studied for association with overall survival (OS).

RESULTS

In the multivariate model including SNPs and clinicopathologic features, the rs285744 A allele and the rs2960436 A allele showed favorable association with survival. The hazard ratios for rs285744 C/A and A/A genotypes were 0.38 (95% CI: 0.18-0.66) and 0.20 (95% CI: 0.09-0.39), respectively. The hazard ratios for rs2960436 G/A and A/A genotypes were 0.41 (95% CI: 0.25-0.68) and 0.35 (95% CI: 0.16-0.58), respectively. Bonferroni-corrected p-values for the rs285744 A/A genotype and the rs2960436 A/A genotype were 0.012 and 0.024, respectively. There was linkage disequilibrium between the four variants and there were four common haplotypes (>5% estimated frequency). The most common haplotype (GCAA) included all alleles causing IGFBP-3 upregulation and their carriers demonstrated the best outcome in the log-rank comparison of survival curves.

CONCLUSION

Genetic regulation of the IGFBP-3 impacts on survival of patients with advanced gastric cancer. This finding deserves additional studies because of its prognostic and therapeutic implications.

Nuclear export and mitochondrial and endoplasmic reticulum localization of IGF-binding protein 3 regulate its apoptotic properties

Tumor suppression by IGF-binding protein 3 (IGFBP3) may occur in an IGF-independent manner, in addition to its role as a regulator of IGF bioavailability. After secretion, IGFBP3 is internalized, rapidly localized to the nucleus, and is later detected in the cytoplasm. We identified a putative nuclear export sequence (NES) in IGFBP3 between amino acids 217 and 228, analogous to the leucine-rich NES sequence of p53 and HIV Rev. Mutation of the NES prevents nucleocytoplasmic shuttling of IGFBP3 and blocks its ability to induce apoptosis. Targeting of IGFBP3 to the mitochondria and endoplasmic reticulum (ER) was confirmed by co-localization with organelle markers using fluorescence confocal microscopy and subcellular fractionation. Mitochondrial targeting was also demonstrated in vivo in IGFBP3-treated prostate cancer xenografts. These results show that IGFBP3 shuttles from the nucleus to the mitochondria and ER, and that nuclear export is essential for its effects on prostate cancer apoptosis.

Insulin-like growth factor-binding protein-3 promotes transforming growth factor-{beta}1-mediated epithelial-to-mesenchymal transition and motility in transformed human esophageal cells

Insulin-like growth factor-binding protein (IGFBP)-3 is overexpressed frequently in esophageal squamous cell carcinoma. Yet, the role of IGFBP3 in esophageal tumor biology remains to be elucidated. We find that IGFBP3 facilitates transforming growth factor (TGF)-beta1-mediated epithelial-to-mesenchymal transition (EMT) in transformed human esophageal epithelial cells, EPC2-hTERT-EGFR-p53(R175H). In organotypic 3D culture, a form of human tissue engineering, laser-capture microdissection revealed concurrent upregulation of TGF-beta target genes, IGFBP3 and EMT-related genes in the cells invading into the stromal compartment. IGFBP3 enhanced TGF-beta1-mediated EMT as well as transcription factors essential in EMT by allowing persistent SMAD2 and SMAD3 phosphorylation. TGF-beta1-mediated EMT and cell invasion were enhanced by ectopically expressed IGFBP3 and suppressed by RNA interference directed against IGFBP3. The IGFBP3 knockdown effect was rescued by IGFBP3(I56G/L80G/L81G), a mutant IGFBP3 lacking an insulin-like growth factor (IGF)-binding capacity. Thus, IGFBP3 can regulate TGF-beta1-mediated EMT and cell invasion in an IGF or insulin-like growth factor 1 receptor-independent manner. IGFBP3(I56G/L80G/L81G) also promoted EMT in vivo in a Ras-transformed human esophageal cell line T-TeRas upon xenograft transplantation in nude mice. In aggregate, IGFBP3 may have a novel IGF-binding independent biological function in regulation of TGF-beta1-mediated EMT and cell invasion.

Relationship of insulin-like growth factors system gene polymorphisms with the susceptibility and pathological development of hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the major causes of cancer-related death worldwide. The insulin-like growth factors (IGFs) system consists of a group of proteins which may induce cell proliferation and inhibit cell apoptosis through several signal pathways, leading to transformation of normal cells into cancer cells. However, the impact of genetic polymorphisms of the IGFs system on HCC has not been clarified.

METHODS

In this case-control study, a total of 102 HCC patients and 306 age- and gender-matched controls were recruited. The genetic polymorphisms of the IGFs system genes, including IGF-1, IGF-2, IGF-1receptor (IGF-1R), IGF-2R, IGF binding protein (IGFBP-3), and insulin (INS) genes, were analyzed by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) and real-time PCR genotyping analysis.

RESULTS

A significant difference (p = 0.02) between case and control group in the distribution frequency of IGF-2 +3580 polymorphism was observed. Multiple regression model analysis showed that the presence of AA or AG at IGF-2R may exhibit a potential protective effect against hepatitis C [odds ratio (OR) = 0.35, 95% confidence interval (CI) = 0.15-0.82]. The combination of IGF-2 +3580 AA genotype and IGF-2R GG genotype may present a significantly lower risk of HCC (OR = 0.20, 95% CI = 0.05-0.87). Additionally, no polymorphisms of any IGFs system genes were associated with liver-related clinicopathological markers in serum.

CONCLUSIONS

Among IGFs system genes, IGF-2 and IGF-2R gene polymorphisms and combination could be considered as the most important factors contributing to increased susceptibility and pathological development of HCC.

Opposing roles of insulin-like growth factor binding protein 3 and humanin in the regulation of testicular germ cell apoptosis

Modulating germ cell death and survival have significant therapeutic potential for male infertility and contraception. We have shown previously that IGF binding protein 3 (IGFBP3) gene expression is up-regulated in human testis when germ cell apoptosis is induced by intratesticular hormonal deprivation created by testosterone administration. Humanin (HN) is a binding partner of IGFBP3, and both are expressed in rat testes. We therefore hypothesized that IGFBP3, a proapoptotic factor, and HN, an antiapoptotic factor, are important regulators of male germ cell apoptosis. Whereas baseline apoptosis in the testis was equivalent between Igfbp3 knockout and wild-type mice, treatment with GnRH antagonist (GnRH-A) for 2 wk induced germ cell apoptosis in wild type, which was dramatically reduced in Igfbp3 knockout mice. To investigate the direct effects of IGFBP3 and HN on germ cell apoptosis, intratesticular administration of IGFBP3 for 5 d in rats induced a 4.2- and 3.8-fold increase in apoptosis at stages VII-VIII and XIV-I of the seminiferous epithelium cycle, respectively. GnRH-A treatment for 5 d increased apoptosis, mainly at stages VII-VIII. Addition of IGFBP3 to GnRH-A treatment enhanced apoptosis to 39.3-fold at stages VII-VIII, which was higher than either treatment alone. Intratesticular injection of HN significantly decreased GnRH-A-induced apoptosis at stages XIV-I but not stages VII-VIII. We conclude that IGFBP3 and HN play key roles in the coordinated regulation of testicular germ cell homeostasis. Perturbation of this interaction is important in enhancing or preventing germ cell death, providing new targets for future therapies.

Failure to recover somatotropic axis function is associated with mortality from pediatric sepsis-induced multiple organ dysfunction syndrome

OBJECTIVES

To describe the associations between mediators of the somatotropic axis and mortality from sepsis-induced multiple organ dysfunction syndrome in children; and to examine the relationship between immune function and the somatotropic axis in this setting.

DESIGN

Retrospective study using banked plasma.

SETTING

Single mixed surgical/medical intensive care unit at a quaternary level children's hospital.

PATIENTS

A total of 24 children (n = 17 survivors, 7 nonsurvivors) with severe sepsis or septic shock and dysfunction of >or=2 organ systems.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Plasma samples were available from days 3, 7, and 14 of multiple organ dysfunction syndrome. Insulin-like growth factor 1 and insulin-like growth factor binding protein 3 levels were measured by chemiluminescence. Immune function was quantified using previously determined ex vivo lipopolysaccharide-induced tumor necrosis factor-alpha production levels and absolute lymphocyte counts. Insulin-like growth factor 1 levels were lower in nonsurvivors compared with survivors (p = .004) with the greatest difference seen on day 14 (25 [25-69] ng/mL vs. 314 [123-582] ng/mL; p = .038). insulin-like growth factor binding protein 3 levels were reduced similarly over time (p = .019). A drop in plasma insulin-like growth factor binding protein 3 level at any time after day 3 of illness resulted in a 35-fold increased odds of death (odds ratio, 35 [1.6-750]; p = .004). Both ex vivo tumor necrosis factor-alpha and absolute lymphocyte count were reduced in nonsurvivors compared with survivors, but these differences occurred earlier (days 3 and 7).

CONCLUSIONS

These data suggest that prolonged reduction of somatotropic axis function is associated with mortality from pediatric sepsis-induced multiple organ dysfunction syndrome. Reductions in innate and adaptive immune function are common in this population and are associated with failure of recovery of the somatotropic axis, although the nature of these relationships remains incompletely understood.

Interaction of insulin-like growth factor-binding protein-3 and BAX in mitochondria promotes male germ cell apoptosis

Germ cell apoptosis is crucial for spermatogenesis and can be triggered by various stimuli, including intratesticular hormone deprivation. This study proposes a role for insulin-like growth factor binding protein-3 (IGFBP-3) in male germ cell apoptosis. Groups of adult Sprague-Dawley male rats received one of the following treatments for 5 days: (i) daily intratesticular (IT) injections with saline (control); (ii) a single subcutaneous injection of the gonadotropin-releasing hormone antagonist (GnRH-A), acyline, on day 1 and a daily IT injection of saline; (iii) daily IT injection of IGFBP-3; and (iv) a GnRH-A injection on day 1 and a daily IT injection of IGFBP-3. Germ cell apoptosis increased significantly after IGFBP-3 or GnRH-A treatment which was further enhanced by the combined treatment. After co-immunoprecipitation with BAX antibody, IGFBP-3 association with BAX was demonstrated in total and mitochondrial fractions but not in the cytosol of testis extracts. BAX-associated IGFBP-3 expression was increased in mitochondria after treatment compared with control, which was confirmed by an IGFBP-3 enzyme-linked immunosorbent assay. Dot blot studies further validated the BAX-IGFBP-3 binding in vitro. IGFBP-3 as well as BAX induced release of cytochrome c and DIABLO from isolated testicular mitochondria in vitro. IGFBP-3, when combined with an ineffective dose of BAX, triggered release of these proteins from isolated mitochondria at a 4-fold lower dose than IGFBP-3 alone. Our data demonstrate that the IGFBP-3 and BAX interaction activates germ cell apoptosis via the mitochondria-dependent pathway. This represents a novel pathway regulating germ call homeostasis that may have significance for male fertility and testicular disease.

Genetic and plasma variation of insulin-like growth factor binding proteins in relation to prostate cancer incidence and survival

BACKGROUND

Binding proteins regulate bioavailability of insulin-like growth factor-I (IGF-I) in the circulation and affect apoptosis of tumor cells in the prostate. We analyzed genetic variation within genes coding for IGF binding proteins in relation to prostate cancer incidence and survival. We also investigated if circulating IGFBP3 affects prostate cancer-specific survival.

MATERIALS AND METHODS

Eleven haplotype tagging SNPs and two single SNPs in the IGFBP1, IGFBP3, and IGFALS genes were genotyped within the CAncer Prostate in Sweden (CAPS) study including 2,774 cases and 1,736 controls. Plasma samples for analyses of total- and intact IGFBP3 levels were available for 1,521 cases and 909 controls. Complete follow-up of vital status was achieved by linkage to the Swedish Cause of Death Register.

RESULTS

We found no clear association between the genetic variants and prostate cancer incidence or survival. The rare allele of the IGFBP3 SNP rs2854744 was associated with elevated plasma levels of total IGFBP3 (P(trend) = 9 x 10(-8)), but not intact IGFBP3 (P(trend) = 0.16). Elevated levels of total- (P(trend) = 0.03) and intact IGFBP3 (P(trend) = 6 x 10(-14)) were associated with increased risk of prostate cancer specific death. Treatment and tumor characteristics accounted for the association with total IGFBP3, whereas the association with intact IGFBP3 was attenuated, but still statistically significant in adjusted analysis (P(trend-adjusted) = 0.0004). Elevated intact IGFBP3 was also significantly associated with increased risk of prostate cancer-specific death among patients who were chemically or surgically castrated (P(trend-adjusted) = 0.0003), and among patients who had not been treated (P(trend-adjusted) = 0.02).

CONCLUSIONS

Circulating levels of intact IGFBP3 measured after diagnosis is associated with increased risk of prostate cancer-specific death.

Levonorgestrel enhances spermatogenesis suppression by testosterone with greater alteration in testicular gene expression in men

Prior studies have demonstrated that combined treatment of testosterone with a progestin induces a more rapid and greater suppression of spermatogenesis than testosterone treatment alone. We hypothesized that the suppressive effects of the combination of testosterone undecanoate (TU) injections plus oral levonorgestrel (LNG) on spermatogenesis may be mediated through a greater perturbation of testicular gene expression than TU alone. To test this hypothesis, we performed open testicular biopsy on 12 different adult healthy subjects: 1) four healthy men as controls; 2) four men 2 wk after TU treatment; and 3) four men 2 wk after TU + LNG administration. RNA isolated from biopsies was used for DNA microarray using the Affymetrix Human Genome U133 Plus 2.0 oligonucleotide microarrays. Gene expression with >or=2-fold changes (P < 0.05) compared with control was analyzed using the National Institutes of Health Database for Annotation, Visualization, and Integrated Discovery 2008 resource. The TU treatment altered the gene expression in 109 transcripts, whereas TU + LNG altered the gene expression in 207 transcripts compared with control. Both TU and TU + LNG administration suppressed gene expression of insulin-like 3; cytochrome P450, family 17, subfamily A1 in Leydig cells; and inhibin alpha in Sertoli cells; they increased proapoptotic transcripts BCL2-like 14, insulin-like growth factor-binding protein 3; and they decreased X-linked inhibitor of apoptosis protein. In comparison with TU treatment alone, TU + LNG treatment upregulated insulin-like 6 and relaxin 1, and downregulated RNA-binding protein transcripts. We conclude that TU + LNG administration induces more changes in testicular gene expression than TU alone. This exploratory study provided a novel and valuable database to study the mechanisms of action of hormonal regulation of spermatogenesis in men and identified testicular-specific molecules that may serve as potential targets for male contraceptive development.

Plasma insulin-like growth factors, insulin-like binding protein-3, and outcome in metastatic colorectal cancer: results from intergroup trial N9741

PURPOSE

Insulin-like growth factor (IGF)-I and IGF-II stimulate neoplastic cell growth and inhibit apoptosis, whereas IGF-binding protein-3 (IGFBP-3) inhibits the bioavailability of IGF-I and has independent proapoptotic activity. We examined the influence of baseline plasma levels of IGF-I, IGF-II, IGFBP-3, and C-peptide on outcome among patients receiving first-line chemotherapy for metastatic colorectal cancer.

EXPERIMENTAL DESIGN

The plasma levels of IGF-I, IGF-II, IGFBP-3, and C-peptide as well as data on prognostic factors and body size were measured at baseline among 527 patients participating in a randomized trial of first-line chemotherapy for metastatic colorectal cancer.

RESULTS

Higher baseline plasma IGFBP-3 levels were associated with a significantly greater chemotherapy response rate (P = 0.03) after adjusting for other prognostic factors, whereas neither IGF-I nor IGF-II levels significantly predicted tumor response. Higher levels of IGF-I, IGF-II, and IGFBP-3 were all univariately associated with improved overall survival (P = 0.0001 for all). In a model that mutually adjusted for IGF-I and IGFBP-3, as well as other prognostic factors, increasing baseline-circulating IGFBP-3 was associated with a significantly longer time to tumor progression (P = 0.03), whereas circulating IGF-I was not associated with disease progression (P = 0.95). Levels of C-peptide were not associated with any measure of patient outcome.

CONCLUSION

Among colorectal cancer patients receiving first-line chemotherapy, increasing levels of IGFBP-3, an endogenous antagonist to IGF-I, are associated with an improved objective treatment response and a prolonged time to cancer progression. The IGF pathway may represent an important target for future treatment strategies.

Quantitative ontogeny of murine insulin-like growth factor (IGF)-I, IGF-binding protein-3 and the IGF-related acid-labile subunit

OBJECTIVE

The mouse serves as an important model for insulin-like (IGF)-related research. However, lack of homologous mouse assays has prevented studies of the normal ontology of the murine IGF system. Therefore, we developed and validated immunoaassays for murine IGF-I, IGFBP-3 and ALS and studied levels of these analytes in mice.

METHODS

Using commercially available reagents, we developed and validated specific enzyme-linked immunosorbent assays (ELISAs) for murine IGF-I, IGFBP-3, and ALS. Levels of these analytes were measured in sera from CD-1 mice, male and female, sampled at 1, 2, 4, 8, 20 and 32 weeks of age. In addition, sera from pregnant and postpartum CD-1 mice were also studied.

RESULTS

Validation of specific ELISAs for murine IGF-I, IGFBP-3 and ALS are described; all 3 assays were highly sensitive, precise and accurate. As measured by our homologous ELISA, IGF-I levels (ng/mL, mean+/-SD) in male mice were relatively low at 1 week (53+/-8), rising sharply to peak at 8 weeks of age (636+/-48), and gradually declining thereafter, reaching 395+/-64 at 32 weeks. IGF-I levels in non-pregnant female mice peaked at 4 weeks of age (548+/-77) declined at 8 weeks (417+/-61), then recovered to plateau at 539+/-78 and 535+/-88 at 20 and 32 weeks, respectively. In male mice, trends in IGFBP-3 were similar to the patterns of IGF-I. However, in non-pregnant female mice, the IGFBP-3 levels declined relatively slowly after peaking at 4-weeks of age, unlike IGF-I levels during this period. ALS levels followed the same pattern as IGF-I in both sexes. IGF-I to IGFBP-3 molar ratios (percent) were similar between sexes, rising continuously with age: approximately 30% at 1 week, 80% at 4 weeks, 135% at 32 weeks. IGF-I was reduced in 8 week old mice in mid-pregnancy (354+/-75 vs 417+/-61 in non-pregnant 8 week females), reaching a nadir in late-term (146+/-40), and only partially recovering in the postpartum period (239+/-23). IGFBP-3 was also lower in late-pregnancy (1245+/-100 vs 1925+/-439) and remained depressed postpartum. In contrast to IGF-I and IGFBP-3, ALS increased more than threefold in mid-pregnancy (12180+/-1641 vs 3741+/-910), followed by a 4-fold decrease in late-pregnancy (2964+/-489), recovering postpartum (6104+/-1178).

CONCLUSIONS

We report the first ontological studies of IGF-I, IGFBP-3 and ALS in mice using newly-characterized sensitive, homologous immunoassays. Our results indicate that mice have a generally similar pattern in IGF-related axis components, with low levels early in life, increasing to peak during sexual maturation and declining thereafter. Significant gender differences in non-pregnant levels and dramatic changes during pregnancy were also found. Knowledge of the normal developmental changes in the murine IGF system and accurate tools for investigations of this system are a necessary foundation for research in this field.

Growth hormone therapy does not alter the insulin-like growth factor-I/insulin-like growth factor binding protein-3 molar ratio in growth hormone-deficient children

BACKGROUND

Recent studies have linked raised levels of IGF-I and/or reduced levels of its main binding protein, IGF binding protein (IGFBP)-3, with the risk of developing cancer. A GH dose-dependent increase in IGF-I/IGFBP-3 molar ratio has been reported in subjects treated with GH, raising concern about the long-term safety.

OBJECTIVE

The aim of this study was to evaluate changes in serum IGF-I, IGFBP-3, and IGF-I/IGFBP-3 molar ratio over the first 12 months of replacement GH therapy in GH deficient (GHD) children.

METHODS

The study included 20 GHD children who had not previously received GH treatment, and 40 untreated non-GHD short children closely matched for age, gender, pubertal stage, and body mass index (BMI), as controls. Serum IGF-I, IGFBP-3 levels were measured before and after 12 months of GH treatment. Based on the molecular weight of IGF-I (7500) and IGFBP- 3 (40,000, mean of glycosylated variants), we calculated the molar ratio of IGF-I/IGFBP-3.

RESULTS

IGF-I/IGFBP-3 molar ratio significantly increased during GH therapy (p=0.01). No significant difference in IGF-I/IGFBP-3 ratio was found between GHD children and controls at the different time points. In the multiple regression analysis, BMI (beta=0.33) and age (beta=0.33) proved to be the major predictors of the IGF-I/IGFBP-3 molar ratio (adjusted r2=0.53, p<0.0001).

CONCLUSIONS

Our results suggest that at a conventional replacement dose GH does not alter the IGF-I/IGFBP-3 molar ratio. Potential fears related to long-term cancer risk are likely to be greatest in patients exposed to high-dose GH therapy and with genetic predisposition to high IGF-I and/or low IGFBP-3 concentrations.

Hepatic IGFBP1 is a prosurvival factor that binds to BAK, protects the liver from apoptosis, and antagonizes the proapoptotic actions of p53 at mitochondria

Liver is generally refractory to apoptosis induced by the p53 tumor suppressor protein, but the molecular basis remains poorly understood. Here we show that p53 transcriptional activation leads to enhanced expression of hepatic IGFBP1 (insulin-like growth factor-binding protein-1). Exhibiting a previously unanticipated role, a portion of intracellular IGFBP1 protein localizes to mitochondria where it binds to the proapoptotic protein BAK and hinders BAK activation and apoptosis induction. Interestingly, in many cells and tissues p53 also has a direct apoptotic function at mitochondria that includes BAK binding and activation. When IGFBP1 is in a complex with BAK, formation of a proapoptotic p53/BAK complex and apoptosis induction are impaired, both in cultured cells and in liver. In contrast, livers of IGFBP1-deficient mice exhibit spontaneous apoptosis that is accompanied by p53 mitochondrial accumulation and evidence of BAK oligomerization. These data support the importance of BAK as a mediator of p53's mitochondrial function. The results also identify IGFBP1 as a negative regulator of the BAK-dependent pathway of apoptosis, whose expression integrates the transcriptional and mitochondrial functions of the p53 tumor suppressor protein.

IGFBP-3 regulates esophageal tumor growth through IGF-dependent and independent mechanisms

Insulin-like growth factor binding protein (IGFBP)-3 exerts either proapoptotic or growth stimulatory effects depending upon the cellular context. IGFBP-3 is overexpressed frequently in esophageal cancer. Yet, the role of IGFBP-3 in esophageal tumor biology remains elusive. To delineate the functional consequences of IGFBP-3 overexpression, we stably transduced Ha-Ras(V12)-transformed human esophageal cells with either wild-type or mutant IGFBP-3, the latter incapable of binding Insulin-like growth factor (IGFs) as a result of substitution of amino-terminal Ile56, Leu80, and Leu81 residues with Glycine residues. Wild-type, but not mutant, IGFBP-3 prevented IGF-1 from activating the IGF-1 receptor and AKT, and suppressed anchorage-independent cell growth. When xenografted in nude mice, in vivo bioluminescence imaging demonstrated that wild-type, but not mutant IGFBP-3, abrogated tumor formation by the Ras-transformed cells with concurrent induction of apoptosis, implying a prosurvival effect of IGF in cancer cell adaptation to the microenvironment. Moreover, there was more aggressive tumor growth by mutant IGFBP-3 overexpressing cells than control cell tumors, without detectable caspase-3 cleavage in tumor tissues, indicating an IGF-independent growth stimulatory effect of mutant IGFBP-3. In aggregate, these data suggest that IGFBP-3 contributes to esophageal tumor development and progression through IGF-dependent and independent mechanisms.

Growth inhibitory concentrations of androgens up-regulate insulin-like growth factor binding protein-3 expression via an androgen response element in LNCaP human prostate cancer cells

IGF binding protein-3 (IGFBP-3), the most abundant circulating IGF binding protein, inhibits cell growth and induces apoptosis by both IGF-I-dependent and -independent pathways. The ability of IGFBP-3 to inhibit tumor growth has been demonstrated in many cancers including prostate cancer (PCa). High concentrations of androgens, which inhibit the growth of the LNCaP human PCa cell line, have been shown to have both positive and negative effects on IGFBP-3 expression by different laboratories. To further explore the relationship between IGFBP-3 and androgens, we examined IGFBP-3 expression in LNCaP cells. We demonstrate that IGFBP-3 expression can be induced by 10 nm of the synthetic androgen R1881 or dihydrotestosterone. Transactivation assays show that the 6-kb IGFBP-3 promoter sequence directly responds to androgen treatment. In silico analysis identified a putative androgen response element (ARE) at -2,879/-2,865 in the IGFBP-3 promoter. A single point mutation in this ARE disrupted transactivation by R1881. Combining the data obtained from EMSA, chromatin immunoprecipitation and mutational analysis, we conclude that a novel functional ARE is present in the IGFBP-3 promoter that directly mediates androgen induction of IGFBP-3 expression. Furthermore, we found that the combination of androgens and calcitriol significantly potentiated the IGFBP-3 promoter activity, suggesting that enhanced induction of the expression of the endogenous IGFBP-3 gene may contribute to the greater inhibition of LNCaP cell growth by combined calcitriol and androgens. Because androgens are well known to stimulate PCa growth and androgen deprivation therapy causes PCa to regress, the stimulation by androgens of this antiproliferative and proapoptotic protein is paradoxical and raises interesting questions about the role of androgen-stimulated IGFBP-3 in PCa.