Nonsecreted insulin-like growth factor binding protein-3 (IGFBP-3) can induce apoptosis in human prostate cancer cells by IGF-independent mechanisms without being concentrated in the nucleus

The role of IGFBP-3 in tumor development and progression: enlightenment for diagnosis and treatment

IGFBP-3 is aberrantly expressed in many tumor types, and its serum and tumor tissue levels provide auxiliary information for assessing the degree of tumor malignancy and patient prognosis, making it a potential therapeutic target for human malignancies and conferring it remarkable clinical value for determining patient prognosis. In this review, we provide a comprehensive overview of the aberrant expression, diverse biological effects, and clinical implications of IGFBP-3 in tumors and its role as a potential prognostic marker and therapeutic target for tumors. In addition, we summarize the signaling pathways through which IGFBP-3 exerts its effects. IGFBP-3 comprises an N-terminal, an intermediate region, and a C-terminal structural domain, each exerting different biological effects in several tumor cell types in an IGF-dependent/non-independent manner. IGFBP-3 shares an intricate relationship with the tumor microenvironment, thereby affecting tumor growth. Overall, IGFBP-3 is an essential regulatory factor that mediates tumor occurrence and progression. Gaining deeper insights into the fundamental characteristics of IGFBP-3 and its role in various tumor types will provide new perspectives and allow for the development of novel strategies for cancer diagnosis, treatment, and prognostic evaluation.

Fluoroquinolones upregulate insulin-like growth factor-binding protein 3, inhibit cell growth and insulin-like growth factor signaling

Fluoroquinolones (FQs), commonly known for their antibiotic properties, exhibit additional pharmacological potential with anti-proliferative effects on various malignant cell types and immunomodulatory responses. Despite these observed effects, the precise mechanisms of action remain elusive. This study elucidates the biological impact of FQs on insulin-like growth factor-binding protein 3 (IGFBP-3) productions in a p53-dependent manner. Cultured cells and mouse models treated with FQs demonstrated increased IGFBP-3 mRNA expression and protein secretion. The FQ-induced IGFBP-3 was identified to impede cell growth by inhibiting IGF-I signaling and exerting effects through an IGF-independent pathway. Notably, FQ-mediated suppression of cell proliferation was reversed in p53-null and p53 knockdown cells, suggesting the pivotal role of p53 in FQ-induced IGFBP-3 production and IGFBP-3-mediated growth inhibition. Additionally, ciprofloxacin, a clinically used FQ, exhibited the induction of tumor cell apoptosis and attenuation of tumor growth in a syngeneic mouse hepatocellular carcinoma (HCC) model. These findings unveil a novel mechanism through which FQs act as anti-proliferative agents, prompting further exploration of their potential utility or derivative compounds in cancer treatment and prevention.

Association Study of IGF-1 rs35767 and rs6214 Gene Polymorphisms with Cancer Susceptibility and Circulating Levels of IGF-1, IGFBP-2, and IGFBP-3 in Colorectal Cancer Patients

Early detection of colorectal cancer (CRC) increases the 5-year survival rate by 90%; therefore, non-invasive biomarkers such as measurable circulating proteins for early detection and prognosis are crucial. Insulin-like growth factor-1 (IGF-1) is involved in the regulation of cell proliferation and apoptosis. IGF binding proteins (IGFBPs) bind and inhibit the activity of IGF-1. It was inconsistently reported that high IGF-1 and IGFBP-2 and low IGFBP-3 circulating levels are associated with high cancer risk, poor prognosis, and tumor metastasis in several cancers. A total of 175 patients with CRC and 429 controls were enrolled in this study. We genotyped for IGF-1 rs35767 and rs6214 gene polymorphisms and assessed their association with circulating levels of IGF-1 and/or the risk for CRC. We also determined plasma levels of IGF-1, IGFBP-2, and IGFBP-3. Neither rs35767 nor rs2614 were associated with cancer risk or IGF-1 levels in our study cohort. IGF-1 and IGFBP-3 levels were higher in controls than in patients, whereas IGFBP-2 was higher in patients than in controls. Only IGFBP-2 was associated with increased tumor grade but not stage. Therefore, IGF-1, IGFBP-2, and IGFBP-3 may be useful as early detection and prognostic biomarkers in CRC.

Roles of IGFBP-3 in cell migration and growth in an endophytic tongue squamous cell carcinoma cell line

Insulin-like growth factor binding protein-3 (IGFBP-3) is a member of the IGFBP family that has high affinity for IGFs and functions as either an oncogene or tumor suppressor in various types of cancer. We previously found that IGFBP3 mRNA levels are higher in endophytic-type human tongue squamous cell carcinoma (TSCC) that is more invasive and more prone to metastasis than exophytic and superficial types. This finding prompted us to investigate the roles of IGFBP-3 in TSCC using SAS cells, which were originally derived from endophytic-type TSCC. Specifically, we used SAS cells that express a fluorescent ubiquitination-based cell-cycle indicator (Fucci). RNA-sequencing analysis indicated that IGFBP-3 is associated with cell migration and cell growth. In fact, IGFBP-3 knockdown downregulates cell migration and causes cells to arrest in G₁. This migratory potential appears to be cell cycle–independent. IGFBP-3 knockdown also reduced levels of secreted IGFBP-3; however, decreased migratory potential was not rescued by exogenous recombinant human IGFBP-3. Furthermore, ERK activity was downregulated by IGFBP-3 depletion, which suggests that MEK/ERK signaling may be involved in IGFBP-3-mediated cell migration. We therefore conclude that intracellular IGFBP-3 enhances cell migration independently of the cell cycle in TSCC with a higher metastatic potential.

The role of the IGF system in mammary physiology of ruminants

The IGF system plays a central role in all stages of mammary development, lactation and involution. IGFs exert their effects on the mammary gland through both endocrine and paracrine/autocrine mechanisms and the importance of circulating versus local IGF action remains an open question, especially in ruminants. At the whole organ level, a critical role for IGFs in ductal morphogenesis and lobuloalveolar development has been established, while at the cellular level the ability of IGFs to stimulate cell proliferation and control cell survival contributes to the number of milk-secreting cells in the gland. Much of this work has been conducted in rodents which provide an affordable research model and allow for genetic manipulation of specific components of the IGF system. Research into the role of the IGF system in dairy cows has generally supported information obtained with rodents though large gaps in our knowledge remain and species differences are not well defined. Examples include whether exogenous somatotropin exerts its effects on the mammary gland through local IGF-1 synthesis which is accepted dogma in rodents, what the role of IGF-1 versus IGF-2 is in the mammary gland, and how the IGFBPs regulate IGF bioactivity. This last area is particularly under-investigated in ruminants both at the whole animal and the cellular and molecular levels. Given that the IGF system may underlie many management practices that could contribute to enhancing productive efficiency of lactation, more research into the basic biology of this important system is warranted.

Receptor tyrosine kinases as a therapeutic target by natural compounds in cancer treatment

Background

Receptor tyrosine kinases (RTKs) are single-pass transmembrane proteins that play significant roles in regulating cellular processes, including cell division and growth. Overexpression and mutations of RTKs have been found in clinical manifestations of different forms of cancer. Therefore, RTKs have received considerable interest as a therapeutic biomarker in the treatment of cancer cells.

Main body of the abstract

Comprehensive data on RTKs, pharmacological and biological properties of natural compounds were systematically searched up to 2021 using relevant keywords from various databases, such as Google Scholar, PubMed, Web of Science, and Scopus. The scientific search by various standard electronic resources and databases unveils the effectiveness of medicinal plants in the treatment of various cancers. In vitro and in vivo studies suggested that bioactive compounds such as flavonoids, phenols, alkaloids, and many others can be used pharmacologically as RTKs inhibitors (RTKI) either by competing with ATP at the ATP binding site of the tyrosine kinase domain or competing for the receptor extracellular domain. Additionally, studies conducted on animal models indicated that inhibition of RTKs catalytic activity by natural compounds is one of the most effective ways to block the activation of RTKs signaling cascades, thereby hampering the proliferation of cancer cells. Furthermore, various pharmacological experiments, transcriptomic, and proteomic data also reported that cancer cells treated with different plants extracts or isolated phytochemicals exhibited better anticancer properties with minimal side effects than synthetic drugs. Clinically, natural compounds have demonstrated significant anti-proliferative effect via induction of cell apoptosis in cancer cell lines.

Short conclusion

An in-depth knowledge of the mechanism of inhibition and structural characterization of RTKs is important to the design of novel and selective RTKIs. This review focuses on the molecular mechanisms and structures of natural compounds RTKI targeting vascular endothelial growth factor, epidermal growth factor receptor, insulin receptor, and platelet-derived growth factor while also giving future directions to ameliorate the scientific burden of cancer.

Graphic abstract

Colostrogenesis: Role and Mechanism of the Bovine Fc Receptor of the Neonate (FcRn)

Colostrogenesis is a separate and unique phase of mammary epithelial cell activity occurring in the weeks before parturition and rather abruptly ending after birth in the bovine. It has been the focus of research to define what controls this process and how it produces high concentrations of specific biologically active components important for the neonate. In this review we consider colostrum composition and focus upon components that appear in first milked colostrum in concentrations exceeding that in blood serum. The Fc Receptor of the Neonate (FcRn) is recognized as the major immunoglobulin G (IgG) and albumin binding protein that accounts for the proteins' long half-lives. We integrate the action of the pinocytotic (fluid phase) uptake of extracellular components and merge them with FcRn in sorting endosomes. We define and explore the means of binding, sorting, and the transcytotic delivery of IgG1 while recycling IgG2 and albumin. We consider the means of releasing the ligands from the receptor within the endosome and describe a new secretion mechanism of cargo release into colostrum without the appearance of FcRn itself in colostrum. We integrate the insulin-like growth factor family, some of which are highly concentrated bioactive components of colostrum, with the mechanisms related to FcRn endosome action. In addition to secretion, we highlight the recent findings of a role of the FcRn in phagocytosis and antigen presentation and relate its significant and abrupt change in cellular location after parturition to a role in the prevention and resistance to mastitis infections.

Insulin-like growth factor binding protein 3 gene of golden pompano (TroIGFBP3) promotes antimicrobial immune defense

Insulin-like growth factor binding protein 3 (IGFBP3), an important member of the IGFBP family, plays an important biological role in regulating cellular proliferation, differentiation, growth, apoptosis, and innate immunity. However, studies concerning IGFBP3 in teleosts are very limited and IGFBP3 function remains unclear. In this study, we conducted both in vivo and in vitro functional analyses of an IGFBP3 (TroIGFBP3) from the teleost fish golden pompano (Trachinotus ovatus). TroIGFBP3 is composed of 286 amino acid residues and shares a high amino acid sequence similarity (50.18%-93.71%) with other IGFBP3 sequences in humans and teleosts. TroIGFBP3 was widely distributed in various tissues, with the highest expression in the liver. TroIGFBP3 expression was significantly upregulated following Vibrio harveyi infection. The results of in vitro assays showed that TroIGFBP3 could stimulate macrophage activation and promote peripheral blood leukocytes (PBLs) proliferation. Meanwhile, TroIGFBP3 overexpression significantly inhibited bacterial infection in fish tissues, whereas TroIGFBP3 knockdown resulted in increased bacterial dissemination and colonization in golden pompano tissues in vivo. Furthermore, recombinant TroIGFBP3 could inhibit cellular proliferation and promote apoptosis of mouse tumor cells. Taken together, these results indicated that TroIGFBP3 plays a significant role in innate antibacterial immunity and provides a theoretical foundation for investigating the function of IGFBP3 in fish immune response.

IGFBP-3/IGFBP-3 Receptor System as an Anti-Tumor and Anti-Metastatic Signaling in Cancer

Insulin-like growth factor binding protein-3 (IGFBP-3) is a p53 tumor suppressor-regulated protein and a major carrier for IGFs in circulation. Among six high-affinity IGFBPs, which are IGFBP-1 through 6, IGFBP-3 is the most extensively investigated IGFBP species with respect to its IGF/IGF-I receptor (IGF-IR)-independent biological actions beyond its endocrine/paracrine/autocrine role in modulating IGF action in cancer. Disruption of IGFBP-3 at transcriptional and post-translational levels has been implicated in the pathophysiology of many different types of cancer including breast, prostate, and lung cancer. Over the past two decades, a wealth of evidence has revealed both tumor suppressing and tumor promoting effects of IGF/IGF-IR-independent actions of IGFBP-3 depending upon cell types, post-translational modifications, and assay methods. However, IGFBP-3′s anti-tumor function has been well accepted due to identification of functional IGFBP-3-interacting proteins, putative receptors, or crosstalk with other signaling cascades. This review mainly focuses on transmembrane protein 219 (TMEM219), which represents a novel IGFBP-3 receptor mediating antitumor effect of IGFBP-3. Furthermore, this review delineates the potential underlying mechanisms involved and the subsequent biological significance, emphasizing the clinical significance of the IGFBP-3/TMEM219 axis in assessing both the diagnosis and the prognosis of cancer as well as the therapeutic potential of TMEM219 agonists for cancer treatment.

Insulin-Like Growth Factor Binding Protein-3 (IGFBP-3): Unraveling the Role in Mediating IGF-Independent Effects Within the Cell

Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3), one of the six members of the IGFBP family, is a key protein in the IGF pathway. IGFBP-3 can function in an IGF-dependent as well as in an IGF-independent manner. The IGF-dependent roles of IGFBP-3 include its endocrine role in the delivery of IGFs from the site of synthesis to the target cells that possess IGF receptors and the activation of associated downstream signaling. IGF-independent role of IGFBP-3 include its interactions with the proteins of the extracellular matrix and the proteins of the plasma membrane, its translocation through the plasma membrane into the cytoplasm and into the nucleus. The C-terminal domain of IGFBP-3 has the ability to undergo cell penetration therefore, generating a short 8-22-mer C-terminal domain peptides that can be conjugated to drugs or genes for effective intracellular delivery. This has opened doors for biotechnological applications of the molecule in molecular medicine. The aim of this this review is to summarize the complex roles of IGFBP-3 within the cell, including its mechanisms of cellular uptake and its translocation into the nucleus, various molecules with which it is capable of interacting, and its ability to regulate IGF-independent cell growth, survival and apoptosis. This would pave way into understanding the modus operandi of IGFBP-3 in regulating IGF-independent processes and its pleiotropic ability to bind with potential partners thus regulating several cellular functions implicated in metabolic diseases, including cancer.

Paracrine senescence of human endometrial mesenchymal stem cells: a role for the insulin-like growth factor binding protein 3

Stress-induced premature cell senescence is well recognized to be accompanied by emerging the senescence-associated secretory phenotype (SASP). Secreted SASP factors can promote the senescence of normal neighboring cells through autocrine/paracrine pathways and regulate the senescence response, as well. Regarding human endometrium-derived mesenchymal stem cells (MESCs), the SASP regulation mechanisms as well as paracrine activity of senescent cells have not been studied yet. Here, we examined the role of insulin-like growth factor binding protein 3 (IGFBP3) in the paracrine senescence induction in young MESCs. The H₂O₂-induced premature senescence of MESCs led to increased IGFBP3 in conditioned media (CM). The inhibitory analysis of both MAPK and PI3K signaling pathways showed that IGFBP3 releasing from senescent cells is mainly regulated by PI3K/Akt pathway activity. IGFBP3 appears to be an important senescence-mediating factor as its immunodepletion from the senescent CM weakened the pro-senescent effect of CM on young MESCs and promoted their growth. In contrast, young MESCs acquired the senescence phenotype in response to simultaneous addition of recombinant IGFBP3 (rIGFBP3). The mechanism of extracellular IGFBP3 internalization was also revealed. The present study is the first to demonstrate a significant role of extracellular IGFBP3 in paracrine senescence induction of young MESCs.

IGFBP-3 Induced by Ribotoxic Stress Traffics From the Endoplasmic Reticulum to the Nucleus in Mammary Epithelial Cells

IGF-binding protein (IGFBP)-3 is a multifunctional protein that can exert IGF-independent effects on apoptosis. Anisomycin (ANS) is a potent inducer of IGFBP-3 production in bovine mammary epithelial cells (MECs), and knockdown of IGFBP-3 attenuates ANS-induced apoptosis. IGFBP-3 is present in the nucleus and the conditioned media in response to ANS. The goal of this study was to determine whether ribotoxic stress induced by ANS or a second ribotoxin, deoxynivalenol (DON), specifically regulates transport of IGFBP-3 to the nucleus and to determine the pathway by which it traffics. In ribotoxin-treated cells, both endogenous IGFBP-3 and transfected IGFBP-3 translocated to the nucleus. Inhibition of the nuclear transport protein importin-β with importazole reduced ribotoxin-induced nuclear IGFBP-3. Immunoprecipitation studies showed that ANS induced the association of IGFBP-3 and importin-β, indicating that ribotoxins specifically induce nuclear translocation via an importin-β‒dependent mechanism. To determine whether secretion of IGFBP-3 is required for nuclear localization, cells were treated with Pitstop 2 or brefeldin A to inhibit clathrin-mediated endocytosis or overall protein secretion, respectively. Neither inhibitor affected nuclear localization of IGFBP-3. Although the IGFBP-3 present in both the nucleus and conditioned media was glycosylated, secreted IGFBP-3 exhibited a higher molecular weight. Deglycosylation experiments with endoglycosidase Hf and PNGase indicated that secreted IGFBP-3 completed transit through the Golgi apparatus, whereas intracellular IGFBP-3 exited from the endoplasmic reticulum before transit through the Golgi. In summary, ANS and DON specifically induced nuclear localization of nonsecreted IGFBP-3 via an importin-β‒mediated event, which may play a role in their ability to induce apoptosis in MECs.

Involvement of p53 in insulin-like growth factor binding protein-3 regulation in the breast cancer cell response to DNA damage

Chemotherapy drugs that induce apoptosis by causing DNA double-strand breaks, upregulate the tumor suppressor p53. This study investigated the regulation of the growth-regulatory protein insulin-like growth factor binding protein-3 (IGFBP-3), a p53 target, by DNA-damaging agents in breast cancer cells. IGFBP-3 was upregulated 1.4- to 13-fold in response to doxorubicin and etoposide in MCF-10A, Hs578T, MCF-7 and T47D cells, which express low to moderate basal levels of IGFBP-3. In contrast, IGFBP-3 was strongly downregulated by these agents in cells with high basal levels of IGFBP-3 (MDA-MB-231, MDA-MB-436 and MDA-MB-468). In MDA-MB-468 cells containing the R273H p53 mutation, reported to display gain-of-function properties, chemotherapy-induced suppression of IGFBP-3 was not reversed by the p53 reactivating drug, PRIMA-1, or by p53 silencing, suggesting that the decrease in IGFBP-3 following DNA damage is not a mutant p53 gain-of-function response. SiRNA-mediated downregulation of endogenous IGFBP-3 modestly attenuated doxorubicin-induced apoptosis in MDA-MB-468 and Hs578T cells. IGFBP-3 downregulation in some breast cancer cell lines in response to DNA-damaging chemotherapy may have clinical implications because suppression of IGFBP-3 may modulate the apoptotic response. These observations provide further evidence that endogenous IGFBP-3 plays a role in breast cancer cell responsiveness to DNA damaging therapy.

Endogenous IGFBP-3 Mediates Intrinsic Apoptosis Through Modulation of Nur77 Phosphorylation and Nuclear Export

In nontransformed bovine mammary epithelial cells, the intrinsic apoptosis inducer anisomycin (ANS) induces IGFBP-3 expression and nuclear localization and knockdown of IGFBP-3 attenuates ANS-induced apoptosis. Others have shown in prostate cancer cells that exogenous IGFBP-3 induces apoptosis by facilitating nuclear export of the orphan nuclear receptor Nur77 and its binding partner, retinoid X receptor-α (RXRα). The goal of the present work was to determine whether endogenous IGFBP-3 plays a role in ANS-induced apoptosis by facilitating nuclear transport of Nur77 and/or RXRα in nontransformed cells. Knockdown of Nur77 with siRNA decreased ANS-induced cleavage of caspase-3 and -7 and their downstream target, PARP, indicating a role for Nur77 in ANS-induced apoptosis. In cells transfected with IGFBP-3, IGFBP-3 associated with RXRα but not Nur77 under basal conditions, however, IGFBP-3 co-precipitated with phosphorylated forms of both proteins in ANS-treated cells. Indirect immunofluorescence and cell fractionation techniques showed that ANS induced phosphorylation and transport of Nur77 from the nucleus to the cytoplasm and these effects were attenuated by knockdown of IGFBP-3. These data suggest that endogenous IGFBP-3 plays a role in intrinsic apoptosis by facilitating phosphorylation and nuclear export of Nur77 to the cytoplasm where it exerts its apoptotic effect. Whether this mechanism involves a physical association between endogenous IGFBP-3 and Nur77 or RXRα remains to be determined.

Involvement of insulin-like growth factor binding protein-3 in peroxisome proliferator-activated receptor gamma-mediated inhibition of breast cancer cell growth

We have previously reported that insulin-like growth factor binding protein-3 (IGFBP-3), a protein with dichotomous effects on both cell proliferation and cell survival, interacts with peroxisome proliferator-activated receptor gamma (PPARγ) and inhibits adipogenic PPARγ signaling. We now show that IGFBP-3 and PPARγ interact in breast cancer cells, through amino- and carboxyl-terminal residues of IGFBP-3. IGFBP-3 and the PPARγ ligands, rosiglitazone or 15-deoxy-Δ(12,14)-prostaglandin J2, separately inhibited the proliferation of MCF-7, MDA-MB-231 and MDA-MB-468 breast cancer cells. However, growth inhibition by IGFBP-3 and PPARγ ligand combined was greater than by either alone. Two IGFBP-3 mutants with reduced PPARγ binding caused no growth inhibition when used alone and abolished the inhibitory effect of rosiglitazone when used in combination with PPARγ ligand. Cell growth inhibition by PPARγ ligands was substantially blocked by IGFBP-3 siRNA and restored by exogenous IGFBP-3. We conclude that the interaction between IGFBP-3 and PPARγ is important for the growth-inhibitory effect of PPARγ ligands in human breast cancer cells, suggesting that IGFBP-3 expression by breast tumors may regulate their sensitivity toward PPARγ ligands.

Growth suppression and cell death by pyridoxal is dependent on p53 in the human breast cancer cell line MCF-7

Vitamin B6 compound, pyridoxine (PN), has shown antitumor action. Our previous experiments showed that PN induces expression of insulin-like growth factor binding protein-3 to arrest proliferation and induce cell death. This induction is inhibited by the p53-specific inhibitor pifithrin-α. Here, we report that another B6 compound, pyridoxal (PL), strongly inhibited MCF-7 cell growth compared to PN. PL induced the G0/G1 arrest and the accumulation of subG1 population. Although p53 mRNA was not changed by PL, 0.5 mM PL increased the protein level in MCF-7 cells. The cell growth suppression by 0.5 mM PL did not occur when p53 expression was knocked down using siRNA. Together, these data suggest that PL accumulate p53 and PL-induced cell growth suppression is dependent on p53 in MCF-7 breast cancer cells.

IGFBP-3: a cell fate pivot in cancer and disease

One of the hallmarks in the advancement of cancer cells is an ability to overcome and acquire resistance to adverse conditions. There has been a large amount of cancer research on IGFBP-3 as a pro-apoptotic molecule in vitro. These pro-apoptotic properties, however, do not correlate with several studies linking high IGFBP-3 levels in breast cancer tissue to rapid growth and poor prognosis. Evidence is emerging that IGFBP-3 also exhibits pro-survival and growth-promoting properties in vitro. How IGFBP-3 pivots cell fate to either death or survival, it seems, comes down to a complex interplay between cells' microenvironments and the presence of cellular IGFBP-3 binding partners and growth factor receptors. The cytoprotective actions of IGFBP-3 are not restricted to cancer but are also observed in other disease states, such as retinopathy and brain ischaemia. Here we review the literature on this paradoxical nature of IGFBP-3, its pro-apoptotic and growth-inhibitory actions versus its cytoprotective and growth-potentiating properties, and discuss the implications of targeting IGFBP-3 for treatment of disease.

Activation of various downstream signaling molecules by IGFBP-3

Insulin-like growth factor binding protein-3 (IGFBP-3), a secretory protein, is the most abundant IGF binding protein present in human serum among all IGF binding proteins. IGFBP-3 shows decreased level of expression in cancerous cells but has been known to be present in significant amounts in normal or non-cancerous cells. IGFBP-3 can induce apoptosis in prostate cancer cells either in an IGF-dependent manner or independently of IGF binding. Although putative cell death specific Insulin-like growth factor binding protein-3 (IGFBP-3R) receptor(s) has recently been identified by which IGFBP-3 may induce its anti-tumor effects, IGFBP-3 has also been known to activate various downstream intracellular signaling molecules via a different mechanistic pathway. Stat-1 has been known to be one of the candidate molecules activated by IGFBP-3. IGFBP-3 can also inhibit Akt/IGF-1 survival pathway in MCF- 7 breast cancer cells which ultimately leads to the induction of apoptosis in these cells. All these studies clearly demonstrate that IGFBP-3 regulates cell proliferation and promotes its pro-apoptotic effects in cancer cells in two different pathways,1) sequester IGF-I to bind to IGF-I receptor to inhibit cell proliferation and induce apoptosis, 2) independent of IGF-I pathway, IGFBP-3 binds to some putative receptor and activate various downstream pro-apoptotic molecules involved in cell death.

Linking pre-diabetes with benign prostate hyperplasia. IGFBP-3: a conductor of benign prostate hyperplasia development orchestra?

Benign prostatic hyperplasia (BPH) represents a pattern of non-malignant growth of prostatic fibromuscular stroma. Metabolic disturbances such us pre-diabetes and metabolic syndrome may have a role in BPH pathophysiology. A potential explanation for the above relationship involves the insulin-like growth factor (IGF) axis as well as IGF binding proteins, (IGFBPs) of which the most abundant form is IGFBP-3. Therefore, the aim of the present study was to investigate the association between intra-prostatic levels of IGF-1, IGF-2 as well as to evaluate the role of locally expressed IGFBP-3 in BPH development in pre-diabetes. A total of 49 patients admitted to the Urology department of a tertiary urban Greek hospital, for transurethral prostate resection, or prostatectomy and with pre-diabetes [impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) or both] were finally included. The majority of the sample consisted of subjects with IGT (51.0%), followed by IFG and IGT (32.7%) and isolated IFG (16.3%). For all participants a clinical examination was performed and blood samples were collected. In addition, total prostate (TP) volume or transitional zone (TZ) volume were estimated by transrectal ultrasonography. The results of the multivariate analysis regarding TP volume showed that higher PSA (p<0.001), larger waist circumference (p=0.007) and higher IGFBP-3 expression levels (p<0.001) independently predicted higher TP volume. The results regarding the volume of the TZ showed that higher PSA (p<0.001), larger waist circumference (p<0.001) and higher IGFBP-3 expression levels (p=0.024) were independently associated with higher TZ volume. Our findings show that intra-prostatic levels of IGFBP-3, PSA and waist circumference, but not overall obesity, are positively associated with prostate volume. IGFBP-3 seems to be a multifunctional protein, which can potentiate or inhibit IGF activity.

CRL4B promotes tumorigenesis by coordinating with SUV39H1/HP1/DNMT3A in DNA methylation-based epigenetic silencing

Cullin 4B (CUL4B) is a component of the Cullin4B-Ring E3 ligase complex (CRL4B) that functions in proteolysis and is implicated in tumorigenesis. Here, we report that CRL4B is associated with histone methyltransferase SUV39H1, heterochromatin protein 1 (HP1) and DNA methyltransferases 3A (DNMT3A). We showed that CRL4B, through catalyzing H2AK119 monoubiquitination, facilitates H3K9 tri-methylation and DNA methylation, two key epigenetic modifications involved in DNA methylation-based gene silencing. Depletion of CUL4B resulted in loss of not only H2AK119 monoubiquitination but also H3K9 trimethylation and DNA methylation, leading to derepression of a collection of genes, including the tumor suppressor IGFBP3. We demonstrated that CUL4B promotes cell proliferation and invasion, which are consistent with a tumorigenic phenotype, at least partially by repressing IGFBP3. We found that the expression of CUL4B is markedly upregulated in samples of human cervical carcinoma and is negatively correlated with the expression of IGFBP3. Our experiments unveiled a coordinated action between histone ubiquitination/methylation and DNA methylation in transcription repression, providing a mechanism for CUL4B in tumorigenesis.

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.

Role of insulin-like growth factor binding protein-3 in 1, 25-dihydroxyvitamin-d 3 -induced breast cancer cell apoptosis

Insulin-like growth factor I (IGF-I) is implicated in breast cancer development and 1, 25-dihydroxyvitamin D₃ (1, 25-D₃) has been shown to attenuate prosurvival effects of IGF-I on breast cancer cells. In this study the role of IGF binding protein-3 (IGFBP-3) in 1, 25-D₃-induced apoptosis was investigated using parental MCF-7 breast cancer cells and MCF-7/VD^R cells, which are resistant to the growth inhibitory effects of 1, 25-D₃. Treatment with 1, 25-D₃ increased IGFBP-3 mRNA expression in both cell lines but increases in intracellular IGFBP-3 protein and its secretion were observed only in MCF-7. 1, 25-D₃-induced apoptosis was not associated with activation of any caspase but PARP-1 cleavage was detected in parental cells. IGFBP-3 treatment alone produced cleavage of caspases 7, 8, and 9 and PARP-1 in MCF-7 cells. IGFBP-3 failed to activate caspases in MCF-7/VD^R cells; however PARP-1 cleavage was detected. 1, 25-D₃ treatment inhibited IGF-I/Akt survival signalling in MCF-7 but not in MCF-7/VD^R cells. In contrast, IGFBP-3 treatment was effective in inhibiting IGF-I/Akt pathways in both breast cancer lines. These results suggest a role for IGFBP-3 in 1, 25-D₃ apoptotic signalling and that impaired secretion of IGFBP-3 may be involved in acquired resistance to vitamin D in breast cancer.

Signal Transduction Pathways Mediated by Secreted and Non-secreted Forms of intact Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) and its 1-97 N-terminal Fragment in PC-3 Human Prostate Cancer Cells

Our previous results indicated that both the secreted and the intracellular form of full length and 1-97 N-terminal fragment of IGFBP-3 induces apoptosis in PC-3 human prostate cancer cells in an IGF-dependent and independent manner. This study was undertaken to delineate possible down-stream signaling pathways that are involved in this process. Intact IGFBP-3 and its N-terminal 1-97 fragments with or without a signal pro-peptide was fused to YFP and expressed in PC-3 human prostate cancer cells. In some cases, the putative IGF-binding site present in full length IGFBP-3 and its N-terminal fragment was also mutated. Extent of apoptosis was quantified using FACS. Up-regulation of total Stat-1 and activation of phospho-Stat-1 was shown by western blot. TGF-β signal was measured by luciferase reporter assay. Results from inhibitor studies indicated that both the Caspase 8 and caspase 9 pathways are involved in IGFBP-3 (non-secreted form) induced apoptosis in PC-3 cells. Exogenous addition of IGFBP-3 to PC-3 cells increased Stat-1 protein expression/tyrosine phosphorylation. Interestingly, results also showed that knockdown of Stat-1 by siRNA potentiated the IGFBP-3 induced apoptosis in PC-3 cells. In addition, both full-length IGFBP-3 and its 1-97 N-terminal fragments inhibited TGFβ signaling in these cells. This is the first report that compares the signal transduction pathways involved in apoptotic pathways mediated by IGFBP-3 in PC-3 human prostate cancer cells. Non-secreted form of full length IGFBP-3 and its N-terminal fragments induced apoptosis in PC-3 cells via activation of caspase 8 and caspase 9. We noted that both secreted and non-secreted forms of IGFBP-3 are involved in modulating Stat-1 and TGF-β pathways to induce apoptotic actions in PC-3 cells. Surprisingly, only non-secreted form of IGFBP-3 and its N-terminal fragments are involved in the induction of apoptosis in PC-3 cells via caspase 8 and caspase 9 activation. These studies clearly demonstrate that secreted and non-secreted FL and its 1-97 N-terminal fragments induce apoptosis in PC-3 cells by regulating different mechanistic pathways.

Nimotuzumab promotes radiosensitivity of EGFR-overexpression esophageal squamous cell carcinoma cells by upregulating IGFBP-3

Background

Epidermal growth factor receptor (EGFR) is suggested to predict the radiosensitivity and/or prognosis of human esophageal squamous cell carcinoma (ESCC). The objective of this study was to investigate the efficacy of Nimotuzumab (an anti-EGFR monoclonal antibody) on ESCC radiotherapy (RT) and underlying mechanisms.

Methods

Nimotuzumab was administrated to 2 ESCC cell lines KYSE30 and TE-1 treated with RT. Cell growth, colony formation and apoptosis were used to measure anti-proliferation effects. The method of RNA interference was used to investigate the role of insulin-like growth factor binding protein-3 (IGFBP-3) in ESCC cells radiosensitivity treated with Nimotuzumab. In vivo effect of Nimotuzumab on ESCC radiotherapy was done using a mouse xenograft model.

Results

Nimotuzumab enhanced radiation response of KYSE30 cells (with high EGFR expression) in vitro, as evidenced by increased radiation-inhibited cell growth and colony formation and radiation-mediated apoptosis. Mechanism study revealed that Nimotuzumab inhibited phosphorylated EGFR (p-EGFR) induced by EGF in KYSE30 cells. In addition, knockdown of IGFBP-3 by short hairpin RNA significantly reduced KYSE30 cells radiosensitivity (P<0.05), and even after the administration of Nimotuzumab, the RT response of IGFBP-3 silenced KYSE30 cells was not enhanced (P>0.05). In KYSE30 cell xenografts, Nimotuzumab combined with radiation led to significant tumor growth delay, compared with that of radiation alone (P=0.029), and also with IGFBP-3 up-regulation in tumor tissue.

Conclusions

Nimotuzumab could enhance the RT effect of ESCC cells with a functional active EGFR pathway. In particular, the increased ESCC radiosensitivity by Nimotuzumab might be dependent on the up-regulation of IGFBP-3 through EGFR-dependent pathway.

Insulin-like factor binding protein-3 promotes the G1 cell cycle arrest in several cancer cell lines

Insulin-like growth factor binding protein-3 (IGFBP-3) is a multi-functional protein known to induce apoptosis of various cancer cells in an insulin-like growth factor (IGF)-dependent and IGF-independent manner. In our previous study, we found that IGFBP-3 induced apoptosis through the activation of caspases in 786-O cells. In this study, we further examined that whether IGFBP-3 induced apoptosis through the induction of cell cycle arrest in 786-O, A549 and MCF-7 cells. Our results showed that overexpressed IGFBP-3 resulted in typical apoptotic ultrastructures in A549 cells under transmission electron microscope. The result of flow cytometry analysis indicated that IGFBP-3 arrested the cell cycle at G1-S phase in 786-O, A549 and MCF-7 cells. In A549 cells, quantitative real-time PCR and Western blot analysis showed a significant change in the expression of cell cycle-regulated proteins-a decrease in cyclin E1 expression, an increase in p21 expression. These results indicate a possible mechanism for G1 cell cycle arrest by IGFBP-3. Taken together, cyclin E1 and p21 may play important roles in the IGFBP-3-inducing G1 cell cycle arrest and apoptosis in several human cancer cells.

IGFBP-3 sensitizes antiestrogen-resistant breast cancer cells through interaction with GRP78

IGFBP-3 is known to possess intrinsic biological activities such as anti-tumor property in addition to its IGF/IGF-R axis-dependent actions in a variety of human cancers including breast cancer. To investigate the molecular mechanisms underlying the intrinsic biological actions of IGFBP-3 on breast cancer cells, we performed yeast two-hybrid screening and found GRP78, known to cause drug-resistance, as a binding partner of IGFBP-3. Overexpression of IGFBP-3 in antiestrogen-resistant LCC9 cells showed that IGFBP-3 interacted with GRP78, resulting in disruption of the GRP78-caspase-7 complex, thereby activating caspase-7, and further inducing apoptosis. Combination of overexpression of IGFBP-3 and application of siRNAs against GRP78 led to decrease in cell viability upon ICI 182,780 treatment. These data suggest that IGFBP-3 could sensitize antiestrogen-resistant breast cancer cells to ICI 182,780 by preventing the anti-apoptotic function of GRP78.

Insulin-like growth factor binding protein-3 suppresses vascular endothelial growth factor expression and tumor angiogenesis in head and neck squamous cell carcinoma

Angiogenesis, the process by which new blood vessels are recruited to existing ones, is essential for tumor development. Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3), which modulates bioavailability of IGF, has been studied for its potential role in angiogenesis during tissue regeneration and cancer development. In this study, we assessed the role of IGFBP-3 in tumor angiogenesis in head and neck squamous cell carcinoma (HNSCC) and human umbilical vein endothelial cells (HUVECs) using adenoviral (Ad-BP3) and recombinant (rBP3) IGFBP-3. Using an in vivo orthotopic tongue tumor model, we confirmed that both Ad-BP3 and rBP3 suppress the growth of UMSCC38 HNSCC cells in vivo. Ad-BP3 inhibited vascularization in tongue tumors and chorio-allantoic membrane, and suppressed angiogenesis-stimulating activities in UMSCC38 cells. In HUVECs, Ad-BP3 decreased migration, invasion, and tube formation. rBP3 also suppressed production of vascular endothelial growth factor (VEGF) in HUVECs and UMSCC38 cells. IGFBP-3-GGG, a mutant IGFBP-3 with loss of IGF binding capacity, suppressed VEGF production. In addition, we found that IGFBP-3 suppressed VEGF expression, even in mouse embryonic fibroblasts from an IGF-1R-null mouse. Finally, we demonstrated that IGFBP-3-GGG inhibits tumor angiogenesis and growth to the same degree as wild-type IGFBP-3. Taken together, these results support the hypothesis that IGFBP-3 has anti-angiogenic activity in HNSCC, at least in part due to IGF-independent suppression of VEGF production from vascular endothelial cells and cancer cells.

Role of insulin-like growth factors (IGFs), their receptors and genetic regulation in the chondrogenesis and growth of the mandibular condylar cartilage

Growth of the mandibular condylar cartilage (MCC) is reviewed as a function of genetic and epigenetic factors. The growth centers around the differential spatial concentration of the chondrocytes, influence of growth factors like TGF-β and heterogeneity in the number of IGF receptors, control the action of IGF. Besides these factors, growth of the mandibular condyle is influenced by differential response of chondrocytes as a function of their source/ageing, which in turn is regulated by TGF-β, BMPs and IGFs. While IGF-1 promotes proteoglycan synthesis and survival of the chondrocytes to maintain cartilage homeostasis, TGF-β synergistically catalysed the effect of IGF-1, while BMPs catalysed proteolysis as and when physiologically needed. To understand these processes, role of IGF-1 and its six receptors is at the center to a number of physiological processes being regulated by its mode of application for the growth and differentiation. Probing deeper, biological functions of IGFs seemed to depend on their level of free status rather than bound status to respective IGF-binding proteins (IGF-BPs), considered prerequisite to modulate their biological functions. Genetic regulation of their secretion has thrown light on their insulin-like structural homology, level and response in osteo-arthritis (OA), rheumatic arthritis (RA) and diabetes type-II. Biochemistry and spatial distribution of IGF receptors in different domains exerts control on IGF-1 activities. In ultimate analysis, IGF-axis conserved during the evolution to regulate cell growth and proliferation affect nearly every organ in the body as judged from the techniques determining skeletal maturity and decision making dependent on it for orthodontic, orthognathic/orthopedic and dental implant applications.

Functional roles and clinical values of insulin-like growth factor-binding protein-5 in different types of cancers

Insulin-like growth factor-binding proteins (IGFBPs) are critical regulators of the mitogenic activity of insulin-like growth factors (IGFs). IGFBP5, one of these IGFBPs, has special structural features, including a nuclear transport domain, heparin-binding motif, and IGF/extracellular matrix/acid-labile subunit-binding sites. Furthermore, IGFBP5 has several functional effects on carcinogenesis and even normal cell processes, such as cell growth, death, motility, and tissue remodeling. These biological effects are sometimes related with IGF (IGF-dependent effects) and sometimes not (IGF-independent effects). The functional role of IGFBP5 is most likely determined in a cell-type and tissue-type specific manner but also depends on cell context, especially in terms of the diversity of interacting proteins and the potential for nuclear localization. Clinical findings show that IGFBP5 has the potential to be a useful clinical biomarker for predicting response to therapy and clinical outcome of cancer patients. In this review, we summarize the functional diversity and clinical importance of IGFBP5 in different types of cancers.

Differential impacts of insulin-like growth factor-binding protein-3 (IGFBP-3) in epithelial IGF-induced lung cancer development

The IGF axis has been implicated in the risk of various cancers. We previously reported a potential role of tissue-derived IGF in lung tumor formation and progression. However, the role of IGF-binding protein (IGFBP)-3, a major IGFBP, on the activity of tissue-driven IGF in lung cancer development is largely unknown. Here, we show that IGF-I, but not IGF-II, protein levels in non-small-cell lung cancer (NSCLC) were significantly higher than those in normal and hyperplastic bronchial epithelium. We found that IGF-I and IGFBP-3 levels in NSCLC tissue specimens were significantly correlated with phosphorylated IGF-IR (pIGF-IR) expression. We investigated the impact of IGFBP-3 expression on the activity of tissue-driven IGF-I in lung cancer development using mice carrying lung-specific human IGF-I transgene (Tg), a germline-null mutation of IGFBP-3, or both. Compared with wild-type (BP3(+/+)) mice, mice carrying heterozygous (BP3(+/-)) or homozygous (BP3(-/-)) deletion of IGFBP-3 alleles exhibited decreases in circulating IGFBP-3 and IGF-I. Unexpectedly, IGF(Tg) mice with 50% of physiological IGFBP-3 (BP3(+/-); IGF(Tg)) showed higher levels of pIGF-IR/IR and a greater degree of spontaneous or tobacco carcinogen [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone]-induced lung tumor development and progression than did the IGF(Tg) mice with normal (BP3(+/+;) IGF(Tg)) or homozygous deletion of IGFBP-3 (BP3(-/-); IGF(Tg)). These data show that IGF-I is overexpressed in NSCLC, leading to activation of IGF-IR, and that IGFBP-3, depending on its expression level, either inhibits or potentiates IGF-I actions in lung carcinogenesis.

Relationship of insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) gene polymorphism with the susceptibility to development of prostate cancer and influence on serum levels of IGF-I, and IGFBP-3

The bioavailability of IGF-I is controlled by the binding protein, IGF binding protein-3 (IGFBP-3). In addition, IGFBP-3 is a strong anti-proliferative protein that provokes apoptosis and inhibits cell proliferation in prostate cancer. We conducted this study to investigate the association between IGFBP-3 gene polymorphism and serum levels of IGF-I and IGFBP-3 and the incidence of prostate cancer (PCa) and benign prostatic hyperplasia (BPH). DNA isolation was performed in peripheral blood samples obtained from all participants. Required areas were amplified with polymerase chain reaction restriction fragment length polymorphism (PCR-RLFP) technique by using proper primers belonging to this gene area. We also measured serum IGF-I and IGFBP-3 levels. The IGFBP-3 -202 A/C polymorphism genotype frequencies showed a significant difference between PCa patients and controls (χ(2)=6.27, df=2.0, P=0.026), as well as between BPH patients and controls (χ(2)=11.57, df=4.0, P=0.014). The AA genotype frequency was significantly decreased in PCa and BPH patients compared to control group and the risk of PCa and BPH occurrence of this genotype was decreased accordingly (PCa; OR=0.28, 95% CI=0.17-0.44, P=0.0001; BPH: OR=0.48, 95% CI=0.29-0.77, P=0.001). Age-adjusted mean serum IGFBP-3 concentrations were highest in the individuals with the AA genotype and diminished significantly in a stepwise manner in the presence of 1 or 2 copies of the C allele (4577 ng/ml, 3929 ng/ml and 3349 ng/ml, respectively). Patients with PCa and BPH had lower serum IGF-1 (P=0.001, and P=0.01, respectively) and IGFBP-3 levels (P=0.001, and P=0.01, respectively) compared with controls. The AA genotype at IGFBP-3 gene polymorphism is associated with reduced risks of PCa and BPH. Both IGF-I and IGFBP-3 concentrations, are associated with modified risks of PCa and BPH.

A novel interaction between insulin-like growth factor binding protein-6 and the vitamin D receptor inhibits the role of vitamin D3 in osteoblast differentiation

Insulin-like growth factor binding protein-6 (IGFBP-6) is a secreted glycoprotein that reduces the bioavailability of IGFs. It has both IGF-dependent and -independent effects on cell growth, however the mechanisms responsible for its IGF-independent actions of IGFBP-6 are not fully understood. In previous studies, we have shown that recombinant IGFBP-6 can be internalized and translocated to the nucleus. The present study shows that IGFBP-6 interacts with the vitamin D receptor (VDR). Physical interactions between IGFBP-6 and the VDR were confirmed by GST pulldown and co-immunoprecipitation assays. We also determined that the interaction binding sites were on the C-terminal region of the VDR. This interaction can influence retinoid X receptor (RXR):VDR heterodimerization. Furthermore, immunofluorescence colocalization studies showed that IGFBP-6 colocalized with the VDR predominantly in the cell's nucleus. Inductions of osteocalcin and growth hormone promoter activities by 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) were significantly decreased when cells were co-transfected with IGFBP-6 and the VDR compared with cells transfected with the VDR only. Moreover, we found that alkaline phosphatase activity (ALP, a general marker of osteoblast differentiation) was significantly decreased in osteoblast-like cells when they were transfected with IGFBP-6 in the presence of 1,25(OH)(2)D(3). No obvious difference in ALP activity was observed when cells were transfected with IGFBP-6 and endogenous VDR was knocked down by siRNA. These results demonstrate that IGFBP-6 inhibits osteoblastic differentiation mediated by 1,25(OH)(2)D(3) and the VDR through interacting with the VDR and inhibiting its function. This is a novel mechanism for IGFBP-6.

Antiangiogenic antitumor activities of IGFBP-3 are mediated by IGF-independent suppression of Erk1/2 activation and Egr-1-mediated transcriptional events

Most antiangiogenic therapies currently being evaluated in clinical trials target the vascular endothelial growth factor pathway; however, the tumor vasculature can acquire resistance to vascular endothelial growth factor-targeted therapy by shifting to other angiogenesis mechanisms. Insulin-like growth factor binding protein-3 (IGFBP-3) has been reported to suppress tumor growth and angiogenesis by both IGF-dependent and IGF-independent mechanisms; however, understanding of its IGF-independent mechanisms is limited. We observed that IGFBP-3 blocked tumor angiogenesis and growth in non-small cell lung cancer and head and neck squamous cell carcinoma. Conditioned media from an IGFBP-3-treated non-small cell lung cancer cell line displayed a significantly decreased capacity to induce HUVEC proliferation and aortic sprouting. In cancer cells, IGFBP-3 directly interacted with Erk1/2, leading to inactivation of Erk1/2 and Elk-1, and suppressed transcription of early growth response protein 1 and its target genes, basic fibroblast growth factor and platelet-derived growth factor. These data suggest that IGF-independent Erk1/2 inactivation and decreased IGFBP-3-induced Egr-1 expression block the autocrine and paracrine loops of angiogenic factors in vascular endothelial and cancer cells. Together, these findings provide a molecular framework of IGFBP-3's IGF-independent antiangiogenic antitumor activities. Future studies are needed for development of IGFBP-3 as a new line of antiangiogengic cancer drug.

Incidental non-secreting adrenal masses in cancer patients: intra-individual comparison of 18F-fluorodeoxyglucose positron emission tomography/computed tomography with computed tomography and shift magnetic resonance imaging

The ability of integrated (18)F-fluorodeoxyglucose positron emission tomography and computed tomography (FDG PET/CT) to distinguish between benign and malignant incidental non-secreting adrenal masses was evaluated in cancer patients. Results were compared with those of CT and shift magnetic resonance imaging (MRI). A total of 1832 cancer patients who had undergone FDG PET/CT scans were retrospectively evaluated. Visual interpretation, tumour maximum standardized uptake value (SUV(max)), liver SUV(max) and tumour/liver SUV(max) ratios were correlated with the findings of CT, shift MRI and final diagnosis (based on biopsy or clinical/radiological follow-up). A total of 109 adrenal masses were found: 49 were malignant and 60 were benign on final diagnosis. A tumour/liver SUV(max) ratio threshold of 1.0 was more accurate in differentiating the tumour type than tumour SUV(max) or visual interpretation alone. Diagnostic accuracy of CT and shift MRI (92 - 97%) was similar to that for FDG PET/CT (94 - 97%). In conclusion, FDG PET/CT accurately characterizes adrenal tumours, with excellent sensitivity and specificity. Use of 1.0 as the threshold for the tumour/liver SUV(max) ratio seems to be promising for distinguishing benign from malignant adrenal masses in cancer patients.

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.

Identification of a novel cell death receptor mediating IGFBP-3-induced anti-tumor effects in breast and prostate cancer

Insulin-like growth factor-binding protein-3 (IGFBP-3), a major regulator of endocrine actions of IGFs, is a p53-regulated potent apoptotic factor and is significantly suppressed in a variety of cancers. Recent epidemiologic studies suggest that IGFBP-3 contributes to cancer risk protection in a variety of cancers, and a polymorphic variation of IGFBP-3 influences cancer risk, although other studies vary in their conclusions. Some antiproliferative actions of IGFBP-3 have been reported to be independent of IGFs, but the precise biochemical/molecular mechanisms of IGF-independent, antiproliferative actions of IGFBP-3 are largely unknown. Here we report a new cell death receptor, IGFBP-3R, that is a single-span membrane protein and binds specifically to IGFBP-3 but not other IGFBP species. Expression analysis of IGFBP-3 and IGFBP-3R indicates that the IGFBP-3/IGFBP-3R axis is impaired in breast and prostate cancer. We also provide evidence for anti-tumor effect of IGFBP-3R in vivo using prostate and breast cancer xenografts in athymic nude mice. Further in vitro studies demonstrate that IGFBP-3R mediates IGFBP-3-induced caspase-8-dependent apoptosis in various cancer cells. Knockdown of IGFBP-3R attenuated IGFBP-3-induced caspase activities and apoptosis, whereas overexpression of IGFBP-3R enhanced IGFBP-3 biological effects. IGFBP-3R physically interacts and activates caspase-8, and knockdown of caspase-8 expression or activity inhibited IGFBP-3/IGFBP-3R-induced apoptosis. Here, we propose that IGFBP-3R represents a novel cell death receptor and is essential for the IGFBP-3-induced apoptosis and tumor suppression. Thus, the IGFBP-3/IGFBP-3R axis may provide therapeutic and prognostic value for the treatment of cancer.

In-vivo transfection of pcDNA3.1-IGFBP7 inhibits melanoma growth in mice through apoptosis induction and VEGF downexpression

BACKGROUND

Genome-wide RNA interference screening study revealed that loss of expression of insulin-like growth factor binding protein 7 (IGFBP7) is a critical step in development of a malignant melanoma (MM), and this secreted protein plays a central role in apoptosis of MM. In this study we constructed pcDNA3.1-IGFBP7 to obtain high expression of IGBPF7 and to inhibit the growth of MM in C57BL/6J mice.

METHODS

pcDNA3.1-IGFBP7 was transfected into B16-F10 cell, the expression of IGFBP7 was detected by RT-PCR and western blot. The proliferations and apoptosis rates of transfected and control cells were measured by CCK8 and FCM, respectively. The tumorigenicity and tumor growth in both pcDNA3.1-IGFBP7 group and control groups were studied in C57BL/6J mice model. IGFBP7, caspase-3, and VEGF expressions in tumor tissue were measured by immunohistochemistry. Apoptosis of tumors were detected by TUNEL.

RESULTS

We demonstrated this plasmid inhibited proliferation of B16-F10 melanoma cells efficiently in vivo, exploiting the high expression of IGFBP7. More importantly, in-vivo transfection of pcDNA3.1-IGFBP7 inhibited MM growth in C57BL/6J mice. The inhibition of MM growth was proved owing to apoptosis and reduced expression of VEGF induced by pcDNA3.1-IGFBP7.

CONCLUSIONS

These results suggest a potential new clinical strategy for MM gene treatment.

Role of insulin-like growth factor binding protein 2 in lung adenocarcinoma: IGF-independent antiapoptotic effect via caspase-3

Insulin-like growth factor (IGF) signaling plays a pivotal role in cell proliferation and mitogenesis. Secreted IGF-binding proteins (IGFBPs) are important modulators of IGF bioavailability; however, their intracellular functions remain elusive. We sought to assess the antiapoptotic properties of intracellular IGFBP-2 in lung adenocarcinomas. IGFBP-2 overexpression resulted in a decrease in procaspase-3 expression; however, it did not influence the phosphorylation status of either IGF receptor or its downstream targets, including Akt and extracellular signal-regulated kinase. Apoptosis induced by camptothecin was significantly inhibited by IGFBP-2 overexpression in NCI-H522 cells. Conversely, selective knockdown of IGFBP-2 using small-interfering RNA resulted in an increase in procaspase-3 expression and sensitization to camptothecin-induced apoptosis in NCI-H522 cells. LY294002, an inhibitor of phosphatidyl-inositol 3-kinase, caused a decrease in IGFBP-2 levels and enhanced apoptosis in combination with camptothecin. Immunohistochemistry demonstrated that intracellular IGFBP-2 was highly expressed in lung adenocarcinomas compared with normal epithelium. Intracellular IGFBP-2 and procaspase-3 were expressed in a mutually exclusive manner. These findings suggest that intracellular IGFBP-2 regulates caspase-3 expression and contributes to the inhibitory effect on apoptosis independent of IGF. IGFBP-2, therefore, may offer a novel therapeutic target and serve as an antiapoptotic biomarker for lung adenocarcinoma.

Promoter methylation of IGFBP-3 and p53 expression in ovarian endometrioid carcinoma

Background

Insulin-like growth factor binding protein (IGFBP-3) is an antiproliferative, pro-apoptotic and invasion suppressor protein which is transcriptionally regulated by p53. Promoter methylation has been linked to gene silencing and cancer progression. We studied the correlation between IGFBP-3 and p53 expression as well as IGFBP-3 promoter methylation in ovarian endometrioid carcinoma (OEC) by immunohistochemical staining and quantitative methylation-specific PCR (qMSP). Additionally, we assessed the molecular regulatory mechanism of wild type (wt) p53 on IGFBP-3 expression using two subclones of OEC, the OVTW59-P0 (low invasive) and P4 (high invasive) sublines.

Results

In 60 cases of OEC, 40.0% showed lower IGFBP-3 expression which was significantly correlated with higher IGFBP-3 promoter methylation. p53 overexpression was detected in 35.0% of OEC and was unrelated to clinical outcomes and IGFBP-3. By Kaplan-Meier analysis, patients with lower IGFBP-3, higher IGFBP-3 promoter methylation, and normal p53 were associated most significantly with lower survival rates. In OEC cell line, IGFBP-3 expression was correlated with IGFBP-3 promoter methylation. IGFBP-3 expression was restored after treatment with a DNA methy-transferase inhibitors (5-aza-deoxycytidine) and suppressed by a p53 inhibitor (pifithrin-α). The putative p53 regulatory sites on the promoter of IGFBP-3 were identified at -210, -206, -183 and -179 bases upstream of the transcription start site. Directed mutagenesis at these sites quantitatively reduced the transcription activity of IGFBP-3.

Conclusion

Our data suggests that IGFBP-3 silencing through IGFBP-3 promoter methylation in the absence of p53 overexpression is associated with cancer progression. These results support a potential role of IGFBP-3 methylation in the carcinogenesis of OEC.

Gli2 and p53 cooperate to regulate IGFBP-3- mediated chondrocyte apoptosis in the progression from benign to malignant cartilage tumors

Clinical evidence suggests that benign cartilage lesions can progress to malignant chondrosarcoma, but the molecular events in this progression are unknown. Mice that develop benign cartilage lesions due to overexpression of Gli2 in chondrocytes developed lesions similar to chondrosarcomas when they were also deficient in p53. Gli2 overexpression and p53 deficiency had opposing effects on chondrocyte differentiation, but had additive effects negatively regulating apoptosis. Regulation of Igfbp3 expression and insulin-like growth factor (IGF) signaling by Gli and p53 integrated their effect on apoptosis. Treatment of human chondrosarcomas or fetal mouse limb explants with IGFBP3 or by blocking IGF increased the apoptosis rate, and mice expressing Gli2 developed substantially fewer tumors when they were also deficient for Igf2. IGF signaling-meditated apoptosis regulates the progression to malignant chondrosarcoma.

Unraveling insulin-like growth factor binding protein-3 actions in human disease

The IGF system plays critical roles in somatic growth in an endocrine fashion (somatomedin hypothesis) as well as proliferation and differentiation of normal and malignant cells in a paracrine/autocrine fashion. IGFBP-3 is known to modulate the actions of IGFs in circulation as well as the immediate extracellular environment. Interestingly, apart from the ability to inhibit or enhance IGF actions, IGFBP-3 also exhibits very clear, distinct biological effects independent of the IGF/IGF-I receptor axis. Over the past decade it has become widely appreciated that IGF/IGF-IR-independent actions of IGFBP-3 (antiproliferative and proapoptotic effects) contribute to improving the pathophysiology of a variety of human diseases, such as cancer, diabetes, and malnutrition. Recent studies have implicated interaction of IGFBP-3 with a variety of proteins or signaling cascades critical to cell cycle control and apoptosis; however, the actual mechanism of IGFBP-3 action is still unclear. This review reinforces the concept in support of the IGF/IGF-IR axis-independent actions of IGFBP-3 and delineates potential underlying mechanisms involved and subsequent biological significance, focusing in particular on functional binding partners and the clinical significance of IGFBP-3 in the assessment of cancer risk.

Potentiation of growth factor signaling by insulin-like growth factor-binding protein-3 in breast epithelial cells requires sphingosine kinase activity

We have investigated the mechanism underlying potentiation of epidermal growth factor receptor (EGFR) and type 1 insulin-like growth factor receptor (IGFR1) signaling by IGF-binding protein-3 (IGFBP-3) in MCF-10A breast epithelial cells, focusing on a possible involvement of the sphingosine kinase (SphK) system. IGFBP-3 potentiated EGF-stimulated EGF receptor activation and DNA synthesis, and this was blocked by inhibitors of SphK activity or small interference RNA-mediated silencing of SphK1, but not SphK2, expression. Similarly, IGFR1 phosphorylation and DNA synthesis stimulated by LR3-IGF-I (an IGF-I analog not bound by IGFBP-3), were enhanced by IGFBP-3, and this was blocked by SphK1 silencing. SphK1 expression and activity were stimulated by IGFBP-3 approximately 2-fold over 24 h. Silencing of sphingosine 1-phosphate receptor 1 (S1P1) or S1P3, but not S1P2, abolished the effect of IGFBP-3 on EGF-stimulated EGFR activation. The effects of IGFBP-3 could be reproduced with exogenous S1P or medium conditioned by cells treated with IGFBP-3, and this was also blocked by inhibition of S1P1 and S1P3. These data indicate that potentiation of growth factor signaling by IGFBP-3 in MCF-10A cells requires SphK1 activity and S1P1/S1P3, suggesting that S1P, the product of SphK activity and ligand for S1P1 and S1P3, is the "missing link" mediating IGF and EGFR transactivation and cell growth stimulation by IGFBP-3.

Insulin-like growth factor and epidermal growth factor treatment: new approaches to protecting steatotic livers against ischemia-reperfusion injury

Hepatic steatosis is a major risk factor in ischemia-reperfusion (I/R). IGF-binding proteins (IGFBPs) modulate IGF-I action by transporting circulating IGF-I to its sites of action. Epidermal growth factor (EGF) stimulates IGF-I synthesis in vitro. We examined the effect of IGF-I and EGF treatment, separately or in combination, on the vulnerability of steatotic livers to I/R. Our results indicated that I/R impaired IGF-I synthesis only in steatotic livers. Only when a high dose of IGF-I (400 microg/kg) was given to obese animals did they show high circulating IGF-I:IGFBP levels, increased hepatic IGF-I levels, and protection against damage. In lean animals, a dose of 100 microg/kg IGF-I protected nonsteatotic livers. Our results indicated that the combined administration of IGF-I and EGF resulted in hepatic injury parameters in both liver types similar to that obtained by IGF-I and EGF separately. IGF-I increased egf expression in both liver types. The beneficial role of EGF on hepatic I/R injury may be attributable to p38 inhibition in nonsteatotic livers and to PPAR gamma overexpression in steatotic livers. In conclusion, IGF-I and EGF may constitute new pharmacological strategies to reduce the inherent susceptibility of steatotic livers to I/R injury.

Enhancing the apoptotic potential of insulin-like growth factor-binding protein-3 in prostate cancer by modulation of CK2 phosphorylation

IGF-binding protein 3 (IGFBP-3) promotes apoptosis by both IGF-dependent and -independent mechanisms. We have previously reported that phosphorylation of IGFBP-3 (S156) by DNA-dependent protein kinase enhances its nuclear accumulation and is essential for its ability to interact with retinoid X receptor-alpha and induce apoptosis in cultured prostate cancer cells. Using specific chemical inhibitors and small interfering RNA, we demonstrate that preventing casein kinase 2 (CK2) activation enhanced the apoptotic potential of IGFBP-3. We mapped potential CK2 phosphosphorylation sites in IGFBP-3 to S167 and S175 and identified that wild-type IGFBP-3- and IGFBP-3-S175A-induced apoptosis to a comparable extent. In contrast, IGFBP-3-S167A was far more potently apoptosis inducing due to inability to undergo CK2 phosphorylation. Pretreatment of 22RV1 cells with IGFBP-3 small interfering RNA also limits the ability of high doses of CK2 inhibitor to induce apoptosis. These effects can be reversed by the addition of exogenous IGFBP-3 protein, suggesting reciprocal regulation of cell survival and apoptosis by IGFBP-3 and CK2. These studies reveal multisite phosphorylation of IGFBP-3 that both positively and negatively regulate its apoptotic potential. Understanding such intrinsic regulation of IGFBP-3 action may enhance the development of potential cancer therapies.

IGFBP-3, hypoxia and TNF-alpha inhibit adiponectin transcription

The thiazolidinedione rosiglitazone, an agonist ligand for the nuclear receptor PPAR-gamma, improves insulin sensitivity in part by stimulating transcription of the insulin-sensitizing adipokine adiponectin. It activates PPAR-gamma-RXR-alpha heterodimers bound to PPAR-gamma response elements in the adiponectin promoter. Rosiglitazone-stimulated adiponectin protein synthesis in 3T3-L1 mouse adipocytes has been shown to be inhibited by IGFBP-3, which can be induced by hypoxia and the proinflammatory cytokine, TNF-alpha, two inhibitors of adiponectin transcription. The present study demonstrates that IGFBP-3, the hypoxia-mimetic agent cobalt chloride, and TNF-alpha inhibit rosiglitazone-induced adiponectin transcription in mouse embryo fibroblasts that stably express PPAR-gamma2. Native IGFBP-3 can bind RXR-alpha and inhibited rosiglitazone stimulated promoter activity, whereas an IGFBP-3 mutant that does not bind RXR-alpha did not. These results suggest that IGFBP-3 may mediate the inhibition of adiponectin transcription by hypoxia and TNF-alpha, and that IGFBP-3 binding to RXR-alpha may be required for the observed inhibition.

IGFBP3 colocalizes with and regulates hypocretin (orexin)

Background

The sleep disorder narcolepsy is caused by a vast reduction in neurons producing the hypocretin (orexin) neuropeptides. Based on the tight association with HLA, narcolepsy is believed to result from an autoimmune attack, but the cause of hypocretin cell loss is still unknown. We performed gene expression profiling in the hypothalamus to identify novel genes dysregulated in narcolepsy, as these may be the target of autoimmune attack or modulate hypocretin gene expression.

Methodology/Principal Findings

We used microarrays to compare the transcriptome in the posterior hypothalamus of (1) narcoleptic versus control postmortem human brains and (2) transgenic mice lacking hypocretin neurons versus wild type mice. Hypocretin was the most downregulated gene in human narcolepsy brains. Among many additional candidates, only one, insulin-like growth factor binding protein 3 (IGFBP3), was downregulated in both human and mouse models and co-expressed in hypocretin neurons. Functional analysis indicated decreased hypocretin messenger RNA and peptide content, and increased sleep in transgenic mice overexpressing human IGFBP3, an effect possibly mediated through decreased hypocretin promotor activity in the presence of excessive IGFBP3. Although we found no IGFBP3 autoantibodies nor a genetic association with IGFBP3 polymorphisms in human narcolepsy, we found that an IGFBP3 polymorphism known to increase serum IGFBP3 levels was associated with lower CSF hypocretin-1 in normal individuals.

Conclusions/Significance

Comparison of the transcriptome in narcolepsy and narcolepsy model mouse brains revealed a novel dysregulated gene which colocalized in hypocretin cells. Functional analysis indicated that the identified IGFBP3 is a new regulator of hypocretin cell physiology that may be involved not only in the pathophysiology of narcolepsy, but also in the regulation of sleep in normal individuals, most notably during adolescence. Further studies are required to address the hypothesis that excessive IGFBP3 expression may initiate hypocretin cell death and cause narcolepsy.

The role of insulin-like growth factor-I and its binding proteins in glucose homeostasis and type 2 diabetes

This review addresses the possible role of the insulin-like growth factor (IGF)-axis in normal glucose homoeostasis and in the etiopathogenesis of type 2 diabetes. IGF-I, a peptide hormone, shares amino acid sequence homology with insulin and has insulin-like activity; most notably, the promotion of glucose uptake by peripheral tissues. Type 2 diabetes as well as pre-diabetic states, including impaired fasting glucose and impaired glucose tolerance, are associated cross-sectionally with altered circulating levels of IGF-I and its binding proteins (IGFBPs). Administration of recombinant human IGF-I has been reported to improve insulin sensitivity in healthy individuals as well as in patients with insulin resistance and type 2 diabetes. Further, IGF-I may have beneficial effects on systemic inflammation, a risk factor for type 2 diabetes, and on pancreatic beta-cell mass and function. There is considerable inter-individual heterogeneity in endogenous levels of IGF-I and its binding proteins; however, the relationship between these variations and the risk of developing type 2 diabetes has not been extensively investigated. Large prospective studies are required to evaluate this association.

IGF binding proteins (IGFBPs) and regulation of breast cancer biology

The IGFBP family comprises six proteins with high affinity for the IGFs. Changes in the balance of the components of the IGF system may contribute to the progression of breast cancer. In tumours the abundance of IGFBPs relates to the estrogen receptor status and their production in the breast is controlled by hormones, principally estrogen and progesterone. Important interactions occur between IGFBPs and key growth regulators such as TGF-beta, PTEN and EGF which are reviewed. The conflicting observations between the effects of IGFBPs on the risk of breast cancer, in particular IGFBP-3, obtained from epidemiology studies in comparison to in vivo observations are highlighted and potential explanations provided. The functional activity of IGFBPs can also be affected by proteolysis, phosphorylation and glycosylation and the implications of these are described. The IGFs are generally present at levels far in excess of that required for maximal receptor stimulation, and the IGFBPs are critical regulators of their cellular actions. IGFBPs can affect cell function in an IGF-dependent or independent manner. The key mechanisms underlying the intrinsic actions of the IGFBPs are still in debate. IGF bioactivity locally in the breast is influenced not only by local tissue expression and regulation of IGFs, IGFBPs and IGFBP proteases, but also by these factors delivered from the circulation. Finally, the therapeutic potential of IGFBPs-2 and -3 are considered together with key questions that still need to be addressed.

Insulin-like growth factor binding protein-3 (IGFBP-3) in the prostate and in prostate cancer: local production, distribution and secretion pattern indicate a role in stromal-epithelial interaction

BACKGROUND

Insulin-like growth factor binding protein 3 (IGFBP-3) exerts inhibitory and proapoptotic effects on prostate cancer cells. Serum levels of IGFBP-3 were found to be associated with the risk of prostate cancer, but the data are still inconclusive. We present a detailed analysis of the expression and localization of IGFBP-3 in the prostate and a comparison with its expression pattern in tumors.

METHODS

Expression and localization of IGFBP-3 were analyzed in cellular models and tissue by real-time RT-PCR, ELISA, immunohistochemistry, and immunofluorescence.

RESULTS

All cell types of a panel of benign epithelial, stromal and tumor prostate cells expressed IGFBP-3. Significantly higher expression levels were registered in stromal cells. TGF-beta stimulation boosted IGFBP-3 levels 60-fold in stromal cells. The pattern of expression was confirmed in microdissected tissue samples. Protein levels measured by ELISA paralleled the mRNA levels and more than 80% of IGFBP-3 was secreted. On tissue immunostaining, IGFBP-3 was found to be mainly located in the epithelium. The pattern suggested secretion of IGFBP-3, which was confirmed in prostate tissue cultured ex vivo and the ejaculate of vasectomized men. IGFBP-3 levels were increased in primary tumors but did not differ from benign epithelium in metastases and local recurrent tumors.

CONCLUSIONS

We registered a significant local production of IGFBP-3 in the prostate, which may well override the effect of protein entering from blood. The stroma--particularly reactivated stroma--is the main source of IGFBP-3 in the prostate, suggesting that this peptide acts as a mediator of stromal-epithelial interactions.