Enhanced expression of insulin-like growth factor binding protein-3 sensitizes the growth inhibitory effect of anticancer drugs in gastric cancer cells

Insulin-like growth factor (IGF)-I and -II are potent mitogens and their mitogenic effects are modulated by IGF binding proteins (IGFBPs). In this study, we evaluated whether the enhanced expression of IGFBP-3 may increase the sensitivity of human gastric cancer cells to the anticancer drugs. We further investigated the potential mechanism for the growth inhibitory effect of anticancer drug induced-IGFBP-3 expression. These IGFBP-3-expressing gastric cancer cells showed a lower proliferation rate than IGFBP-3-non-expressing cells. Treatment with anticancer drugs resulted in up-regulation of IGFBP-3 expression in IGFBP-3-expressing cells. Interestingly the anticancer drug-induced-growth inhibition was more evident in IGFBP-3-expressing cells causing the IGFBP-3 expressing cells but not the IGFBP-3 non-expressing cells to accumulate in the G1/G0 phase and induce apoptosis. The exogenous addition of IGFBP-3 inhibited the growth of IGFBP-3-non-expressing cells, causing them to undergo apoptosis. Our data suggest that IGFBP-3 may have an important role in the biology of gastric cancer cell growth and provides a potential marker for predicting the responsiveness to anticancer drugs.     

Adenoviral-mediated expression of human insulin-like growth factor-binding protein-3.

Insulin-like growth factors (IGFs) in the circulation are predominantly sequestered into ternary complexes comprising IGF, IGF-binding protein-3 (IGFBP-3), and the acid-labile subunit (ALS). Besides its role in regulating IGF bioavailability in the circulation, IGFBP-3 has both IGF-dependent and IGF-independent actions on cell proliferation. As part of our studies into the structure-function relationships of the multifunctional IGFBP-3, we have evaluated the efficiency of an adenovirus-mediated expression system for rapid, medium-scale production of functional, glycosylated IGFBP-3. Replication-deficient adenovirus containing human IGFBP-3 cDNA was generated using standard techniques. Secreted, recombinant IGFBP-3 (IGFBP-3(Ad)) was purified from the culture medium of virus-infected cells by IGF-I affinity chromatography followed by reverse-phase HPLC. When analyzed by SDS-PAGE, IGFBP-3(Ad) was similar in size (43- to 45-kDa glycoform doublet) to IGFBP-3(Pl) derived from plasma. In addition, IGFBP-3(Ad) was detected by immunoblot using an antibody specific for human IGFBP-3 and by ligand blot using radiolabeled IGF-I. IGFBP-3(Ad) had similar affinities for IGF-I and ALS and an approximately 25% decreased affinity for IGF-II compared to IGFBP-3(Pl). IGFBP-3(Ad) showed no significant difference in its susceptibility to an IGFBP-3 protease present in medium conditioned by MCF-7 breast cancer cells compared to IGFBP-3(Pl), but appeared more resistant to the IGFBP-3 protease present in pregnancy serum. IGFBP-3(Ad) also exhibited increased binding to T47D cells which may be related to the glycosylation state of the protein.     

Epigenetic regulation of insulin-like growth factor binding protein-3 (IGFBP-3) in cancer

Epigenetics refers to heritable changes in gene expression that are independent of alterations in DNA sequence. It is now accepted that disruption of epigenetic mechanisms plays a key role in the pathogenesis of cancer: culminating in altered gene function and malignant cellular transformation. DNA methylation and histone modifications are the most widely studied changes but non-coding RNAs such as miRNAs are also considered part of the epigenetic machinery. The insulin-like growth factor (IGF) axis is composed of two ligands, IGF-I and –II, their receptors and six high affinity IGF binding proteins (IGFBPs). The IGF axis plays a key role in cancer development and progression. As IGFBP genes have consistently been identified among the most common to be aberrantly altered in tumours, this review will focus on epigenetic regulation of IGFBP-3 in cancer for which the majority of evidence has been obtained.     

Potential of proteomics towards the investigation of the IGF-independent actions of IGFBP-3

Early investigations into the insulin-like growth factor (IGF)-independent actions of insulin-like growth factor-binding protein (IGFBP)-3 have implicated a large array of signaling proteins with links to cell cycle control and apoptosis. However, the actual mechanism of IGFBP-3 action is still unclear. In an effort to clearly understand the mechanism of IGF-independent IGFBP-3 actions, a proteomic approach to identify the actual proteins involved in interaction with IGFBP-3 from different cell compartments, the phosphorylation status of IGFBP-3 under different physiologic conditions and the proteins upregulated by IGFBP-3 are briefly reviewed. The IGF system is a well-recognized key player in diseases such as cancer, diabetes and malnutrition. It is only after the signaling pathways of the IGF-independent actions of IGFBP-3 are clearly understood that the system can be manipulated to affect these disorders.     

Cervical scrapes levels of insulin-like growth factor-II and insulin-like growth factor binding protein 3 in women with squamous intraepithelial lesions and cervical cancer

A growing number of studies have demonstrated an association between serum levels of insulin-like growth factors (IGFs) and IGF binding protein-3 (IGFBP-3) and increased risk for various cancers. The aim of this study was to evaluate the relationship between levels of IGF-II or IGFBP-3 in cervical scrapes with cervical cancer and precancerous lesions: low-grade squamous intraepithelial lesion (LSIL) and high-grade squamous intraepithelial lesion (HSIL). 4 groups of cases were examined: LSIL (n=20), HSIL (n=28), cervical cancer (n=45), and controls (n=51). Control subjects were women with normal, HPV DNA-negative Papanicolau (Pap) test. IGF-II and IGFBP-3 levels in cervical scrapes were measured by ELISA. Results show that median protein levels of IGF-II were significantly lower in cervical cancer cases vs. controls (446.5 ng/mg vs. 1,168.6 ng/mg, p<0.001). Significantly higher values of IGFBP-3 were found in HSIL vs. controls (median: 549.5 ng/mg vs. 216 ng/mg; p=0.018), and were not affected by HR HPV infection, meanwhile no significant differences were observed in IGFBP-3 levels between LSIL or cervical cancer as compared to controls. These data suggests that the progression to cervical cancer is associated with alterations in the IGF system and not affected by HR HPV infection. More studies are needed to understand the possible role of IGFBP-3 in cervical carcinogenesis.     

Potential of proteomics towards the investigation of the IGF-independent actions of IGFBP-3

Early investigations into the insulin-like growth factor (IGF)-independent actions of insulin-like growth factor-binding protein (IGFBP)-3 have implicated a large array of signaling proteins with links to cell cycle control and apoptosis. However, the actual mechanism of IGFBP-3 action is still unclear. In an effort to clearly understand the mechanism of IGF-independent IGFBP-3 actions, a proteomic approach to identify the actual proteins involved in interaction with IGFBP-3 from different cell compartments, the phosphorylation status of IGFBP-3 under different physiologic conditions and the proteins upregulated by IGFBP-3 are briefly reviewed. The IGF system is a well-recognized key player in diseases such as cancer, diabetes and malnutrition. It is only after the signaling pathways of the IGF-independent actions of IGFBP-3 are clearly understood that the system can be manipulated to affect these disorders.     

Matrix metalloproteinase-7 degrades all insulin-like growth factor binding proteins and facilitates insulin-like growth factor bioavailability

Proteolytic modification of insulin-like growth factor binding proteins (IGFBPs) plays an important physiological role in regulating insulin-like growth factor (IGF) bioavailability. Recently, we demonstrated that matrix metalloproteinase-7 (MMP-7)/Matrilysin produced by various cancer cells catalyzes the proteolysis of IGFBP-3 in vitro and regulates IGF bioavailability, resulting in an anti-apoptotic effect against anchorage-independent culture. In the present study, we investigated whether MMP-7 contributes to proteolysis of the other five IGFBPs, IGFBP-1, IGFBP-2, IGFBP-4, IGFBP-5, and IGFBP-6, and whether this results in phosphorylation of the IGF type 1 receptor (IGF-1R). MMP-7 cleaved all six IGFBPs, resulting in IGF-mediated IGF-1R phosphorylation, which was inhibited by EDTA treatment. These results suggest that MMP-7 derived from cancer cells can regulate IGF bioavailability in the microenvironment surrounding the tumor, where various kinds of IGF/IGFBP complexes are found, thereby favoring cancer cell growth and survival during the processes of invasion and metastasis.     

Insulin-like growth factor-I and binding protein-3 and risk of cancer

Insulin-like growth factor (IGF)-I is an important mitogen required by some cell types to progress from the G1 phase to the S phase of the cell cycle. IGF binding proteins (IGFBPs) can have opposing actions, in part by binding IGF-I, but also by direct inhibitory effects on target cells. As mitogens and anti-apoptotic agents, IGFs may be important in carcinogenesis, possibly by increasing the risk of cellular transformation by enhancing cell turnover. Indeed, many types of neoplastic cells express or overexpress IGF-I receptors, which stimulate mitogenesis when activated by IGF-I in vitro. In vivo, tissue IGF bioactivity is determined not only by circulating IGF-I and IGFBP levels, but also by local production of IGFs, IGFBPs, and possibly IGFBP proteases that enhance IGF-I availability by cleaving IGFBPs. Because determinants of tissue IGF bioactivity appear to be regulated in parallel with circulating IGF-I level, it is reasonable to hypothesize that the substantial intraindividual variability in circulating levels of IGF-I and IGFBP-3 may be important in determining risk of some cancers. In recent epidemiologic studies, relatively high plasma IGF-I and low IGFBP-3 levels have been independently associated with greater risk of prostate cancer in men, breast cancer among premenopausal women, and colorectal adenoma and cancer in men and women and possibly lung cancer. These include prospective data from the Physicians' Health Study and the Nurses' Health Study. In general, two- to fourfold elevated risks have been observed for prostate cancer in men in the top quartile of IGF-I relative to those in the bottom quartile, and low levels of IGFBP-3 were associated with an approximate doubling of risk. For breast cancer, an association with IGF-I for postmenopausal women was not apparent, but strong associations were observed for premenopausal cases in the Nurses' Health Study. Further study is needed to confirm this subgroup finding in women. Recent data also indicate that high IGF-I and low IGFBP-3 increase risk of colorectal cancer and large or villous adenomas. Of note, for colorectal neoplasia, fourfold elevated risks were observed in men and women with low IGFBP-3, whereas high IGF-I was associated with a doubling of risk. These emerging epidemiologic data indicate that high levels of IGF-I and low levels of IGFBP-3 are associated with an increased risk of at least several types of carcinoma that are common in economically developed countries. Further study is required to determine the clinical relevance of these findings.     

Insulin-like growth factor-binding protein-3 plays an important role in regulating pharyngeal skeleton and inner ear formation and differentiation

Insulin-like growth factor-binding protein (IGFBP)-3 is the major insulin-like growth factor (IGF) carrier protein in the bloodstream. IGFBP-3 prolongs the half-life of circulating IGFs and prevents their potential hypoglycemic effect. IGFBP-3 is also expressed in many peripheral tissues in fetal and adult stages. In vitro, IGFBP-3 can inhibit or potentiate IGF actions and even possesses IGF-independent activities, suggesting that local IGFBP-3 may also have paracrine/autocrine function(s). The in vivo function of IGFBP-3, however, is unclear. In this study, we elucidate the developmental role of IGFBP-3 using the zebrafish model. IGFBP-3 mRNA expression is first detected in the migrating cranial neural crest cells and subsequently in pharyngeal arches in zebrafish embryos. IGFBP-3 mRNA is also persistently expressed in the developing inner ears. To determine the role of IGFBP-3 in these tissues, we ablated the IGFBP-3 gene product using morpholino-modified antisense oligonucleotides (MOs). The IGFBP-3 knocked down embryos had delayed pharyngeal skeleton morphogenesis and greatly reduced pharyngeal cartilage differentiation. Knockdown of IGFBP-3 also significantly decreased inner ear size and disrupted hair cell differentiation and semicircular canal formation. Furthermore, reintroduction of a MO-resistant form of IGFBP-3 "rescued" the MO-induced defects. These findings suggest that IGFBP-3 plays an important role in regulating pharyngeal cartilage and inner ear development and growth in zebrafish.     

Role of insulin-like growth factors and their binding proteins in growth control and carcinogenesis

Interest in the role of the insulin-like growth factor (IGF) axis in growth control and carcinogenesis has recently been increased by the finding of elevated serum insulin-like growth factor I (IGF-I) levels in association with three of the most prevalent cancers in the United States: prostate cancer, colorectal cancer, and lung cancer. IGFs serve as endocrine, autocrine, and paracrine stimulators of mitogenesis, survival, and cellular transformation. These actions are mediated through the type 1 IGF-receptor (IGF-1R), a tyrosine kinase that resembles the insulin receptor. The availability of free IGF for interaction with the IGF-1R is modulated by the insulin-like growth factor-binding proteins (IGFBPs). IGFBPs, especially IGFBP-3, also have IGF-independent effects on cell growth. IGF-independent growth inhibition by IGFBP-3 is believed to occur through IGFBP-3-specific cell surface association proteins or receptors and involves nuclear translocation. IGFBP-3-mediated apoptosis is controlled by numerous cell cycle regulators in both normal and disease processes. IGFBP activity is also regulated by IGFBP proteases, which affect the relative affinities of IGFBPs, IGFs and IGF-1R. Perturbations in each level of the IGF axis have been implicated in cancer formation and progression in various cell types.     

Transferrin binds insulin-like growth factors and affects binding properties of insulin-like growth factor binding protein-3.

In the circulation, most of the insulin-like growth factors (IGFs) are bound to a ternary 150 kDa complex with IGF-binding protein (IGFBP)-3 and the acid labile subunit. In the current study, we identify transferrin (Tf) by mass spectrometry, and immunoprecipitation as a component of a major IGF-binding fraction separated from human plasma. IGF ligand blotting, cross-linkage experiments and surface plasmon resonance spectrometry have been used to demonstrate the capability of Tf to bind IGFs specifically. In combination with Tf, IGFBP-3 showed a 5-fold higher affinity for IGF-II than IGFBP-3 alone. The data suggest that Tf may play an important role in regulating IGF/IGFBP-3 functions.     

The IGF axis and programmed cell death.

Insulin-like growth factors (IGF) are mitogenic peptides that have been implicated as positive regulators of cellular proliferation. In recent years, several studies have suggested an additional role for the IGF axis in the regulation of apoptosis. Signalling through the IGF receptor has been shown to have a potent survival function and protect cells from a variety of apoptotic stimuli. The actions of IGF are regulated by a family of high-affinity IGF binding proteins (IGFBP), which sequester the IGF from the IGF receptor. However, there is some evidence that one of these binding proteins, IGFBP-3, may have its own pro-apoptotic effects that are independent of its ability to modulate IGF bioavailability. In addition, it has been suggested that the tumour suppressor p53, a crucial mediator of apoptosis in response to cellular stress, may elicit several of its apoptotic effects through manipulation of components of the IGF axis. This review summarizes what is currently known about the role of the IGF system in the regulation of apoptosis, highlighting its implications in the context of tumorigenesis.     

Distinct patterns of insulin-like growth factor binding protein (IGFBP)-2 and IGFBP-3 expression in oxidant exposed lung epithelial cells

Oxygen (O(2)) species are involved in a large variety of pulmonary diseases. Among the various cell types that compose the lung, the epithelial cells of the alveolar structure appear to be a major target for oxidant injury. Despite their importance in the repair processes, the mechanisms which regulate the replication of the stem cells of the alveolar epithelium, the type 2 cells, remain poorly understood. Based on the results of several studies which have documented the involvement of the insulin-like growth factor (IGF) system in lung epithelial cell replication, and which have also suggested a role for IGF binding proteins (IGFBPs) in the control of cell proliferation, the aim of the present work was to determine whether IGFBPs could be involved in the modulation of growth of human lung epithelial cells exposed to oxidants. Experiments were performed using a human lung adenocarcinoma cell line (A549) which was exposed for various durations to hyperoxia (95% O(2)). We observed a rapid and reversible growth arrest of the cells after only 24 h of O(2) exposure. When oxidant injury was prolonged, growth arrest was followed by induction of apoptosis with activation of the Fas pathway. These effects were associated with an increased expression of IGFBP-2 and IGFBP-3. In addition, study of localization of these proteins revealed distinct patterns of distribution. IGFBP-3 was mainly present in the extracellular compartment. In comparison, the fraction of IGFBP-2 secreted was less abundant whereas the IGFBP-2 fraction in the intracellular compartment appeared stronger. In addition, analysis of the subcellular localization provided data indicating the presence of IGFBP-2 in the nucleus. Taken together these data support a role for IGFBP-2 and IGFBP-3 in the processes of growth arrest and apoptosis in lung epithelial cells upon oxidant exposure. They also suggest that distinct mechanisms may link IGFBP-2 and IGFBP-3 to the key regulators of the cell cycle.     

Role of insulin-like growth factor binding protein-3 (IGFBP-3) in the differentiation of primary human adult skeletal myoblasts

Although muscle satellite cells were identified almost 40 years ago, little is known about the induction of their proliferation and differentiation in response to physiological/pathological stimuli or to growth factors/cytokines. In order to investigate the role of the insulin-like growth factor (IGF)/IGF binding protein (IGFBP) system in adult human myoblast differentiation we have developed a primary human skeletal muscle cell model. We show that under low serum media (LSM) differentiating conditions, the cells secrete IGF binding proteins-2, -3, -4 and -5. Intact IGFBP-5 was detected at days 1 and 2 but by day 7 in LSM it was removed by proteolysis. IGFBP-4 levels were also decreased at day 7 in the presence of IGF-I, potentially by proteolysis. In contrast, we observed that IGFBP-3 initially decreased on transfer of cells into LSM but then increased with myotube formation. Treatment with 20 ng/ml tumour necrosis factor-alpha (TNFalpha), which inhibits myoblast differentiation, blocked IGFBP-3 production and secretion whereas 30 ng/ml IGF-I, which stimulates myoblast differentiation, increased IGFBP-3 secretion. The TNFalpha-induced decrease in IGFBP-3 production and inhibition of differentiation could not be rescued by addition of IGF-I. LongR(3)IGF-I, which does not bind to the IGFBPs, had a similar effect on differentiation and IGFBP-3 secretion as IGF-I, both with and without TNFalpha, confirming that increased IGFBP-3 is not purely due to increased stability conferred by binding to IGF-I. Furthermore reduction of IGFBP-3 secretion using antisense oligonucleotides led to an inhibition of differentiation. Taken together these data indicate that IGFBP-3 supports myoblast differentiation.     

IGFs and human cancer: implications regarding the risk of growth hormone therapy

Perturbations of the insulin-like growth factor (IGF) axis, including the autocrine production of IGFs, IGF binding proteins (IGFBPs) and IGFBP proteases such as prostate specific antigen (PSA), and cathepsin D have been identified in prostate, lung and breast cancer cells and tissues. Serum IGFBP-3 levels have been found to be negatively correlated to the risk of cancer. Interestingly, IGFBP-3 is a potent inhibitor of IGF action and also mediates apoptosis via an IGF-independent mechanism. Recent case-control studies have found an approximately 10% increase in the serum levels of IGF-I in patients with prostate, breast and lung cancers, which are among the most frequently diagnosed cancers. While the studies indicate an association between serum IGF-I levels and cancer risk, causality has not been established. Thus, serum IGF-I level may actually be a confounding variable, serving as a marker for autocrine tissue IGF-I production. Growth hormone (GH) therapy raises both IGF-I and IGFBP-3 levels in serum. However, the role of GH in controlling prostate, breast and lung growth and carcinogenesis remains unclear from animal studies. Increased GH levels as seen in acromegaly have been associated with benign prostatic hyperplasia but not with prostate, breast or lung cancers, although colon cancer mortality may be increased. Should serum IGF-I levels be proven to play a causal role in the pathogenesis of cancer, interpreting the risk associated with therapies such as GH replacement must take into account both the duration of exposure and the risk magnitude associated with the degree of serum IGF-I elevation. Since GH-deficient patients often have a subnormal IGF-I serum level, which normalizes on therapy, their cancer risk on GH therapy probably does not increase substantially above that of the normal population. Until further research in the area dictates otherwise, ongoing surveillance and routine monitoring of IGF-I levels in GH recipients should become standard of care.     

Rapid apoptosis induction by IGFBP-3 involves an insulin-like growth factor-independent nucleomitochondrial translocation of RXRalpha/Nur77

Insulin-like growth factor-binding protein-3 (IGFBP-3) induces apoptosis by its ability to bind insulin-like growth factors (IGFs) as well as its IGF-independent effects involving binding to other molecules including the retinoid X receptor-alpha (RXRalpha). Here we describe that in response to IGFBP-3, the RXRalpha binding partner nuclear receptor Nur77 rapidly undergoes translocation from the nucleus to the mitochondria, initiating an apoptotic cascade resulting in caspase activation within 6 h. This translocation is a type 1 IGF receptor-signaling independent event as IGFBP-3 induces Nur77 translocation in R-cells. IGFBP-3 and Nur77 are additive in inducing apoptosis. GFP-Nur77 transfection into RXRalpha wild-type and knock-out mouse embryonic fibroblasts and subsequent treatment with IGFBP-3 show that RXRalpha is required for IGFBP-3-induced Nur77 translocation and apoptosis. Addition of IGFBP-3 to 22RV1 cell lysates enhanced the ability of GST-RXRalpha to "pull down" Nur77, and overexpression of IGFBP-3 enhanced the accumulation of mitochondrial RXRalpha. This unique nongenotropic nuclear pathway supports an emerging role for IGFBP-3 as a novel, multicompartmental signaling molecule involved in induction of apoptosis in malignant cells.     

Role of N- and C-terminal residues of insulin-like growth factor (IGF)-binding protein-3 in regulating IGF complex formation and receptor activation

Insulin-like growth factor-binding protein-3 (IGFBP-3), the major IGFBP in the circulation, sequesters IGF in a stable ternary complex with the acid-labile subunit. The high affinity IGF-binding site is proposed to reside within an N-terminal hydrophobic domain in IGFBP-3, but C-terminal residues have also been implicated in the homologous protein IGFBP-5. We have mutated in various combinations Leu(77), Leu(80), and Leu(81) in the N terminus and Gly(217) and Gln(223) in the C terminus of IGF-BP-3. All mutants retained immunoreactivity toward a polyclonal IGFBP-3 antibody, whereas IGF ligand blotting showed that all of the mutants had reduced binding to IGFs. Both solution IGF binding assays and BIAcore analysis indicated that mutations to the N-terminal region caused greater reduction in IGF binding activity than C-terminal mutations. The combined N- and C-terminal mutants showed undetectable binding to IGF-I but retained <10% IGF-II binding activity. Reduced ternary complex formation was seen only in mutants that had considerably reduced IGF-I binding, consistent with previous studies indicating that the binary IGF.IGFBP-3 complex is required for acid-labile subunit binding. Decreased IGF binding was also reflected in the inability of the mutants to inhibit IGF-I signaling in IGF receptor overexpressing cells. However, when present in excess, IGFBP-3 analogs defined as non-IGF-binding by biochemical assays could still inhibit IGF signaling. This suggests that residual binding activity of IGFBP-3 mutants may still be sufficient to inhibit IGF biological activity and questions the use of such analogs to study IGF-independent effects of IGFBP-3.     

IGF1(CA)19 and IGFBP-3-202A/C Gene Polymorphism and Cancer Risk: A Meta-analysis

Insulin-like growth factor 1 (IGF1)(CA)19 and insulin-like growth factor-binding protein-3 (IGFBP-3)-202A/C gene polymorphisms had been focused by many epidemiological studies recently, which were associated with common cancer risk including colorectal, breast, prostate, and lung cancer. However, the findings of epidemiological investigations are not coincident. We did a systematic review and meta-analysis of case–control studies, including studies nested in cohorts, of the association between IGF1(CA)19 and IGFBP-3-202A/C gene polymorphism and prostate, colorectal, premenopausal and postmenopausal breast cancer. We identified 17 eligible studies (24 datasets), which included 9,744 cases and 11,332 controls. The result displays that individuals carrying (CA)19 allele had a subtly decreased risk of all cancer sites [OR(95 % CI) 0.92(0.87,0.97); 0.882(0.809,0.962); 0.902(0.849,0.958)] and postmenopausal breast cancer [OR(95 % CI) 0.893(0.832,0.959); 0.834(0.719,0.968); 0.862(0.776,0.958)] in allele contrast model, CA19/CA19 vs. non-CA19/non-CA19 model, and recessive genetic model. In subgroup analysis according to ethnicities, (CA)19 repeat polymorphism had an increased risk of common cancers in Asian [OR (95 % CI) of allele contrast model: 1.105(1.000,1.224); additive model: 1.103(0.844,1.441), 1.197(1.013,1.413); recessive model: 1.039(0.831,1.300); and dominant model: 1.191(1.030,1.376)]. On the other hand, IGFBP-3-202A/C gene polymorphism did not seem to be associated with all the cancer sites in any genetic model and ethnicity. In conclusion, the result of this meta-analysis indicates that the IGF1(CA)19 polymorphism is a candidate gene polymorphism for cancer susceptibility regardless of environmental factors, especially in Asian.     

Hypoxia impairs primordial germ cell migration in zebrafish (Danio rerio) embryos

Background

As a global environmental concern, hypoxia is known to be associated with many biological and physiological impairments in aquatic ecosystems. Previous studies have mainly focused on the effect of hypoxia in adult animals. However, the effect of hypoxia and the underlying mechanism of how hypoxia affects embryonic development of aquatic animals remain unclear.

Methodology/Principal Findings

In the current study, the effect of hypoxia on primordial germ cell (PGC) migration in zebrafish embryos was investigated. Hypoxic embryos showed PGC migration defect as indicated by the presence of mis-migrated ectopic PGCs. Insulin-like growth factor (IGF) signaling is required for embryonic germ line development. Using real-time PCR, we found that the mRNA expression levels of insulin-like growth factor binding protein (IGFBP-1), an inhibitor of IGF bioactivity, were significantly increased in hypoxic embryos. Morpholino knockdown of IGFBP-1 rescued the PGC migration defect phenotype in hypoxic embryos, suggesting the role of IGFBP-1 in inducing PGC mis-migration.

Conclusions/Significance

This study provides novel evidence that hypoxia disrupts PGC migration during embryonic development in fish. IGF signaling is shown to be one of the possible mechanisms for the causal link between hypoxia and PGC migration. We propose that hypoxia causes PGC migration defect by inhibiting IGF signaling through the induction of IGFBP-1.