Developmentally regulated expression of IGF binding protein-3 (IGFBP-3) in human placental fibroblasts: effect of exogenous IGFBP-3 on IGF-1 action

Role of EZH2-mediated H3K27me3 in placental ADAM12-S expression: implications for fetoplacental growth

BACKGROUND

Enhancer of zeste homolog 2 (EZH2)-mediated histone 3 lysine 27 trimethylation (H3K27me3) is a transcription silencing mark, which is indispensable for cell lineage specification at the early blastocyst stage. This epigenetic repression is maintained in placental cytotrophoblasts but is lifted when cytotrophoblasts differentiate into syncytiotrophoblasts. However, the physiological impact of this lift remains elusive. Here, we investigated whether lifting EZH2-mediated H3K27me3 during syncytialization upregulates the expression of a short secretory isoform of a disintegrin and metalloprotease 12 (ADAM12-S), a well-recognized placenta-derived protease that cleaves insulin-like growth factor binding protein 3 to increase insulin-like growth factor (IGF) bioavailability for the stimulation of fetoplacental growth. The transcription factor and the upstream signal involved were also explored.

METHODS

Human placenta tissue and cultured primary human placental cytotrophoblasts were utilized to investigate the role of EZH2-mediated H3K27me3 in ADAM12-S expression and the associated transcription factor and upstream signal during syncytialization. A mouse model was used to examine whether inhibition of EZH2-mediated H3K27me3 regulates placental ADAM12-S expression and fetoplacental growth.

RESULTS

EZH2 and ADAM12 are distributed primarily in villous cytotrophoblasts and syncytiotrophoblasts, respectively. Increased ADAM12-S expression, decreased EZH2 expression, and decreased EZH2/H3K27me3 enrichment at the ADAM12 promoter were observed during syncytialization. Knock-down of EZH2 further increased ADAM12-S expression in trophoblasts. Syncytialization was also accompanied by increased STAT5B expression and phosphorylation as well as its enrichment at the ADAM12 promoter. Knock-down of STAT5B attenuated ADAM12-S expression during syncytialization. Epidermal growth factor (EGF) was capable of inducing ADAM12-S expression via stimulation of STAT5B expression and phosphorylation during syncytialization. Mouse studies revealed that administration of an EZH2 inhibitor significantly increased ADAM12-S levels in maternal blood and fetoplacental weights along with decreased H3K27me3 abundance and increased ADAM12-S expression in the placenta.

CONCLUSIONS

Lifting EZH2-mediated H3K27me3 increases ADAM12-S expression during syncytialization with the participation of EGF-activated STAT5B, which may lead to elevation of ADAM12-S level in maternal blood resulting in increased IGF bioavailability for the stimulation of fetoplacental growth in pregnancy. Our studies suggest that the role of EZH2-mediated H3K27me3 may switch from cell lineage specification at the early blastocyst stage to regulation of fetoplacental growth in later gestation.

Embryo gene expression in pig pregnancy

Pregnancy is a complex process in which significant changes occur continually in both the corpora lutea and in the endometrium of the females and varies depending on the embryonic, pre-implantation or foetal stages. In the embryonic stages, the majority of genes expressed in the pig embryo correspond to the loss of cellular pluripotency. In contrast, the implantation consists of three phases: elongation of the conceptus, adhesion and union of the embryo to the endometrial epithelium. During these phases, many factors are expressed, including growth factors, molecules that facilitate adhesion and cytokines. All these changes are ultimately regulated by different lipid and hormonal substances, specifically by progesterone, oestradiol and prostaglandins, which regulate the expression of many proteins necessary for the development of the embryo, endometrial remodelling and embryo-maternal communication. This paper is a review of primary gene regulatory mechanisms in pigs during different stages of implantation.

Placental IGF-1 and IGFBP-3 expression correlate with umbilical cord blood PAH and PBDE levels from prenatal exposure to electronic waste

Electronic waste recycling produces Polycyclic Aromatic Hydrocarbons (PAHs) and Polybrominated Diphenyl Ethers (PBDEs) which may affect fetal growth and development by altering the insulin-like-growth factor (IGF) system. Questionnaires were administered to pregnant women (Guiyu, an e-waste site, n = 101; control, n = 53), and umbilical cord blood (UCB) and placentas were collected upon delivery. PBDEs and PAHs in UCB and placental IGF-1 and IGFBP-3 mRNA levels were analyzed using GC-MS and real-time PCR, respectively. Infant birth length and Apgar scores were lower in Guiyu. All PAHs (except Fl, Chr, IP, BbF and BP), total 16-PAHs, total/individual PBDEs, placental IGF-1 (median 0.23 vs 0.19; P < 0.05) and IGFBP-3 (median 1.91 vs 0.68; P < 0.001) levels were significantly higher in Guiyu. Spearman correlation showed that BDE-154, BDE-209 and ∑5ring-PAHs positively correlate with IGF-1 while PBDEs, 4 rings and total PAHs correlate with IGFBP-3 expression. Increased placental IGF-1 level might indirectly affect fetal growth and development.

IGF-1 receptor and IGF binding protein-3 might predict prognosis of patients with resectable pancreatic cancer

BACKGROUND

The present study aimed to elucidate the clinicopathologic role of insulin-like growth factor-1 receptor (IGF1R) and IGF binding protein-3 (IGFBP3) in patients with pancreatic cancer. The function of IGFBP3 is controversial, because both inhibition and facilitation of the action of IGF as well as IGF-independent effects have been reported. In this study, IGF1R and IGFBP3 expression was examined, and their potential roles as prognostic markers in patients with pancreatic cancer were evaluated.

METHODS

Clinicopathological features of 122 patients with curatively resected pancreatic cancer were retrospectively reviewed, and expression of IGF1R and IGFBP3 was immunohistochemically analyzed.

RESULTS

Expression of IGF1R and IGFBP3 was observed in 50 (41.0%) and 37 (30.3%) patients, respectively. IGF1R expression was significantly associated with histological grade (p = 0.037). IGFBP3 expression had a significant association with tumor location (p = 0.023), and a significant inverse association with venous invasion (p = 0.037). Tumors with IGF1R-positive and IGFBP3-negative expression (n = 32) were significantly frequently Stage II and III (p = 0.011). The prognosis for IGF1R positive patients was significantly poorer than that for IGF1R negative patients (p = 0.0181). IGFBP3 protein expression did not correlate significantly with patient survival. The subset of patients with both positive IGF1R and negative IGFBP3 had worse overall survival (8.8 months versus 12.6 months, respectively, p < 0.001).

CONCLUSION

IGF1R signaling might be associated with tumor aggressiveness, and IGFBP3 might show antiproliferative effects in pancreatic cancer. Both high IGF1R expression and low IGFBP3 expression represent useful prognostic markers for patients with curatively resected pancreatic cancer.

Transforming growth factor-{beta} (TGF{beta}) receptors I/II differentially regulate TGF{beta}1 and IGF-binding protein-3 mitogenic effects in the human placenta

Maternal IGFs regulate cytotrophoblast proliferation and, thereby, placental growth and function. IGF bioavailability is controlled by IGF-binding proteins (IGFBPs); in placenta, IGFBP-3 is particularly abundant. In other systems, IGFBP-3 can regulate cellular events independently of IGFs; these effects are thought to be mediated by TGFbeta receptors (TbetaR). We have examined IGFBP-3 regulation of IGF-dependent and -independent cytotrophoblast proliferation in first-trimester placental explants and the role of TbetaRII in mediating these effects. In the presence of IGFBP-3 (50 nm), IGF-induced (10 nm) proliferation (monitored by immunohistochemical analysis of Ki67 expression and bromodeoxyuridine incorporation) was significantly reduced (P < 0.05). IGFBP-3 also reduced basal proliferation independently of IGF receptor signaling. Immunohistochemical analysis demonstrated that TGFbeta signaling molecules [TGFbeta receptor I (TbetaRI), TbetaRII, TbetaRV, Smad-2, and ERK] are expressed in syncytium and/or cytotrophoblast. TGFbeta1 (10 ng/ml) enhanced cytotrophoblast proliferation and activated both Smad-2 and ERK-1/2, whereas IGFBP-3 activated only Smad-2. The function of both TGFbeta1 and IGFBP-3 was attenuated by a TbetaRII function-blocking antibody and by small interfering RNA-mediated knockdown of TbetaRII (P < 0.05); this was accompanied by a reduction in Smad-2 activation. This study demonstrates that both TGFbeta1 and IGFBP-3 signal through TbetaRI/II to influence human cytotrophoblast proliferation. However, downstream pathways are distinct, because IGFBP-3 acts only through Smad-2, whereas TGFbeta1 also phosphorylates ERK, resulting in opposite effects on cytotrophoblast proliferation. The effects of maternal growth signals on placental growth and function therefore depend on the balance of ligands, receptors, and signaling molecules at the syncytiotrophoblast surface. Therapeutic manipulation of this balance might offer a strategy to optimize placental development and pregnancy outcome.

The IGF axis and placental function. a mini review

It is well known that the insulin-like growth factor (IGF) axis is an important regulator of foetal growth and in recent years, it has been suggested that the ligands IGF-I and IGF-II may, in part, mediate this effect by promoting proper placental development and function. In other tissues, IGF effects on metabolism, proliferation and differentiation are primarily mediated via IGF binding protein-regulated interaction of IGFs with the type 1 IGF receptor and therefore here, we review the placental expression and postulated role, of each of the IGF axis components and discuss the cellular mechanisms through which these effects are exerted.

Characterization of gene expression profiles in early bovine pregnancy using a custom cDNA microarray

Gene expression analysis comparing nonpregnant with pregnant bovine uteri, including placenta, was performed with a custom cDNA microarray containing 1,933 independent genes. These genes were classified into six categories according to biological function, as follows: cell and tissue structural dynamics (108 genes), intercellular communication (221), intracellular metabolism (265), cell cycle and apoptosis (26), regulation of gene expression (113), expressed sequence tag (EST) and function unknown (617), and uncomplemented genes (583 clones). This array possessed bovine placental/endometrial specificity, as it included many pregnancy-specific molecules, such as pregnancy-associated glycoprotein-1 (PAGs), placental lactogen (PLs), and prolactin-related protein-1 (PRPs). A total of 77 genes were induced and 12 repressed in the placenta/endometrium. Our results point to a fundamental role for bovine placental-specific genes such as PAGs, PLs, and PRPs, in implantation and placentogenesis, and document that cDNA microarray analysis from bovine placenta/endometrium is possible and is a specific tool for monitoring genome-wide gene expression during the establishment and maintenance of pregnancy.

Insulin-like growth factor (IGF) binding protein-3 potentiation of IGF action is mediated through the phosphatidylinositol-3-kinase pathway and is associated with alteration in protein kinase B/AKT sensitivity

Cell-association and processing of insulin-like growth factor binding protein-3 (IGFBP-3) by cultured bovine fibroblasts results in markedly enhanced type I IGF receptor signaling at a step distal to ligand binding. The purpose of the present study was to determine the intracellular mediators of IGFBP-3's potentiating effect. Preincubation of cultured bovine fibroblasts with 50 nM IGFBP-3 had no effect alone, but enhanced by 3- to 4-fold IGF-I-stimulated 3H-aminoisobutryric acid (AIB) uptake. IGFBP-3-induced potentiation was specifically prevented if an inhibitor of phosphatidylinositol 3 (PI3)-kinase activation (LY294002), but not an inhibitor of mitogen-activated protein kinase activation (PD98059), was present during the preincubation period. IGFBP-3 did not directly activate the downstream effector of PI3-kinase, protein kinase B (PKB)/Akt. However, the sensitivity of PKB/Akt to activation by IGF-I was increased by 2- to 4-fold with IGFBP-3 pretreatment. This increased sensitivity was accompanied by altered mobility of PKB/Akt on SDS-polyacrylamide gels, suggestive of a diminished phosphorylation state. Consistent with this, okadaic acid, a potent serine/threonine phosphatase inhibitor, was able to block the potentiation effect of IGFBP-3 and prevent the altered mobility of the PKB/Akt molecule in response to IGFBP-3 treatment. PKB/Akt immunoprecipitated from IGFBP-3-pretreated cells was no longer recognized by an antibody specific for phosphorylated threonine followed by proline. These data indicate that IGFBP-3 modulates type I IGF receptor signaling through an effect on PI-3-kinase pathway substrates and suggest a novel mechanism of dephosphorylation whereby PKB/Akt is transformed into a more sensitive substrate of type I IGF receptor signaling.

Insulin-like growth factor binding protein-3: its biological effect on bovine granulosa cells

This study was aimed at testing the hypothesis that insulin-like growth factor binding protein (IGFBP)-3 can modulate hormone-dependent differentiation of granulosa cells in vitro. Granulosa cells from small (1 to 5 mm) follicles were collected from cattle, cultured for 2 d in medium containing 10% fetal calf serum, washed, and then treated for an additional 2 d in serum-free medium with follicle-stimulating hormone (FSH) (50 ng/ml), recombinant human IGF-I (0, 1.3, 4.0, or 13.3 nM), or recombinant human IGFBP-3 (0 to 4.26 nM). In one series of experiments, IGFBP-3 (0.53 and 2.13 nM) inhibited (51% to 92% decreases; P < 0.05) progesterone and estradiol production induced by 1.3 nM of IGF-I, but did not influence (P > 0.10) granulosa cell numbers or steroidogenesis in the absence of IGF-I. Only 4.26 nM of IGFBP-3 inhibited (by 35%) the increase in granulosa cell numbers induced by 1.3 nM of IGF-I. In another series of experiments, 13.3 nM of IGF-I, but not 4.0 nM of IGF-I, was able to completely overcome the inhibitory effect of 4.26 nM of IGFBP-3 on estradiol production. The increase in cell numbers induced by 4.0 and 13.3 nM of IGF-I was attenuated (P < 0.001) by 4.26 nM of IGFBP-3. In a third series of experiments, IGFBP-3 inhibited 125I-IGF-I binding to granulosa cells. These results indicate that IGFBP-3 has a pronounced inhibitory effect on IGF-I action in cultured bovine granulosa cells, and that this inhibitory effect is likely attributable to IGFBP-3 binding/sequestering IGF-I. Thus, IGFBP-3 may play a significant role in regulating granulosa cell proliferation and steroidogenesis during follicular development in cattle.

Membrane-associated insulin-like growth factor-binding protein-3 inhibits insulin-like growth factor-I-induced insulin-like growth factor-I receptor signaling in ishikawa endometrial cancer cells

The function of cell surface-associated insulin-like growth factor-binding proteins (IGFBPs) is controversial. Both inhibition and facilitation of IGF action as well as IGF-independent effects have been reported. We examined the influence of endogenous cell surface-associated IGFBPs on IGF-I receptor (IGF-IR) function in Ishikawa endometrial cancer cells by comparing the effects of IGF-I and its truncated analog des-(1-3)-IGF-I on several components of the IGF-IR signal transduction pathway in the absence of significant amounts of soluble IGFBPs. IGF-I and des-(1-3)-IGF-I are known to have similar affinities for IGF-IR, although the affinity of des-(1-3)-IGF-I for IGFBPs is greatly reduced. Here we show that the two ligands were equipotent not only in IGF-IR binding but also in receptor activation in NIH 3T3 cells overexpressing IGF-IR and possessing a relatively small number of cell surface-associated IGFBPs. In contrast, des-(1-3)-IGF-I manifested a remarkably higher potency as compared with IGF-I in inducing short and middle term cellular responses in IGF-IR-transfected Ishikawa endometrial cancer cells possessing a high number of both the receptor and the cell membrane-bound IGFBP-3. Thus, this difference in the effects of IGF-I and des-(1-3)-IGF-I can be attributed to the attenuation of IGF-I-mediated IGF-IR signaling by membrane-bound IGFBP-3.