Molecular regulation of the IGF-binding protein-4 protease system in human fibroblasts: identification of a novel inducible inhibitor

Proteomics Studies in Gestational Diabetes Mellitus: A Systematic Review and Meta-Analysis

Gestational Diabetes Mellitus (GDM) is the most common metabolic complication during pregnancy and is associated with serious maternal and fetal complications such as pre-eclampsia and stillbirth. Further, women with GDM have approximately 10 times higher risk of diabetes later in life. Children born to mothers with GDM also face a higher risk of childhood obesity and diabetes later in life. Early prediction/diagnosis of GDM leads to early interventions such as diet and lifestyle, which could mitigate the maternal and fetal complications associated with GDM. However, no biomarkers identified to date have been proven to be effective in the prediction/diagnosis of GDM. Proteomic approaches based on mass spectrometry have been applied in various fields of biomedical research to identify novel biomarkers. Although a number of proteomic studies in GDM now exist, a lack of a comprehensive and up-to-date meta-analysis makes it difficult for researchers to interpret the data in the existing literature. Thus, we undertook a systematic review and meta-analysis on proteomic studies and GDM. We searched MEDLINE, EMBASE, Web of Science and Scopus from inception to January 2022. We searched Medline, Embase, CINHAL and the Cochrane Library, which were searched from inception to February 2021. We included cohort, case-control and observational studies reporting original data investigating the development of GDM compared to a control group. Two independent reviewers selected eligible studies for meta-analysis. Data collection and analyses were performed by two independent reviewers. The PROSPERO registration number is CRD42020185951. Of 120 articles retrieved, 24 studies met the eligibility criteria, comparing a total of 1779 pregnant women (904 GDM and 875 controls). A total of 262 GDM candidate biomarkers (CBs) were identified, with 49 CBs reported in at least two studies. We found 22 highly replicable CBs that were significantly different (nine CBs were upregulated and 12 CBs downregulated) between women with GDM and controls across various proteomic platforms, sample types, blood fractions and time of blood collection and continents. We performed further analyses on blood (plasma/serum) CBs in early pregnancy (first and/or early second trimester) and included studies with more than nine samples (nine studies in total). We found that 11 CBs were significantly upregulated, and 13 CBs significantly downregulated in women with GDM compared to controls. Subsequent pathway analysis using Database for Annotation, Visualization and Integrated Discovery (DAVID) bioinformatics resources found that these CBs were most strongly linked to pathways related to complement and coagulation cascades. Our findings provide important insights and form a strong foundation for future validation studies to establish reliable biomarkers for GDM.

IGFBP-4 and PAPP-A in normal physiology and disease

Insulin-like growth factor (IGF) binding protein-4 (IGFBP-4) is a modulator of the IGF system, exerting both inhibitory and stimulatory effects on IGF-induced cellular growth. IGFBP-4 is the principal substrate for the enzyme pregnancy-associated plasma protein-A (PAPP-A). Through IGF-dependent cleavage of IGFBP-4 in the vicinity of the IGF receptor, PAPP-A is able to increase IGF bioavailability and stimulate IGF-mediated growth. Recently, the stanniocalcins (STCs) were identified as novel inhibitors of PAPP-A proteolytic activity, hereby adding additional members to the seemingly endless list of proteins belonging to the IGF family. Our understanding of these proteins has advanced throughout recent years, and there is evidence to suggest that the role of IGFBP-4 and PAPP-A in defining the relationship between total IGF and IGF bioactivity can be linked to a number of pathological conditions. This review provides an overview of the experimental and clinical findings on the IGFBP-4/PAPP-A/STC axis as a regulator of IGF activity and examines the conundrum surrounding extrapolation of circulating concentrations to tissue action of these proteins. The primary focus will be on the biological significance of IGFBP-4 and PAPP-A in normal physiology and in pathophysiology with emphasis on metabolic disorders, cardiovascular diseases, and cancer. Finally, the review assesses current new trajectories of IGFBP-4 and PAPP-A research.

Insulin- like Growth Factor-Binding Protein Action in Bone Tissue: A Key Role for Pregnancy- Associated Plasma Protein-A

The insulin-like growth factor (IGF) axis is required for the differentiation, development, and maintenance of bone tissue. Accordingly, dysregulation of this axis is associated with various skeletal pathologies including growth abnormalities and compromised bone structure. It is becoming increasingly apparent that the action of the IGF axis must be viewed holistically taking into account not just the actions of the growth factors and receptors, but also the influence of soluble high affinity IGF binding proteins (IGFBPs).There is a recognition that IGFBPs exert IGF-dependent and IGF-independent effects in bone and other tissues and that an understanding of the mechanisms of action of IGFBPs and their regulation in the pericellular environment impact critically on tissue physiology. In this respect, a group of IGFBP proteinases (which may be considered as ancillary members of the IGF axis) play a crucial role in regulating IGFBP function. In this model, cleavage of IGFBPs by specific proteinases into fragments with lower affinity for growth factor(s) regulates the partition of IGFs between IGFBPs and cell surface IGF receptors. In this review, we examine the importance of IGFBP function in bone tissue with special emphasis on the role of pregnancy associated plasma protein-A (PAPP-A). We examine the function of PAPP-A primarily as an IGFBP-4 proteinase and present evidence that PAPP-A induced cleavage of IGFBP-4 is potentially a key regulatory step in bone metabolism. We also highlight some recent findings with regard to IGFBP-2 and IGFBP-5 (also PAPP-A substrates) function in bone tissue and briefly discuss the actions of the other three IGFBPs (-1, -3, and -6) in this tissue. Although our main focus will be in bone we will allude to IGFBP activity in other cells and tissues where appropriate.

Prospects of electrochemical immunosensors for early diagnosis of preeclampsia

Preeclampsia is a vascular multisystem disorder that accounts for varying degree of morbidity and mortality of mother and the fetus. This can be significantly averted if diagnosed at an early (18-20 weeks) stage of gestation, as there is no known way to prevent preeclampsia. In spite of extensive work on biomarker discovery, the existing method for its detection is mostly based on colorimetric immunoassays whose sensitivity is ranging in nanomolar range. Further, it has also been observed that change in the expression of a single biomarker is not sufficient to diagnose this condition. So, for early diagnosis (by 18-20 weeks), an immuno-diagnostic platform with detection limits in picomolar range and beyond along with the ability to do simultaneous detection of multiple analyte would be of great importance. A nano-immunosensors with an electrochemical readout system can be a potential alternative that promises for the ultrasensitive detection of analyte with high specificity as well as suitability for on-site analysis. Coupling the lateral flow technology with immunosensors would make it feasible to detect more than one biomarker simultaneously on a microchip. This review intends to summarize the potential preeclampsia biomarkers, limitations of existing diagnostic methods along with the recent advancements, and prospects to develop electrochemical immunosensors for early clinical diagnosis.

Potential markers of preeclampsia--a review

Preeclampsia is a leading cause of maternal and fetal/neonatal mortality and morbidity worldwide. The early identification of patients with an increased risk for preeclampsia is therefore one of the most important goals in obstetrics. The availability of highly sensitive and specific physiologic and biochemical markers would allow not only the detection of patients at risk but also permit a close surveillance, an exact diagnosis, timely intervention (e.g. lung maturation), as well as simplified recruitment for future studies looking at therapeutic medications and additional prospective markers. Today, several markers may offer the potential to be used, most likely in a combinatory analysis, as predictors or diagnostic tools. We present here the current knowledge on the biology of preeclampsia and review several biochemical markers which may be used to monitor preeclampsia in a future, that, we hope, is not to distant from today.

Duplication and diversification of the hypoxia-inducible IGFBP-1 gene in zebrafish

Background

Gene duplication is the primary force of new gene evolution. Deciphering whether a pair of duplicated genes has evolved divergent functions is often challenging. The zebrafish is uniquely positioned to provide insight into the process of functional gene evolution due to its amenability to genetic and experimental manipulation and because it possess a large number of duplicated genes.

Methodology/Principal Findings

We report the identification and characterization of two hypoxia-inducible genes in zebrafish that are co-ortholgs of human IGF binding protein-1 (IGFBP-1). IGFBP-1 is a secreted protein that binds to IGF and modulates IGF actions in somatic growth, development, and aging. Like their human and mouse counterparts, in adult zebrafish igfbp-1a and igfbp-1b are exclusively expressed in the liver. During embryogenesis, the two genes are expressed in overlapping spatial domains but with distinct temporal patterns. While zebrafish IGFBP-1a mRNA was easily detected throughout embryogenesis, IGFBP-1b mRNA was detectable only in advanced stages. Hypoxia induces igfbp-1a expression in early embryogenesis, but induces the igfbp-1b expression later in embryogenesis. Both IGFBP-1a and -b are capable of IGF binding, but IGFBP-1b has much lower affinities for IGF-I and -II because of greater dissociation rates. Overexpression of IGFBP-1a and -1b in zebrafish embryos caused significant decreases in growth and developmental rates. When tested in cultured zebrafish embryonic cells, IGFBP-1a and -1b both inhibited IGF-1-induced cell proliferation but the activity of IGFBP-1b was significantly weaker.

Conclusions/Significance

These results indicate subfunction partitioning of the duplicated IGFBP-1 genes at the levels of gene expression, physiological regulation, protein structure, and biological actions. The duplicated IGFBP-1 may provide additional flexibility in fine-tuning IGF signaling activities under hypoxia and other catabolic conditions.

Differential regulation of pregnancy associated plasma protein-A in human coronary artery endothelial cells and smooth muscle cells

BACKGROUND

Pregnancy-associated plasma protein-A (PAPP-A), a metalloproteinase that serves to modulate local insulin-like growth factor (IGF) action, is upregulated in atherosclerotic plaque. However, little is known about the cellular mechanisms underlying this elevated PAPP-A.

OBJECTIVE

To continue study of PAPP-A expression and its regulation in human vascular cells, with a focus on endothelial cells.

DESIGN

Primary cultures of human coronary artery endothelial cells (ECs) were treated without and with cytokines, growth factors, or low density lipoprotein (LDL). PAPP-A mRNA, protein, and protease activity were assessed using real-time PCR, ultra-sensitive PAPP-A ELISA and cell-free proteolysis of IGF binding protein (IGFBP-4), respectively. In addition, vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), monocyte chemotactic protein (MCP-1), IGF-I, IGF-I receptor, and IGFBP-4 and -5 mRNA expression levels were determined.

RESULTS

ECs in culture show little basal PAPP-A expression. The pro-inflammatory cytokines, tumor necrosis factor (TNF)-alpha and interleukin (IL)-beta, stimulated PAPP-A expression (TNF-alpha>>IL-1beta), whereas there was no effect of IL-6, transforming growth factor-beta, IGF-I, insulin, fibroblast growth factor or epidermal growth factor in these cells. Stimulation of PAPP-A expression by TNF-alpha was associated with significantly increased VCAM, ICAM, and MCP-1 expression but without major changes in other IGF system components. TNF-alpha-induced VCAM, ICAM, and MCP-1 expression (4h) preceded PAPP-A expression (24h). The anti-oxidant, N-acetyl cysteine, inhibited TNF-alpha-induced PAPP-A expression without altering the induction in VCAM, ICAM, and MCP-1. Treatment with native or oxidized LDL had no effect on PAPP-A expression in ECs. Comparative results in human coronary smooth muscle cells indicated qualitative and quantitative differences in PAPP-A expression and regulation between the two vascular cell types.

CONCLUSIONS

Human coronary artery ECs express PAPP-A mRNA and functional protein when activated by the pro-inflammatory cytokine, TNF-alpha. This study complements work on PAPP-A expression in human coronary artery SMCs and human monocyte-derived macrophages and suggests an interactive model of PAPP-A regulation and action in human atherosclerotic plaque.

Stromally expressed c-Jun regulates proliferation of prostate epithelial cells

Stromal-epithelial interactions play a critical role in development of benign prostatic hyperplasia. We have previously shown that stromal cells associated with prostatic carcinoma can potentiate proliferation and reduce cell death of prostatic epithelial cells. Genetic alterations in stromal cells affect stromal-epithelial interactions and modulate epithelial growth. The c-Jun proteins that are early transcription factor molecules have been shown to regulate stromal-epithelial interactions via paracrine signals. Moreover, the Jun-family member proteins have been shown to play an important role in proper development of the genitourinary organs. In this study, we show that c-Jun protein in fibroblasts regulates production and paracrine signals of insulin-like growth factor-1 (IGF-1). c-jun(+/+) fibroblasts secrete higher levels of IGF-1 and stimulate benign prostatic hyperplasia-1 cellular proliferation. In addition, stromally produced IGF-1 up-regulates epithelial mitogen-activated protein kinase, Akt, and cyclin D protein levels while down-regulating the cyclin-dependent kinase inhibitor p27. These data suggest that stromally expressed c-Jun may promote prostatic epithelial proliferation through IGF-1 as a paracrine signal that, in turn, can promote prostate epithelial proliferation. Identification of the signal transduction pathways between prostate epithelial cells and the surrounding stromal cells will improve our understanding of the normal and abnormal biology in prostatic diseases.

Surface association of pregnancy-associated plasma protein-A accounts for its colocalization with activated macrophages

Intense immunostaining for pregnancy-associated plasma protein-A (PAPP-A), a newly characterized metalloproteinase in the insulin-like growth factor system, colocalizes with activated macrophages in human atherosclerotic plaque. To determine macrophage regulation of PAPP-A expression, we developed two models of human macrophages with basal and activated phenotypes. THP-1 cells and peripheral blood monocytes could be differentiated into macrophages and activated upon specific treatment regimens with phorbol myristate acetate, macrophage colony-stimulating factor, and interleukin-1β. Activation was assessed by cell secretion of tumor necrosis factor-α, which increased 30- to 100-fold with activation. Activated macrophages also secreted matrix metalloproteinase-9. However, no PAPP-A mRNA or PAPP-A antigen could be detected in these cells under any condition. Upon incubation with recombinant PAPP-A, we found that activated macrophages bound and internalized more PAPP-A than unactivated macrophages or monocytes. Internalization accounted for at least 50% of macrophage-associated PAPP-A, as assessed in studies with cytochalasin B. Membrane-bound PAPP-A retained protease activity, whereas internalized PAPP-A had little or no activity. Similar experiments carried out with a mutated variant of PAPP-A, which retains functionality as a protease but is unable to bind surface-associated glycosaminoglycan, showed no macrophage association or internalization. Absence of PAPP-A expression was confirmed in activated macrophages isolated from a hypercholesterolemic rabbit model of atherosclerosis. We therefore conclude that PAPP-A is not synthesized in, but rather is bound and internalized by, macrophages. Our findings likely account for the observed intense immunostaining for PAPP-A colocalizing with activated macrophages and may have physiological significance in the development of vulnerable plaque.

Pregnancy-Associated Plasma Protein-A Is Markedly Expressed by Monocyte-Macrophage Cells in Vulnerable and Ruptured Carotid Atherosclerotic Plaques

OBJECTIVES

The study aim was to evaluate serologic expression of pregnancy-associated protein-A (PAPP-A) in patients affected by cerebrovascular accidents and to correlate it with histopathologic carotid plaque complexity.

BACKGROUND

Little is known about PAPP-A expression in carotid atherosclerotic disease and whether this protein represents a marker of plaque vulnerability also in carotid district.

METHODS

Seventy-two carotid plaques from patients submitted to surgical endarterectomy (19 who suffered a major stroke, 24 transient ischemic attack, and 29 asymptomatic) were evaluated. Serologic PAPP-A levels were determined by enzyme-linked immunoadsorbent assay. Plaques were divided in three groups based on histology: 1) stable (n = 38); 2) vulnerable (n = 13); 3) ruptured with thrombus (n = 14). Immunohistochemical staining for PAPP-A, smooth muscle cells, macrophages, and T-lymphocytes was performed in all cases. Real-time polymerase chain reaction assessed local PAPP-A production, and double immunofluorescence confocal microscopy (ICM) characterized cell type expressing PAPP-A.

RESULTS

Pregnancy-associated protein-A (serologic values were 4.02 +/- 0.18 mIU/l in Group 1, 7.43 +/- 0.97 mIU/l in Group 2, and 6.97 +/- 0.75 mIU/l in Group 3 [1 vs. 3, p = 0.01; 1 vs. 2, p = 0.004; 2 vs. 3, p = 0.71, respectively]). Pregnancy-associated protein-A (expression showed a mean score value of 0.62 +/- 0.06 for stable plaques, 2.54 +/- 0.14 for vulnerable plaques, and 2.71 +/- 0.12 for ruptured plaques [1 vs. 2, p = 0.001; 1 vs. 3, p = 0.001; 2 vs. 3, p = 0.37, respectively]). Real-time polymerase chain reaction demonstrated local messenger ribonucleic acid PAPP-A production, and double ICM confirmed monocyte/macrophage expression of PAPP-A in Groups 2 and 3 but not Group 1.

CONCLUSIONS

This study suggests that PAPP-A is a marker of carotid plaque destabilization and rupture. Further studies are necessary to determine if PAPP-A can represents a new target for stratifying the risk of cerebrovascular events.

Cytokine stimulation of pregnancy-associated plasma protein A expression in human coronary artery smooth muscle cells: inhibition by resveratrol

Through specific cleavage of proteins that bind and inhibit insulin-like growth factor-I (IGF-I), pregnancy-associated plasma protein-A (PAPP-A) enhances local IGF-I availability, and, consequently, receptor activation. PAPP-A expression is increased in experimental models of vascular injury and in human atherosclerotic plaque; however, little is known about the regulation of PAPP-A gene expression in vascular cells. In this study, we tested the hypothesis that proinflammatory cytokines involved in the vascular injury response stimulate PAPP-A gene expression in human coronary artery smooth muscle cells (hCASMC) in culture. Tumor necrosis factor (TNF)-α and interleukin (IL)-1β stimulated PAPP-A gene expression in a time- and dose-dependent manner. The effect of these cytokines appears to be at the level of transcription because actinomycin D completely prevented the induction of PAPP-A gene expression. Accumulation of PAPP-A in cell-conditioned medium paralleled mRNA synthesis, as did proteolytic activity against IGF binding protein-4 (IGFBP-4). Interestingly, pretreatment of hCASMC with resveratrol, a polyphenol found in the skin of grapes and in red wine purported to underlie the “French paradox,” inhibited TNF-α- and IL-1β-induced PAPP-A expression and, hence, its IGFBP-4 proteolytic activity. Resveratrol had no effect on basal PAPP-A expression and protease activity. Our finding that PAPP-A gene expression in hCASMC is stimulated by TNF-α and IL-1β suggests a mechanism for the regulation of PAPP-A in response to vascular injury that may contribute to the enhanced IGF-I bioactivity in intimal hyperplasia and atherosclerotic plaque development. Our results also suggest that PAPP-A may be a target of the cardiovascular system-protective effects of resveratrol.

Studies on regulation of IGF (insulin-like growth factor)-binding protein (IGFBP) 4 proteolysis by pregnancy-associated plasma protein-A (PAPP-A) in cells treated with phorbol ester

PAPP-A (pregnancy-associated plasma protein-A) is produced by hSFs (human skin fibroblasts) and hOBs (human osteoblasts) and enhances the mitogenic activity of IGFs (insulin-like growth factors) by degradation of IGFBP-4 (insulin-like growth factor-binding protein 4). PKC (protein kinase C) activation in these cells led to reduction in IGFBP-4 proteolysis. This study was undertaken to determine the mechanism by which activation of PKC suppresses IGFBP-4 proteolysis. Treatment of hSFs/hOBs with TPA (PMA; 100 nM) reduced IGFBP-4 proteolysis without significantly decreasing the PAPP-A level in the CM (conditioned medium). Immunodepletion of the proform of eosinophil major basic protein (proMBP), a known PAPP-A inhibitor, from CM of TPA-treated cells (TPA CM) failed to increase IGFBP-4 proteolytic activity. Transduction of hSFs with proMBP retrovirus increased the concentration of proMBP up to 30 ng/ml and led to a moderate reduction in IGFBP-4 proteolysis. In contrast, TPA treatment blocked IGFBP-4 proteolysis but failed to induce a detectable amount of proMBP in the CM. While proMBP overexpression led to the formation of a covalent proMBP-PAPP-A complex and reduced the migration of PAPP-A on SDS/PAGE, TPA treatment dose- and time-dependently increased the conversion of a approximately 470 kDa PAPP-A form (PAPP-A470) to a approximately 400 kDa PAPP-A form (PAPP-A400). Since unreduced PAPP-A400 co-migrated with the 400 kDa recombinant PAPP-A homodimer and since PAPP-A monomers from reduced PAPP-A470 and PAPP-A400 co-migrated on SDS/PAGE, conversion of PAPP-A470 to PAPP-A400 is unlikely to be caused by proteolytic cleavage of PAPP-A. Consistent with the data showing that the increase in the ratio of PAPP-A400/PAPP-A470 is correlated with the extent of reduction in IGFBP-4 proteolysis, partially purified PAPP-A400 exhibited a 4-fold reduction in IGFBP-4 proteolytic activity compared with PAPP-A470. These data suggest that a novel mechanism, namely conversion of PAPP-A470 to the less-active PAPP-A400, could account for the TPA-induced suppression of PAPP-A activity.

Inhibition of proteolysis by the proform of eosinophil major basic protein (proMBP) requires covalent binding to its target proteinase

By proteolytic cleavage of insulin-like growth factor binding proteins, the metalloproteinase pregnancy-associated plasma protein-A (PAPP-A) is able to control the biological activity of insulin-like growth factors. PAPP-A circulates in pregnancy as a proteolytically inactive complex, disulfide bound to the proform of eosinophil major basic protein (proMBP). We here demonstrate that co-transfection of mammalian cells with PAPP-A and proMBP cDNA results in the formation of a covalent PAPP-A/proMBP complex in which PAPP-A is inhibited. Formation of the complex also occurs when PAPP-A and proMBP synthesized separately are incubated. Complex formation was monitored by Western blotting, and by using an immunoassay specific for the complex. Using mutagenesis, we further demonstrate that the complex forms in a specific manner and depends on the presence of two proMBP cysteine residues. Mutated proMBP, in which Cys-51 and -169 are replaced by serine, is unable to form the covalent complex with PAPP-A. Of particular interest, such mutated proMBP further lacks the ability to inhibit PAPP-A. For the first time, this conclusively demonstrates that proMBP is a proteinase inhibitor. We further conclude that proMBP inhibits PAPP-A in an unusual manner, not paralleled by other proteinase inhibitors of our knowledge, which requires proMBP to be covalently bound to PAPP-A by disulfide bonds. ProMBP binding to PAPP-A most likely either abrogates substrate access to the active site of PAPP-A or induces a conformational change in the structure of PAPP-A, as we, by further mutagenesis, were able to exclude that the inhibitory mechanism of proMBP is based on a cysteine switch-like mechanism.

Covalent interaction between proform of eosinophil major basic protein (proMBP) and pregnancy-associated plasma protein-A (PAPP-A) is a cell-mediated event and required for proMBP inhibition of the catalytic activity of PAPP-A

This study was undertaken to determine the mechanism by which proform of eosinophil major basic protein (proMBP) inhibits the IGFBP-4 proteolytic activity of pregnancy-associated plasma protein (PAPP)-A. Co-overexpression of PAPP-A with proMBP in 293T cells, or co-incubation of 293T cells, respectively, overexpressing proMBP and PAPP-A resulted in the formation of a covalent proMBP-PAPP-A complex and inhibition of IGFBP-4 proteolysis. Similar results were obtained when recombinant proMBP and PAPP-A were incubated in the presence of U2 osteosarcoma cells or when recombinant proMBP was added to the U2 cells overexpressing PAPP-A. In contrast, no formation of covalent proMBP-PAPP-A complex or inhibition of IGFBP-4 proteolysis was observed when recombinant proMBP and PAPP-A were incubated under cell-free conditions, although proMBP was able to interact with PAPP-A in a non-covalent manner. These new findings suggest that formation of covalent proMBP-PAPP-A complex is a cell-mediated event and is required for proMBP to inhibit the catalytic activity of PAPP-A.

Pregnancy-associated plasma protein a gene expression as a target of inflammatory cytokines

Pregnancy-associated plasma protein A (PAPP-A) cleaves IGF-binding protein-4 (IGFBP-4) and appears to enhance local IGF bioavailability in response to injury. In this study we determined the effects of growth factors and cytokines involved in the healing process on PAPP-A expression in human dermal fibroblasts. There was no effect of platelet-derived growth factor, epidermal growth factor, or basic fibroblast growth factor on PAPP-A mRNA expression in these cells. However, treatment with the proinflammatory cytokines, TNFalpha and IL-1 beta, resulted in time- and dose-dependent increases in PAPP-A mRNA and protein expression (3- to 4-fold maximal effects), which were prevented by actinomycin D. On the other hand, interferon-gamma (IFN gamma) treatment markedly inhibited PAPP-A expression. IGFBP-4 proteolytic activity was increased 4-fold in medium from TNFalpha- and IL-1 beta-treated (1 nm) cells and decreased 40% in medium from IFN gamma-treated (1 nm) cells. IGF-I-stimulated [(3)H]thymidine incorporation was significantly enhanced by pretreatment with 1 nm TNFalpha, and this enhancement was blocked in the presence of protease-resistant IGFBP-4. In conclusion, PAPP-A expression is regulated by inflammatory cytokines in adult human fibroblasts, with functional consequences on IGFBP-4 protease activity and IGF-I bioavailability. These data provide a mechanism for the regulation of PAPP-A in response to injury and further implicate PAPP-A in the wound-healing processes.

Pregnancy-associated plasma protein-A (PAPP-A) expression and insulin-like growth factor binding protein-4 protease activity in normal and malignant ovarian surface epithelial cells

Pregnancy-Associated Plasma Protein-A (PAPP-A) proteolyses insulin-like growth factor binding protein-4 (IGFBP-4), thereby regulating local IGF availability. Reduced PAPP-A mRNA expression has been reported in ovarian cancer specimens compared to normal ovarian surface epithelial cells (OSE). To characterize PAPP-A expression and proteolytic activity in OSE, we developed a lifespan-extended human cell model using a temperature-sensitive mutant of the SV40 large T antigen (SV40LT). These OSE(tsT) cells proliferate at 34 degrees C (i.e., when SV40LT-positive), but not at 39 degrees C, a temperature at which the SV40LT is unstable (SV40LT-negative). Proteolysis of radiolabeled IGFBP-4 in conditioned media from OSE(tsT) lines was IGF-dependent and blocked by anti-PAPP-A antisera. Temperature shifts that eliminated stable SV40LT induced a 7-fold increase in PAPP-A mRNA and a 4-fold increase in protein. The converse experiment (shifting to SV40LT-positive conditions) resulted in decreased levels of PAPP-A mRNA but little change in PAPP-A protein. Nevertheless, there was a marked reduction in IGF-BP-4 proteolytic activity in medium of SV40LT-positive OSE-(tsT) cells. This decreased PAPP-A activity coincided with a nearly 20-fold increase in mRNA encoding a physiological inhibitor of PAPP-A, the precursor form of eosinophil Major Basic Protein (proMBP), and 4- to 5-fold increases in proMBP protein. Primary cultures of unmodified OSE expressed high levels of PAPP-A and undetectable proMBP, and therefore produced abundant IGFBP-4 protease activity. Short-term ovarian tumor cell cultures expressed variable levels of PAPP-A and high levels of proMBP, and consequently secreted little or no IGFBP-4 protease activity. The concurrent regulation of PAPP-A and its inhibitor, proMBP, suggests that IGFBP-4 proteolysis and local regulation of IGF availability may be altered in malignant ovarian epithelial cells.

Transforming growth factor-beta regulation of the insulin-like growth factor binding protein-4 protease system in cultured human osteoblasts

IGFBP-4 is an inhibitor of IGF-I in bone. We show that TGF-beta regulates IGFBP-4 and enhances IGF-I-stimulated growth of cultured human bone cells through increased expression of an IGFBP-4 protease, PAPP-A. This effect of TGF-beta on IGF-I bioavailability may promote local bone formation. Insulin-like growth factor binding protein (IGFBP-4) proteolysis is implicated in the regulation of local insulin-like growth factor (IGF)-I bioavailability during bone remodeling. The IGFBP-4 protease secreted by normal adult human osteoblastic (hOB) cells in culture is a novel metalloproteinase, pregnancy-associated plasma protein-A (PAPP-A). We have recently identified an inhibitor of PAPP-A, the precursor form of major basic protein (proMBP). Very little is known about the molecular regulation of this IGFBP-4 protease system. In the present study, we determined the effect of transforming growth factor (TGF)-beta and IGF-II, the two most abundant growth factors in human bone, on PAPP-A and proMBP expression in primary cultures of hOB cells. Treatment with TGF-beta resulted in time- and dose-dependent increases in PAPP-A mRNA expression, with a maximal 12-fold increase after 24 h of stimulation with 10 ng/ml TGF-beta. Increased PAPP-A levels in hOB cell-conditioned medium paralleled PAPP-A gene expression. In addition, TGF-beta completely suppressed proMBP expression. Treatment of hOB cells with IGF-II had no effect on PAPP-A or proMBP gene expression. However, IGFBP-4 proteolysis in cell-free assay was dependent on IGF-II, and there was increased IGF-II-dependent IGFBP-4 protease activity in conditioned medium from hOB cells that were treated with TGF-beta. IGF-I stimulation of hOB cell proliferation was markedly enhanced by pretreatment with TGF-beta and [Leu27]IGF-II, and this enhancement was prevented with protease-resistant IGFBP-4. In summary, TGF-beta regulates IGFBP-4 proteolysis in hOB cells through increased expression of the protease, PAPP-A, and decreased expression of the inhibitor, proMBP. However, functional activation of the IGFBP-4 protease system is dependent on IGF-II, which acts at a post-translational level. These data support a model whereby local TGF-beta and IGF-II in the bone microenvironment coordinately amplify IGF-I bioavailability through controlled IGFBP-4 proteolysis, which may be a means to promote bone formation.

Detecting vulnerable plaque using peripheral blood: inflammatory and cellular markers

The concept of the vulnerable patient has arrived. Enhanced diagnostic methods will eventually permit accurately finding and treating these patients and their disease. Clinical Cardiologists now recognize that coronary atherosclerosis is two pathophysiologically distinct syndromes: stable and unstable. Stable coronary syndromes result from fixed, severe stenoses limiting blood flow and causing secondary myocardial ischemia. The unstable acute coronary syndromes are frequently catastrophic and are pathophysiologically distinct. They result from different cell subsets causing vascular inflammatory syndromes rather than gradual lumen constriction by plaque. Though pathophysiologically distinct, they may show common pathophysiology when a ruptured plaque heals and progressively becomes a critical stenosis. For the present hs-CRP measurement is the strongest correlative factor for future clinical events due to arterial inflammation: myocardial infarction, unstable angina, stroke, and peripheral vascular disease in both diseased and apparently healthy, asymptomatic patients. The CRP plasma level also is the best risk assessment in patients with either stable or unstable angina, long term after myocardial infarction, and in patients undergoing revascularization therapies. One study showed the only independent cardiovascular risk indicators using multivariate, age adjusted and traditional risk analysis were CRP and Total/HDL cholesterol ratio. If CRP, IL-6, and ICAM-1 levels are added to lipid levels, risk assessment can be improved over lipids alone. The prevalence of high-risk subjects in the general population is low, amplifying diagnostic problems for vulnerable plaque. Since no test yet has high sensitivity or specificity, diagnostic errors are high, with many false positives and negatives. Sensitivity or specificity must be increased by developing a risk marker panel, or by simultaneously finding other markers that themselves are highly sensitive and specific for vulnerable plaque.

Characterization of the common fragile site FRA9E and its potential role in ovarian cancer

Common fragile sites (CFSs) are regions of profound genomic instability that have been hypothesized to play a role in cancer. The major aim of this study was to locate a fragile region associated with ovarian cancer. Differential display (DD)-PCR analysis comparing normal ovarian epithelial cultures and ovarian cancer cell lines identified pregnancy-associated plasma protein-A (PAPPA) because of its frequent loss of expression (LOE) in ovarian cancer cell lines. PAPPA is localized to human chromosome 9q32-33.1, a region associated with significant loss of heterozygosity (LOH) in ovarian tumors (>50%) and in close proximity to the FRA9E CFS. FISH analysis determined that PAPPA was contained within the distal end of FRA9E. Characterization of FRA9E determined that aphidicolin-induced instability extended over 9 Mb, identifying FRA9E as the largest CFS characterized to date. Comprehensive LOH analysis revealed several distinct peaks of LOH within FRA9E. Semiquantitative RT-PCR analysis of 16 genes contained within FRA9E indicated that genes showing LOE in ovarian tumors coincided with regions of high LOH. PAPPA displayed the most significant loss (72%). This study provides evidence to suggest that instability within FRA9E may play an important role in the development of ovarian cancer and lends further support for the hypothesis that CFSs may be causally related to cancer.

Complex of pregnancy-associated plasma protein-A and the proform of eosinophil major basic protein. Disulfide structure and carbohydrate attachment

Pregnancy-associated plasma protein-A (PAPP-A) is a metzincin superfamily metalloproteinase responsible for cleavage of insulin-like growth factor-binding protein-4, thus causing release of bound insulin-like growth factor. PAPP-A is secreted as a dimer of 400 kDa but circulates in pregnancy as a disulfide-bound 500-kDa 2:2 complex with the proform of eosinophil major basic protein (pro-MBP), recently shown to function as a proteinase inhibitor of PAPP-A. Except for PAPP-A2, PAPP-A does not share global similarity with other proteins. Three lin-notch (LNR or LIN-12) modules and five complement control protein modules (also known as SCR modules) have been identified in PAPP-A by sequence similarity with other proteins, but no data are available that allow unambiguous prediction of disulfide bonds of these modules. To establish the connectivities of cysteine residues of the PAPP-A.pro-MBP complex, biochemical analyses of peptides derived from purified protein were performed. The PAPP-A subunit contains a total of 82 cysteine residues, of which 81 have been accounted for. The pro-MBP subunit contains 12 cysteine residues, of which 10 have been accounted for. Within the 2:2 complex, PAPP-A is dimerized by a single disulfide bond; pro-MBP is dimerized by two disulfides, and each PAPP-A subunit is connected to a pro-MBP subunit by two disulfide bonds. All other disulfides are intrachain bridges. We also show that of 13 potential sites for N-linked carbohydrate substitution of the PAPP-A subunit, 11 are occupied. The large number of disulfide bonds of the PAPP-A.pro-MBP complex imposes many restraints on polypeptide folding, and knowledge of the disulfide pattern of PAPP-A will facilitate structural studies based on recombinant expression of individual, putative PAPP-A domains. Furthermore, it will allow rational experimental design of functional studies aimed at understanding the formation of the PAPP-A.pro-MBP complex, as well as the inhibitory mechanism of pro-MBP.