Expression of a TGF-beta superfamily protein, macrophage inhibitory cytokine-1, in the yeast Pichia pastoris

Improving bone morphogenetic protein (BMP) production in CHO cells through understanding of BMP synthesis, signaling and endocytosis

Bone morphogenetic proteins (BMPs) are a group of growth factors with the clinical potential to regulate cartilage and bone formation. Functionally active mature recombinant human BMPs (rhBMPs), produced primarily in Chinese hamster ovary (CHO) cells for clinical applications, are considered difficult to express because they undergo maturation processes, signaling pathways, or endocytosis. Although BMPs are a family of proteins with similar mature domain sequence identities, their individual properties are diverse. Thus, understanding the properties of individual rhBMPs is essential to improve rhBMP production in CHO cells. In this review, we discuss various approaches to improve rhBMP production in CHO cells by understanding the overall maturation process, signaling pathways and endocytosis of individual rhBMPs.

Bidirectional Relationship Between Cancer and Heart Failure: Insights on Circulating Biomarkers

Cancer and heart failure are the two leading causes of death in developed countries. These two apparently distinct clinical entities share similar risk factors, symptoms, and pathophysiological mechanisms (inflammation, metabolic disturbances, neuro-hormonal and immune system activation, and endothelial dysfunction). Beyond the well-known cardiotoxic effects of oncological therapies, cancer and heart failure are thought to be tied by a bidirectional relationship, where one disease favors the other and vice versa. In this context, biomarkers represent a simple, reproducible, sensitive and cost-effective method to explore such relationship. In this review, we recapitulate the evidence on cardiovascular and oncological biomarkers in the field of cardioncology, focusing on their role in treatment-naïve cancer patients. Cardioncological biomarkers are useful tools in risk stratification, early detection of cardiotoxicity, follow-up, and prognostic assessment. Intriguingly, these biomarkers might contribute to better understand the common pathophysiology of cancer and heart failure, thus allowing the implementation of preventive and treatment strategies in cardioncological patients

Functional Activity of Recombinant Forms of Amh and Synergistic Action with Fsh in European Sea Bass Ovary

Although anti-Müllerian hormone (AMH) has classically been correlated with the regression of Müllerian ducts in male mammals, involvement of this growth factor in other reproductive processes only recently come to light. Teleost is the only gnathostomes that lack Müllerian ducts despite having amh orthologous genes. In adult teleost gonads, Amh exerts a role in the early stages of germ cell development in both males and females. Mechanisms involving the interaction of Amh with gonadotropin- and growth factor-induced functions have been proposed, but our overall knowledge regarding Amh function in fish gonads remains modest. In this study, we report on Amh actions in the European sea bass ovary. Amh and type 2 Amh receptor (Amhr2) are present in granulosa and theca cells of both early and late-vitellogenic follicles and cannot be detected in previtellogenic ovaries. Using the Pichia pastoris system a recombinant sea bass Amh has been produced that is endogenously processed to generate a 12–15 kDa bioactive mature protein. Contrary to previous evidence in lower vertebrates, in explants of previtellogenic sea bass ovaries, mature Amh has a synergistic effect on steroidogenesis induced by the follicle-stimulating hormone (Fsh), increasing E2 and cyp19a1a levels.

Treatment with GDF15, a TGFβ superfamily protein, induces protective effect on retinal ganglion cells

Growth differentiation factor 15 (GDF15) is a protein belonging to the transforming growth factor beta (TGF-β) superfamily. The precursor GDF15 is cleaved and activated as a mature GDF15 by protease. GDF15 has been detected in the aqueous humor of the primary open angle glaucoma patients, however the localization and the effect on the retinal ganglion cells (RGCs) are still unknown. Thus, the purpose of this study was to elucidate the effect of GDF15 on mouse optic nerve crush (ONC) model and primary culture of rat RGCs. Immunostaining showed that the GDF15 was in the ganglion cell layer (GCL), and colocalized with GFAP-positive cells in the GCL and the optic nerve. Western blotting analysis showed that the mature GDF15 was upregulated in the retina and the optic nerve after the ONC. Intravitreal injection of GDF15 suppressed RGCs loss of the ONC model mice in vivo. The neurites length of the primary culture of rat RGCs were increased by mature GDF15 treatment. In addition, the neurotrophic effect of GDF15 was canceled by RET inhibitor treatment. These findings indicate that GDF15 has neuroprotective effect on RGCs via GFRAL-RET pathway. Therefore, GDF15 may be one of novel therapeutic targets in RGC degenerative diseases.

Biochemical and Molecular Characterization of Pichia pastoris Cells Expressing Multiple TMOF Genes (tmfA) for Mosquito Larval Control

Trypsin modulating oostatic factor (TMOF), a decapeptide hormone synthesized by female mosquito ovaries, ganglia and the central nervous system of Aedes aegypti, terminates trypsin biosynthesis in larvae, and blood-fed female mosquitoes. Earlier, TMOF was cloned and expressed as a single copy in Chlorella dessicata and in Saccharomyces cerevisiae cells as a potential larvicide. Here we report the use of a methylotrophic yeast cells, Pichia pastoris, that efficiently express multi copies of heterologous proteins, that are readily ingested by mosquito larvae. P. pastoris was engineered using pPICZB (Invitrogen, CA, United States), and 2 genes: gfp-tmfA and tmfA inserted between KpnI and XbaI in the multiple cloning site. The plasmid carries a strong AOXI promoter and P. pastoris KM71 and KM71H cells were transformed by homologous recombination. The synthesis of GFP-TMOF was followed using UV and clones were analyzed using southern and Northern blot analyses. Cloning tmfA into KM71H and selection on high Zeocin concentration (2.0 mg/mL) identified a clone that carried 10 copies of tmfA. A comparison between a single and high copy (10 genes) insertions using Northern blot analyses showed that a tmfA transcript was highly expressed even after 120 h. SDS-PAGE analysis of KM71 cells transformed with gfp-tmfA identified a protein band that ran at the expected M_r of 31 kDa. Enzyme Linked Immunoadsorbant Assay (ELISA) analysis of the recombinant cells showed that 1.65 × 10⁸ and 8.27 × 10⁷ cells produce 229 and 114 μM of TMOF, respectively, and caused 100% larval mortality when fed to groups of 5 larvae in 25 mL water. These results indicate that the recombinant P. pastoris cells could be used in the future in the marsh to control mosquito populations.

Growth differentiation factor-15 slows the growth of murine prostate cancer by stimulating tumor immunity

Growth Differentiation Factor-15 (GDF15) is a divergent TGF-beta superfamily cytokine that is overexpressed by most cancers and is induced by anticancer therapy. Transgenic and induced animal models suggest that it protects from cancer development but the mechanisms are uncertain. We investigated the role of immunity in GDF15 induced reduction in prostate cancer (PCa) growth. The C57BL/6 transgenic TRAMP prostate cancer prone mice were bred with mice that were immunodeficient and/or systemically overexpressed GDF15. We developed a novel orthotopic TRAMP PCa model in which primary TRAMP tumor cells were implanted into prostates of mice to reduce the study time. These mice were administered recombinant mouse GDF15, antibody to CD8, PD1 or their respective controls. We found that GDF15 induced protection from tumor growth was reversed by lack of adaptive immunity. Flow cytometric evaluation of lymphocytes within these orthotopic tumors showed that GDF15 overexpression was associated with increased CD8 T cell numbers and an increased number and proportion of recently activated CD8+CD11c+ T cells and a reduced proportion of "exhausted" CD8+PD1+ T cells. Further, depletion of CD8 T cells in tumor bearing mice abolished the GDF15 induced protection from tumor growth. Infusion of GDF15 into mice bearing orthotopic TRAMP tumor, substantially reduced tumor growth that was further reduced by concurrent PD1 antibody administration. GDF15 overexpression or recombinant protein protects from TRAMP tumor growth by modulating CD8 T cell mediated antitumor immunity and augments the positive effects of anti-PD1 blockers.

The MIC-1/GDF15-GFRAL Pathway in Energy Homeostasis: Implications for Obesity, Cachexia, and Other Associated Diseases

MIC-1/GDF15 is a stress response cytokine and a distant member of the transforming growth factor beta (TGFb) superfamily, with no close relatives. It acts via a recently identified receptor called glial-derived neurotrophic factor (GDNF) receptor alpha-like (GFRAL), which is a distant orphan member of the GDNF receptor family that signals through the tyrosine kinase receptor Ret. MIC-1/GDF15 expression and serum levels rise in response to many stimuli that initiate cell stress and as part of a wide variety of disease processes, most prominently cancer and cardiovascular disease. The best documented actions of MIC-1/GDF15 are on regulation of energy homeostasis. When MIC-1/GDF15 serum levels are substantially elevated in diseases like cancer, it subverts a physiological pathway of appetite regulation to induce an anorexia/cachexia syndrome initiated by its actions on hindbrain neurons. These effects make it a potential target for the treatment of both obesity and anorexia/cachexia syndromes, disorders lacking any highly effective, readily accessible therapies.

Efficient expression of recombinant human telomerase inhibitor 1 (hPinX1) in Pichia pastoris

PinX1 encoded by a remarkable tumor suppressor gene and located in human chromosome 8p23 is known as telomerase inhibitor. In recent years, this protein has been of interest as clinically tumor suppressor. Pichia pastoris expression system is preferred to produce heterologous proteins and is suitable for industrial and research purposes. In the present study, human PinX1 gene (hPinX1) was cloned in E. coli One Shot TOP10 cells and overexpressed in P. pastoris strain X-33 intracellularly, using a strong AOX (alcohol oxidase) promoter. The recombinant cells were grown in shaking flask. Induction time, methanol concentration and initial pH were optimized for obtaining high levels of hPinX1 protein production. Recombinant protein production was confirmed by Western blot analysis and the relative expression levels of rhPinX1 were quantified. According to Western blot analysis, molecular mass of produced hPinX1 was determined as 47.5 kDa. At the end of optimization studies, the best fermentation conditions were determined as induction time 48 h, methanol concentration 3% and initial culture pH 5.0. This process would be an applicable way for obtaining recombinant hPinX1 using P. pastoris expression system. This is the first report on recombinant production of hPinX1 in P. pastoris.

Growth differentiation factor 15 is associated with left atrial/left atrial appendage thrombus in patients with nonvalvular atrial fibrillation

BACKGROUND

There is evidence suggesting that growth differentiation factor 15 (GDF-15) appears to be associated with stroke in patients with atrial fibrillation (AF). AF-related thromboembolic stroke is predominantly attributed to the thrombus from the left atrium (LA) or left atrial appendage (LAA).

HYPOTHESIS

GDF-15 is related to LA/LAA thrombus in nonvalvular AF (NVAF) patients.

METHODS

A total of 894 patients with NVAF without anticoagulation therapy were included in this study. All patients routinely underwent transesophageal echocardiography for detection of LA/LAA thrombus. GDF-15 was measured by enzyme-linked immunosorbent assay. Logistic regression models were used to test for association.

RESULTS

LA/LAA thrombus was detected by transesophageal echocardiography in 69 (7.72%) patients with AF. The GDF-15 levels in the patients with LA/LAA thrombus were significantly higher than those without LA/LAA thrombus (log₁₀ GDF-15: 2.989 ± 0.023 ng/L vs 2.831 ± 0.007 ng/L; P < 0.001). Logistic regression analysis showed that GDF-15 was an independent risk factor for LA/LAA thrombus (odds ratio [per quarter]: 1.799, 95% confidence interval: 1.381-2.344, P < 0.001) after adjusting for potential clinical risk factors. The optimal cutoff point for GDF-15 predicting LA/LAA thrombus was 809.9 ng/L (sensitivity, 75.3%; specificity, 61.5%), determined by ROC curve. The area under the curve was 0.709 (95% confidence interval: 0.644-0.770, P < 0.001).

CONCLUSIONS

Elevated GDF-15 indicated a significantly increased risk for LA/LAA thrombus in NVAF patients. Thus, GDF-15 might be a potentially useful adjunct in discriminating LA/LAA thrombus in NVAF patients.

Heterologous Secretory Expression and Characterization of Dimerized Bone Morphogenetic Protein 2 in Bacillus subtilis

Recombinant human Bone Morphogenetic Protein 2 (rhBMP2) has important applications in the spine fusion and ortho/maxillofacial surgeries. Here we first report the secretory expression of biological active dimerized rhBMP2 from Bacillus subtilis system. The mature domain of BMP2 gene was amplified from pTz57R/BMP2 plasmid. By using pHT43 expression vector two constructs, pHT43-BMP2-M (single BMP2 gene) and pHT43-BMP2-D (two BMP2 genes coupled with a linker to produce a dimer), were designed. After primary cloning (DH5α strain) and sequence analysis, constructs were transformed into Bacillus subtilis for secretory expression. Expression conditions like media (2xYT) and temperature (30°C) were optimized. Maximum 35% and 25% secretory expression of monomer (~13 kDa) and dimer (~25 kDa), respectively, were observed on SDS-PAGE in SCK6 strain. The expression and dimeric nature of rhBMP2 were confirmed by western blot and native PAGE analysis. For rhBMP2 purification, 200 ml culture supernatant was freeze dried to 10 ml and dialyzed (Tris-Cl, pH 8.5) and Fast Protein Liquid Chromatography (6 ml, Resource Q column) was performed. The rhBMP2 monomer and dimer were eluted at 0.9 M and 0.6 M NaCl, respectively. The alkaline phosphatase assay of rhBMP2 (0, 50, 100, 200, and 400 ng/ml) was analyzed on C2C12 cells and maximum 200 ng/ml activity was observed in dose dependent manner.

Serum Growth Differentiation Factor 15 in Parkinson Disease

BACKGROUND

Growth differentiation factor 15 (GDF15) has been shown to be protective for dopaminergic neurons in animal and ex vivo experiments. However, little is known about its effect on the human body.

OBJECTIVE

This study investigated associations between serum GDF15 levels and clinical parameters in patients with Parkinson disease (PD).

METHODS

Idiopathic PD patients (n = 104) and age-matched controls (n = 88) were enrolled. Serum GDF15 levels were measured by human enzyme-linked immunosorbent assay. Univariate and multivariate analyses investigated correlations between GDF15 and clinical characteristics, including disease severity by the Unified PD Rating Scale (UPDRS)-III. The diagnostic value of GDF15 was evaluated by receiver-operating characteristic curve (ROC) analysis.

RESULTS

The serum GDF15 levels of the PD patients were significantly higher than those of the healthy controls. In PD patients, serum GDF15 levels in men were significantly higher than in women. GDF15 levels correlated with age, gender, disease duration, and UPDRS-III score. After adjusting for confounding factors, multiple linear regression analysis showed that the serum GDF15 level (β = 0.015, p = 0.001) was an independent risk factor for UPDRS-III score. In ROC analysis, GDF15 achieved an area under the curve of 0.86 for the identification of PD, with a sensitivity of 71.15% and a specificity of 87.50%.

CONCLUSION

GDF15 may be a potential biomarker for the diagnosis and monitoring of motor severity in PD.

Accuracy of novel diagnostic biomarkers for hepatocellular carcinoma: An update for clinicians (Review)

Hepatocellular carcinoma (HCC) is the most common liver malignancy and a leading cause of cancer-related mortality worldwide. Accurate detection and differential diagnosis of early HCC can significantly improve patient survival. Currently, detection of HCC in clinical practice is performed by diagnostic imaging techniques and determination of serum biomarkers, most notably α-fetoprotein (AFP), fucosylated AFP and des-γ-carboxyprothrombin. However, these methods display limitations in sensitivity and specificity, especially with respect to early stages of HCC. Recently, high-throughput technologies have elucidated many new pathways involved in hepatocarcinogenesis and have led to the discovery of a plethora of novel, non-invasive serum biomarkers. In particular, the combination of AFP with these new candidate molecules has yielded promising results. In this review, we aimed at recapitulating the most recent (2013–2015) developments in HCC biomarker research. We compared promising novel diagnostic serum protein biomarkers, such as annexin A2, the soluble form of the receptor tyrosine kinase Axl and thioredoxin, as well as their combinations with AFP. High diagnostic performance (area under the curve >0.75) as shown by threshold-independent receiver operating characteristic curve analysis was a prerequisite for inclusion in this review. In addition, we discuss the role and potential of microRNAs in HCC diagnosis and associated methodological challenges.

Concise review: growth differentiation factor 15 in pathology: a clinical role?

Growth differentiation factor 15 (GDF15) is a divergent member of the transforming growth factor β family discovered in a broad range of cells, as indicated by the diversity of its nomenclature. However, the only tissue that expresses a high amount of GDF15 in the physiologic state is placenta. GDF15 is easily detected in blood, and its concentration varies with age. In fact, increased blood concentration of GDF15 is associated with numerous pathological conditions. However, the biological significance underlying these observations is far from clear. GDF15 could have a positive or negative role depending on the state of cells or their environment. Furthermore, study of its biology is hampered by lack of knowledge of its receptor and thus the signaling pathways that drive its action. GDF15 seems to be an integrative signal in pathologic conditions, giving information on severity of disease. Its effectiveness in classifying patients to modulate treatment remains to be shown. Development of therapeutic interventions with GDF15 or anti-GDF15 agents remains difficult until we uncover the mechanism that drives its activity.

Expression, purification, and immunogenic characterization of Epstein-Barr virus recombinant EBNA1 protein in Pichia pastoris

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus associated with the development of both lymphoid and epithelial tumors. EBNA1 is the only viral protein expressed in all EBV-associated malignancies and plays important roles in EBV latency. Thus, EBNA1 is thought to be a promising antigen for immunotherapy of all EBV-associated malignancies. This study was undertaken to produce recombinant EBNA1 protein in Pichia pastoris and evaluate its immunogenicity. The truncated EBNA1 (E1ΔGA, codons 390-641) was expressed as a secretory protein with an N-terminal histidine tag in the methylotrophic yeast P. pastoris and purified by Ni-NTA affinity chromatography. The purified proteins were then used as antigens to immunize BALB/c mice for production of polyclonal antibodies. Western blot analysis showed that the polyclonal antibodies specifically recognized the EBNA1 protein in B95-8 cell lysates. The recombinant E1ΔGA also induced strong lymphoproliferative and Th1 cytokine responses in mice. Furthermore, mice immunized with E1ΔGA developed CD4+ and CD8+ T cell responses. These findings showed that the yeast-expressed E1ΔGA retained good immunogenicity and might be a promising vaccine candidate against EBV-associated malignancies.

Growth differentiation factor 15 in erythroid health and disease

PURPOSE OF REVIEW

Growth differentiation factor 15 (GDF15) was identified as a hepcidin-suppression factor that is expressed at high levels in patients with ineffective erythropoiesis. This review addresses the regulation, expression and potential functions of GDF15 in the context of erythroid biology.

RECENT FINDINGS

GDF15 expression during late erythroid differentiation was discovered as part of an erythroblast transcriptome project. As GDF15 expression is associated with cellular stress or apoptosis, further investigation of the cytokine was focused upon its involvement in ineffective erythropoiesis. Remarkably high serum levels were detected in patients with thalassemia syndromes, congenital dyserythropoiesis and some acquired sideroblastic anemias. High-level GDF15 expression is not a feature of normal erythropoiesis, or erythroid recovery after bone-marrow transplantation. As GDF15 is a transforming growth factor-beta superfamily member, it was investigated as an effector of ineffective erythropoiesis that suppresses hepcidin expression despite iron overloading.

SUMMARY

In contrast to the low levels of GDF15 expressed during normal erythropoiesis, ineffective erythropoiesis causes high-level expression of GDF15. In patients with thalassemia and related anemias, GDF15 expression may contribute to iron overloading or other features of the disease phenotype.

Synthesis, purification and bioactivity of recombinant human activin A expressed in the yeast Pichia pastoris

The transforming growth factor-beta (TGF-beta) superfamily member, activin A, plays a central role in the regulation of multiple physiological processes including cell differentiation, mitogenesis, embryogenesis, apoptosis and inflammation. In normal cells, activin A signalling is regulated to maintain cellular and tissue health and suppress tumour growth. Disruption of activin A signalling has been implicated in tumour formation and progression. Hence, the availability of activin A is an important target for the development of diagnostics and drugs for therapeutic intervention. To this end, we have expressed human activin A in Pichia pastoris, permitting its secretion into culture medium and purification as the mature homodimer. A construct was engineered encoding the monomeric precursor protein with a N-terminal FLAG affinity tag (DYKDDDDK) and a cleavage site (EKR) for Kex2p protease. Procedures for the two-step purification of human activin A by ion-exchange and anti-FLAG antibody affinity chromatography, and for the removal of the FLAG affinity tag from purified recombinant human activin A by enteropeptidase, are described. The molecular weights of the FLAG-tagged and de-tagged human activin A were confirmed by MALDI-TOF mass spectroscopy. The biological activity of these recombinant activins was assessed for their effects on modulating the secretion of Endothelin-1 (ET-1) by human umbilical vein endothelial cells (HUVECs). The recombinant human activin A containing the intact FLAG tag resulted in a reduced ET-1 secretion from HUVECs, whereas upon removal of this affinity purification tag the purified recombinant human activin A restored ET-1 secretion to levels comparable to the positive control. These results document an approach of considerable potential for the simple, large-scale expression and purification of this important human growth factor for use in diagnostic and therapeutic purposes.

Macrophage inhibitory cytokine 1 mediates a p53-dependent protective arrest in S phase in response to starvation for DNA precursors

p53 is essential for the cellular responses to DNA damage that help to maintain genomic stability. Protective p53-dependent cell-cycle checkpoints are activated in response to a wide variety of stresses, including not only DNA damage but also arrest of DNA synthesis and of mitosis. In addition to its role in activating the G(1) and G(2) checkpoints, p53 also helps to protect cells in S phase when they are starved for DNA precursors by treatment with the specific aspartate transcarbamylase inhibitor N-phosphonacetyl-l-aspartate (PALA), which blocks the synthesis of pyrimidine nucleotides. Even though p53 is activated, PALA-treated cells expressing low levels of p53 or lacking expression of p21 do not arrest in G(1) or G(2) but are blocked in S phase instead. In the complete absence of p53, PALA-treated cells continue to synthesize DNA slowly and eventually progress through S phase, suffering severe DNA damage that in turn triggers apoptosis. Expression of the secreted protein macrophage inhibitory cytokine 1 (MIC-1), a member of the TGF-beta superfamily, increases substantially after PALA treatment, and application of exogenous MIC-1 or its constitutive expression from a cDNA provides remarkable protection of p53-null cells from PALA-mediated apoptosis, arguing that the p53-dependent secretion of MIC-1 provides a major part of such protection. Stimulation of MIC-1-dependent S phase arrest in normal gut epithelial cells might help to revitalize the clinical use of PALA, which has been limited by gut toxicity.

GDF15/MIC-1 functions as a protective and antihypertrophic factor released from the myocardium in association with SMAD protein activation

Here we identified growth-differentiation factor 15 (GDF15) (also known as MIC-1), a secreted member of the transforming growth factor (TGF)-beta superfamily, as a novel antihypertrophic regulatory factor in the heart. GDF15 is not expressed in the normal adult heart but is induced in response to conditions that promote hypertrophy and dilated cardiomyopathy. To elucidate the function of GDF15 in the heart, we generated transgenic mice with cardiac-specific overexpression. GDF15 transgenic mice were normal but were partially resistant to pressure overload-induced hypertrophy. Expression of GDF15 in neonatal cardiomyocyte cultures by adenoviral-mediated gene transfer antagonized agonist-induced hypertrophy in vitro. Transient expression of GDF15 outside the heart by intravenous adenoviral delivery, or by direct injection of recombinant GDF15 protein, attenuated ventricular dilation and heart failure in muscle lim protein gene-targeted mice through an endocrine effect. Conversely, examination of Gdf15 gene-targeted mice showed enhanced cardiac hypertrophic growth following pressure overload stimulation. Gdf15 gene-targeted mice also demonstrated a pronounced loss in ventricular performance following only 2 weeks of pressure overload stimulation, whereas wild-type controls maintained function. Mechanistically, GDF15 stimulation promoted activation of SMAD2/3 in cultured neonatal cardiomyocytes. Overexpression of SMAD2 attenuated cardiomyocyte hypertrophy similar to GDF15 treatment, whereas overexpression of the inhibitory SMAD proteins, SMAD6/7, reversed the antihypertrophic effects of GDF15. These results identify GDF15 as a novel autocrine/endocrine factor that antagonizes the hypertrophic response and loss of ventricular performance, possibly through a mechanism involving SMAD proteins.

The propeptide of the transforming growth factor-beta superfamily member, macrophage inhibitory cytokine-1 (MIC-1), is a multifunctional domain that can facilitate protein folding and secretion

Macrophage inhibitory cytokine-1 (MIC-1) is a divergent member of the transforming growth factor-beta (TGF-beta) superfamily. While it is synthesized in a pre-pro form, it is unique among superfamily members because it does not require its propeptide for correct folding or secretion of the mature peptide. To investigate factors that enable these propeptide independent events to occur, we constructed MIC-1/TGF-beta1 chimeras, both with and without a propeptide. All chimeras without a propeptide secreted less efficiently compared with the corresponding constructs with propeptide. Folding and secretion were most affected after replacement of the predicted major alpha-helix in the mature protein, residues 56-68. Exchanging the human propeptide in this chimera with either the murine MIC-1 or TGF-beta1 propeptide resulted in secretion of the unprocessed, monomeric chimera, suggesting a specific interaction between the human MIC-1 propeptide and mature peptide. Propeptide deletion mutants enabled identification of a region between residues 56 and 78, which is important for the interaction between the propeptide and the mature peptide. Cotransfection experiments demonstrated that the propeptide must be in cis with the mature peptide for this phenomenon to occur. These results suggest a model for TGF-beta superfamily protein folding.

Epitope mapping of the transforming growth factor-beta superfamily protein, macrophage inhibitory cytokine-1 (MIC-1): identification of at least five distinct epitope specificities

Macrophage inhibitory cytokine-1 (MIC-1) is a divergent member of the transforming growth factor-beta (TGF-beta) superfamily whose increased expression is associated with macrophage activation and which is expressed highly in placenta as compared to other tissues. There are two known allelic forms of human MIC-1 due an amino acid substitution at position 6 of the mature protein. We have raised four monoclonal antibodies (MAbs) and one polyclonal antiserum to the mature protein region of human MIC-1 and have used an extensive panel of MIC-1 relatives, mutants, and chimeras to map their epitopes. None of the MAbs were able to cross-react with either the murine homologue of MIC-1 or with hTGF-beta1, and all of the MAb epitopes were conformation-dependent. A distinct cross-reactivity pattern with the various antigens was observed for each of the monoclonal and polyclonal antibodies suggesting the presence of at least five immunogenic regions on the MIC-1 surface. One of the MAbs is directed against the amino terminus of the protein and can distinguish between the two allelic forms of MIC-1. The epitopes for the other three MAbs were located near the tips of the so-called "fingers" of the protein and appeared to be partially overlapping as each involved amino acids in the region 24-37. In one case, it was possible to mutate murine MIC-1 so that it could be recognized by one of the MAbs. Finally, the use of another mutant in which Cys 77 was replaced by serine enabled confirmation of the location of the MIC-1 interchain disulfide bond.