Chain Of Platelet-derived Growth Factor Research Articles

Evaluating mRNA expression of tax, B chain of PDGFand PDGF-β receptorsas well as HTLV-I proviral load in ATL patients and healthy carriers.

Adult T-cell leukemia (ATL) is a life-threatening malignant neoplasm of CD4+ T cells resulted from human T-cell leukemia virus type I (HTLV-I). Tax1 protein of HTLV-I can induce malignant proliferation of T-cells bymodulating the expression of growth factors such as platelet-derived growth factor (PDGF). Here, we aimed to investigate the proviral load (PVL) of HTLV-I in ATLand also to evaluate the mRNA expression of B chain of PDGF and PDGF-β receptors in ATL patients and HTLV-I-infected healthy carriers. To this end, peripheral blood mononuclear cells (PBMCs) were isolated by using Ficoll-Histophaque density centrifugation. The mean of HTLV-I PVL in ATL patients (42,759 ± 15,737 copies/104 cells [95% CI, 9557-75962]) was significantly (p = .01) higher than that in healthy carriers (650 ± 107 copies/104 cells [95% CI, 422-879], respectively. The HTLV-I PVL in ATL patients exhibited a significant correlation with PBMC count (R = .495, p = .001). The mRNA expression of Tax, B chain of PDGF, and PDGF-β receptor genes was significantly higher in healthy carriers than in patients with ATL. In conclusion, the expression of the canonical PDGFβ and its receptor, and their correlation with Tax expression cannot be a suitable indicator and/or prognostic factor for progression of ATL in HTLV-I carriers.

Berberine cooperates with adrenal androgen dehydroepiandrosterone sulfate to attenuate PDGF-induced proliferation of vascular smooth muscle cell A7r5 through Skp2 signaling pathway

Platelet-derived growth factor (PDGF) is released from vascular smooth muscle cell (VSMC), after percutaneous coronary intervention and is related with neointimal proliferation and restenosis. Adrenal steroid dehydroepiandrosterone sulfate (DHEAS), the sulfated prohormone of dehydroepiandrosterone has shown remarkable biological activity against proliferation of VSMC in some animal and clinical studies. Combinations of DHEAS with other agents have also shown promising results, with acquiring more efficient effect. Berberine is a naturally occurring isoquinoline alkaloid. To investigate their effects in combination, a VSMC cell line A7r5 was stimulated by PDGF-BB (dimer of the B chain of PDGF), and then treated with berberine and/or DHEAS in the current study. Cell proliferation assay, cell cycle assay, Western blot, and co-immunoprecipitation were analyzed in A7r5 cells. Antiproliferative effects of berberine and/or DHEAS targeting the Skp2/p27 pathways were evaluated. Berberine and DHEAS can both inhibit the growth of A7r5 cells. Berberine induces cell cycle arrest and potentiates the inhibitory effect of DHEAS through disrupting the binding of p27, p21 with Skp2. Berberine and DHEAS decreased the expression of CDK2, CDK4, PCNA, cyclin D1, and cyclin E, which was induced by PDGF-BB. Being treated with berberine and DHEAS also promoted p27 and p21 bind to CDK2, so the proliferation of A7r5 cells induced by PDGF-BB was inhibited. The data provide evidence that berberine acts through the inhibition of p27-Skp2 and p21-Skp2 with subsequent activation of the cell cycle arrest, which leads to the increase in sensitivity to DHEAS. In summary, the findings suggest that combined berberine and DHEAS will be active in the prevention of restenosis after angioplasty treatment, and the treatment of atherosclerosis.

Selection of aptamers for a non-DNA binding protein in the context of cell lysate

Aptamer-facilitated Protein Isolation from Cells (AptaPIC) is a recently introduced method that allows, in particular, generation of aptamers for a protein target in a context of a crude cell lysate. The approach enables efficient, tag-free, affinity purification of target proteins which are not available in a pure form a priori, and for which no affinity ligands are available. In the proof-of-principle work, AptaPIC was used to develop aptamers for and purify MutS, a DNA mismatch repair protein. The DNA-binding nature of MutS raised concerns that AptaPIC was not a generic technique and could be inapplicable to protein targets that do not possess native nucleic acid-binding properties. Here we prove that these concerns are invalid. We used AptaPIC to generate pools of aptamers for human Platelet-Derived Growth Factor chain B (PDGF-B) protein, a non-DNA binding protein, in the context of a bacterial cell lysate, and subsequently purify it from the same lysate. Within a small number of rounds, the efficiencies of aptamer selection were similar in conventional Systematic Evolution of Ligands by Exponential Enrichment (SELEX) for pure protein and in AptaPIC for protein in the cell lysate. The conventional selection approach resulted in an aptamer pool with an EC 50 value of 2.0 ± 0.1 μM, while the AptaPIC selection approach resulted in a pool with an EC 50 value of 3.9 ± 0.4 μM. Our results clearly demonstrate that selection of aptamers for proteins in the cell lysate is not only realistic but also efficient.

Platelet derived growth factor B and epithelial mesenchymal transition of peritoneal mesothelial cells

Platelet derived growth factor (PDGF) is involved in wound healing in various organ systems. Its potential role in the context of peritoneal injury following long-term peritoneal dialysis is unclear. We used an adenovirus expressing the B chain of PDGF (AdPDGF-B) to assess its effect on pro-fibrotic pathways in the peritoneal membrane. To assess the transforming growth factor (TGF) β independent effects of PDGF, we over-expressed PDGF-B in the peritoneum of either wild-type mice (Smad3 +/+) or those with a deletion of the TGFβ signaling protein Smad3 (Smad3 −/−). PDGF-B induced sustained angiogenesis in both Smad3 +/+ and Smad3 −/− mice. Despite increased collagen gene expression, collagen accumulation was transient and fibrogenesis was associated with induction of collagenase activity. We observed epithelial to mesenchymal transition (EMT) involving the peritoneal mesothelial cells, as shown by increased SNAIL and decreased E-Cadherin expression with evidence of mesothelial cells expressing both epithelial and mesenchymal markers. Unlike TGFβ-induced EMT, PDGF-B exposure did not lead to mobilization of the mesothelial cells; they remained as a single monolayer throughout the observation period. This “non-invasive” EMT phenomenon is a novel finding and may have implications concerning the role of EMT in peritoneal fibrosis and injury to other organ systems. The observed effects were similar in Smad3 −/− and Smad3 +/+ animals, suggesting that the PDGF-B effects were independent of TGFβ or Smad signaling.

Differentiation and Detection of PDGF Isomers and Their Receptors by Tunable Aptamer Capillary Electrophoresis

Tunable aptamer capillary electrophoresis (CE) techniques were developed to enable the separation and detection of platelet derived growth factor (PDGF) isomers and their receptors. Using an aptamer that formed a stable complex with the B chain but not with the A chain of PDGF, we were able to tweak the electrophoretic mobilities of the PDGF isomers for their separation. PDGF-AB bound to a single aptamer molecule was well resolved from PDGF-BB bound to two aptamer molecules. Simultaneous determination of 50 pM of two isomers was accomplished in a single analysis. Furthermore, PDGF-AB was used as a connector to bring receptor alpha and fluorescent aptamer into a single complex molecule. As a result, the formation of a (receptor alpha)-(PDGF-AB)-(fluorescent aptamer) ternary complex enabled the detection of the receptor alpha by tunable aptamer CE. A competitive assay was developed to determine receptor beta, making use of the competition between the receptor beta and fluorescent aptamer in binding to PDGF-BB. Detection limits were 0.5 nM for PDGF receptor alpha and 3 nM for receptor beta. Determination of PDGF isomers and their receptors in diluted serum samples showed no interference from the sample matrix.

Immunohistochemical detection of insulin‐like growth factors, platelet‐derived growth factor, and their receptors in ameloblastic tumors

To evaluate the roles of growth factors in oncogenesis and cytodifferentiation of odontogenic tumors, expression of insulin-like growth factors (IGFs), platelet-derived growth factor (PDGF), and their receptors was analyzed in ameloblastic tumors as well as in tooth germs. Tissue specimens of 10 tooth germs, 47 ameloblastomas, and five malignant ameloblastic tumors were examined immunohistochemically with the use of antibodies against IGF-I, IGF-II, IGF-I receptor (IGF-IR), PDGF A-chain, PDGF B-chain, PDGF alpha-receptor, and PDGF beta-receptor. Immunohistochemical reactivity for IGFs, PDGF chains, and their receptors was detected predominantly in odontogenic epithelial cells near the basement membrane in tooth germs and in benign and malignant ameloblastic tumors. The expression levels of IGF-II and PDGF chains were significantly higher in ameloblastic tumors than in tooth germs. Malignant ameloblastic tumors showed higher reactivity for PDGF chains than benign ameloblastomas and higher reactivity for platelet-derived growth factor receptors than tooth germs. The expression levels of PDGF chains were significantly higher in follicular ameloblastomas than in plexiform ameloblastomas. Desmoplastic ameloblastomas showed higher expression of IGFs and IGF-IR when compared with other ameloblastoma subtypes. Expression of IGFs, PDGF, and their receptors in tooth germs and ameloblastic tumors suggests that these growth factor signals contribute to cell proliferation or survival in both normal and neoplastic odontogenic tissues. Expression of these molecules in odontogenic tissues possibly affects interactions with the bone microenvironment during tooth development and intraosseous progression of ameloblastic tumors. Altered expression of the ligands and receptors in ameloblastic tumors may be involved in oncogenesis, malignant potential, and tumor cell differentiation.

Alteration on the Expression of IL-1, PDGF, TGF-β, EGF, and FGF Receptors and c-Fos and c-Myc Proteins in Bone Marrow Mesenchymal Stroma Cells from Advanced Untreated Lung and Breast Cancer Patients

Previously, we reported a deficient cloning capacity of the bone marrow (BM) mesenchymal stem cells to give colony-forming unit fibroblast (CFU-F) and an inefficient confluence capacity of BM stromal cells in advanced untreated lung cancer patients (LCP) and breast cancer patients (BCP). Moreover, a decreased level of bFGF at day 7 in the conditioned media from BM CFU-F cultures was found in both cancer groups when compared to the normal range. The current study was specially undertaken, to evaluate the percentage of subconfluent fibroblasts expressing receptors (R) of interleukin-1 (IL-1), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), transforming growth factor (TGF-beta), epidermal growth factor (EGF), and the proteins c-Fos and c-Myc in BM primary cultures from untreated LCP and BCP. An immunocytochemical study on subconfluent BM fibroblast cultures from 13 healthy patients, 16 LCP, and 8 BCP was performed, using as primary antibodies, anti-type I of IL-1 R (IL-1R-1), anti-alpha, beta chains of PDGF R (PDGFR-alpha, PDGFR-beta), anti-type I of FGF R (FGFR-I), anti-type I, II, and III of TGF-beta R (TGF-betaR-I, TGF- betaR-II, and TGF-betaR-III), anti-EGF R, anti-c-Fos, and anti-c-Myc. A diminished percentage of subconfluent fibroblasts expressing PDGFR-alpha, TGFbetaR-I, II, III, EGFR, and FGFR-I was found in LCP and BCP compared to healthy patients. A diminished percentage of subconfluent fibroblasts expressing c-Fos and c-Myc was found in patients when compared to healthy patients. The alterations we describe could help to explain the deficiency regarding the proliferative and confluence capacity of BM stroma cells in cancer patients.

Early Growth Response Factor-1 Mediates Prostaglandin E2-dependent Transcriptional Suppression of Cytokine-induced Tumor Necrosis Factor-α Gene Expression in Human Macrophages and Rheumatoid Arthritis-affected Synovial Fibroblasts

Tumor necrosis factor-alpha (TNF-alpha) is a pleiotropic proinflammatory cytokine that modulates a broad range of inflammatory and immunological processes. We have investigated the potential immunomodulatory properties of prostaglandin E2 (PGE2) by examining the molecular mechanism by which the eicosanoid suppresses T-cell-derived interleukin-17 (IL-17)-induced TNF-alpha mRNA expression and protein synthesis in human macrophages and rheumatoid arthritis-affected synovial fibroblasts. Initial studies confirmed that PGE2 induces egr-1 mRNA expression and protein synthesis by restricted SAPK2/p38 MAPK-dependent activating transcription factor-2 (ATF-2) dimer transactivation of the egr-1 promoter as judged by studies using wild-type (WT) and deletion mutant egr-1 promoter constructs, Northern and Western blotting, and standard and supershift electrophoretic mobility shift analyses. Using human leukemic monocytic THP-1 cells stably transfected with WT and dominant-negative mutant expression constructs of Egr-1, cotransfected or not with a WT pTNF-615SVOCAT construct, we observed that PGE2 inhibition of IL-17-stimulated TNF-alpha mRNA expression and promoter activity was dependent on Egr-1 expression, as mutants of Egr-1, alone or in combination, markedly abrogated any inhibitory effect of PGE2. Standard and supershift electrophoretic mobility shift analysis, signaling "decoy" overexpression studies, and pTNF-615SVOCAT promoter assays using WT and mutant promoter constructs revealed that IL-17-up-regulated promoter activity was largely dependent on ATF-2/c-Jun transactivation. PGE2 suppression of IL-17-induced ATF-2/c-Jun transactivation and DNA binding was dependent on Egr-1-mediated inhibition of induced c-Jun expression. We suggest that egr-1 is an immediate-early PGE2 target gene that may be a key regulatory factor in mediating eicosanoid control of genes involved in the immune and inflammatory responses.

PDGF-D and Renal Disease

Life in the platelet-derived growth factor (PDGF) world used to be simple for the last twenty years. The system consisted of two PDGF chains, PDGF-A and -B, that are secreted as homodimers or heterodimers and bind to dimeric PDGF receptors composed of α- and/or β-chains. Whereas PDGF-A binds to

Synthetic DNA aptamers to detect protein molecular variants in a high-throughput fluorescence quenching assay.

Real-time protein detection in homogeneous solutions is necessary in many biotechnology and biomedical studies. The recent development of molecular aptamers, combined with fluorescence techniques, may provide an easy and efficient approach to protein elucidation. This report describes the development of a fluorescence-based assay with synthetic DNA aptamers that can detect and distinguish molecular variants of proteins in biological samples in a high-throughput process. We used an aptamer with high affinity for the B chain of platelet-derived growth factor (PDGF), labeled it with a fluorophore and a quencher at the two termini, and measured fluorescence quenching by PDGF. The specific quenching can be used to detect PDGF at picomolar concentrations even in the presence of serum and other cell-derived proteins in cell culture media. This is the first successful application of a synthetic aptamer for the detection of tumor-related proteins directly from the tumor cells. We also show that three highly related molecular variants of PDGF (AA, AB, and BB dimers) can be distinguished from one another in this single-step assay, which can be readily adapted to a microtiter plate assay for high-throughput analysis. The use of fluorescence quenching as a measure of binding between the DNA probe and the target protein eliminates potential false signals that may arise in traditional fluorescence enhancement assays as a result of degradation of the DNA aptamer by contaminating nucleases in biological specimens. This assay is applicable to proteins that are not naturally DNA binding. The excellent specificity, ultrahigh sensitivity, and simplicity of this one-step assay addresses a growing need for high-throughput methods that detect changes in the expression of gene products and their variants in cell cultures and biological specimens.

Endogenous neutralizing antibodies against platelet-derived growth factor-aa inhibit atherogenesis in the cholesterol-fed rabbit.

Previous studies have shown that the B chain of platelet-derived growth factor (PDGF) has an important role in atherogenesis. In this study we have investigated the contribution of PDGF-A chain in cholesterol-induced atherogenesis in the New Zealand White rabbit. High titers of antibodies to PDGF-AA or to platelet cytosolic protein (PCP) were induced in these animals by immunization against recombinant human PDGF-AA or human PCP. Rabbits were then fed a 0.25% to 1% cholesterol-containing diet for 10 weeks to induce atherosclerotic lesions; the rabbits were then humanely killed and perfusion-fixed and their aortas were removed. The extent of atherosclerosis in the thoracic aortas was determined by quantitative morphometry after staining with oil red O. The intimal and medial areas in histological sections taken at the level of the first intercostal branch were quantified by image analysis. Immunization against PDGF-AA and PCP, but not against adjuvant alone, resulted in rising titers of antibodies within 2 weeks, the levels of which reached a plateau by 8 weeks. The antibodies to PDGF-AA were isoform-specific, recognized both human and rabbit PDGF-AA, and neutralized the biological activity of PDGF-AA in vitro. Integrated plasma cholesterol levels were similar in both groups. Compared with nonimmune rabbits (n=10), animals immunized against PDGF-AA (n=10) or PCP (n=10) had significantly smaller areas of the aorta covered by atherosclerotic lesions (24.6+/-5.1% and 18.7+/-4.2%, respectively, vs 34.4+/-4.3%; P<0.05). This was associated with a reduced aortic intimal-medial area ratio in PDGF-AA-immunized (0.009+/-0.006) and PCP-immunized (0.025+/-0.017) rabbits than in nonimmune animals (0.159+/-0.066; P<0.05). These data suggest that PDGF-AA is actively involved in cholesterol-induced atherosclerosis in the rabbit.

Differentiation-induced internal translation of c-sis mRNA: analysis of the cis elements and their differentiation-linked binding to the hnRNP C protein.

In previous reports we showed that the long 5' untranslated region (5' UTR) of c-sis, the gene encoding the B chain of platelet-derived growth factor, has translational modulating activity due to its differentiation-activated internal ribosomal entry site (D-IRES). Here we show that the 5' UTR contains three regions with a computer-predicted Y-shaped structure upstream of an AUG codon, each of which can confer some degree of internal translation by itself. In nondifferentiated cells, the entire 5' UTR is required for maximal basal IRES activity. The elements required for the differentiation-sensing ability (i.e., D-IRES) were mapped to a 630-nucleotide fragment within the central portion of the 5' UTR. Even though the region responsible for IRES activation is smaller, the full-length 5' UTR is capable of mediating the maximal translation efficiency in differentiated cells, since only the entire 5' UTR is able to confer the maximal basal IRES activity. Interestingly, a 43-kDa protein, identified as hnRNP C, binds in a differentiation-induced manner to the differentiation-sensing region. Using UV cross-linking experiments, we show that while hnRNP C is mainly a nuclear protein, its binding activity to the D-IRES is mostly nuclear in nondifferentiated cells, whereas in differentiated cells such binding activity is associated with the ribosomal fraction. Since the c-sis 5' UTR is a translational modulator in response to cellular changes, it seems that the large number of cross-talking structural entities and the interactions with regulated trans-acting factors are important for the strength of modulation in response to cellular changes. These characteristics may constitute the major difference between strong IRESs, such as those seen in some viruses, and IRESs that serve as translational modulators in response to developmental signals, such as that of c-sis.

Cellular localization of PDGF mRNAs in developing human forebrain.

Platelet-derived growth factor (PDGF) has been implicated in the processes regulating gliogenesis in the CNS. Conflicting in vivo data in rodents have variously implicated either glia or neurons as being the primary source of PDGF. We have used in situ hybridization and immunocytochemical analysis to study the in vivo expression and cellular localization of PDGF-A, sis/PDGF-B, together with the two PDGF receptors alpha and beta, in developing human forebrain. In this study we demonstrate the strong expression of mRNA and protein of both PDGF chains, A and B, and their receptors, alpha and beta, in human embryonic glial cells. The neurons, in contrast to glial cells, expressed lower levels of PDGF and PDGF-receptor mRNAs and protein. Identification of the cell types expressing the PDGF and PDGF-receptor mRNAs was achieved by counterstaining with antibodies specific for glial cells (GFAP) and neurons (NF). The predominant glial-specific expression of both PDGF-A and PDGF-B, together with the coexpression of their receptors alpha and beta, suggests an important role for the PDGF isoforms in the development of human embryonic glial cells and neurons in vivo.

Autocrine growth stimulation of human meningioma cells by platelet-derived growth factor.

The authors have previously shown that meningioma-derived conditioned medium profoundly stimulates the in vitro proliferation of meningioma cells. In this paper, self mitogenic agents found in the conditioned medium-autocrine growth-stimulatory factors actually secreted by human meningioma cells-are characterized as proteins related to the B chain of platelet-derived growth factor (PDGF) and possibly to the A chain of PDGF as well. The addition to conditioned medium of a neutralizing antibody against PDGF-BB caused a significant inhibition of the conditioned medium-stimulated DNA synthesis in all three meningioma cultures studied. A similar neutralizing effect was observed with an anti-PDGF-AA antibody in one meningioma culture studied. Gel filtration chromatography of concentrated conditioned medium from two different meningiomas using a Sephadex G-100 column revealed similar profiles from both conditioned media with a major peak of mitogenic activity against meningioma cells at a molecular weight (M(r)) of approximately 32 to 36 kD, accompanied by a minor peak at approximately 22 kD. The major peak mitogenic activity was significantly reduced by addition of an anti-PDGF-BB antibody. Western blot analysis of protein extracts from five meningioma specimens was performed using a monoclonal antibody against the B chain of PGDF, and a major band of PDGF-B immunoreactivity was detected at an M(r) of approximately 19 kD in all five meningiomas under both reducing and nonreducing conditions. Exogenous human and porcine PDGFs both exhibited a significant dose-dependent stimulation of DNA synthesis in two of three and three of five meningioma cultures examined, respectively. Although not all meningiomas investigated proved to share the biological activity associated with PDGF and these results may be preliminary, it seems that the autocrine growth-stimulatory loop established by PDGF-B-related molecules plays an important functional role in meningioma cell proliferation.

Platelet-derived growth factor.

Platelet-derived growth factor (PDGF) is a potent activator for cells of mesenchymal origin. Two different PDGF chains termed A and B encoded by different genes have been identified leading to three different PDGF isoforms, the AA and BB homodimers and the AB heterodimer. All three forms have been observed in vivo and possess biological activity in vitro with the AA homodimer being the poorest cellular mitogen. The availability of highly purified recombinant PDGF isoforms was the initial basis for comparative studies in order to specify the different spectra of activity of the various PDGF species. This review is particularly focused on the AB heterodimer as from the standpoint of heterologous gene expression, this species is the one with the highest demands concerning expression and purification protocols. This explains the fact that, in comparison to PDGF-BB, only very limited data on the in vivo application of PDGF-AB are available so far.

The Growth-Inhibitory Block of TGF-β Is Located Close to the G1/S Border in the Cell Cycle

Transforming growth factor-β (TGF-β) inhibits DNA synthesis in dense cultures of young human embryonic fibroblasts and antagonizes the mitogenic action of platelet-derived growth factor (PDGF). The inhibition of the PDGF-BB action by TGF-β was independent of the induction of mRNAs for the PDGF-A chain and PDGF-β receptor, the predominant types of PDGF receptor in human fibroblasts. The TGF-β-mediated inhibition did not influence the expression of various genes that are involved in the transition from the arrested (G0) state to the S phase of the cell cycle. Indeed, TGF-β upregulated the "early" genes c-myc, c-fos, and jun B and downregulated the growth arrest-specific (gas) genes. These results suggest that the inhibition of DNA synthesis by TGF-β in human fibroblasts is independent of modulation of expression of early and gas genes, placing the TGF-β block comparatively late in the G0 to S transition. In cultures of senescent human fibroblasts TGF-β stimulated DNA synthesis but, nevertheless, had the same effect as in young cells on the expression of PDGF chains and receptor genes, as well as on early and gas genes, with the exception of a significantly lower induction of c-fos.

The expression of platelet-derived growth-factor gene in Dupuytren contracture.

Dupuytren contracture is a disease of the palmar fascia characterized by nodular fibroblastic proliferation; its etiology and pathogenesis are poorly understood. Growth factors are polypeptides that regulate cell growth and differentiation and extracellular matrix production. Platelet-derived growth factor is known to cause fibroblastic proliferation, and it may be involved in the pathogenesis of Dupuytren contracture. The purpose of this study was to determine if the gene for the B chain of platelet-derived growth factor is expressed in Dupuytren contracture. Tissue from patients who had Dupuytren disease was examined immunohistochemically with the 5B5 antibody, which is a marker for fibroblasts. Polymerase chain reaction, gel electrophoresis, Southern blotting, and in situ hybridization were also used to study gene expression in the tissue as well as in normal fascia, A172 cells, and MRC5 cells. Total cellular RNA was extracted from tissue and cells. Polymerase chain reaction was done with oligonucleotide primers complementary to a portion of the platelet-derived growth-factor-B and platelet-derived growth-factor-receptor genes. The platelet-derived growth-factor-B gene was expressed in all six specimens from the patients who had Dupuytren contracture as well as in the A172 cells, but not in the normal fascia lata or the MRC5 cells. These results were confirmed with Southern blotting of the products of the reaction with a platelet-derived growth-factor-B probe. The gene for the platelet-derived growth-factor receptor was expressed by all tissues and cells studied.(ABSTRACT TRUNCATED AT 250 WORDS)

The biology of SPARC, a protein that modulates cell‐matrix interactions

An extracellular matrix-associated glycoprotein expressed in a variety of tissues during embryogenesis and repair, SPARC contains modular domains that can function independently to bind cells and matrix components. Because SPARC can selectively disrupt cellular contacts with matrix and thereby effect changes in cell shape, it has been referred to as an antiadhesin. Inhibition of the expression of SPARC altered axial development in frogs, and deregulated expression in nematode worms resulted in a derangement of muscle attachment and embryonic lethality. SPARC also inhibits cell cycle progression in vitro, in part through a cationic, disulfide-bonded region that is homologous to a repeated domain in the cytokine inhibitor, follistatin. Moreover, SPARC binds specifically to the B chain of platelet-derived growth factor and alters the response of cells to several cytokines. Although information concerning the expression, biochemical properties, and cellular activities of SPARC has increased significantly over the last decade, the precise function of the protein has not been resolved. Goals of future studies include characterization of cell-surface receptors for SPARC and the interactions with morphogens and growth factors that regulate specific activities during animal development.

Effect of tumor necrosis factor and interferon-gamma on platelet-derived growth factor (PDGF) A and B gene expression in THP-1 monocytic cells

Platelet-derived growth factor (PDGF) is a potent mitogen of mesenchymal cells. A and B chains of PDGF are transcribed in atherosclerotic plaques but details of the mechanism of the expression of either chains in vivo are not understood. It has been suggested that differentiated macrophages, which are the major origin of foam cells, but not monocytes hardly secrete PDGF in vitro. In the present study, we investigated the effect of 1) tumor necrosis factor-alpha (TNF-alpha), a macrophage derived cytokine which promote the differentiation from monocytes to macrophages, and 2) interferon-gamma (IFN-gamma), a T cell derived macrophage activating factor, on the production and mRNA expression of PDGF A and B chains in a human monocytic leukemia cell line THP-1. THP-1 cells were cultured in the presence of one of the experimental cytokines with or without the addition of phorbol 12-myristate 13-acetate (PMA). PMA is known to induce the differentiation of monocytes (including THP-1 cells) to macrophages within a period of 24 hours. Thus the treatment of THP-1 cells with a cytokine and/or PMA in vitro was expected to mimic the effect of the cytokine during the differentiation of monocytes to macrophages in vivo. Unstimulated THP-1 cells expressed no detectable amount of PDGF A or B mRNA. The treatment of THP-1 cells with PMA resulted in the strong expression of both PDGF A and B mRNAs. Stimulated with TNF-alpha (50 U/ml) on day 0, THP-1 cells expressed PDGF A mRNA significantly from 1 up to 3 days after the treatment, whereas the expression of PDGF B and mRNA was only weakly detected on day 2. The maximum signal of PDGF A mRNA was ten times stronger than that of PDGF B mRNA. Within the same period, relatively small number of TNF-alpha treated THP-1 cells had differentiated to macrophages as detected by the reduction of nitro blue tetrazolium (NBT) (35% of total cells) and by the counting of adherent cells (35% of total cells). THP-1 cells simultaneously treated with TNF-alpha and PMA strongly expressed PDGF A and B gene. Most remarkably, the expression of PDGF B mRNA was greatly enhanced with compared to the treatment with PMA alone. In addition, TNF-alpha augmented the secretion of PDGF proteins in PMA stimulated THP-1 cells. In contrast, INF gamma per se had no effect on PDGF gene expression, NBT reducing activity and cell adherence in unstimulated THP-1 cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth Factor mRNA Profiles in Unstimulated Human Mononuclear Cells: Identification of Genes Which Are Constitutively and Variably Expressed

Quiescent human mononuclear cells (MNC) as studied ex vivo express highly specific mRNA patterns of growth factors: We recently demonstrated that unstimulated MNC constitutively express the genes for the A and B chains of platelet-derived growth factor (PDGF). This expression was down-regulated by dietary ω-3 fatty acids. We now report that unstimulated human MNC express the genes for platelet-derived endothelial cell growth factor (PD-ECGF), insulin-like growth factor (IGF-1A, -1B) and transforming growth factor-β1 (TGF-β1). In contrast, acidic and basic fibroblast GF (FGFs), insulin-like GF-2 (IGF-2), transforming GF-α (TGF-α) and epidermal GF (EGF) were not expressed in MNC, nor were α- and β- receptors for PDGF. Quantitatively, as measured over a period of six weeks, expression of PD-ECGF was constant, whereas TGF-β1, IGF-1A, and IGF-1B were expressed at varying levels and all independently of each other. Dietary ω-3 fatty acids had no effect on gene expression. Our results also indicate that down-regulation of PDGF gene expression represents a specific and possibly therapeutic effect of dietary fish oil supplementation.