Aptamer-based colorimetric detection of platelet-derived growth factor using unmodified gold nanoparticles

We developed a simple method for the detection of platelet-derived growth factors (PDGFs) based on base stacking effect coupled with an unmodified gold nanoparticle (AuNP) indicator. In the absence of a target, an aptamer probe and a capture probe stably co-exist in a solution, as it is difficult to sustain an interaction between both these probes due to the short 8bp duplex. However, when a target protein binds to the aptamer probe, the strong base stacking effect can lead to a favorable and stable interaction between the aptamer and capture probes. Hence, the capture probe dissociates from the AuNP surfaces, inducing AuNP aggregation. Compared with other AuNP-based aptasensors for PDGFs, using this base stacking effect can overcome a structured-aptamer method's limitation of requiring thiolated-aptamer-modified AuNPs. Under optimal detection conditions, this label-free colorimetric sensor could detect PDGFs down to 6nM with high selectivity in the presence of other interferring proteins. This simple detection approach provides viable methods for a structured-aptamer sensing protocol.

High-level secretory production of recombinant human platelet-derived growth factor--BB by Saccharomyces cerevisiae under the non-selective conditions

Recombinant human platelet-derived growth factor-BB (rhPDGF-BB) was produced by Saccharomyces cerevisiae. A two-stage cultivation strategy with mixture of glucose and galactose was developed to enhance rhPDGF-BB production, with its concentration being 32 mg/l fermentation broth under optimal conditions: corn steep powder as nitrogen source, 2 g/1 of glucose concentration at the beginning of induction phase, a pH of 5.0 and 6.5 for cell growth and rhPDGF-BB accumulation. The purification process consisted of yeast supernatant ultrafiltration followed by ion exchange chromatography and molecular sieve, and the recovery of rhPDGF-BB was estimated to be 20.28%. Biological activity of the purified rhPDGF-BB was 3.05 ng/ml.

Preliminary separation of the growth factors in platelet-rich plasma: effects on the proliferation of human marrow-derived mesenchymal stem cells

BACKGROUND

Platelet-rich plasma (PRP) as a storage vehicle of growth factors has been successfully used in clinical applications, but in most cases the platelets were autologous. However, the large volume of blood withdrawn has detrimental effects on patients with anemia or poor general health. To overcome these limitations, this study was designed to separate the growth factors in homologous platelet-rich plasma.

METHODS

The gel chromatography with Superdex-75 column was applied to separate PRP supernatants into 4 major fractions. Then the four fractions were vacuumed freeze-dried and re-dissolved in phosphate buffered saline. Proteins concentrations in PRP and in four fractions were detected by bicinchoninic acid protein assay; platelet derived growth factor-AB (PDGF-AB) and transforming growth factor beta1 (TGF-beta1) levels were determined by sandwich enzyme-linked immunosorbent assays. The effects of fractions on the proliferation of human marrow-derived mesenchymal stem cells (MSCs) were determined by 3-(4, 5- dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay.

RESULTS

PRP supernatants were separated into four major fractions by gel chromatography. The proteins recovery was 96.72%. Of the four fractions, fraction B contained the highest TGF-beta1 and PDGF-AB levels, and the highest proteins concentrations. Cell proliferation curves of MSC demonstrated that fraction B and C induced a remarkable increase of MTT values compared to the untreated culture (P < 0.05), and the effects of fraction B and C showed no significant difference compared to the PRP group (P > 0.05). Fraction A and D showed no significant difference to the negative control group (P > 0.05).

CONCLUSIONS

The growth factors in PRP supernatants could be preliminarily separated into four fractions by gel chromatography, and the freeze-drying fractions retained the biological activity of growth factors. The growth factors were mostly presented in fraction B and C, and they promoted cell proliferation effectively.

The molecular cloning of platelet-derived growth factor-C (PDGF-C) gene of Gekko japonicus and its expression change in the spinal cord after tail amputation

The platelet-derived growth factor-C (PDGF-C) gene of Gekko japonicus was obtained from a brain and spinal cord cDNA library. The results of Northern blot showed that transcript of PDGF-C gene of gecko is 2.8 kb in length, and it was abundantly expressed in tissues of heart, lung, kidney, and ovary. In situ hybridization (ISH) revealed that positive hybridization signals were present in both gray matter and white matter of the spinal cord. The change of PDGF-C expression in the spinal cord after tail amputation was examined by reverse transcription polymerase chain reaction (RT-PCR) and Western blot. The expression of PDGF-C in the spinal cord showed highest level at 1 day after tail amputation, and gradually decreased until 2 weeks, which indicated that the expression level of PDGF-C might be associated with the process of spinal cord injury and regeneration.

Platelet-rich plasma and platelet gel preparation using Plateltex

BACKGROUND

The platelet gel is made by embedding concentrate platelets within a semisolid (gel) network of polymerized fibrin. It is believed that this blood component will be used more and more in the treatment of several clinical conditions and as an adjunctive material in tissue engineering. Several systems are available to produce platelet-rich plasma (PRP) for topical therapy. Recently, a new system became commercially available, Plateltex. Here we report the technical performance of this system in comparison with the performance of other commercially available systems: PRGF, PRP-Landesber, Curasan, PCCS, Harvest, Vivostat, Regen and Fibrinet.

MATERIAL AND METHODS

Both the PRP and the gel were prepared according to the manufacturer's directions. The blood samples of 20 donors were used. The yield, the efficiency, and the amount of platelet-derived growth factor AB (PDGF-AB), transforming growth factor beta, vascular endothelial growth factor and fibroblast growth factor were measured in the resulting PRP. The feature of the batroxobin-induced gelation was evaluated.

RESULTS

The yield, the collection efficiency and the growth factor content of Plateltex were comparable to those of most of the other available systems. The gelation time was not dependent on the fibrinogen concentration; however, it was strongly influenced by the contact surface area of the container where the clotting reaction took place (P < 0.0001).

CONCLUSIONS

Plateltex provided platelet recovery, collection efficiency and PDGF-AB availability close to those provided by other systems marketed with the same intended use. Batroxobin, the enzyme provided to induce gelation, acts differently from thrombin, which is used by most other systems. Platelets treated with thrombin become activated; they release their growth factors quickly. Furthermore, thrombin-platelet interaction is a physiological mechanism that hastens the clot-retraction rate. On the contrary, platelets treated with batroxobin do not become activated; they are passively entrapped within the fibrin network, and their growth factor release occurs slowly. In these conditions, the clot retraction takes longer to occur. According to these differences between thrombin and batroxobin, it is expected that batroxobin-induced PRP activation will tailor slow release of the platelet content, thus, providing longer in loco availability of trophic factors. In selected clinical conditions, this durable anabolic factor availability might be preferable to quick thrombin-induced growth factor release.

[The effect of serum rich in platelet-released growth factors on proliferation of rat osteoblast in vitro]

OBJECTIVE

To study the effect of serum rich in platlelet-released growth factors on the biological functions of rat osteoblast.

METHODS

Rat osteoblasts were isolated from parietal bone of fetal Spraque-Dawley (SD) rat. Platelet-rich plasma(PRP) and platelet-poor plasma (PPP) obtained from healthy SD rat were activated by thrombin to get serum rich in growth factors (SRGF) or serum poor in growth factors (SPGF). The cells were treated with 1.25%, 2.5%, 5% SRGF or SPGF, and cellular mitogenic activity was evaluated by thiazoly blue (MTT) colorimetric assay. Results When compared with SPGF at the same concentration, SRGF promoted the proliferation of rat osteoblast significantly (P = 0.002 - 0.004), and the proliferation seemed to correlate with the concentration of SRGF (Spearman's correlation coefficient, r(s) = 0.834).

CONCLUSION

SRGF is capable of upregulating the proliferation of rat osteoblast.

Light-switching excimer probes for rapid protein monitoring in complex biological fluids

Quantitative protein bioanalysis in complex biological fluids presents considerable challenges in biological studies and disease diagnosis. The major obstacles are the background signals from both the probe and the biological fluids where the proteins reside. We have molecularly engineered light-switching excimer aptamer probes for rapid and sensitive detection of a biomarker protein, platelet-derived growth factor (PDGF). Labeled with one pyrene at each end, the aptamer switches its fluorescence emission from approximately 400 nm (pyrene monomer) to 485 nm (pyrene excimer) upon PDGF binding. This fluorescence wavelength change from monomer to excimer emission is a result of aptamer conformation rearrangement induced by target binding. The excimer probe is able to effectively detect picomolar PDGF in homogeneous solutions. Because the excimer has a much longer fluorescence lifetime (approximately 40 ns) than that of the background (approximately 5 ns), time-resolved measurements were used to eliminate the biological background. We thus were able to detect PDGF in a cell sample quantitatively without any sample pretreatment. This molecular engineering strategy can be used to develop other aptamer probes for protein monitoring. Combined with lifetime-based measurements and molecular engineering, light-switching excimer aptamer probes hold great potential in protein analysis for biomedical studies.

Unique in vivo modifications of coagulation factor V produce a physically and functionally distinct platelet-derived cofactor: characterization of purified platelet-derived factor V/Va

Platelet- and plasma-derived factor Va (FVa) serve essential cofactor roles in prothrombinase-catalyzed thrombin generation. Platelet-derived FV/Va, purified from Triton X-100 platelet lysates was composed of a mixture of polypeptides ranging from approximately 40 to 330 kDa, mimicking those visualized by Western blotting of platelet lysates and releasates with anti-FV antibodies. The purified, platelet-derived protein expressed significant cofactor activity such that thrombin activation led to only a 2-3-fold increase in cofactor activity yet expression of a specific activity identical to that of purified, plasma-derived FVa. Physical and functional differences between the two cofactors were identified. Purified, platelet-derived FVa was 2-3-fold more resistant to activated protein C-catalyzed inactivation than purified plasma-derived FVa on the thrombin-activated platelet surface. The heavy chain subunit of purified, platelet-derived FVa contained only a fraction ( approximately 10-15%) of the intrinsic phosphoserine present in the plasma-derived FVa heavy chain and was resistant to phosphorylation at Ser(692) catalyzed by either casein kinase II or thrombin-activated platelets. MALDI-TOF mass spectrometric analyses of tryptic digests of platelet-derived FV peptides detected an intact heavy chain uniquely modified on Thr(402) with an N-acetylglucosamine or N-acetylgalactosamine, whereas Ser(692) remained unmodified. N-terminal sequencing and MALDI-TOF analyses of platelet-derived FV/Va peptides identified the presence of a full-length heavy chain subunit, as well as a light chain subunit formed by cleavage at Tyr(1543) rather than Arg(1545) accounting for the intrinsic levels of cofactor activity exhibited by native platelet-derived FVa. These collective data are the first to demonstrate physical differences between the two FV cofactor pools and support the hypothesis that, subsequent to its endocytosis by megakaryocytes, FV is modified to yield a platelet-derived cofactor distinct from its plasma counterpart.

Analysis of recombinant human platelet-derived growth factor by reversed-charge capillary zone electrophoresis

Reversed-charge capillary zone electrophoresis (RC-CZE) has been developed as a clipping (proteolysis) assay for homodimeric protein recombinant human platelet-derived growth factor (rhPDGF-BB), a major serum mitogenic factor involved in subcutaneous wound healing. When expressed in yeast, the protein is excreted as a fully folded homodimeric protein consisting of two antiparallel B chains held together by two interchain disulfide bonds. During fermentation, internal proteolysis (clipping between residues Arg32 and Thr33) and C-terminal truncation (Arg32 and Thr109) may occur. Internal proteolysis yields three potential forms of rhPDGF-BB: intact (both B chains are intact), single-clipped (one B chain is clipped), and double-clipped (both B chains are clipped). Clipping also creates new C-terminal sites for further C-terminal truncations and leads to a very complex mixture of isoforms. Routine baseline resolution of these three forms by various modes of HPLC proved unsuccessful. When the disulfide bonds of antiparallel chains are reduced, the complex peptide mixture can be analyzed by RP-HPLC; however, only the level of total clipping is identified. Since RC-CZE separation relies upon differences in molecular charge/size ratio, it can resolve the three rhPDGF-BB forms differing in the additional exposed residues. The choice of reversed-charge CZE columns (amine-coated column) allows proteins of high pI such as rhPDGF-BB (pI > 10) to be readily analyzed while minimizing protein loss from column adsorption. To simplify the electropherogram of clipped forms, the sample is treated first with carboxypeptidase B to reduce the charge microheterogeneity of partial Arg32 truncation. Analysis of rhPDGF-BB by RC-CZE yields a baseline separation between the three forms, intact and single- and double-clipped rhPDGF-BB.

Platelet-rich plasma: Growth factor enhancement for bone grafts

Platelet-rich plasma is an autologous source of platelet-derived growth factor and transforming growth factor beta that is obtained by sequestering and concentrating platelets by gradient density centrifugation. This technique produced a concentration of human platelets of 338% and identified platelet-derived growth factor and transforming growth factor beta within them. Monoclonal antibody assessment of cancellous cellular marrow grafts demonstrated cells that were capable of responding to the growth factors by bearing cell membrane receptors. The additional amounts of these growth factors obtained by adding platelet-rich plasma to grafts evidenced a radiographic maturation rate 1.62 to 2.16 times that of grafts without platelet-rich plasma. As assessed by histomorphometry, there was also a greater bone density in grafts in which platelet-rich plasma was added (74.0% +/- 11%) than in grafts in which platelet-rich plasma was not added (55.1% +/- 8%; p = 0.005).

Gastric epithelial cells secrete a PDGF-like peptide, a potent mitogen for human gastric fibroblasts

To investigate whether gastric epithelial cells secrete growth factors involved in stromal cell growth, we examined the effects of conditioned media obtained from gastric cancer cells on murine BALB/c 3T3 cells and primary cultured human gastric fibroblasts. Conditioned media from MKN-1 gastric cancer cells were applied to a heparin-affinity column. The fraction eluted from the column at 0.4 M NaCl stimulated DNA synthesis and phosphorylation of PDGF alpha-receptors on tyrosine in BALB/c 3T3 cells. The fraction-induced stimulation of DNA synthesis in gastric fibroblasts was more marked than in BALB/c 3T3 cells. However, the fraction failed to stimulate DNA synthesis in CHO-ER cells overexpressing EGF receptors and phosphorylation of PDGF beta-receptors on tyrosine in BALB/c 3T3 cells. Immunoblot analysis of the media confirmed that PDGF-AA-like peptides are released from gastric cancer cells, immortalized gastric epithelial cells, and primary cultured gastric epithelial cells. Anti-PDGF neutralizing antibodies produced only a partial inhibition of 0.4 M NaCl fraction-induced enhanced DNA synthesis. Thus, in addition to PDGF-AA peptide, other bioactive substance(s) are probably released from MKN-1 gastric cancer cells. Our results suggest that gastric epithelial cells secrete PDGF-AA-like peptides responsible for stromal cell growth through paracrine mechanisms.

Tractional force generation by porcine Müller cells: stimulation by growth factors in human vitreous

PURPOSE

To examine the levels of Müller cell contraction-stimulating activity in human vitreous, correlate these levels with clinical presentation, and identify, the causative growth factors.

METHODS

Human vitreous was collected from patients undergoing pars plana vitrectomy (n = 84). Müller cells were isolated from porcine retina and maintained in tissue culture. Tractional forces generated by cells incubated on three-dimensional collagen gels were measured as changes in gel thickness. Contraction-stimulating activity in vitreous (VA) was calculated from the close-response profiles of gel contraction to vitreous protein. The contributions of individual growth factors to vitreous activity (n = 10) were assessed by inhibition with specific neutralizing antibodies.

RESULTS

The mean VA of patients with retinal detachment (3.65) and proliferative vitreoretinopathy stages A, B, and C (2.06) were elevated above that of patients without retinal pathology (vitreous activity = 0.23) or retinal defects alone (0.57). Mean activities in patients with epimacular proliferation (1.22) and vitreous hemorrhage (1.40) were also significantly elevated. The percentage of this activity attributable to insulin-like growth factor 1 (IGF-1) varied from 9.2% to 84.5% with a mean of 61.3%. Similarly, the percent contribution of platelet-derived growth factor (PDGF) ranged from 6.8% to 49.0% with a mean of 26.5%.

CONCLUSIONS

The vitreous of patients with retinal detachment, proliferative retinal disease, and vitreous hemorrhage contain varying amounts of growth factors that stimulate tractional force generation by Müller cells. The majority of the activity can be attributed to IGF-1 and a smaller proportion to PDGF.

Platelet-derived growth factor in bronchiolitis obliterans-organizing pneumonia

Bronchiolitis obliterans-organizing pneumonia (BOOP) is a disorder characterized by intraluminal proliferation of connective tissue in distal air spaces. As part of a general investigation of the role of growth factors in this process, the present study examined the expression of the mitogen, platelet-derived growth factor (PDGF), and one of its receptors, PDGFR-beta, in this disease. Serial sections of lung biopsy specimens from 20 patients with BOOP and 10 control subjects were stained with antibodies against PDGF, PDGFR-beta, and the monocyte/macrophage marker CD68. Stereologic point counting showed that PDGF+ cells represented 4.6 +/- 1.6% (mean +/- SD) of the volume occupied by lung tissue in BOOP and 2.1 +/- 0.7% in the control subjects (p < 0.0001). In both groups the positive cells were tissue macrophages, and CD68+ macrophages accounted for 10.7 +/- 4.7% of the lung tissue in BOOP as compared with 5.4 +/- 3.7% in the control subjects (p < 0.005). PDGFR-beta immunoreactivity was present in some alveolar epithelial cells in BOOP, but was absent in control subjects. We conclude that PDGF+ cells and CD68+ macrophages are found in greater numbers in lungs with BOOP, and an increased expression of PDGFR-beta epitopes was observed in some patients with BOOP. We speculate that these molecules are important in the pathogenesis of the destructive fibroproliferative process that characterizes this disease.

Mistranslation of a TGA termination codon as tryptophan in recombinant platelet-derived growth factor expressed in Escherichia coli

The mature 109-amino-acid human platelet-derived growth factor B (PDGF-B) peptide is derived by intracellular processing from a 241-amino-acid precursor synthesized in mammalian cells, with removal of 81 N-terminal and 51 C-terminal amino acids. In order to produce directly the mature 109-amino acid PDGF-B peptide as a recombinant protein in Escherichia coli, a CGA codon at position 110 of a DNA sequence encoding the full-length precursor form of PDGF-B was converted into the translation termination codon TGA by in vitro mutagenesis. Expression of this DNA via a plasmid vector in E. coli resulted in production of two distinct PDGF-B proteins having apparent molecular masses of 15 and 19 kDa, with the latter species predominating. Structural characterization employing N- and C-terminal amino acid sequencing and MS analyses indicated that the 15 kDa protein is the expected 109-amino-acid PDGF-B, and that the 19 kDa protein represents a C-terminal extended PDGF-B containing 160 amino acids. Characterization of a unique tryptic peptide derived from the 19 kDa protein revealed that this longer form of PDGF-B results from mistranslation of the introduced TGA termination codon at position 110 as tryptophan, with translation subsequently proceeding to the naturally occurring TAG termination codon at position 161. Owing to the high rate of translation readthrough of TGA codons in this and occasionally other proteins, it appears that the use of TGA as a translation termination codon for proteins to be expressed in E. coli should be avoided when possible.

Inhibition of platelet-derived growth factor-BB-induced fibroblast proliferation by plasmin-activated alpha 2-macroglobulin is mediated via an alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein-dependent mechanism

alpha 2-Macroglobulin (alpha 2M) is a potentially important regulator of platelet-derived growth factor-BB (PDGF-BB)-stimulated cell growth due to our previous observation that PDGF-BB binds to alpha 2M noncovalently (Bonner, J. C., Goodell, A. L., Lasky, J. A., and Hoffman, M. R. (1992) J. Biol. Chem. 267, 12837-12844). We examined the in vitro effect of native and plasmin-activated (receptor-recognized) alpha 2M on the PDGF-BB-induced proliferation of mouse Swiss 3T3 and rat lung fibroblasts. Nondenaturing polyacrylamide gel electrophoresis showed that plasmin converted alpha 2M to its electrophoretically "fast" form at a 2:1 molar ratio and that 125I-PDGF-BB bound both alpha 2M and alpha 2M-plasmin. PDGF-BB-induced growth was not affected by native alpha 2M (0.3 microM) or plasmin (0.6 microM). The combination of plasmin and alpha 2M (2:1 molar ratio) inhibited PDGF-BB-induced cell proliferation 80-90%. Complexes of PDGF-BB.alpha 2M purified by gel filtration chromatography retained growth promoting activity, but the PDGF-BB.alpha 2M-plasmin complex did not. Preincubation of fibroblasts (37 degrees C for 24 h) with alpha 2M-plasmin did not change 125I-PDGF-BB binding or affect gene expression of the 6.5-kilobase PDGF-alpha receptor or 5.2-kilobase PDGF-beta receptor mRNA. However, preincubation with alpha 2M-plasmin (0-4 degrees C for 4 h) increased 125I-PDGF-BB binding 2-fold, and this increase was blocked by a receptor-associated protein antagonist of the alpha 2M-receptor/low density lipoprotein receptor-related protein. The receptor-associated protein antagonist blocked 125I-alpha 2M-methylamine binding, inhibited PDGF-BB-alpha 2M-plasmin uptake from fibroblast-cultured supernatants, and abolished the inhibitory effect of alpha 2M-plasmin on PDGF-stimulated growth. These data suggest that inhibition of PDGF-stimulated proliferation by alpha 2M-plasmin is mediated in part by clearance of PDGF-BB-alpha 2M-plasmin through the lipoprotein receptor-related protein.

p53 expression during normal tissue regeneration in response to acute cutaneous injury in swine

The present studies investigated the in vivo expression of the p53 suppressor gene and protein product in response to acute cutaneous injury in swine, along with the parallel expression of the c-sis/PDGF-B mitogen and its receptor beta (PDGF-R beta). p53 expression was shown to be suppressed during the period of active cellular proliferation in the injured tissue and to reemerge during the stages of healing. In contrast, c-sis/PDGF-B and PDGF-R beta were expressed during the early phase of active cellular proliferation and they were suppressed upon healing. This inverse relationship between mitogenic growth factors and p53 suggests the presence of well-controlled physiologic mechanisms that regulate in vivo the processes of normal tissue repair in response to injury. At the stages of tissue regeneration, these mechanisms include both the expression of growth factors that promote cell proliferation and the suppression of p53 that downregulates proliferation. At the stages of healing, the expression of the mitogenic growth factors is suppressed and that of p53 reemerges, reaching its peak at the time of complete epithelialization and healing of the injured tissue. These studies are the first to link the response of p53 protein to physiologic processes of tissue regeneration in vivo.

Characterization of disulfide linkages in platelet-derived growth factor AA

Intermolecular and intramolecular disulfide linkages of recombinant human platelet-derived growth factor A chain dimer were determined by chemical methods including selective reduction-alkylation, peptide isolation, or detection of diphenylthiohydantoin derivative of cystine from Edman reactions. Cys-37 and Cys-46 were selectively reduced with reducing agents under native conditions and revealed to be involved in intermolecular bridges. Other disulfide linkages including Cys-10-Cys-54, Cys-43-Cys-91, and Cys-47-Cys-93 form intramolecular bridges. The disulfide structure is homologous to that of platelet-derived growth factor B chain dimer.

Glucocorticoid inhibits thrombin-induced expression of platelet-derived growth factor A-chain and heparin-binding epidermal growth factor-like growth factor in human aortic smooth muscle cells

Proliferation of smooth muscle cells (SMCs) in atherosclerosis may be modulated by several growth regulatory molecules. At least two mitogens for SMCs, platelet-derived growth factor (PDGF) A-chain and heparin-binding epidermal growth factor-like growth factor (HB-EGF), can be produced by SMCs themselves and may stimulate smooth muscle proliferation in an autocrine or paracrine fashion. We examined the effects of thrombin, which may be generated at the site of vascular injury during atherogenesis, and the potent anti-inflammatory glucocorticoid, dexamethasone (DEX), on the expression of the genes encoding these two growth factors. Since both PDGF A-chain and HB-EGF have affinity for heparin, we also examined the effect of thrombin and DEX on the release of heparin binding mitogenic activity from SMCs. Treatment of SMCs with thrombin resulted in increases both in the level of the PDGF-A and HB-EGF transcripts in the cells, as well as in released heparin-binding growth factor activity. DEX inhibits the thrombin-stimulated release of mitogenic activity in a dose-dependent manner. An enzyme-linked immunoadsorbent assay showed that DEX inhibits both constitutive and thrombin-stimulated release of PDGF-AA. DEX also decreases both constitutive and thrombin-stimulated mRNA levels for PDGF A-chain and HB-EGF and destabilizes the transcripts for both growth factors. A nuclear run-on assay revealed that DEX acts, in addition, to inhibit constitutive and thrombin-stimulated transcription of the PDGF A-chain and HB-EGF genes. Thus, these findings indicate that expression of PDGF A-chain and HB-EGF may be regulated by thrombin and glucocorticoid at the transcription level. Our results are consistent with the involvement of thrombin-induced growth factor expression in neointimal SMC proliferation and suggest the possibility that intimal proliferation may be attenuated by glucocorticoids.

Growth factor production by human thyroid carcinoma cells: abundant expression of a platelet-derived growth factor-B-like protein by a human papillary carcinoma cell line

As papillary thyroid carcinoma cells grow surrounding finger-like structures of stromal tissue, we postulated they may secrete a growth factor(s) for mesenchymal cells and that these would be distinct from any mitogenic factors elaborated by follicular carcinomas. Conditioned medium from both the human papillary carcinoma cell line NPA and the follicular carcinoma cell line WRO evoked a 20- to 30-fold increase in [3H]thymidine incorporation into NIH3T3 cell DNA. NPA cell growth factor activity largely eluted with 0.5 mol/L NaCl from a heparin-Sepharose column. NPA-conditioned medium competed in a platelet-derived growth factor-B (PDGF-B) RRA, and the mitogenic activity was partially blocked by an anti-PDGF-BB antibody. An immunoprecipitated PDGF-B-like protein from NPA cells was about 17 kilodaltons in a reducing gel, but, in contrast to wild-type PDGF-BB, did not change its electrophoretic mobility in an unreduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis. NPA cells expressed an abundant 1.4-kilobase RNA that hybridized to probes for the 5'-untranslated and amino-terminal domains of PDGF-B and was distinct from the 4.2-kilobase wild-type PDGF-B chain transcript. There were no structural changes in the PDGF-B gene, as determined by cytogenetic analysis and restriction mapping. However, the PDGF-B gene in the NPA cells was hypomethylated compared to that in normal thyroid tissue or WRO cells. In contrast, the mitogenic activity of WRO cells bound to heparin with high affinity and was blocked by a basic fibroblast growth factor (bFGF) antibody. WRO cells contained abundant bFGF mRNA. Both cell lines abundantly expressed transforming growth factor-beta mRNA. Thus, NPA and WRO cells express powerful, yet distinct, mesenchymal cell growth factors. Whereas WRO cells express abundant bFGF, NPA cells produce a novel PDGF-B-like protein, which may correspond to a mutated form of PDGF-B-chain.

Mechanism of tetracycline-hydrochloride-induced pleurodesis. Tetracycline-hydrochloride-stimulated mesothelial cells produce a growth-factor-like activity for fibroblasts

Intrapleural instillation of tetracycline hydrochloride (TCN) is an effective means of achieving pleural fibrosis. However, its mechanism of action remains unknown. To evaluate the hypothesis that TCN stimulates pleural mesothelial cells to release growth-factor-like activity for fibroblasts we performed the following experiments. Rat visceral pleural mesothelial cells were incubated with TCN at doses ranging from 0.01 microgram/ml to 100 mg/ml. The conditioned media (CM) were collected after incubation for 2 to 48 h. CM caused fibroblasts to increase incorporation of thymidine when compared with CM that was unexposed to TCN (p less than 0.05). This growth-factor-like activity continued to be produced by mesothelial cells for 48 h after removal of TCN from the medium. There was a dose-response relationship since increasing doses of TCN to as much as 1 mg/ml caused increasing production of growth-factor-like activity without mesothelial cell injury as measured by trypan blue exclusion. The growth factor activity was a competence-type activity. It coeluted with human PDGF at a molecular weight of 31,000. It was heat-stable (100 degrees C for 10 min) and sensitive to trypsin and papain but not to heat-inactivated trypsin. Addition of cycloheximide or actinomycin D inhibited its production. TCN did not have any direct effect on fibroblasts. Bleomycin CM did not contain growth-factor-like activity for fibroblasts. These data demonstrate that TCN stimulates mesothelial cells to release a growth-factor-like activity for fibroblasts. This phenomenon may play an important role in TCN-induced pleural fibrosis.

Platelet-derived growth factor and alternative splicing: a review

The mitogenic and chemotactic potency of platelet-derived growth factor (PDGF) has linked this polypeptide to the pathogenesis of several disease states including atherosclerosis and neoplasia. We have reviewed the recent literature on aspects relating to the structure, distribution and biology of PDGF and its high-affinity cell-surface and intracellular receptors. In addition to platelets, several normal and tumor cells secrete the mitogen in one or more of three possible dimeric configurations. Alternative splicing of exon 6 in PDGF A-chain RNA results in the formation of two protein species with different carboxy-termini. Initially, it was thought that the longer A-chain variant was processed only by transformed cells. However, recent evidence indicates that alternative splicing occurs in several cells which express the A-chain, including early Xenopus embryos. The functional significance of the exon 6 product, a highly basic region spanned by 18 amino acid residues (A194-211), is not precisely clear. We have summarized recent findings which implicate roles for A194-211 in the processing, secretion, and mitogenesis of the A-chain homodimer, nuclear transport signalling, and heparin binding. Thus, alternative splicing could play an important role in the modulation of the functional properties of the PDGF A-chain variants per se and in the complex interactive network of polypeptide growth factors and cytokines.

Absence of PDGF-induced, PKC-independent c-fos expression in a chemically transformed C3H/10T1/2 cell clone

The effect of platelet-derived growth factor (PDGF) on c-fos mRNA transcription was studied in the immortalized mouse embryo fibroblast C3H/10T1/2 Cl 8 (10T1/2) cells and the chemically transformed, tumorigenic subclone C3H/10T1/2 Cl 16 (Cl 16). In the 10T1/2 cells as well as the Cl 16 subclone, the dose-dependent PDGF stimulation of c-fos mRNA synthesis was similar in both logarithmically growing and confluent cultures. c-fos mRNA was induced severalfold by 12-O-tetradecanoylphorbol-13-acetate (TPA) in both 10T1/2 and Cl 16. Down-regulation of protein kinase C (PKC) activity by TPA pretreatment inhibited PDGF-stimulated c-fos mRNA expression in Cl 16 cells but did not affect this induction in the 10T1/2 cells. This inhibition was not a general phenomenon of 3-methylcholanthrene-mediated transformation of 10T1/2 cells since experiments with another transformed 10T1/2 cell clone, C3H/10T1/2 TPA 482, gave qualitatively the same results as the 10T1/2 cells. Receptor binding experiments showed that the nontransformed and transformed cells had a comparable number of PDGF receptors, 1.3 x 10(5) and 0.7 x 10(5) receptors per cell, respectively. Furthermore, cAMP-induced c-fos expression induced by forskolin is formerly shown to be independent of PKC down-regulation. In our experiments, forskolin induced c-fos expression in both clones. However, PKC down-regulation inhibited the forskolin-induced c-fos expression in Cl 16 cells. This apparently demonstrates cross talk between PKC and PKA in the c-fos induction pathway. The present results provide evidence for an impaired mechanism for activating c-fos expression through PKC-independent, PDGF-induced signal transduction in the chemically transformed Cl 16 fibroblasts compared to that in nontransformed 10T1/2 cells.

Proteins derived from platelet alpha granules modulate the uptake of oxidized low density lipoprotein by macrophages

Activated platelets secrete from their alpha granules a protein-like factor which stimulates the uptake of oxidized low-density lipoprotein (Ox-LDL) by macrophages. The aim of the present study was to evaluate the effect of three purified proteins obtained from platelet alpha granules: platelet-derived growth factor (PDGF), platelet factor-4 (PF-4), and beta-thromboglobulin (B-TG), on the uptake of Ox-LDL by macrophages. Cellular degradation of Ox-LDL by the J-774 A.1 macrophage-like cell line, that was preincubated for 18 h at 37 degrees C, with increasing concentrations of partially purified PDGF, (designated PDGF-CMS-III) was increased by up to 36% in comparison to control cells preincubated without PDGF. This effect was due to PDGF-mediated increase in the number of macrophage receptors for Ox-LDL. The enhanced uptake of Ox-LDL by PDGF resulted in an increase in cellular cholesterol content. Preincubation of macrophages with two types of recombinant PDGF dimers (10 ng/ml), revealed that PDGF-BB stimulated Ox-LDL cellular degradation by 64%, whereas PDGF-AB demonstrated only 34% stimulation, in comparison to control cells that were not treated with PDGF. The stimulatory effect of PDGF-CMS-III and PDGF-AB were reduced by 20% and 28%, respectively, when incubated in the presence of H-7, a specific protein kinase C inhibitor. When macrophages were preincubated with B-TG, cellular uptake of Ox-LDL was reduced by up to 30% at 100 ng B-TG/ml. This effect, however, was obtained only when B-TG was present in the incubation medium. Cellular degradation of Ox-LDL was not affected by preincubation of the cells with PF-4. Pretreatment of PCM with anti-PDGF or anti-B-TG antibodies abolished the effects of PCM on Ox-LDL degradation by macrophages. PDGF, thus, may represent the protein-like factor present in PCM which stimulates Ox-LDL degradation by macrophages, whereas B-TG may have a role in the recognition of PCM particles by the macrophage scavenger receptor. Modulation of macrophage cholesterol content by proteins secreted from activated platelets may have an important role in foam cell formation and atherosclerosis.

Changes in growth factor levels in human wound fluid

BACKGROUND

It has been suggested that platelet-derived growth factor (PDGF) plays a central role in wound healing. Analysis of human wound fluid revealed the presence of PDGF AA (30 kd) and monocyte/macrophage-derived growth factor (MDGF) (12 to 14 kd) in the immediate postoperative period.

METHODS

The amount of PDGF AA present was assayed by Western blot analysis. The chemotactic and mitogenic potential of purified wound fluid containing PDGF AA and MDGF was determined on a responsive cell line. The biologic activity of MDGF was assayed with a cell line that is unresponsive to the PDGF AA found in wound fluid.

RESULTS

Both the concentration and the biologic activity were highest in the immediate postoperative period and declined to negligible levels by 24 hours after surgery. The chemotactic activity of MDGF was highest in the immediate postoperative period and declined during the first 24 hours in a manner similar to that of the combined PDGF AA and MDGF activity.

CONCLUSIONS

These data demonstrate the changing levels of PDGF and MDGF in human wound fluid over time, supporting the cascade model of wound repair. By demonstrating that MDGF acts on cell lines unresponsive to the PDGF AA found in wound fluid, these data suggest that MDGF may also play an important role in wound healing.

Isolation and purification of a biologically active human platelet-derived growth factor BB expressed in Escherichia coli

Human platelet-derived growth factor (PDGF) was expressed in Escherichia coli from a high-level cytoplasmic expression vector. A cDNA fragment encoding the mature form of the human PDGF B chain (hPDGF-B) was cloned into a plasmid under transcriptional control of the inducible E. coli Tac promoter. Expression of hPDGF-B from the final construct, pTacBIq, is regulated by the lactose repressor (LacIq). Upon induction, a polypeptide of approximately 14 kDa that had the same molecular mass and immunoreactivity as authentic hPDGF-B was produced. The production of recombinant hPDGF-B was significantly increased in an E. coli strain (CAG629) defective in expression of the lon protease. Expression of hPDGF-B in the CAG629 strain accounted for approximately 1% of total cell protein. In this system, hPDGF-B is expressed as an insoluble, intracellular protein and can readily be obtained in a partially purified form after differential centrifugation. Amino acid sequence determination of the purified protein has verified that the amino-terminal portion of the recombinant PDGF is correct. After renaturation into dimers, the purified recombinant hPDGF is fully functional in assays for receptor binding and mitogenesis.

Ligand-induced polyubiquitination of the platelet-derived growth factor beta-receptor

We have analyzed the nature of ligand-induced shift to higher molecular weight forms of the beta-receptor for platelet-derived growth factor expressed in porcine aortic endothelial cells. The modification of the beta-receptor was found to be due to polyubiquitination, as judged by immunoblotting using an anti-ubiquitin antiserum. A mutant beta-receptor made kinase negative by a point mutation (K634A mutant) did not undergo ubiquitination in response to ligand stimulation. A mutant in which carboxyl-terminal 98 amino acids were deleted (CT98 mutant) and which retained kinase activity was likewise not ubiquitinated. These data suggest that the kinase activity, as well as the carboxyl-terminal 98 amino acids, is required for ubiquitination of the beta-receptor. Ligand-induced degradation of the receptor-bound ligand, as well as of the receptor itself, was partially impaired in the CT98-receptor-expressing cells, suggesting that the ubiquitination is of importance for efficient degradation of the ligand-receptor complex.

Characterization of the structure and conformation of platelet-derived growth factor-BB (PDGF-BB) and proteinase-resistant mutants of PDGF-BB expressed in Saccharomyces cerevisiae

A detailed biophysical study of the secondary and tertiary structures of recombinant platelet-derived growth factor (PDGF)-BB produced in yeast has been carried out. The secondary structure of the molecule is composed of 54% beta-sheet with less than 5% ordered helix. The single tryptophan residue has been shown to be solvent-accessible; however, the ability of the side chain to rotate is severely restricted. The fluorescence emission is quenched at pH 7.0 and in the presence of high salt, but dequenched by titration to lower pH with a pK of 5.8. Two proteinase-resistant mutants of PDGF [( Ser28]- and [Pro32]-PDGF-BB) have also been characterized and shown to have secondary and tertiary structures indistinguishable from wild-type PDGF-BB. These are, therefore, suitable stable background molecules in which to carry out structure-activity-relationship studies on PDGF-BB.

Purification and analysis of proteinase-resistant mutants of recombinant platelet-derived growth factor-BB exhibiting improved biological activity

Recombinant platelet-derived growth factor (PDGF)-BB was expressed and secreted from yeast in order to study the structure-function relationships of this mitogen. A simple purification scheme has been developed which yields greater than 95% pure PDGF-BB. Analysis of this recombinant PDGF-BB shows partial proteolysis after arginine-32. Substitution of this arginine residue, or arginine-28 [a potential KEX2 (lysine-arginine endopeptidase) cleavage site], prevents or reduces cleavage of PDGF-BB respectively. These mutations result in a 5-fold increase in expression levels of PDGF-BB, and the resulting mutant proteins show higher activity in a number of biological assays than the cleaved wildtype PDGF-BB. These data are in accord with previous work by Giese, LaRochelle, May-Siroff, Robbins & Aaronson [(1990) Mol. Cell Biol. 10, 5496-5501] suggesting that the region isoleucine-25-phenylalanine-37 is involved in PDGF-receptor binding.

Human wound fluid from acute wounds stimulates fibroblast and endothelial cell growth

One proposed mechanism for the beneficial effect of occlusive dressings on healing is the maintenance of contact between the wound bed and accumulated wound fluid, which is thought to contain growth stimulatory substances. We have examined the effect of human wound fluid on the in vitro growth of human dermal fibroblasts and umbilical vein endothelial cells. Acute wound fluid was collected from six patients undergoing split-thickness skin grafting. The acute wound fluid was sterilely collected daily from underneath a vapor-permeable membrane applied to the donor site and changed every 24 hours for 3 days postoperatively. After seeding in optimal growth media (control) on day 0, cultures of human dermal fibroblasts and umbilical vein endothelial cells were supplemented with or without acute wound fluid on the next day (day 1) and on day 3. As determined by cell counts, 2% acute wound fluid stimulated the growth of human dermal fibroblasts (p less than 0.05) and umbilical vein endothelial cells (p less than 0.01) when these cells were cultured in 2% fetal bovine serum and endothelial growth medium, respectively. Wound fluid from postoperative days 1 or 3 caused the same level of stimulation. The addition of an anti-platelet-derived growth factor antibody to wound fluid resulted in a 45% mean reduction in its stimulatory effect on fibroblast growth (p less than 0.02), suggesting that platelet-derived growth factor contributes to the observed effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential proliferation of rat lung fibroblasts induced by the platelet-derived growth factor-AA, -AB, and -BB isoforms secreted by rat alveolar macrophages

Platelet-derived growth factor (PDGF)-like molecules secreted by alveolar macrophages have been postulated to be mediators of lung fibrogenesis since these cytokines stimulate the proliferation and chemotaxis of lung fibroblasts. We are studying the biology and biochemistry of rat macrophage-derived PDGF and have identified for the first time the specific isoforms of PDGF (-AA, -AB, and -BB) that these macrophages secreted in vitro following activation with either chrysotile asbestos or carbonyl iron spheres. Subsequently, the proliferative response of rat lung fibroblasts (RLF) to the different PDGF isoforms was established. Using several antibodies raised against the distinct isoforms, we established that two different PDGF-like factors with molecular masses of 30 to 34 kD and 16 to 18 kD were contained in alveolar macrophage-conditioned medium. Within each of these molecular mass regions was a mixture of all three PDGF isoforms. We estimated that the 30- to 34-kD PDGF was mainly PDGF-BB (approximately 50%), while the remaining consisted of PDGF-AA (approximately 13%) and PDGF-AB (approximately 37%). Purified recombinant PDGF isoforms were tested for their ability to stimulate the growth of early-passage RLF and Swiss 3T3 cells in a 3-day cell proliferation assay. PDGF-BB and PDGF-AB were the most potent inducers of RLF proliferation and stimulated growth half-maximally at approximately 1 ng/ml and approximately 7 ng/ml, respectively. While these two B-chain-containing dimers stimulated lung fibroblast growth by as much as 150% above control medium, the PDGF-AA homodimer stimulated lung fibroblast proliferation less than 25% above control medium at the highest concentrations tested (20 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Connective tissue growth factor: a cysteine-rich mitogen secreted by human vascular endothelial cells is related to the SRC-induced immediate early gene product CEF-10

Human umbilical vein endothelial (HUVE) cells have been previously reported to express the genes for the A and B chains of PDGF and to secrete PDGF-related factors into culture media. Antihuman PDGF IgG affinity chromatography was used to purify PDGF-related activity from HUVE cell-conditioned media. Immunoblot analysis of the affinity-purified proteins with anti-PDGF IgG and antibodies specific for the A or B chain peptides of PDGF combined with chemotactic and mitogenic assays revealed that the major PDGF immunorelated molecule secreted by HUVE cells is a monomer of approximately 36-38 kD and that less than 10% of the purified biologically active molecules are PDGF A or B chain peptides. Screening of an HUVE cell cDNA library in the expression vector lambda gtl 1 with the anti-PDGF antibody resulted in the cloning and sequencing of a cDNA with an open reading frame encoding a 38-kD cysteine-rich secreted protein which we show to be the major PDGF-related mitogen secreted by human vascular endothelial cells. The protein has a 45% overall homology to the translation product of the v-src-induced CEF-10 mRNA from chick embryo fibroblasts. We have termed this new mitogen connective tissue growth factor.

Isolation and partial characterization of mitogenic factors from cementum

Cementum is the mineralized structure through which soft connective tissues are attached to the teeth. It is a unique calcified tissue characterized by a low metabolic turnover, lack of blood supply, and presence of very few cells. However, it contains substances that influence the biological activities of fibroblasts of adjacent soft tissues. We have partially characterized cementum proteins that have mitogenic activity toward fibroblasts. Cementum was harvested from bovine teeth, and mitogenic factors were extracted in 0.5 M CH3COOH. Heparin-Sepharose chromatography separated the mitogenic activity into a major and a minor fraction eluted by 0.5 and 2.0 M NaCl, respectively. The distribution of cementum mitogens in heparin-Sepharose fractions was different from that of alveolar bone and other bones. The cementum mitogenic factor eluting with 2.0 M NaCl from a heparin-Sepharose column was shown to be basic fibroblast growth factor (bFGF) on the basis of inhibition by anti-bFGF antibody and Western blots. The 0.5 M NaCl fraction was purified by HPLC with use of a combination of a DEAE-3W column followed by TSK-250 and C18 columns. NaDodSO4-polyacrylamide gel electrophoresis revealed that the purified fraction contained two protein bands with Mr 22,000 and 19,000, and mitogenic activity was associated with the Mr 22,000 species. The activity of this mitogen, designated as CGF, was potentiated by small quantities of plasma-derived serum or epidermal growth factor. It was heat resistant, but was destroyed by reduction. Assays of CGF preparations revealed that they contained no detectable platelet-derived growth factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Separation and microanalysis of growth factors by Phast system gel electrophoresis and by DNA synthesis in cell culture

A simple, micro-scale method was established for the characterization of growth factors at picogram levels using Phast system gel electrophoresis followed by monitoring the mitogenic activity by DNA synthesis in cell culture instead of staining methods. The separations and bioassays were carried out with a procedure involving Phast polyacrylamide gel electrophoresis or isoelectric focusing, gel slicing along the template, elution of growth factors through Transwell membranes and measurement of [3H]thymidine incorporation into DNA of normal rat kidney (NRK) fibroblasts. Transwell cell culture chamber inserts separated sliced gel pieces from culture cells and also permitted the direct elution of growth factors into the culture medium. The lower limit of sensitivity for human epidermal growth factor (hEGF) and transforming growth factor type alpha (TGF-alpha) were about 50 and 200 pg, respectively. At these concentrations, they were not detectable by the current most sensitive silver staining technique. Iodinated hEGF and TGF-alpha were also used to demonstrate the feasibility of determining the isoelectric point and molecular weight of peptides at picogram levels. This method is reliable, reproducible and can improve current methods for the characterization of growth factors.

Rat alveolar macrophage-derived platelet-derived growth factor is chemotactic for rat lung fibroblasts

Alveolar macrophages and their products are thought to be important mediators of the inflammatory lesions and consequent interstitial fibrosis caused by inhalation of inorganic particles. Identification of a homolog of platelet-derived growth factor (PDGF) produced by rat alveolar macrophages that were stimulated with carbonyl iron particles and asbestos fibers motivated our studies on the biologic activity of this potent cytokine. Macrophage-derived PDGF (MD-PDGF) competes for specific membrane receptors on rat lung fibroblasts, initiating DNA synthesis and cell replication. The present report demonstrates that purified human PDGF and the MD-PDGF are chemotactic for early passage rat lung fibroblasts, but not for lung macrophages. Rat lung fibroblasts exhibit a typical bell-shaped, dose-related curve and respond optimally between 2 and 4 ng/ml PDGF. We found that alveolar macrophage-conditioned medium (AMCM), fractionated by gel filtration in 1 M acetic acid, induced a clear chemotactic response in the same fractions (20 to 22 ml) where PDGF was identified by enzyme immunoassay. In contrast, AMCM fractionated by gel filtration in phosphate-buffered saline did not induce any chemotactic activity unless the fractions were treated further with 1 M acetic acid. In this case, chemotactic activity was observed in those fractions with molecular weights of 150 and greater than 200 kD. All chemotactic activity observed with fractionated AMCM was blocked greater than 90% by an anti-PDGF antibody. These observations demonstrate that MD-PDGF is chemotactic for rat lung fibroblasts if it first is released from its binding protein, alpha-macroglobulin (alpha-M), which is secreted into the medium along with PDGF.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of a macrophage-derived heparin-binding growth factor

Human mononuclear cells were plated in culture, and the conditioned media of these cells were analyzed by heparin-Sepharose affinity chromatography. The fractions were tested for growth factor activity as measured by the stimulation of DNA synthesis in BALB/c 3T3 cells. After 2 d in culture, two peaks of heparin-binding growth factor (HBGF) activity were detected, one eluting with 0.5 M NaCl, which could be shown to be platelet-derived growth factor (PDGF)-like, and the other eluting with 1.0 M NaCl. After 7-11 d in culture, when monocytes had clearly differentiated into macrophages, greater than 95% of the HBGF activity in conditioned medium consisted of the 1.0 M NaCl elution peak. This activity, which was designated macrophage-derived HBGF (MD-HBGF), was found to be a cationic heat-resistant polypeptide with a molecular weight in the range of 14-25 kDa. Analysis using Western blots and specific neutralizing antisera, as well as comparative heparin affinity analysis, indicated that MD-HBGF was not identical to other heparin-binding 3T3 cell growth factors known to be produced by macrophages, such as PDGF (AB, AA, and BB forms), acidic fibroblast growth factor, and basic fibroblast growth factor. In addition to stimulating mitogenesis in 3T3 cells, MD-HBGF also stimulated the proliferation of vascular smooth muscle cells, but did not stimulate the proliferation of vascular endothelial cells.

Localization of platelet-derived endothelial cell growth factor in human placenta and purification of an alternatively processed form

Platelet-derived endothelial cell growth factor (PD-ECGF) was purified to homogeneity from human term placenta, an organ characterized by extensive angiogenesis. N-terminal amino acid sequencing revealed that placental PD-ECGF was proteolytically processed at Thr-6, in contrast to PD-ECGF purified from human platelets, which is processed at Ala-11. The purified factor stimulated porcine aortic endothelial cells as well as two choriocarcinoma cell lines. Immunohistochemical staining revealed that PD-ECGF was present in the connective tissue cells of the placenta. The possibility that PD-ECGF is involved in the development of the placenta is discussed.

Early signals in the mitogenic response of Swiss 3T3 cells: a comparative study of purified PDGF homodimers

Platelet-derived growth factor (PDGF) occurs as three dimeric isoforms, AA, BB, and AB. Two distinct receptor subunits, alpha and beta, have been identified which bind either all three isoforms of PDGF (alpha) or PDGF-BB only (beta). Here, we have compared the effect of purified PDGF homodimers on the early intracellular signaling events and mitogenesis in Swiss 3T3 cells, which possess equivalent numbers of the alpha and beta subunits. Both PDGF-AA and PDGF-BB stimulated receptor phosphorylation, inositol phosphate formation, activation of protein kinase C, calcium mobilization, EGF receptor transmodulation, sodium uptake, arachidonic acid release, cyclic AMP accumulation, and c-fos induction in a comparable, dose-dependent manner (half-maximal values for all these response were in the 2-10 ng/ml range for both homodimers). At high concentrations of PDGF (greater than 10 ng/ml), the BB homodimer effect on early membrane and cytosolic signals was 20-30% greater than PDGF-AA, reflecting the greater number of available binding sites for PDGF-BB. DNA synthesis studies indicated that PDGF-AA and PDGF-BB were potent mitogens for Swiss 3T3 cells, displaying identical dose-response effects. Moreover, the mitogenic activities of both homodimers were equally potentiated in the presence of insulin. These results indicate that both PDGF-AA and PDGF-BB stimulate the full complement of molecular responses required for the synergistic interactions mediating long-term mitogenesis. We conclude that alpha and beta receptor subunits do not differ in their ability to transduce PDGF-mediated signals leading to DNA synthesis in Swiss 3T3 cells.

Characterization of biologically active, platelet-derived growth factor-like molecules produced by murine erythroid cells in vitro and in vivo

Platelet-derived growth factor (PDGF) is an important serum regulator of erythropoiesis in vitro. We have now obtained evidence suggesting that PDGF-like molecules may also modulate erythropoiesis in vivo. Western blot analysis of cytoplasmic extracts from Rauscher murine erythroleukemia cells and phenylhydrazine-treated mouse splenic erythroid cells revealed the presence of several PDGF-like proteins. The presence of PDGF-like proteins in the cytoplasm of these two erythroid cell types was confirmed by immunohistochemical staining. Using a serum-free biologic assay, PDGF-like biological activity was found in cell lysates and conditioned medium of both Rauscher cells and phenylhydrazine-treated mouse erythroid cells. Subcellular localization experiments revealed the biological activity to be concentrated in the cytosolic fraction. Using a series of antibodies to hematopoietic growth factors we demonstrated that PDGF-like biological activity was specifically immunoprecipitated by both monoclonal and polyclonal anti-human PDGF antibodies but not by antibodies to burst-promoting activity, granulocyte-macrophage colony-stimulating factor, IL-3, or erythropoietin. Taken together, the data are consistent with the hypothesis that PDGF-like molecules play a role in the regulation of mammalian erythropoiesis in vivo.

Large-scale preparation of recombinant platelet-derived growth factor AA secreted from recombinant baby hamster kidney cells

The short isoform of platelet-derived growth factor A (PDGF-A) was expressed in a mammalian host (BHK-21 cell). A cell line was obtained that secreted up to 0.3 micrograms/10(6) cells recombinant PDGF-A chain homodimer/day into the medium. For large-scale production of supernatant, cells were grown either in roller bottles or in 2.5-1 stirred tank fermenters. A simple two-step procedure was developed to purify recombinant PDGF-AA (rPDGF-AA). The first step was adsorption onto porous glass and the final step was reversed-phase high-performance liquid chromatography. The yield was 0.2 mg/l supernatant. A total amount of 20-30 mg pure rPDGF-AA may be obtained from a single fermenter run. Sequence analysis showed the correct amino terminus and no internal proteolytic cleavages. The specific activity was 5 ng/ml for mouse AKR-2B cells. [125I]rPDGF-AA had an affinity constant of approximately 0.5 nM to these cells and 25,000 binding sites were estimated/cell.

Coagulation increases neutrophil CR1 and CR3 expression: primary role for platelet-derived growth factor

Neutrophil receptors for C3b(CR1) and C3bi(CR3) mediate a number of functions important for infection control and tissue repair, such as adherence, aggregation, orientation in chemotactic gradients, and phagocytosis of opsonized particles. We studied the effect of the coagulation of whole blood on the induction of neutrophil complement receptor (CR) expression in vitro. Neutrophils incubated in serum for 1 hour at 37 degrees C increased the expression of CR1 3.43-fold and CR3 3.06-fold compared with incubation in buffer (p less than 0.001). In contrast, incubation in plasma did not induce such an increase. The serum factor responsible for this CR-inducing effect appeared to be a platelet constituent, because (1) serum derived from platelet-rich plasma, but not platelet-poor plasma, contained the CR-inducing factor; (2) pretreatment with aspirin inhibited the adenosine diphosphate-induced expression of this factor in platelet-rich plasma; (3) the CR-inducing factor was also contained in supernatants derived from frozen/thawed platelets; (4) pure platelet-derived growth factor (PDGF) induced CR expression to the same extent as did whole serum; and (5) the CR-inducing activity of serum and platelet supernatants was inhibited by incubation with antibody against PDGF but not by antibody against C5. Thus, a platelet component that is probably PDGF appears to be the major CR-inducing factor generated during in vitro coagulation and may play a vital role in mediating the neutrophil response to tissue injury and inflammation.

Human platelet-derived mitogens. I. Identification of insulinlike growth factors I and II by purification and N alpha amino acid sequence analysis

Human platelet lysates contained potent mitogenic activities for MCF-7 human breast-cancer cells in serum-free-defined media. Because these activities were not replaced by known platelet mitogens, such as platelet-derived growth factor or transforming growth factor beta, we sought to identify the breast cancer cell mitogens by purification and N alpha amino-acid sequencing. Acetic acid extracts of outdated human platelets were concentrated by ammonium sulfate precipitation and fractionated on Sephadex G-50 and Bio-Gel P-10 columns in 0.5 mol/L acetic acid. Two major activities were resolved by molecular sieve methods and fractionated further by reverse-phase high-performance liquid chromatography (HPLC). Purifications (70,000 to 870,000-fold) were accomplished yielding mol wt 7,400 products that were homogeneous as determined by iodination, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and autoradiography. The factors were identified as insulinlike growth factor I (IGF-I) and II (IGF-II) and truncated IGF-I by N alpha amino acid microsequencing. In dose-response experiments, platelet-derived IGF-I and IGF-II promoted multiple divisions of the MCF-7 cells with ED50 values of 12 and 100 pg/mL, respectively. The specific activities and other bioassay characteristics of platelet-derived IGF-I and IGF-II were similar to those of recombinant-produced human growth factors. This is the first report of the purification of insulinlike growth factors from human platelet lysates.

Expression and purification of biologically active v-sis/platelet-derived growth factor B protein by using a baculovirus vector system

Malignant transformation induced by simian sarcoma virus is mediated by its v-sis protein, the monkey homolog of the platelet-derived growth factor (PDGF) B chain. By use of an appropriately engineered baculovirus expression vector, the v-sis protein was expressed in the insect cell line Spodoptera frugiperda (Sf9) at a level 50- to 100-fold higher than that observed with overexpression in mammalian-cell transfectants. The sis protein produced by Sf9 cells underwent processing similar to that observed in mammalian cells, including efficient disulfide-linked dimer formation. Moreover, the recombinant sis protein was capable of binding PDGF receptors and inducing DNA synthesis as efficiently as PDGF-B synthesized by mammalian cells. A significant fraction of sis protein was released from Sf9 cells, which made possible a one-step immunoaffinity purification to near homogeneity with a 40% recovery of biological activity. These results demonstrate that a protein whose normal processing requires both intrachain and interchain disulfide-bridge formation can be efficiently expressed in a biologically active form in insect cells by using a baculovirus vector system.

Two peptides related to platelet-derived growth factor are present in human wound fluid

Platelet-derived growth factor (PDGF) has been suggested to play an important role in wound healing. In this study wound fluid collected from patients after radical mastectomy was analyzed for PDGF-related factors. Analysis revealed the presence of two PDGF-related peptides of 16-17 kDa and 34-36 kDa. These PDGF-related peptides were purified by using anti-PDGF immunoaffinity techniques and found to possess both chemotactic and mitogenic activities for NIH 3T3 cells in vitro. Surprisingly, we could not detect authentic native PDGF (30 kDa) or PDGF A or B chain in any of the wound-fluid samples examined. These results indicate that PDGF-related peptides are present in normal human wound fluid, whereas PDGF A- and B-chain peptides are absent or only present in trace amounts relative to the total PDGF-related biological activity.

Preparation of biologically active platelet-derived growth factor type BB from a fusion protein expressed in Escherichia coli

Preparations of the mitogen platelet-derived growth factor (PDGF) from human platelets contain two related polypeptides termed A chain and B chain. PDGF-B is highly homologous to a portion of p28v-sis, the transforming protein of simian sarcoma virus. We have studied the mitogenic potential of a PDGF-BB-like homodimer by expressing the sequence coding for the mature part of PDGF-B in Escherichia coli. Expression was achieved as cro-beta-gal-PDGF-B fusion protein which was exclusively found in the "inclusion bodies". A monomeric PDGF-B fragment shortened by 12 amino acid residues from the NH2 terminus was excised from the fusion protein by CNBr cleavage. After protection of thiols by S-sulfonation, this fragment was purified by gel permeation chromatography and reversed-phase high-performance liquid chromatography. This monomeric protein was dimerized in the presence of a mixture of reduced and oxidized glutathione to yield biologically active rPDGF-BB with an overall yield of approximately 0.7 mg of rPDGF-BB/L of culture. Escherichia coli rPDGF-BB stimulated [3H]thymidine incorporation into AKR2B fibroblast at concentrations of about 1 ng/mL.

Growth factor expression in aorta of normotensive and hypertensive rats

Hypertension causes biochemical and morphological changes in the vessel wall by unknown mechanisms. Locally produced substances may have a role in mediating these vascular changes. We have studied the expression of platelet-derived growth factor (PDGF) B chain and PDGF A chain, insulin-like growth factor (IGF)-I and IGF-II, endothelial cell growth factor (ECGF), basic fibroblast growth factor (bFGF), and transforming growth factor-beta (TGF-beta) in aortic tissue from normotensive rats and rats made hypertensive by deoxycorticosterone (DOC)/salt treatment. Using Northern blotting, we found that genes for each of these growth factors were transcriptionally active in the aorta of both normotensive and hypertensive rats. TGF-beta aortic mRNA levels increased up to threefold as a result of DOC/salt hypertension. In contrast, no major changes in the expression of either PDGF chain, IGF-I or II, ECGF, or bFGF were detectable. The results indicate that at least seven genes coding for growth factors that were shown previously to influence growth and function of vascular cells in vitro, are expressed in rat aorta in vivo. These findings support the hypothesis that synthesis and release of growth factors in the arterial wall are involved in autocrine and/or paracrine regulatory mechanisms. In addition, the increased expression of TGF-beta in vivo may have a role in mediating the aortic changes induced by hypertension.

High-yield purification of platelet-derived endothelial cell growth factor: structural characterization and establishment of a specific antiserum

Platelet-derived endothelial cell growth factor (PD-ECGF) is a 45-kDa protein that stimulates the growth of endothelial cells [Miyazono, K., et al. (1987) J. Biol. Chem. 262, 4098-4103]. Here, we describe a method to purify large quantities of PD-ECGF from human platelet lysate at a high yield (14% overall recovery). The purification method involves five steps, using high-performance liquid chromatography grade hydroxylapatite and hydrophobic chromatographies as the two final steps. The purified material contained two major components of apparent molecular weight values of 46,000 and 44,000. These components coeluted in a high-resolving reversed-phase chromatography and were found to give similar peptide maps after treatments with staphylococcal V8 protease, suggesting that the 44-kDa form is related to the 46-kDa molecule. Partial tryptic digestion of native PD-ECGF revealed that the molecule contains a trypsin-resistant domain of 37-39 kDa. A rabbit antiserum was produced against the purified material and was found to specifically recognize PD-ECGF in immunoblotting. When added to the cell culture medium, an immunoglobulin fraction of the antiserum neutralized the activity of purified PD-ECGF. Furthermore, it completely neutralized the endothelial cell mitogenic activity of platelet lysate, indicating that PD-ECGF is the only mitogen in platelet lysate for this cell type.

Expression of three recombinant homodimeric isoforms of PDGF in Saccharomyces cerevisiae: evidence for difference in receptor binding and functional activities

Three recombinant homodimeric isoforms of platelet-derived growth factor (PDGF) were produced and purified in milligram quantities by expression of PDGF A- and B-chains in yeast cells. Structural analysis of the purified short and long variants of PDGF-AA (PDGF-AAS and PDGF-AAL) and PDGF-BB showed that they had been properly processed and assembled into dimers. PDGF-AAS and PDGF-AAL were found to bind only to the PDGF A-type receptor on human fibroblasts, with affinities of 0.1 and 0.2 nM, respectively. PDGF-BB bound to cells with A- and B-type receptors and to cells with B-type receptor only with affinities of 0.6 nM in both cases. Each fibroblast appeared to express about 4-5 times more B-type receptors than A-type receptors. The maximal mitogenic response to PDGF-BB of human fibroblasts was almost 2-fold higher than that induced by either of the two PDGF-AA forms. The three isoforms of PDGF also stimulated growth in soft agar of human fibroblasts with PDGF-BB inducing a higher maximal response.

Synthesis and assembly of a functionally active recombinant platelet-derived growth factor AB heterodimer

A Chinese hamster ovary cell line that stably expresses transfected human platelet-derived growth factor (PDGF) A and B chain precursors was established. All three dimeric combinations of PDGF chains were produced by this cell line; their biosynthesis, assembly, and processing were followed by pulse-chase analyses. PDGF-AA, PDGF-AB, and PDGF-BB were processed to Mr values of about 30,000 and were accumulated in these forms in the medium. In addition, PDGF-BB was further processed to a 24-kDa component, which remained cell-associated. The major secreted component was PDGF-AB, which was purified and shown to have structural and functional characteristics indistinguishable from PDGF-AB purified from human platelets.