Human Platelet-derived Growth Factor B-chain Research Articles

A rhPDGF-BB/bovine type I collagen/β-TCP mixture for the treatment of critically sized non-union tibial defects: An in vivo study in rabbits.

Non-union during healing of bone fractures affects up to ~5% of patients worldwide. Given the success of recombinant human platelet-derived growth factor-B chain homodimer (rhPDGF-BB) in promoting angiogenesis and bone fusion in the hindfoot and ankle, rhPDGF-BB combined with bovine type I collagen/β-TCP matrix (AIBG) could serve as a viable alternative to autografts in the treatment of non-unions. Defects (~2 mm gaps) were surgically induced in tibiae of skeletally mature New Zealand white rabbits. Animals were allocated to one of four groups-(1) negative control (empty defect, healing for 8 weeks), (2 and 3) acute treatment with AIBG (healing for 4or 8weeks), and (4) chronic treatment with AIBG (injection 4 weeks post defect creation and then healing for 8 weeks). Bone formation was analyzed qualitatively and semi-quantitatively through histology. Samples were imaged using dual-energy X-ray absorptiometry and computed tomography for defect visualization and volumetric reconstruction, respectively. Delayed healing or non-healing was observed in the negative control group, whereas defects treated with AIBG in an acute setting yielded bone formation as early as 4 weeks with bone growth appearing discontinuous. At 8 weeks (acute setting), substantial remodeling was observed with higher degrees of bone organization characterized by appositional bone growth. The chronic healing, experimental, group yielded bone formation and remodeling, with no indication of non-union after treatment with AIBG. Furthermore, bone growth in the chronic healing group was accompanied by an increased presence of osteons, osteonal canals, and interstitial lamellae. Qualitatively and semiquantitatively, chronic application of AI facilitated complete bridging of the induced non-union defects, while untreated defects or defects treated acutely with AIBG demonstrated a lack of complete bridging at 8 weeks.

Fluorescence Anisotropy Reduction of Allosteric Aptamer for Sensitive and Specific Protein Signaling

Real time protein signaling in a complex medium may provide a promising way for high-throughput protein analysis, but it is largely unmet due to the challenge of signal transduction and the interferences of nonspecific binding and high background. Our recent work indicates that a fluorescent aptamer can display a protein binding-induced reduction of fluorescence anisotropy (FA) (Zhang, D.; Lu, M.; Wang, H. J. Am. Chem. Soc. 2011, 133, 9188-9191), which is exclusively different from a traditionally simplified concept hinting a molecular size increase-induced FA increase. Inspired by this unexpected observation, we describe a novel FA reduction approach for protein signaling. The feasibility of this approach is demonstrated through the assays of a blood protein human α-thrombin and an oncoprotein human platelet-derived growth factor B-chain (PDGF-BB) using two screened fluorescent aptamers, respectively. By the developed FA reduction method, the spiked human α-thrombin in diluted serum can be detected at the concentration as low as 250 pM. In contrast, in a traditional molecular size-dependent FA assay, the thrombin spiked in diluted serum cannot induce reliable FA change even at a 256-fold higher concentration (64 nM). The results clearly show that the FA reduction approach has a dramatically enhanced specificity against target protein and high sensitivity in complex medium and is applicable to the no-separation based detection of proteins in biological matrixes.

Cloning, expression and functional analyses of human platelet-derived growth factor-B chain peptide for wound repair of cat corneal endothelial cells

To investigate the biological function of platelet-derived growth factor B (PDGF-B) on the survival and proliferation of cat corneal endothelial cells so as to provide bases for further studies of its role in wound repair and its clinical application. Total RNA was extracted from the placenta tissues of healthy pregnant women undergoing hysterotokotomy and PDGF cDNA was obtained with reverse transcription-polymerase chain reaction (RT-PCR). The prokaryotic expression vector pET-PDGF-B was constructed and expressed the recombinant PDGF-B in Escherichia coli (E. coli) BL21 (DE3). After purification and refolding on Ni2+-chelation affinity chromatography (NTA) column, it was used to culture cat corneal endothelial cells. Cell proliferation was tested by modified tertrazolium salt (MTT) and flow cytometer. And the morphologic change and the ultrastructure were observed under an inverted phase contrast microscope, a scanning electron microscope and a transmission electon microscope, respectively. PDGF-B chain peptide (PDGF-BB) gene was successfully inserted into the prokaryotic expression vector, pET-28a (+). The purified recombined protein pET-PDGF-B showed a single band on sodium dodecyl sulfate polyacrylamide gel electropheresis (SDS-PAGE) with the molecular weight of about 27 u, which was in agreement with the deduced value. MTT and flow cytometry showed that PDGF-BB promoted the survival and proliferation of cat corneal endothelial cells. The construction of recombinant prokaryotic expression vector pET-PDGF-B and the preparation of PDGF-BB protein provide a foundation for further study of the function of PDGF-BB and producing biological PDGF-BB protein. The expressed PDGF-BB promotes the proliferation of cultured cat corneal endothelial cells.

Dependence of autocrine growth factor stimulation in platelet-derived growth factor-B-induced mouse brain tumor cells.

In human gliomas, platelet-derived growth factor (PDGF) ligand and receptor mRNA are often co-expressed, which suggests the presence of an autocrine loop. To further investigate the significance of PDGF stimulation in brain tumors, we used a previously developed mouse tumor model, in which malignant brain tumors of neuroepithelial origin were induced by injecting a murine retrovirus containing the human PDGF B-chain gene into the brains of neonatal mice. In the present investigation, we have characterized a cell line established from such an experimentally induced tumor in an INK4a-/- mouse. Cultured tumor cells expressed nestin and NG2 chondroitin sulfate proteoglycan and are thus most likely derived from an oligodendrocyte precursor cell. Tumor cells produced PDGF-B protein and displayed constitutively activated PDGF alpha receptors. Autocrine receptor activation could be blocked with the specific PDGF receptor tyrosine kinase inhibitor CGP 57148B, which led to almost complete inhibition of cell proliferation, which was much less affected by a PDGF B-chain aptamer that inhibits binding of PDGF-B to PDGF receptors and is unlikely to be able to pass through the plasma membrane. Our results imply an important role for PDGF autocrine stimulation in both initiation and progression of a subtype of gliomas.

Becaplermin

Becaplermin is a recombinant human platelet-derived growth factor B-chain homodimer (rh-PDGF-BB) for topical treatment of full-thickness diabetic neuropathic ulcers and pressure ulcers. rh-PDGF-BB promotes wound healing, probably by increasing granulation tissue formation via increased migration and proliferation of cells, with subsequent extracellular matrix deposition. Accelerated healing has been demonstrated in healthy and healing-impaired animals and in patients with lower extremity diabetic neuropathic ulcers and pressure ulcers. Pharmacokinetic studies in humans have shown that systemic absorption of becaplermin after topical administration to ulcers is minimal. A clinical trial in patients with stage III or IV diabetic neuropathic ulcers of the lower extremities which had adequate perfusion showed that becaplermin 100 microg/g applied once daily in conjunction with a standardised programme of good wound care significantly increased the proportion of patients with complete healing of the ulcer and reduced the time to complete healing compared with placebo or good wound care alone. Becaplermin was also superior to placebo in patients with pressure sores. Becaplermin was well tolerated in clinical trials and the rate of discontinuation because of adverse events was similar to that among placebo recipients. Rash, which occurred in 2% of becaplermin and 2% of placebo recipients, may be attributable to the vehicle used.

Identification of a Thrombin Response Element in the Human Platelet-derived Growth Factor B-chain (c-sis) Promoter

Thrombin is a coagulation system protease that also serves as a potent stimulator of gene expression in several cell types, including endothelial cells (EC). We and others have previously demonstrated that the transcription of platelet-derived growth factor (PDGF) B-chain (c-sis) by EC is stimulated severalfold by thrombin. Here we examine the molecular mechanism of this regulatory process using bovine aortic EC transiently transfected with a vector containing the chloramphenicol acetyltransferase (CAT) gene under the control of a 400-base pair fragment of the human PDGF B-chain promoter. Thrombin treatment of these cells caused a severalfold increase in CAT expression. Deletion analysis and site-directed mutagenesis revealed that the region spanning nucleotides -61 to -53 from the transcription initiation site (referred to as the thrombin response, or ThR, region) was critical for the transcriptional response to thrombin. Electrophoretic mobility shift assays with an oligonucleotide corresponding to the region -64 to -44, which contained the ThR region, led to the identification of a thrombin-inducible nuclear factor (TINF) in extracts from thrombin-treated, but not control, EC. TINF was formed as early as 40 min post-thrombin treatment, persisted for at least 7 h, but was no longer present after 24 h. TINF appeared in the absence of de novo protein synthesis. The ThR region consists of a repeat of a CCACCC element in an ABBA configuration, which, based on mutation analysis and transfection assays, appears to be critical in mediating thrombin stimulation of the PDGF B-chain gene. The conservation of the ThR region in the promoter of the PDGF B-chain among three species (human, feline, and murine) further supports the importance of this region as a cis-acting regulatory element.

Novel cis-acting elements in the human platelet-derived growth factor B-chain core promoter that mediate gene expression in cultured vascular endothelial cells.

Platelet-derived growth factor (PDGF) is a potent mitogen and chemoattractant constitutively expressed by a variety of normal and transformed cells. Transient transfection and deletion analysis of the human c-sis proto-oncogene in cultured vascular endothelial cells revealed a minimal core promoter region extending 82 base pairs upstream from the TATA box. Two novel and functional cis-acting elements were identified within the core that share considerable sequence homology with consensus binding elements for transacting factors of the ETS class and those involved in AP-1 complexes. Deletion or mutation of either the ETS-like site or the AP-1-like site resulted in significant attenuation in the ability of the core to drive transcription. Electrophoretic mobility shift assays revealed that proteins from bovine aortic and human umbilical vein endothelial nuclear extracts bound to these elements in a specific manner and that both sites were essential for protein binding. Ferguson analysis predicted a combined molecular mass of 153 kDa for these proteins. In addition, transient transfection, gel shift, and DNase I footprint analysis were used to identify a functional Sp1 binding site downstream of these elements in the core promoter. By localizing the functional cis-acting elements in the PDGF-B promoter, it may be possible to elucidate the normal transcriptional control of the gene, as well as the mechanisms that activate it in pathologic settings.

Characterization and purification of the biologically active v- sis protein generated in silkworm larvae with the Bombyx mori nuclear polyhedrosis virus vector system

The v- sis oncogene of simian sarcoma virus encodes a protein which is homologous to the human platelet-derived growth factor B-chain. The biologically active v- sis protein was expressed in silkworm larvae using the Bombyx mori nuclear polyhedrosis virus vector system. The v- sis protein purified from infected silkworm larvae is a 30 kDa disulfide-linked homodimer. Mitogenic activity of the v- sis protein was comparable to that of PDGF and inhibited by the pretreatment with anti-PDGF antibody. These results show that the recombinant v- sis protein is biologically and antigenically related to PDGF.

Characterization of v-sis Protein Expressed in Silkworm Larvae Using the Bombyx mori Nuclear Polyhedrosis Virus Vector1

The v-sis oncogene of simian sarcoma virus encodes a protein which is homologous to the human platelet-derived growth factor B-chain. The v-sis protein undergoes a series of processing steps including dimer formation and proteolytic digestion to generate several molecular sizes of the protein. Two of these v-sis proteins were expressed alone or as polyhedrin-sis fusion proteins using the Bombyx mori nuclear polyhedrosis virus vector. The polyhedrin-sis fusion proteins contained a collagenase-sensitive site at the junction. The expression levels of the fusion proteins whose polyhedrin portions consisted of only 8 amino-terminal amino acids were 3-4 times higher than those of non-fusion proteins. One of these fusion proteins was expressed in silkworm larvae and the v-sis protein was isolated from the fusion protein by collagenolysis followed by chromatography. Because the purified v-sis protein exhibited the same molecular size on SDS-polyacrylamide gels under reducing and non-reducing conditions, it was concluded to be monomeric in structure. It possessed chemotactic activity but lacked mitogenic activity. In addition, a small amount (approximately 1%) of monomeric v-sis protein was converted in vitro to the mitogenically active v-sis protein, which could be a homo-dimer.

Platelet-derived growth factor and transforming growth factor-beta enhance tissue repair activities by unique mechanisms.

Platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) markedly potentiate tissue repair in vivo. In the present experiments, both in vitro and in vivo responses to PDGF and TGF-beta were tested to identify mechanisms whereby these growth factors might each enhance the wound-healing response. Recombinant human PDGF B-chain homodimers (PDGF-BB) and TGF-beta 1 had identical dose-response curves in chemotactic assays with monocytes and fibroblasts as the natural proteins from platelets. Single applications of PDGF-BB (2 micrograms, 80 pmol) and TGF-beta 1 (20 micrograms, 600 pmol) were next applied to linear incisions in rats and each enhanced the strength required to disrupt the wounds at 5 d up to 212% of paired control wounds. Histological analysis of treated wounds demonstrated an in vivo chemotactic response of macrophages and fibroblasts to both PDGF-BB and to TGF-beta 1 but the response to TGF-beta 1 was significantly less than that observed with PDGF-BB. Marked increases of procollagen type I were observed by immunohistochemical staining in fibroblasts in treated wounds during the first week. The augmented breaking strength of TGF-beta 1 was not observed 2 and 3 wk after wounding. However, the positive influence of PDGF-BB on wound breaking strength persisted through the 7 wk of testing. Furthermore, PDGF-BB-treated wounds had persistently increased numbers of fibroblasts and granulation tissue through day 21, whereas the enhanced cellular influx in TGF-beta 1-treated wounds was not detectable beyond day 7. Wound macrophages and fibroblasts from PDGF-BB-treated wounds contained sharply increased levels of immunohistochemically detectable intracellular TGF-beta. Furthermore, PDGF-BB in vitro induced a marked, time-dependent stimulation of TGF-beta mRNA levels in cultured normal rat kidney fibroblasts. The results suggest that TGF-beta transiently attracts fibroblasts into the wound and may stimulate collagen synthesis directly. In contrast, PDGF is a more potent chemoattractant for wound macrophages and fibroblasts and may stimulate these cells to express endogenous growth factors, including TGF-beta, which, in turn, directly stimulate new collagen synthesis and sustained enhancement of wound healing over a more prolonged period of time.

Generation of fibrosarcomas in vivo by a retrovirus that expresses the normal B chain of platelet-derived growth factor and mimics the alternative splice pattern of the v-sis oncogene.

A retrovirus containing the entire human platelet-derived growth factor B-chain (PDGF-B) gene was constructed in order to investigate the in vivo biological activity of its encoded growth factor. When this virus was introduced into newborn mice, it reproducibly generated fibrosarcomas at the site of inoculation. Proviruses in each fibrosarcoma analyzed had lost 149 nucleotides downstream of the PDGF-B coding region. This deletion originated from an alternative or aberrant splice event that occurred within exon 7 of the PDGF-B gene and mimicked the v-sis oncogene. Thus, deletion of this region may be necessary for efficient retrovirus replication or for more potent transforming function. Evidence that the normal growth factor coding sequence was unaltered derived from RNase protection studies and immunoprecipitation analysis. Tumors were generally polyclonal but demonstrated clonal subpopulations. Moreover, tumor-derived cell lines became monoclonal within a few tissue culture passages and rapidly formed tumors in vivo. These findings argue that overexpression of the normal human PDGF-B gene product under retrovirus control can induce the fully malignant phenotype.