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.

Gel matrix vehicles for growth factor application in nerve gap injuries repaired with tubes: a comparison of biomatrix, collagen, and methylcellulose

The repair of nerve gap injuries with tubular nerve guides has been used extensively as an in vivo test model in identifying substances which may enhance nerve regeneration. The model has also been used clinical nerve repair. The objective of this study was to compare three different gel matrix-forming materials as potential vehicles for growth factors in this system. The vehicles included a laminin containing extracellular matrix preparation (Biomatrix), collagen, and a 2% methylcellulose gel. The growth factor test substance consisted of a combination of platelet-derived growth factor BB (PDGF-BB) and insulin-like growth factor I (IGF-I). An 8-mm gap in rat sciatic nerve was repaired with a silicone tube containing each of the vehicles alone or with a combination of each vehicle plus PDGF-BB and IGF-I. At 4 weeks after injury, the application of the growth factor combination significantly stimulated axonal regeneration when applied in methylcellulose or collagen, but not in Biomatrix. A similar trend was present between the vehicle control groups. By 8 weeks after injury, nerves repaired with methylcellulose as a vehicle had significantly greater conduction velocity than either collagen or Biomatrix. It was concluded that a 2% methylcellulose gel was the best of the three matrices tested, both in its effects on nerve regeneration and flexibility of formulation.

Expression of platelet-derived growth factor (PDGF)-A, PDGF-B and the PDGF-alpha receptor, but not the PDGF-beta receptor, in human malignant melanoma in vivo

There has been considerable interest in the potential role of growth factors in the initiation and development of cutaneous malignant melanoma (CMM). Platelet-derived growth factor (PDGF) has been shown to be secreted by melanoma cell lines and by metastatic melanoma in vivo. PDGF also has been reported to stimulate the development of tumour stroma and new blood vessels. We studied the expression of PDGF and its receptors by both immunohistochemistry (IHC) and in situ hybridization (ISH) in primary and metastatic melanoma and in normal skin specimens. Cryostat sections were incubated with 35S-labelled riboprobes and antibodies for PDGF-AA, PDGF-alpha receptor, PDGF-BB and PDGF-beta receptor. Both primary and metastatic melanoma exhibited significant expression of PDGF-AA, PDGF-BB and PDGF-alpha receptor by both IHC and ISH, compared with only background expression in normal skin. We did not observe expression of PDGF-beta receptor in melanoma. Our results suggest that PDGF may function as an autocrine growth factor, as well as an angiogenesis factor, in CMM tumour development. This expression of the PDGF-alpha receptor rather than the beta receptor may be unique among solid tumours.

Synthesis of inositol 2-phosphate-quercetin conjugates

The antiproliferative flavonoid, quercetin, is limited in its pharmacological utility by its low water solubility. In this paper, we describe the synthesis of two quercetin analogues prepared by linking the hydroxyl group at the 3- or 5-position of the flavonoid to the 1-hydroxyl group of myo-inositol-2-phosphate via a succinate diester linkage. The resulting conjugates were found to have dramatically enhanced water solubility relative to quercetin; the 5-linked quercetin analogue 2 had a water solubility of > 300 mg/mL at 20 degrees C. Comparison of the in vitro cytotoxicity and antiproliferative activity of conjugate 2 with those of quercetin toward cultured human colon adenocarcinoma (SW480) and human glioblastoma (U87MG) cells indicated that this modification of quercetin does not significantly diminish its activity in these assays.

Regulated expression of APE apurinic endonuclease mRNA during wound healing in porcine epidermis

Abasic (AP) sites in DNA are cytotoxic and mutagenic and their repair is initiated by AP endonucleases. The major AP endonuclease of mammalian cells is encoded by the APE gene. Ape protein has also been proposed to modulate the activity of some transcription factors independently of its AP endonuclease activity. We investigated whether APE expression is coordinated with cell division, which could diminish mutagenesis. The level of APE mRNA was followed during wound healing in porcine epidermis, in which surgical wounding prompts rapid cell proliferation followed by a differentiation program to regenerate normal skin. In situ hybridization with a probe from human APE cDNA revealed strongly decreased expression in rapidly proliferating migrating cells during the first 1-3 days following wounding, succeeded by sharply increased APE expression that exceeded the pre-wounding levels by days 9-17. These changes were not observed in the surrounding undamaged tissue. In contrast to the foregoing in vivo results, APE expression in cultured primary human fibroblasts (IMR90) or myeloid leukemia cells (K562) was not coordinated with cell division. This biphasic APE expression during wound healing could relate to transcription factor regulation or it could allow unhindered DNA synthesis or prepare the developing epidermis to handle DNA damage. However, if transient under-expression of APE-encoded repair enzyme does occur, it might render regenerating skin especially vulnerable to mutagenesis during the cell proliferation phase.

The effect of systemically administered PDGF-BB on the rodent skeleton

Platelet-derived growth factor (PDGF), an osteoblast mitogen, has been demonstrated to accelerate fracture healing and periodontal bone repair when applied locally in vivo. To explore whether PDGF could stimulate bone formation in intact bone, we administered it systemically to rats rendered acutely estrogen-deficient. Because PDGF may stimulate bone resorption in vitro, PDGF was administered with and without an antiresorptive agent (alendronate). All treatments were given by intravenous injection 3 times a week for 6 weeks. Spinal bone mineral density (BMD) decreased by 5% in the vehicle-treated ovariectomized (OVX) rats by the end of the study as determined by DXA. Treatment with PDGF prevented this bone loss and significantly (p < 0.05) increased the bone density in the spine (9%) and whole skeleton (5.8%). Combined treatment with PDGF and alendronate resulted in a greater increase at the spine (18%) and whole skeleton (12.8%) than either agent alone. Histomorphometric analysis demonstrated that treatment with PDGF increased the osteoblast number and osteoblast perimeter without consistent changes in osteoclast estimates. Biomechanical testing demonstrated that PDGF administration increased the vertebral body compressive strength and femoral shaft torsional stiffness and resulted in a trend for enhanced femoral head shearing strength. Coadministration of alendronate further increased these indices of bone strength. PDGF administration also caused premature closure of the growth plate, decreased body fat, and resulted in extraskeletal collagen deposition. We therefore demonstrate, for the first time, that systemic administration of PDGF can increase bone density and strength throughout the skeleton.

Combination of platelet-derived growth factor-BB and insulin-like growth factor-I is more effective than platelet-derived growth factor-BB alone in stimulating complete healing of full-thickness wounds in "older" diabetic mice

Platelet-derived growth factor and insulin-like growth factor-I have been shown to interact synergistically to enhance repair of skin wounds in normal healing swine. Platelet-derived growth factor alone has shown promise in treating human chronic ulcers. The objective of this study was to compare the wound healing effects of platelet-derived growth factor-BB alone with those of a combination of platelet-derived growth factor-BB and insulin-like growth factor-I in an improved model with the use of "older" animals with diabetes. Older diabetic (db/db) mice (>15 weeks of age) have less elevated insulin levels compared with young db/db mice. The serum insulin levels in the older animals is 1.0 to 2.5 times that of the nondiabetic animals, a similar increase to that which occurs in human patients with type II diabetes. Healing was evaluated in two studies involving a total of 104 animals. Treatment groups included the following: 4.0 microg/cm(2) of platelet-derived growth factor-BB, 40.0 microg/cm(2) of platelet-derived growth factor-BB, 4.0 microg/cm(2) of both platelet-derived growth factor-BB and insulin-like growth factor-I or vehicle. All growth factors were applied topically in a methylcellulose vehicle to full-thickness wounds every other day for 24 days. Efficacy end points were median and mean time to complete healing and rate of wound closure. The median time to complete healing for animals receiving the platelet-derived growth factor-BB/insulin-like growth factor-I combination was 38% and 33% faster (p < 0.001) than animals receiving 4.0 microg/cm(2) and 40.0 microg/cm(2) of platelet-derived growth factor-BB, respectively. The mean time to complete healing for platelet-derived growth factor/insulin-like growth factor-I treated animals was 31% and 29% faster (p < 0.001) than 4.0 microg/cm(2) and 40.0 microg/cm(2) platelet-derived growth factor-BB treated animals, respectively. Wounds treated with 4.0 microg/cm(2) platelet-derived growth factor-BB/insulin-like growth factor-I healed, on average, in 22 days compared with 31 days for 40.0 microg/cm(2) platelet-derived growth factor-BB alone and 38 days for vehicle. Also, platelet-derived growth factor-BB/insulin-like growth factor-I significantly improved the rate of wound closure throughout the duration of the studies compared with either dose of platelet-derived growth factor-BB alone (p < 0.005) or vehicle (p < 0.001). In conclusion, the data show that the combination of platelet-derived growth factor-BB and insulin-like growth factor-I is more effective than platelet-derived growth factor-BB alone at the doses tested or vehicle treatment in stimulating cutaneous wound healing in older, diabetic mice.

The combination of platelet-derived growth factor-BB and insulin-like growth factor-I stimulates bone repair in adult Yucatan miniature pigs

The combination of insulin-like growth factor-I and platelet-derived growth factor-BB has previously been shown to stimulate healing of soft tissue wounds and the formation of bone and ligament around teeth. The purpose of the present study was to evaluate the effects of platelet-derived growth factor-BB and insulin-like growth factor-I individually and in combination on the healing of osseous wounds. Four standardized cortical wounds were created in each tibia of 11 adult Yucatan miniature pigs. The wounds in one tibia per animal were treated with either purified recombinant human insulin-like growth factor-I, platelet-derived growth factor-BB, or both in a methylcellulose gel. The wounds in each contralateral tibia received placebo gel alone. Coded serial sections of each wound were evaluated by computer-aided histomorphometry 21 days after surgery. The area and perimeter of the newly formed mineralized callus, the thickness of the total callus, and the percentage of mineralized tissue within the callus were significantly increased compared with the values of matched controls only in wounds treated with a combination of insulin-like growth factor-I and platelet-derived growth factor-BB. No significant differences in the measured parameters of callus formation were found in wounds treated with either insulin-like growth factor-I or platelet-derived growth factor-BB alone. Cartilage was present only in sites treated with insulin-like growth factor-I alone. These results suggest that the combination of platelet-derived growth factor-BB and insulin-like growth factor-I stimulates bone formation in wounds in long bones of adult animals and that these growth factors act via different pathways during the repair process.

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.

Expression of monocyte chemoattractant protein 1 in human inflamed gingival tissues

Gingival inflammation is initiated by bacterial colonization on the tooth surface. It is characterized by infiltration of mononuclear cells, a common feature of many forms of chronic inflammation. Monocyte chemoattractant protein 1 (MCP-1) is the predominant monocyte chemoattractant secreted by a variety of different cells in vitro. For this report, we examined MCP-1 expression in bacterially induced gingival inflammation by immunohistochemistry and in situ hybridization. The cell types expressing MCP-1 are identified as vascular endothelial cells and monocytes/macrophages. Correlation analysis shows that the number of cells expressing MCP-1 is related to the degree of inflammation. Our finding that MCP-1 is expressed in inflamed gingival tissue suggests that MCP-1 plays an important role in the recruitment of monocytes and amplification of inflammatory signals in bacterially induced inflammation.

Expression of growth factor and receptor mRNAs in skin epithelial cells following acute cutaneous injury

We report that acute injury induces the expression of selective growth factor and growth factor receptors in the epithelial cells of the wounded tissue. In situ hybridization analysis of skin biopsy specimens obtained after cutaneous injury in swine demonstrated the induction of the expression of transforming growth factor-alpha, its receptor, epidermal growth factor-R, acidic fibroblast growth factor, and basic fibroblast growth factor messenger RNAs in the skin epithelial cells of the wounded tissue. There was no significant expression in the epithelial cells of control, uninjured tissues. The expression levels were maximal during the period of active tissue repair (1 to 5 days after injury) and were totally suppressed upon the healing of the wounded tissues. In contrast, insulinlike growth factor-I, (IGF-I), IGF-I receptor, and IGF-II receptor messenger RNAs were expressed in the epithelial cells of both the control, uninjured tissues and in tissue specimens obtained after injury. There was no significant expression of IGF-II messenger RNA in the epithelial cells before or after injury. It seems that injury induces the coordinated expression of selective growth factor and growth factor receptor genes whose products contribute to the regulation of the complex processes involved in tissue repair and remodeling.

Expression of androgen and progesterone receptors in primary human meningiomas

Meningiomas are common brain tumors that show a predilection for females and become more aggressive during pregnancy and menses. The existence of gender-specific hormone receptors in meningiomas has long been a matter of controversy; the recent cloning of androgen, estrogen, and progesterone receptors has facilitated their direct evaluation. The authors have demonstrated the expression of androgen and progesterone receptor messenger ribonucleic acid and protein product in nine primary human meningiomas by Northern blot analysis. Cellular localization was achieved by in situ hybridization analysis. Estrogen receptor expression was not detected. Normal adult meninges were shown to express very low levels of both androgen and progesterone receptors.

Elevated expression of monocyte chemoattractant protein 1 by vascular smooth muscle cells in hypercholesterolemic primates

Atherosclerosis is marked by an overt inflammatory infiltrate, with enhanced recruitment of monocytes/macrophages observed in both human and experimental atherosclerosis. We previously determined that monocyte chemoattractant protein 1 (MCP-1) accounts for virtually all of the chemotactic activity produced by vascular (aortic) smooth muscle cells in culture. We now report that arteries from a primate model of atherosclerosis with dietary-induced hypercholesterolemia exhibit increased levels of MCP-1 mRNA expression in vivo, whereas their normal counterparts demonstrate minimal MCP-1 expression. Furthermore, immunohistochemistry and in situ hybridization clearly indicate that the expression of MCP-1 protein and mRNA is in the smooth muscle cells of the medial layer of the artery and in monocyte-like and smooth muscle-like cells found in the overlying intimal lesion. These studies indicate that one of the responses to dietary hypercholesterolemia is the expression of MCP-1 by vascular smooth muscle cells. This expression, when augmented with other cellular and molecular factors, could significantly contribute to the recruitment of monocytes/macrophages to the vessel wall.

Expression of c-sis/platelet-derived growth factor B, insulin-like growth factor I, and transforming growth factor alpha messenger RNAs and their respective receptor messenger RNAs in primary human gastric carcinomas: in vivo studies with in situ hybridization and immunocytochemistry

In situ hybridization and immunocytochemistry have been applied to investigate the expression of c-sis/platelet-derived growth factor (PDGF)-B, insulin-like growth factor (IGF)-I, and transforming growth factor alpha mRNAs and their respective receptor mRNAs in three primary human gastric carcinomas and in their adjacent nonmalignant mucosas. Expression of c-sis/PDGF-B mRNA and PDGF-receptor beta mRNA was seen in the tumor cells of the three gastric cancer specimens but not in their adjacent nonmalignant mucosa. The mRNA expression was accompanied by the expression of their respective protein products. IGF-I, IGF-I receptor, and epidermal growth factor receptor mRNAs were seen in both the tumor cells of the gastric cancer specimens and in nonmalignant mucosa. Transforming growth factor alpha mRNA was expressed in gastric tumor cells but not in nonmalignant mucosa. The coexpression of a potent "competence" growth factor, PDGF, and "progression" growth factors, IGF-I and transforming growth factor alpha, in the tumor cells of gastric carcinomas may contribute to their growth and maintenance.

Expression of monocyte chemoattractant protein 1 mRNA in human idiopathic pulmonary fibrosis

Macrophages are thought to play an important role in the pathologic changes associated with idiopathic pulmonary fibrosis (IPF). The mechanisms for increased monocyte/macrophage recruitment in IPF are unknown. Monocyte chemoattractant protein 1 (MCP-1) is the predominant monocyte chemoattractant secreted by a variety of different cell types in culture. We examined the expression of MCP-1 mRNA and its protein product in vivo in IPF and non-IPF lung specimens by in situ hybridization and immunocytochemistry. The cell types expressing MCP-1 in vivo were identified by immunostaining with specific antibodies. We demonstrated the expression of MCP-1 mRNA in pulmonary epithelial cells, in monocytes/macrophages, and in vascular endothelial and smooth muscle cells. Lung epithelial cells in patients with IPF strongly expressed MCP-1 mRNA and its protein product. In contrast, epithelial cells in non-IPF specimens did not express MCP-1 mRNA. Macrophages and vascular endothelial and smooth muscle cells were shown to express MCP-1 in both IPF and non-IPF lung specimens. These findings provide a basis for the understanding of the in vivo physiologic processes that mediate monocyte/macrophage recruitment and infiltration in the lung interstitium and the pathologic state contributing to an increased alveolar monocyte/macrophage population and inflammation in IPF.

Effect of the expression of transforming growth factor-beta 2 in primary human glioblastomas on immunosuppression and loss of immune surveillance

Glioblastomas are malignant brain tumors that are attended by an immunosuppressed state. The authors have studied the expression of transforming growth factor-beta 2, which is known to have potent immunosuppressive and angiogenic properties. Transforming growth factor-beta 2 messenger ribonucleic acid and its protein product are both found to be greatly overexpressed in these tumors and are absent from normal brain tissue. The overexpression of this growth factor may contribute to the escape of neoplastic astrocytes from immune surveillance and, furthermore, to the immunosuppressed state that is characteristic of many of these patients.

Malignant epithelial cells in primary human lung carcinomas coexpress in vivo platelet-derived growth factor (PDGF) and PDGF receptor mRNAs and their protein products

Lung cancer represents one of the major human carcinomas with the highest degree of mortality. Epidemiologic studies have linked this disease to "chronic injury," largely induced by cigarette smoking. In the present studies, we demonstrate the in vivo expression of platelet-derived growth factor (PDGF) and PDGF receptor (PDGF-R) beta mRNAs and their respective protein products in malignant epithelial cells of primary human lung carcinomas. In contrast, nonmalignant epithelial cells in control, normal lung tissue specimen did not express PDGF and PDGF-R mRNAs and did not produce their respective protein products. Epithelial cells in lung specimen from patients with idiopathic pulmonary fibrosis expressed only PDGF mRNA but not PDGF-R beta mRNA. These findings of the inappropriate coexpression of a potent mitogen, PDGF, and its receptor in lung cancer epithelial cells suggest the presence of a powerful in vivo mechanism contributing to the self-stimulation and unregulated growth of lung cancer tumor cells.

Expression of insulin-like growth factors I and II and their receptor mRNAs in primary human astrocytomas and meningiomas;in vivo studies usingin situ hybridization and immunocytochemistry

These studies demonstrate the expression of IGF-1, IGF-11, and their respective receptor mRNAs in primary human astrocytomas and meningiomas. In situ hybridization and immunocytochemistry have localized a strong expression of both IGF-1 and IGF-11 mRNAs and of their protein products in the tumor cells of astrocytomas and meningiomas. The expression of IGF-1 and IGF-11 mRNAs in the tumor cells was accompanied by the co-expression of their respective type-1 and type-11 IGF receptor mRNAs. Control, non-malignant human brain expressed IGF-1 mRNA and IGF-1 and IGF-11 receptor mRNAs. There was no significant expression of IGF-11 MRNA in the control brain specimens. Control pachymeninges (dura mater) expressed low levels of IGF-1 mRNA and IGF-1 receptor mRNA. There was no significant expression of IGF-11 and IGF-11 receptor mRNAs in pachymeninges. The co-expression of IGFs and their receptors in brain tumors may contribute in their development and maintenance. The strong inappropriate expression of IGF-11 mRNA and its protein product in the tumor cells of astrocytomas and meningiomas, but not in normal brain specimens, may serve as molecular markers for the early detection of these tumors.

Expression of monocyte chemotactic protein-1 in human melanoma in vivo

A common feature of human melanoma is infiltration by monocytes at early stages of tumorigenesis. This infiltration may be highly significant since macrophages have the capacity to alter the behavior of tumor cells. The authors previously demonstrated that the predominant monocyte chemoattractant produced by tumor cells in vitro was monocyte chemotactic protein-1 (MCP-1). The authors identify the expression of MCP-1 in pathologic specimens of both primary and metastatic human melanoma but not in normal skin. The finding that MCP-1 is produced by malignant melanoma suggests that specific genes are expressed in tumor cells that can induce the recruitment of monocytes in vivo.

Aggressive fibromatosis

Ten patients with aggressive fibromatosis of the extremities were prospectively followed for 2-6 years. Results of treatment methods were compared. Five patients underwent three-dimensional imaging with and without intravenous contrast, and the images were compared with the anatomic extent of the resected lesion. Pathologic specimens and control tissue were tested for the presence of estrogen and progesterone receptors and for expression of the c-sis oncogene and platelet-derived growth factor (PDGF), potent mitogens for fibrocytes. Wider surgical resection resulted in a lower recurrence rate, but current chemotherapeutic agents were not effective in eradicating the tumors. Intravenous contrast enhanced the lesions. Two thirds of the tumors tested had estrogen or progesterone receptors. All tumors tested had inappropriate expression of c-sis and PDGF. This inappropriate expression may be responsible for the underlying pathobiology and deregulation of control of growth in aggressive fibromatosis.

High-affinity binding of PDGF-AA and PDGF-BB to normal human osteoblastic cells and modulation by interleukin-1

Bone has the capacity for repair and regeneration. The repair process is thought to be locally regulated by growth factors. One of the growth factors that potentially plays a significant role in these processes is platelet-derived growth factor (PDGF). Two different PDGF genes have been identified, PDGF-A and PDGF-B, whose gene products give rise to biologically active dimers. We now report that PDGF-AA and PDGF-BB exhibit saturable binding to normal human osteoblastic cells. By Scatchard analysis we estimate that there are approximately 43,000 PDGF-AA binding sites per cell, with a dissociation constant (Kd) of 2.2 x 10(-10)M, and 55,000 high-affinity PDGF-BB binding sites per cell, with a Kd of 1.2 x 10(-10)M. The functional consequence of PDGF binding was also assessed. PDGF-AA and PDGF-BB both stimulated migration of normal human osteoblastic cells and stimulated thymidine incorporation. To gain insight into potential transmodulation of the PDGF response, we investigated the capacity of interleukin-1 beta (IL-1 beta), a cytokine that induces bone resorption, to modulate PDGF binding and PDGF-induced biological activity. IL-1 beta significantly reduced PDGF-AA binding and significantly decreased both PDGF-AA-mediated cell migration and thymidine incorporation. In contrast, IL-1 beta had only a small effect of PDGF-BB binding and PDGF-BB-induced biological activity in normal human osteoblastic cells.

PDGF: a multifunctional growth factor

hPDGF is the major growth factor of human blood serum. In vivo, it is apparently synthesized by megakaryocytes and is transported in blood stored in the alpha granules of platelets. hPDGF is a heterodimer of two homologous polypeptide chains (PDGF-1(A) and PDGF-2(B] linked together by disulphide bonds. The PDGF-1(A) chain is encoded by a gene localized in chromosome 7 and the PDGF-2(B) chain is encoded by the c-sis proto-oncogene localized in chromosome 22. The hPDGF heterodimer and its two isoforms, the PDGF-1(A) and PDGF-2(B) homodimers, are potent mitogens and chemoattractants for target cells such as diploid fibroblasts, osteoblasts, arterial smooth muscle cells and brain glial cells. The PDGF-1(A) homodimer binds only to its specific receptor alpha, and the hPDGF heterodimer and PDGF-2(B) homodimer bind to both receptors a and b. In addition to their mitogenic action, PDGF stimulates important cellular metabolic activities, including protein, lipid and prostaglandin synthesis. It appears to be an important factor in early development and in vivo appears to modulate tissue regeneration and remodelling during wound healing and osteogenesis. The inappropriate expression of PDGF genes and their mitogenic products has been linked to several proliferative disorders such as fibrosis, atherosclerosis and neoplasia.

The effects of short-term application of a combination of platelet-derived and insulin-like growth factors on periodontal wound healing

Polypeptide growth factors are a class of potent natural biologic mediators which regulate many of the activities of wound healing including cell proliferation, migration, and metabolism. Platelet-derived growth factor (PDGF) and insulin-like growth factor-I (IGF-I) have been shown to regulate DNA and protein synthesis in bone cells in vitro and to interact synergistically to enhance soft tissue wound healing in vivo. We have hypothesized that the combination of PDGF and IGF-I may, therefore, enhance regeneration of both the soft and hard tissue components of the periodontium. To test this hypothesis we performed conventional periodontal surgery on all 4 quadrants of the mouth of 13 beagle dogs with naturally occurring periodontal disease. Following flap reflection, degranulation, and root planing, all premolar teeth in 2 quadrants of each dog received a combination of 3 micrograms of recombinant PDGF-B and IGF-I in a methylcellulose gel, while the premolar teeth in the contralateral quadrants received the gel alone. Teeth in 4 additional animals also received 125I-PDGF or 125I-IGF-I in the treated sites. The clearance rate of the 125I-labeled protein, changes in local bone metabolism, and amount of new bone and cementum with inserting collagen fibers were measured. The clearance studies revealed that the half-life of the factors at the site of application was 3.0 hours for IGF-I and to 4.2 hours for PDGF-B. Greater than 96% of the radio-labeled proteins was cleared by 96 hours and no radioactivity was detected 2 weeks after application. There was a significant (P less than 0.01) 2-fold increase in uptake of the bone-seeking radiopharmaceutical Technetium 99-MDP at 2 and 4 weeks in growth factor treated sites compared to controls, indicating that there was increased metabolic activity within the bone at these sites. Computer-aided histologic analyses of biopsies obtained at 2 and 5 weeks post-operatively revealed a significant (P less than 0.01), 5 to 10 fold increase in new bone and cementum in PDGF-B/IGF-I treated sites at both time points compared to controls receiving the placebo gel. The height and total area of new bone continued to increase from 2 to 5 weeks. The new bone underwent a normal maturation process as judged by histologic appearance. A physiologic periodontal ligament space was also formed between the new bone and new cementum. There was no increase in ankylosis in the treated sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of angiogenic growth factor genes in primary human astrocytomas may contribute to their growth and progression

Astrocytomas are highly malignant brain tumors and are among the most neovascularized solid tumors. We have investigated the expression of the angiogenic growth factors acidic fibroblast growth factor and transforming growth factor-alpha, together with its receptor epidermal growth factor receptor, in 30 primary astrocytomas. Both acidic fibroblast growth factor and transforming growth factor-alpha, together with epidermal growth factor receptor, are found to be greatly overexpressed in these tumors when compared with normal brain. This overexpression of angiogenic growth factors may underlie the intense neovascularization characteristic of astrocytomas.

Injury induces in vivo expression of platelet-derived growth factor (PDGF) and PDGF receptor mRNAs in skin epithelial cells and PDGF mRNA in connective tissue fibroblasts

Platelet-derived growth factor (PDGF) stimulates many of the processes important in tissue repair, including proliferation of fibroblasts and synthesis of extracellular matrices. In this study we have demonstrated with in situ hybridization and immunocytochemistry the reversible expression of c-sis/PDGF-2 and PDGF receptor (PDGF-R) b mRNAs and their respective protein products in epithelial cells and fibroblasts following cutaneous injury in pigs. Epithelial cells in control, unwounded skin did not express c-sis and PDGF-R mRNAs, and fibroblasts expressed only PDGF-R mRNA. The expression levels in the injured site were correlated with the stage of tissue repair, being highest during the initial stages of the repair process and declining at the time of complete re-epithelialization and tissue remodeling. It is suggested that the controlled, reversible expression of a potent mitogen and its receptor induced by injury may function in an autocrine/paracrine manner on both epithelial cells and fibroblasts to bring about their sustained proliferation during the normal healing process. These studies provide a molecular basis for understanding the mechanisms contributing to normal tissue repair. We suggest the possibility that a defect in these mechanisms may be associated with defective wound healing. It is also conceivable that "chronic" injury may induce irreversible gene expression leading to pathologic, unregulated cell growth.

Platelet-derived growth factor in idiopathic pulmonary fibrosis

Fibrosis is a complex process involving an inflammatory reaction, fibroblast proliferation, and abnormal accumulation of interstitial collagens. Mononuclear cells are usually present in lung fibrosis. Activated monocytes and macrophages in culture have been shown to produce several growth factors including platelet-derived growth factor (PDGF). PDGF is a potent mitogen and chemoattractant for fibroblasts and smooth muscle cells and a stimulator of collagen synthesis. We have studied the expression of c-sis/PDGF-2 mRNA in lung tissues derived from five patients with idiopathic pulmonary fibrosis (IPF) and from four control individuals without IPF. Northern blot analysis of specimens obtained from four patients with IPF revealed the expression of the c-sis/PDGF-2 protooncogene. A control lung tissue without IPF did not express the c-sis protooncogene. In situ hybridization extended these studies demonstrating the expression of the c-sis mRNA in the five specimens with IPF but not in the four control specimens without IPF. The expression of c-sis mRNA was localized primarily in the epithelial cells. Invading alveolar macrophages also expressed c-sis mRNA. The expression of c-sis mRNA was accompanied by the expression of PDGF-like proteins in lung specimens with IPF but not in control lung specimens. These findings demonstrate the in vivo expression of the c-sis/PDGF-2 protooncogene and the production of PDGF-like proteins in the epithelial cells and macrophages of the fibrotic tissue. This localized and sustained production of PDGF-like mitogen may constitute an important contributing factor in the abnormal fibroblast proliferation and collagen production, events associated with pulmonary fibrosis.

Human meningiomas co-express platelet-derived growth factor (PDGF) and PDGF-receptor genes and their protein products

The present studies investigated the expression of the platelet-derived growth factor (PDGF) and PDGF-receptor genes in human meningiomas. Northern blot analysis demonstrated that all meningiomas examined expressed both the c-sis/PDGF-2 proto-oncogene and the PDGF-receptor gene. In situ hybridization localized the c-sis mRNA and the PDGF-receptor mRNA in the tumor cells of the meningioma tissues. Control pachymeninges derived from adult individuals, without meningiomas, expressed only PDGF-receptor mRNA but not the c-sis mRNA. Immunocytochemistry studies detected both the c-sis and the PDGF-receptor protein products in meningioma tissues but only the PDGF-receptor protein products in control pachymeninges. These findings indicate the presence of an autocrine mechanism in human meningiomas based on the co-expression of the c-sis/PDGF-2 proto-oncogene and PDGF-receptor gene and their protein products. This co-expression of a potent mitogen and its receptor may contribute to the growth and maintenance of human meningiomas.

Coexpression of platelet-derived growth factor (PDGF) and PDGF-receptor genes by primary human astrocytomas may contribute to their development and maintenance

The present studies investigated the expression of the two PDGF genes (c-sis/PDGF-2 and PDGF-1) and the PDGF-receptor b gene (PDGF-R) in 34 primary human astrocytomas. Northern blot analysis demonstrated the coexpression of the c-sis/PDGF-2 protooncogene and the PDGF-R gene in all astrocytomas examined. The majority of the tumors also expressed the PDGF-1 gene. There was no correlation between the expression of the two PDGF genes. Nonmalignant human brain tissue expressed the PDGF-R and PDGF-1 genes but not the c-sis/PDGF-2 protooncogene. In situ hybridization of astrocytoma tissue localized the expression of the c-sis and PDGF-R mRNA's in tumor cells. Capillary endothelial cells also expressed c-sis mRNA. In contrast, nonmalignant human brain tissue expressed only PDGF-R mRNA but not c-sis/PDGF-2 mRNA. The coexpression of a potent mitogenic growth factor protooncogene (c-sis) and its receptor gene in astrocytoma tumor cells suggests the presence of an autocrine mechanism that may contribute to the development and maintenance of astrocytomas. The expression of c-sis mRNA in tumor cells but not in nonmalignant brain cells may serve as an additional diagnostic criterion for the detection of astrocytomas in small tissue specimen using in situ hybridization for the detection of c-sis mRNA and/or immunostaining for the recognition of its protein product.

A combination of platelet-derived and insulin-like growth factors enhances periodontal regeneration

The combination of platelet-derived growth factor (PDGF) and insulin-like growth factor one (IGF-1) has previously been shown to enhance repair of soft tissue wounds. Here we report initial observations following application of PDGF and IGF-1 to periodontitis-affected teeth in beagle dogs. 1 micrograms of PDGF and IGF-1 in an aqueous gel was applied to the root surfaces of test teeth following open flap debridement. Control sites received the gel alone. Block biopsies of the teeth and surrounding bone were taken 2 weeks after treatment. Histologic analyses of control specimens revealed a long junctional epithelial attachment, and no new bone or cementum formation. In contrast, growth factor treated sites exhibited significant amounts of new bone and cementum formation. A nearly continuous layer of osteoblasts lined the newly formed bone, and there was a dense cellular "front" at the coronal extent of the new bone. These preliminary results suggest that in vivo application of the combination of PDGF and IGF-1 may enhance regeneration of the periodontal structures.

Growth factors in wound healing. Single and synergistic effects on partial thickness porcine skin wounds

Several growth factors are potential mediators of wound healing, although their actual roles, interactions, and therapeutic use are not established. Six well-characterized human growth factors were chosen for detailed investigation by topical application to standardized skin wounds in swine: epidermal growth factor (EGF), transforming growth factors alpha and beta (TGF-alpha and TGF-beta), fibroblast growth factor (FGF), insulin-like growth factor-I (IGF-I), and platelet-derived growth factor (PDGF). When applied singly in doses up to 1,500 ng, only TGF-beta produced a marked tissue response, as demonstrated by an increase in the new connective tissue volume, the collagen content and maturity, and increased angiogenesis. However, TGF-beta enhanced inflammation and caused abnormal epithelial differentiation and decreased epithelial volume, the last reversed by addition of IGF-I. Recombinant PDGF-2 homodimer, if given in combination with recombinant IGF-I, caused a similar increase in the new connective tissue volume and collagen content and maturity, but without increased inflammation. In addition, this combination stimulated increased amounts of epithelium with normal differentiation. The synergy of PDGF-2 and IGF-I was optimal at a ratio of 2:1 by weight. Of the six individual factors and nine combinations tested, the combinations of PDGF-2 and IGF-I or PDGF-2 and TGF-alpha were the most potent stimulators of healing in the absence of increased inflammation.

Platelet-derived growth factor is not chemotactic for human peripheral blood monocytes

PDGF is a mitogenic protein stored in platelets and released upon platelet degranulation. Recent evidence indicates that PDGF plays an important role in both physiologic and pathophysiologic processes, particularly in tumorigenesis, wound healing, pulmonary fibrosis, and atherogenesis. In addition to its mitogenic potential, it has been reported that PDGF stimulates monocyte chemotaxis. Since the recruitment of monocytes from the peripheral vasculature is an important event in vivo, the potential role of PDGF as a monocyte chemoattractant has significant biologic implications. However, we now report that homogeneous human PDGF from platelets and a recombinant PDGF-2 homodimer do not stimulate monocyte chemotaxis. In contrast to previous reports these results indicate that PDGF is not a monocyte chemoattractant.

Characterization of a high-molecular-weight protein immunoprecipitated by platelet-derived growth factor antisera

We previously demonstrated that a high-molecular-weight glycoprotein could be immunoprecipitated from metabolically labeled U-2 OS cells with platelet-derived growth factor (PDGF) antiserum and that it appears to be derived from a different precursor than is the 30 kD PDGF-like mitogen produced by these cells. These findings were unexpected, since the molecular weight of this glycoprotein is too large to be encoded by the PDGF structural genes. From experiments with metabolically labeled U-2 OS human osteosarcoma, fibroblasts, and NRK cells, we report here that a 185 kD protein immunoprecipitated with PDGF antiserum has the following characteristics. 1) It is a PDGF binding protein that is unrelated to alpha 2-macroglobulin. 2) It is phosphorylated in response to PDGF stimulation. 3) It is immunoprecipitated by phosphotyrosine antibodies. 4) It is not a substrate of epidermal growth factor-induced tyrosine kinase activity. These studies indicate that high-molecular-weight proteins immunoprecipitated by antiserum to PDGF represent a complex between PDGF and a binding protein capable of being phosphorylated by a PDGF-induced tyrosine kinase. These characteristics are identical to those of the PDGF receptor.

Expression of platelet-derived growth factor (PDGF)-related transcripts and synthesis of biologically active PDGF-like proteins by human malignant epithelial cell lines

Human malignant epithelial cell lines were analyzed for expression of platelet-derived growth factor (PDGF) genes. Of the 12 cell lines tested, 9, derived from breast, lung, gastric, and ovarian carcinomas, were found to express both PDGF-1 and PDGF-2 genes. The levels of both PDGF-1 and PDGF-2 transcripts were superinduced when these cells were treated with cycloheximide, an inhibitor of protein synthesis. These cells also released an activity that in studies with BALB-c/3T3 cells, inhibited binding of 125I-labeled PDGF and stimulated incorporation of [3H]thymidine. This stimulating activity was inhibited after reduction of the conditioned media by mercaptoethanol or after preincubation with antibodies to PDGF. Moreover, this activity was not affected by heat treatment. Immunoprecipitation studies revealed that breast, lung, and gastric carcinoma cells produced PDGF-like proteins that migrated as 30- and 32-kD species under nonreducing conditions and as 15- and 16-kD species under reducing conditions. In contrast, malignant cells of ovarian origin produced 14-16-kD PDGF-like proteins that were unchanged in mobility after reduction. As PDGF receptors were not detected on these malignant epithelial cells, the production of PDGF-like proteins may affect other cells in the microenvironment by paracrine mechanisms and may contribute to excessive cell proliferation, inflammatory reactions, and connective tissue remodeling seen in certain carcinomas.

Constitutive production of platelet-derived growth factor-like proteins by human prostate carcinoma cell lines

Prostate carcinoma cell lines DU-145 and PC-3 express both platelet derived growth factor (PDGF)-1 and PDGF-2/sis genes. Concomitantly, these cells synthesize and secrete PDGF-like proteins, as judged by indirect immunofluorescence and by direct immunoprecipitation with specific PDGF antiserum. Conditioned media derived from DU-145 and PC-3 cells stimulated the incorporation of [3H]thymidine by 3T3 cells and competed with 125I-labeled PDGF for its binding to cell surface receptors of 3T3 cells. The biological activity was stable to heating at 100 degrees C for 10 min, sensitive to reducing agents, and neutralized by the IgG fraction of PDGF antiserum, properties similar to those of authentic PDGF. Both DU-145 and PC-3 cell lines appear to lack receptors for PDGF as indicated by their inability to mitogenically respond to PDGF and receptor binding of 125I-labeled PDGF. Production of PDGF-like proteins by human prostate carcinoma cells may play an important role in a paracrine mode in the organization of the extracellular matrix of the malignant tissue.

Role of platelet-derived growth factor in wound healing: synergistic effects with other growth factors

Platelet-derived growth factor (PDGF) in vitro stimulates DNA synthesis and chemotaxis of fibroblasts and smooth muscle cells and stimulates collagen, glycosaminoglycan, and collagenase production by fibroblasts. These in vitro properties suggest that PDGF, delivered by platelets to the site of injury in vivo, may play an important role in the initiation of the wound repair process. Studies presented here show that the addition of pure PDGF to a wound site involving the epidermis and dermis has little effect on the morphology or biochemistry of the healing wound. In contrast, the addition of partially purified PDGF resulted in significant dose-dependent increases in the width of the newly synthesized connective tissue and epidermal layers. Autoradiography using [3H]thymidine revealed increased numbers of labeled cells in the new connective tissue and epithelial layers. Furthermore, addition of partially purified PDGF resulted in significant increases in the rate of protein and DNA synthesis and the total content of these components in biopsies taken from the wound site. Similar effects were obtained when insulin-like growth factor I was added in combination with pure PDGF. This combination of factors caused a 2.4-fold increase in the width of the newly formed connective tissue layer and a 95% increase in epidermal thickness compared with controls. Insulin-like growth factor I alone caused no significant morphologic changes. Epidermal growth factor alone or in combination with PDGF resulted in a thickening only of the epidermis. These results indicate that the synergistic actions of other factors with PDGF are important in the modulation of the wound healing process.

Human iliac artery endothelial cells express both genes encoding the chains of platelet-derived growth factor (PDGF) and synthesize PDGF-like mitogen

In human umbilical vein and bovine aortic endothelial cells in culture c-sis gene expression and secretion of platelet-derived growth factor (PDGF) has been previously demonstrated. We now report the presence of PDGF-1 and PDGF-2/sis mRNA transcripts in primary cultures of human iliac artery endothelial cells (HIA-EC). Concomitantly, these cells synthesize and secrete PDGF-like proteins identified by direct immunoprecipitation with specific PDGF antiserum. The PDGF proteins secreted by HIA-EC have molecular weights of 31 and 35 kd under nonreducing conditions. Upon reduction these proteins are converted to the monomeric 15- and 16-kd forms. Conditioned media derived from HIA-EC stimulated the incorporation of 3H-thymidine by 3T3 cells and competed with 125I-PDGF for its binding to 3T3 cell membrane receptors. The biologic activity was stable to heating at 100 degrees C for 10 min and sensitive to reducing agents, properties similar to those of authentic PDGF. Production of PDGF-like mitogen by the human arterial endothelial cells may play an important role in the paracrine modulation of arterial wall regeneration following vascular injury.

Synthesis and secretion of platelet-derived growth factor by human breast cancer cell lines

We report that human breast cancer cells secrete a growth factor that is biologically and immunologically similar to platelet-derived growth factor (PDGF). Serum-free medium conditioned by estrogen-independent MDA-MB-231 or estrogen-dependent MCF-7 cells contains a mitogenic or "competence" activity that is capable of inducing incorporation of [3H]thymidine into quiescent Swiss 3T3 cells in the presence of platelet-poor plasma. In addition, the conditioned medium contains an activity that competes with 125I-labeled PDGF for binding to PDGF receptors on normal human fibroblasts. The secretion of PDGF-like activity by the hormone-responsive cell line MCF-7 is stimulated by 17 beta-estradiol. Like authentic PDGF, the PDGF-like activity produced by breast cancer cells is stable after acid and heat treatment (95 degrees C) and inhibited by reducing agents. The mitogenic activity comigrates with a material of approximately equal to 30 kDa on NaDodSO4/polyacrylamide gels. Immunoprecipitation with PDGF antiserum of proteins from metabolically labeled cell lysates and conditioned medium followed by analysis on nonreducing NaDodSO4/polyacrylamide gels identified proteins of 30 and 34 kDa. Upon reduction, the 30- and 34-kDa bands were converted to 15- and 16-kDa bands suggesting that the immunoprecipitated proteins were made up of two disulfide-linked polypeptides similar to PDGF. Hybridization studies with cDNA probes for the A chain of PDGF and the B chain of PDGF/SIS identified transcripts for both PDGF chains in the MCF-7 and MDA-MB-231 cells. The data summarized above provide conclusive evidence for the synthesis and hormonally regulated secretion of a PDGF-like mitogen by breast carcinoma cells. Production of a PDGF-like growth factor by breast cancer cell lines may be important in mediating paracrine stimulation of tumor growth.

Induction of c-sis gene expression and synthesis of platelet-derived growth factor in human myeloid leukemia cells during monocytic differentiation

Phorbol esters induce the differentiation of human myeloid leukemia cells HL-60 and U-937 along the monocytic-macrophage lineage. This process has been associated with the induction of several cellular protooncogenes, including the c-fos and c-fms genes. We now report that phorbol ester-induced differentiation of the HL-60 and U-937 cells results in the induction of the expression of the c-sis platelet-derived growth factor 2 (PDGF-2) protooncogene. sis mRNA transcripts were not detectable in the uninduced cells but were detectable within 12 hr of phorbol ester induction. Concomitantly, the induced cells were shown to synthesize and secrete biologically active PDGF-like proteins, identified in the conditioned medium of the phorbol ester-treated cells by direct immunoprecipitation with PDGF antiserum. Addition of cycloheximide to phorbol ester-treated HL-60 cells superinduced sis mRNA transcripts. c-sis gene transcripts were also detected in freshly isolated human monocytes but not in human granulocytes or in HL-60 cells induced to differentiate along the granulocytic lineage. Activation of the c-sis/PDGF-2 gene in human hematopoietic cells during monocytic differentiation may serve in the mediation of physiologic functions of the differentiated cells by means of the secretion of potent PDGF-like mitogen.

Human leukemia cells synthesize and secrete proteins related to platelet-derived growth factor

Human leukemia cells in culture (HL-60) synthesize and secrete proteins that are recognized by antiserum to human platelet-derived growth factor (PDGF). The molecular mass of the intracellular proteins immunoprecipitated by PDGF antiserum ranged from 34 kDa to 240 kDa. PDGF-related proteins were also identified in the conditioned medium of the cells. Several of these immunoprecipitated proteins were glycosylated. A single protein of 46 kDa was immunoprecipitated from the cell-free translation products of mRNA obtained from the leukemia cells. Antiserum to the C but not to the N terminus of the predicted amino acid sequence of the transforming protein p28sis/PDGF-2 also immunoprecipitated proteins secreted by the HL-60 cells. These findings provide a direct demonstration for the synthesis and secretion of PDGF-like proteins by leukemia cells in culture. These proteins do not appear to be coded by the known c-sis/PDGF-2 locus since no sis mRNA was detectable in the HL-60 cells.

Identification of processing events in the synthesis of platelet-derived growth factor-like proteins by human osteosarcoma cells

The human osteosarcoma-derived cell line U-2 OS expresses c-sis mRNA and synthesizes platelet-derived growth factor (PDGF)-like proteins. Pulse-chase experiments indicate that proteins of 23 kDa and 180 kDa are synthesized first. The 23-kDa protein undergoes dimerization and proteolysis, giving rise to the 30-kDa dimeric protein secreted by the cells. The 180-kDa protein is proteolytically cleaved in a complex series of steps that give rise to several intracellular species. It is also the likely precursor of high molecular mass PDGF-like or PDGF-associated proteins secreted by these cells. The processing and secretion of the 180-kDa protein is slower than that of the 23-kDa protein. Subcellular fractionation and studies with the antibiotic monensin indicate that the processing events occur in the Golgi-endoplasmic reticulum compartment of U-2 OS cells.

Demonstration of receptors for a PDGF-like mitogen on human osteosarcoma cells

U-2 OS human osteosarcoma cells synthesize, process and secrete a platelet-derived growth factor (PDGF)-like mitogen. Incubation of these cells with 1 mM suramin unmasks PDGF receptor sites which are normally occupied or down regulated by the secreted endogenous PDGF-like mitogen. Partially purified preparations of metabolically labelled U-2 OS conditioned medium binds to U-2 OS cells and binding is inhibited by excess PDGF. These findings suggest that U-2 OS cells are capable of autocrine stimulation.

Synthesis and secretion of proteins resembling platelet-derived growth factor by human glioblastoma and fibrosarcoma cells in culture

Immunoprecipitation of proteins extracted from metabolically labeled human glioblastoma and fibrosarcoma cells with antiserum to platelet-derived growth factor (PDGF) showed that these cells express and secrete proteins that are recognized specifically by the antiserum. The molecular masses of immunoprecipitated proteins in the lysates of the malignant cells ranged from 16 kDa to 140 kDa. Both cell lines secreted a 31-kDa polypeptide with structural, immunological, and biological properties similar to those of human PDGF. These cell lines were shown to synthesize a 4.4-kb mRNA that contained sequences from all the six currently identified exons of the human c-sis gene. These data suggest that the PDGF-like proteins in the two mesenchyme-derived transformed cells are encoded at least in part by the c-sis locus.

Detection of c-sis transcripts and synthesis of PDGF-like proteins by human osteosarcoma cells

Platelet-derived growth factor (PDGF) has been previously shown to be homologous to the transforming gene of simian sarcoma virus (v-sis), and inappropriate expression of the cellular counterpart of the v-sis gene (c-sis) has been implicated in the generation of mesenchymal tumors. The U-2 OS human osteosarcoma line was shown to contain multiple c-sis transcripts. Immunoprecipitation experiments with antiserum to PDGF identified a variety of polypeptides ranging in size from 18,000 to 165,000 daltons that were immunoprecipitated specifically from U-2 OS cell extracts. The osteosarcoma also was shown to secrete a 29,000-dalton protein having the serological and structural characteristics of PDGF.

Simian sarcoma virus--transformed cells secrete a mitogen identical to platelet-derived growth factor

Normal rat kidney (NRK) cells transformed by simian sarcoma virus (SSV) release into the culture medium a biologically active mitogen with properties identical to those of human platelet-derived growth factor (PDGF). Like PDGF, the growth factor derived from SSV-NRK cells was shown to be stable to heat and sensitive to reducing agents. It was capable of inhibiting binding of labeled PDGF to the receptor on human fibroblasts. It also stimulated the phosphorylation of the same membrane protein (185 kilodaltons) in isolated plasma membranes from human fibroblasts. Immunoprecipitation of metabolically labeled proteins released by SSV-NRK cells showed that a 34-kilodalton protein was specifically precipitated by antiserum to PDGF. Upon reduction, this protein had a molecular size of 17 kilodaltons. PDGF has been shown to consist of two 14- to 18-kilodalton proteins linked by disulfide bonds.

Evidence for functional platelet-derived growth factor receptors on MG-63 human osteosarcoma cells

The specific interaction of platelet-derived growth factor (PDGF) with the human osteosarcoma cell line MG-63 was studied. Scatchard analysis of 125I-PDGF binding to MG-63 cells indicated there were 32,000 specific PDGF-binding sites per cell with a Kd of 2.4 X 10(-11) M. Unlabeled PDGF blocked the specific binding of labeled PDGF to MG-63 cells at concentrations greater than 1 ng/ml. When assayed for phosphorylation of MG-63 membrane vesicles, PDGF was shown to stimulate a dose-dependent phosphorylation of a protein (phosphoprotein with a molecular weight of 185,000) which was stable in 1 M NaOH. In the absence of PDGF, a prominent alkali-stable phosphoprotein with a molecular weight of 116,000 was noted. PDGF also stimulated a dose-dependent increase in [3H]aminoisobutyric acid uptake, [3H]thymidine incorporation, and cell proliferation. When tested for secretion of PDGF-like factors, the mitogenic activity of MG-63-conditioned serum-free medium was not blocked by anti-PDGF antiserum. Concentrated MG-63-conditioned medium did not compete with 125I-PDGF for specific receptor sites on diploid fibroblasts. Therefore, MG-63 osteosarcoma cells have functional PDGF receptors and do not secrete PDGF-like mitogens.

Platelet-derived growth factor stimulates mouse 3T3 cell mitogenesis and leukocyte chemotaxis through different structural determinants

Platelet-derived growth factor (PDGF) stimulates both proliferation of fibroblasts and chemotaxis of leukocytes. In this study we compared the mitogenic and chemotactic activities of native PDGF and reduced PDGF. Reduction of PDGF (Mr = 32,000) to its constituent polypeptides (Mr = 14,000 and 17,000) caused a loss of the ability to stimulate proliferation of Balb/c 3T3 cells. However, reduced PDGF retained virtually all of its activity as a chemotactic agent for human neutrophils and monocytes. A half-maximal chemotactic response to both native and reduced PDGF occurred at a concentration of approximately 0.08 nM for neutrophils and 0.1 nM for monocytes. The maximal chemotactic response to reduced PDGF was at least as great as the maximal response to native PDGF. Both native and reduced PDGF stimulated the release of the lysosomal enzyme, beta-glucosaminidase, from neutrophils with a half-maximal response at less than 0.1 nM. However, the net maximum release of this enzyme by PDGF (and reduced PDGF) was significantly less than that stimulated by a maximal concentration of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine. These results indicate that different structural determinants are required for the proliferative response of 3T3 cells to PDGF and for the chemotactic response of leukocytes to PDGF.