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.     

Induction of cell proliferation in mammalian inner-ear sensory epithelia by transforming growth factor alpha and epidermal growth factor.

Regenerative proliferation occurs in the inner-ear sensory epithelial of warm-blooded vertebrates after insult. To determine how this proliferation is controlled in the mature mammalian inner ear, several growth factors were tested for effects on progenitor-cell division in cultured mouse vestibular sensory epithelia. Cell proliferation was induced in the sensory epithelium by transforming growth factor alpha (TGF-alpha) in a dose-dependent manner. Proliferation was also induced by epidermal growth factor (EGF) when supplemented with insulin, but not EGF alone. These observations suggest that stimulation of the EGF receptors by TGF-alpha binding, or EGF (plus insulin) binding, stimulates cell proliferation in the mature mammalian vestibular sensory epithelium.     

Divergent effects of epidermal growth factor and calcipotriol on human rectal cell proliferation.

Vitamin D may protect against colorectal cancer by reducing cell proliferation and inducing differentiation. By contrast, epidermal growth factor (EGF) stimulates cell proliferation and may encourage gastrointestinal mucosal healing. This study investigated the effect of a synthetic vitamin D analogue, calcipotriol, and EGF on human rectal epithelial cell proliferation in patients with familial adenomatous polyposis (FAP). In addition, a new technique to measure the cell cycle time is described. Sigmoidoscopic biopsy specimens were obtained from 14 patients with FAP. Tissue was established in organ culture, with or without the addition of EGF (n = 8), or calcipotriol (n = 6). Proliferation was determined using (a) metaphase arrest to measure the crypt cell production rate, (b) native mitotic index, and (c) the growth fraction using PC10 antibody. EGF receptor expression was shown using a polyclonal antibody AP12E. Calcipotriol reduced crypt cell production rate by 52% from mean (SEM) 5.29 (1.18) to 2.56 (0.80) cells/crypt/hour (p < 0.01) and EGF increased crypt cell production rate by 102% from 3.62 (0.59) to 7.33 (0.90) cells/crypt/hour (p < 0.05), and this tissue expressed the EGF receptor. The growth fraction was 48.40 (4.0)%, and the native mitotic index 1.08 (0.14)%. The cell cycle time was estimated as 94.5 hours and the time for mitosis as one hour. Thus, calcipotriol and EGF have divergent effects on human rectal mucosal proliferation.     

Coordinate control of 3T3 cell proliferation by platelet-derived growth factor and plasma components.

DNA synthesis and cell division were measured in Swiss mouse 3T3 cells cultured in different concentrations of cell-free plasma-derived serum and increasing amounts of a platelet-derived growth factor. In plasma-derived serum alone, the cells were quiescent and they were arrested in the Go/G1 phase of the cell cycle. Addition of a platelet-derived growth factor to quiescent cells maintained in plasma-derived serum stimulated both DNA synthesis and cell division. When plasma components were present at high concentration (5%, vol/vol), the amount of platelet factor added to the cultures determined the number of cell doublings. Plasma-derived molecules were required for the platelet factor to stimulate DNA synthesis and cell division in the maximal number of cells. In addition, plasma components had to be present for recently divided cells to respond to the platelet factor. When 3T3 cells were cultured in excess platelet factor and limiting amounts of plasma-derived serum (0.5%, vol/vol), the cells underwent one doubling and then ceased to proliferate. Addition of fresh plasma-derived serum to these cells induced a second round of cell division. Plasma components and the platelet-derived growth factor acted in a coordinate fashion to regulate the proliferation of Swiss 3T3 cells.     

非小细胞肺癌患者血清血管内皮生长因子、血小板衍生生长因子和表皮生长因子受体测定的临床意义

目的 探讨血清血管内皮生长因子(vascular endothelial growth factor,VEGF)、血小板衍生生长因子(platelet-derived growth factor,PDGF)和表皮生长因子受体(epidermal growth factor receptor,EGFR)测定在非小细胞肺癌(non-small cell lung cancer,NSCLC)诊断和预后判定中的意义.方法 采用双抗体夹心ABC-ELISA法测定31例NSCLC患者及30名健康者血清VEGF、PDGF和EGFR的含量.结果 NSCLC患者血清VEGF、PDGF和EGFR测定值均高于健康对照组(P值均＜0.01).血清VEGF、PDGF和EGFR测定值与NSCLC病理分型无关(P值均＞0.05),与远处转移有关,远处转移组的测定值高于未转移组(P＜0.05～0.01).NSCLC患者血清VEGF与PDGF测定值之间呈显著正相关(r=0.641,P＜0.01),血清VEGF和EGFR测定值呈正相关(r=0.369,P＜0.05).结论 检测血清VEGF、PDGF和EGFR水平对NSCLC的诊断和预后判定具有一定价值.     

Regulation of granulosa cell proliferation: facilitative roles of platelet-derived growth factor and low density lipoprotein

Recent studies suggest that epidermal growth factor (EGF) and/or transforming growth factor-alpha (TGF-alpha) and insulin-like growth factor-I (IGF-I) act synergistically to promote granulosa cell proliferation in vitro suggesting a similar role in vivo. Using a serum-restricted, monolayer culture system containing very low levels of platelet-poor plasma-derived serum (PPPDS), the facilitative roles of platelet-derived growth factor (PDGF) and low density lipoprotein (LDL) with respect to growth factor-stimulated granulosa cell proliferation were investigated. In nutrient medium containing only 0.1% PPPDS, PDGF (1-25 ng/ml) had no effect upon granulosa cell proliferation. When combined with EGF, which alone does not stimulate granulosa cell proliferation, PDGF dose-dependently increased cell proliferation to levels obtained with 10% fetal calf serum (2.4-fold increase relative to controls, P less than 0.05). When combined with EGF and IGF-I, a combination which does stimulate mitosis in granulosa cells, PDGF again dose-dependently enhanced proliferation (P less than 0.05). The extent of proliferation obtained with EGF + IGF-I + PDGF was consistently greater than that obtained with 10% fetal calf serum (P less than 0.05) but significantly less than that obtained with EGF + fetal calf serum, a treatment which stimulates rapid granulosa cell proliferation. LDL has been shown to greatly enhance granulosa cell steroidogenesis by providing exogenous cholesterol. However, cholesterol is also required for plasma membrane biosynthesis and cell growth. LDL alone, had no effect upon porcine granulosa cell proliferation relative to media controls (0.1% PPPDS) nor did it synergize with any single growth factor to induce mitosis. When combined with EGF + IGF-I, and EGF + PDGF, but not PDGF + IGF-I, LDL dose-dependently (1-25 micrograms/ml) enhanced proliferation (P less than 0.05) to levels equivalent to that obtained with 10% fetal calf serum. When combined with EGF, IGF-I, and PDGF, LDL at 10 micrograms/ml enhanced proliferation to an extent equivalent with EGF + fetal calf serum (a 5.4-fold increase relative to media controls). High density lipoprotein did not itself stimulate proliferation nor did it facilitate proliferation mediated by growth factors. When maintained in medium alone (0.1% PPPDS), the cell population doubling time was 8.0 +/- 0.5 days. In the presence of EGF, IGF-I, PDGF, and LDL (10, 10, and 5 ng/ml, and 10 micrograms/ml, respectively) the doubling time was reduced to 2.0 +/- 0.1 days.(ABSTRACT TRUNCATED AT 400 WORDS)     

Modulation of the epidermal growth factor receptor by platelet-derived growth factor and choleragen: Effects on mitogenesis

The addition of fresh medium supplemented with partially purified platelet-derived growth factor (PDGF) to quiescent density-arrested cultures of BALB/c-3T3 cells decreases the subsequent binding of radiolabeled epidermal growth factor (EGF). The decrease in EGF binding can be observed 1 hr after the addition of PDGF. This effect is maximal in 2-3 hr, and binding remains diminished for at least 6 hr. These effects can be accounted for by a decrease in the number of EGF receptors with no change in receptor affinity. The action of PDGF is concentration dependent, but even at very high concentrations of PDGF the reduction in EGF binding is never more than 50%. Similar decreases in EGF binding are produced by other treatments that render BALB/c-3T3 cells competent, such as the addition of fibroblast growth factor or medium previously exposed to the macrophage-like cell line P388D(1). Cholera toxin (choleragen), which alone had no effect on EGF binding, dramatically potentiated the ability of PDGF to down regulate EGF receptors. Two to three hours after the addition of PDGF and choleragen, EGF binding was reduced by 80-90% compared with control values. The ability of PDGF and choleragen together to decrease EGF binding was substantially inhibited by cycloheximide. Autoradiography of [(3)H]thymidine-labeled cells shows that choleragen potentiates the action of PDGF; lower concentrations of PDGF are required to make cells competent after choleragen treatment. Furthermore, cells treated with PDGF and choleragen no longer require EGF for traverse of G(1) phase and initiation of DNA synthesis in defined medium. The reduction in receptor number produced by choleragen and PDGF, which may be due to internalization of the EGF receptor, may mimic the action of EGF and thereby remove the EGF requirement for DNA synthesis.     

Control of bovine adrenal cortical cell proliferation by fibroblast growth factor. Lack of effect of epidermal growth factor.

Primary functional bovine adrenal cortical cell cultures have been developed to study the factors controlling adrenal cell growth. Cells were prepared by the collagenase technique and maintained in F-12 medium containing fetal calf serum and horse serum. Cells contained abundant lipid as demonstrated by staining with Oil Red O and showed strongly positive staining for delta5,3beta-hydroxysteroid dehydrogenase. ACTH inhibited DNA synthesis and stimulated steriodogenesis in these cells. Fibroblast growth factor (FGF) was shown to be a potent stimulator of the growth of normal bovine adrenal cortical cells maintained in tissue culture. The minimal effective dose of FGF was 1 ng/ml with maximal effects being observed at 100 ng/ml. The effect of FGF was dependent on the serum concentration. Inclusion of FGF in F-12 medium containing serum permitted cloning of functional bovine adrenal cortical cells from cultures seeded at low density (4 cells/cm2). ACTH inhibited the mitogenic effects of FGF. In addition to its mitogenic action, FGF is a migratory factor for bovine adrenal cortical cells. Though ACTH inhibited the mitogenic effects of FGF, it did not block the migratory activity. Epidermal growth factor did not affect the growth of either normal bovine adrenal or functional mouse adrenal tumor cells (Y-1) in tissue culture. FGF is the first direct mitogen identified for adrenal cortical cells; ACTH opposes this mitogenic action and functions directly as a differentiate function signal.     

Dual control of cell growth by somatomedins and platelet-derived growth factor.

Quiescent BALB/c 3T3 cells exposed briefly to a platelet-derived growth factor (PDGF) become "competent" to replicate their DNA but do not "progress" into S phase unless incubated with growth factors contained in platelet-poor plasma. Plasma from hypophysectomized rats is deficient in progression activity; it does not stimulate PDGF-treated competent cells to synthesize DNA, demonstrating that somatomedin C is required for progression. Various growth factors were tested for progression activity and competence activity by using BALB/c 3T3 tissue culture assays. Multiplication stimulating activity and other members of the somatomedin family of growth factors are (like somatomedin C) potent mediators of progression. Other mitogenic agents, such as fibroblast growth factor, are (like PDGF) potent inducers of competence. Growth factors with potent progression activity have little or no competence activity and vice versa. In contrast, simian virus 40 provides both competence and progression activity. Coordinate control of BALB/c 3T3 cell growth in vitro by competence factors and somatomedins may be a specific example of a common pattern of growth regulation in animal tissues.     

Characterization and regulation of epidermal growth factor receptors in human placental cell cultures

We have confirmed that cultured human placental cells rapidly release hCG. Preincubation with epidermal growth factor (EGF) for 24 h significantly increased the amount of hCG released and also increased human placental lactogen release by these cells. To better understand the mechanisms of action of EGF on the feto-placental unit, we studied EGF receptor binding and regulation by examining the characteristics and specificity of EGF receptors in human placental syncytiotrophoblast cultures. Maximal [125I]EGF binding occurred at pH 7.5 and 4 C, and exhibited a high degree of specificity. In the presence or absence of Bacitracin at 4 C, specific binding values were similar, and labeled EGF was physically intact, as assessed by trichloroacetic acid precipitation or rebinding to human placental membranes. The percent specific binding was proportional to cell and ligand concentrations and was significantly increased in term (52.9 +/- 1.2%; n = 11) compared to early gestation placental cells (22.7 +/- 3.4%; n = 7; P less than 0.001). Both term and midterm EGF displacement curves generated curvilinear Scatchard plots, suggesting receptor heterogeneity. Pretreatment of cells with EGF resulted in a dose and time-dependent decrease in specific binding, which was maximal (80%) at 200 ng/ml EGF. This loss of binding was due to decreases in the number of both high and low affinity receptor sites, with no significant change in the apparent affinity. The induction of EGF receptor loss by EGF was a specific effect on the EGF receptor. Preincubation of these same cells with insulin caused a decrease in the number of insulin receptors, while the number of EGF receptors remained unaltered. Conversely, preincubation with EGF, in a dose that down-regulated EGF receptors, did not alter insulin receptor number or affinity. Down-regulation of EGF receptors was reversible, with 50% recovery by 16 h. However, cycloheximide (10 micrograms/ml) blocked EGF-induced down-regulation and receptor recovery. The presence of EGF receptors in human placental cells and the ontogenic changes found suggest that EGF may be involved in the regulation of fetal growth and development. These studies indicate the feasibility of using human placental cells in culture as a model system to probe hormone-cell interaction in the fetoplacental unit.     

Chromatin binding of epidermal growth factor, nerve growth factor, and platelet-derived growth factor in cells bearing the appropriate surface receptors.

We analyzed the uptake and intracellular distribution of 125I-labeled epidermal growth factor, nerve growth factor, and platelet-derived growth factor in different cell lines that express or do not express the respective surface receptors for these factors. After 1 hr of incubation, all three growth factors were detected in the cytoplasmic fraction and in the nucleus, tightly bound to chromatin. The amount of chromatin-bound growth factors continued to increase during the incubation, and analysis at 48 hr revealed each chromatin-bound labeled growth factor in a nondegraded form. After limited digestion of chromatin with DNase II (10-20% digested sequences), specific release of all three growth factors was detected only after 1 hr of incubation but not after 24 and 48 hr, suggesting that the DNA regions involved in growth factor binding became nuclease-resistant. Binding of labeled epidermal growth factor and nerve growth factor to isolated chromatin was inhibited by monoclonal antibodies specific for the respective growth factor receptor. The data suggest that chromatin binding may represent an important step in the pathway of growth factor action.     

Stimulation of mammary epithelial cell growth in vitro: interaction of epidermal growth factor and mammogenic hormones

A serum-free primary cell culture system was used to examine the direct effects and interactions of mammogenic hormones and epidermal growth factor (EGF) on the growth of mouse mammary epithelial cells. Epithelial cells were isolated by collagenase dissociation followed by Percoll gradient centrifugation and cultured within collagen gels in a mixture of Ham's F-12-Dulbecco's Minimum Essential Medium (1:1) containing insulin (10 micrograms/ml), crude soybean lecithin, trace elements, trypsin inhibitor, and antioxidants. Progesterone (P; 10(-6) - 10(-8) M) or ovine PRL (1 microgram/ml), in the absence of EGF, stimulated the growth of cells from mature virgin mice 2- to 4-fold over that of controls cultured in basal medium only. P and PRL synergized in stimulating growth 3- to 17-fold. 17 beta-Estradiol (10(-7) - 10(-10) M) alone did not stimulate growth or synergize with P and/or PRL. This lack of growth stimulation by 17 beta-estradiol was also observed in medium containing a low concentration of insulin (0.1 microgram/ml). EGF (10 ng/ml) alone stimulated growth to the same extent as the combination of P and PRL. EGF at 1, but not 10, ng/ml when combined with P and PRL could additively stimulate growth. Cells from midpregnant mice were less responsive than cells from virgin mice to the growth-stimulating effects of the combination of P and PRL (2-fold stimulation at most), but not to EGF (3- to 6-fold stimulation). Corticosterone, deoxycorticosterone, and aldosterone, but not cortisol, could synergize with PRL in stimulating the growth of cells from mature virgin mice. However, only deoxycorticosterone could stimulate growth in the absence of PRL. These results suggest that PRL, P, and adrenal corticoids may directly stimulate the growth of mouse mammary epithelial cells. The physiologically relevent adrenal corticoids, corticosterone and aldosterone, only potentiate the stimulatory effect of PRL. The hormonal stimulation of growth in vitro can be obscured by an optimum concentration (10 ng/ml) of EGF. The relative growth responses to mammogenic hormones and EGF may depend on the degree of differentiation of the cells.     

Differential actions of naftopidil,doxazosin and nifedipine on platelet thromboxane generation and platelet-derived growth factor efflux in vitro

We examined the effects of the alpha(1)-adrenoreceptor blockers naftopidil and doxazosin and the Ca(2+) antagonist nifedipine on platelet function with reference to stimulus-induced thromboxane (TxB(2)) generation and platelet-derived growth factor (PDGF) efflux. Collagen (5 micro g/ml) caused a 12.5-fold increase in TxB(2) generation, from a basal level of 7.69 +/- 1.28 ng/10(8) platelets to 96.34 +/- 13.37 ng/10(8) platelets (P<0.001). Adrenaline (16 micro M) increased TxB(2) production 3-fold from 2.44 +/- 0.61 to 8.02 +/- 1.08 ng/10(8) platelets (P<0.01). Adrenaline-induced TxB(2) generation was inhibited 42.5 +/- 10.3% (P<0.05) and 81.8 +/- 7.5% (P<0.05) by 10 and 40micro M naftopidil, respectively. Collagen-stimulated TxB(2) generation was inhibited 59.5 +/- 9.2% (P<0.01) by 40 micro M naftopidil and 53.7 +/- 11.3% (P<0.01) by 28 micro M nifedipine. Doxazosin (7.5 and 30 micro M) did not influence adrenaline- or collagen-induced TxB(2) synthesis. Collagen increased PDGF efflux from 1.17 +/- 0.39 to 4.25 +/- 0.51 ng/10(8) platelets (P<0.01), whilst adrenaline raised concentrations from 1.08 +/- 0.19 to 5.37 + 1.02 ng/10(8) platelets (P<0.01). Naftopidil had no effect on collagen-induced PDGF release. Adrenaline-stimulated PDGF efflux was, however, inhibited 82.9 +/- 13.7% (P<0.001) and 125.7 +/- 16.3% (P<0.001) by 10 and 40 micro M naftopidil, respectively. Doxazosin (30 micro M) inhibited adrenaline-induced PDGF release by 70.3 +/- 31.5% (P<0.05), whilst nifedipine (28 micro M) had no effect on collagen-stimulated release. We conclude that naftopidil, like nifedipine, may block stimulated TxB(2) generation via inhibition of phospholipase A(2), the Ca(2+)-dependent, rate-limiting enzyme in thromboxane synthesis. Although adrenaline-induced PDGF release was inhibited by naftopidil and doxazosin, collagen-induced release was unaffected by either alpha(1)-adrenoreceptor blocker or nifedipine, indicating that platelet alpha-granular release is not dependent on Ca(2+) mobilisation or thromboxane generation. Thus, the effects of these drugs on PDGF release may be mediated through alternative cellular signalling mechanisms.     

Differential actions of naftopidil,doxazosin and nifedipine on platelet thromboxane generation and platelet-derived growth factor efflux in vitro

We examined the effects of the f 1 -adrenoreceptor blockers naftopidil and doxazosin and the Ca 2+ antagonist nifedipine on platelet function with reference to stimulus-induced thromboxane (TxB 2 ) generation and platelet-derived growth factor (PDGF) efflux. Collagen (5 w g/ml) caused a 12.5-fold increase in TxB 2 generation, from a basal level of 7.69 - 1.28 ng/10 8 platelets to 96.34 - 13.37 ng/10 8 platelets ( P <0.001). Adrenaline (16 w M) increased TxB 2 production 3-fold from 2.44 - 0.61 to 8.02 - 1.08 ng/10 8 platelets ( P <0.01). Adrenaline-induced TxB 2 generation was inhibited 42.5 - 10.3% ( P <0.05) and 81.8 - 7.5% ( P <0.05) by 10 and 40 w M naftopidil, respectively. Collagen-stimulated TxB 2 generation was inhibited 59.5 - 9.2% ( P <0.01) by 40 w M naftopidil and 53.7 - 11.3% ( P <0.01) by 28 w M nifedipine. Doxazosin (7.5 and 30 w M) did not influence adrenaline- or collagen-induced TxB 2 synthesis. Collagen increased PDGF efflux from 1.17 - 0.39 to 4.25 - 0.51 ng/10 8 platelets ( P <0.01), whilst adrenaline raised concentrations from 1.08 - 0.19 to 5.37 + 1.02 ng/10 8 platelets ( P <0.01). Naftopidil had no effect on collagen-induced PDGF release. Adrenaline-stimulated PDGF efflux was, however, inhibited 82.9 - 13.7% ( P <0.001) and 125.7 - 16.3% ( P <0.001) by 10 and 40 w M naftopidil, respectively. Doxazosin (30 w M) inhibited adrenaline-induced PDGF release by 70.3 - 31.5% ( P <0.05), whilst nifedipine (28 w M) had no effect on collagen-stimulated release. We conclude that naftopidil, like nifedipine, may block stimulated TxB 2 generation via inhibition of phospholipase A 2 , the Ca 2+ -dependent, rate-limiting enzyme in thromboxane synthesis. Although adrenaline-induced PDGF release was inhibited by naftopidil and doxazosin, collagen-induced release was unaffected by either f 1 -adrenoreceptor blocker or nifedipine, indicating that platelet f -granular release is not dependent on Ca 2+ mobilisation or thromboxane generation. Thus, the effects of these drugs on PDGF release may be mediated through alternative cellular signalling mechanisms.     

Cell-cell adhesion mediated by binding of membrane-anchored transforming growth factor alpha to epidermal growth factor receptors promotes cell proliferation.

The precursor for transforming growth factor alpha, pro-TGF-alpha, is a cell surface glycoprotein that can establish contact with epidermal growth factor (EGF) receptors on adjacent cells. To examine whether the pro-TGF-alpha/EGF receptor pair can simultaneously mediate cell adhesion and promote cell proliferation, we have expressed pro-TGF-alpha in a bone marrow stromal cell line. Expression of pro-TGF-alpha allows these cells to support long-term attachment of an EGF/interleukin-3-dependent hematopoietic progenitor cell line that expresses EGF receptors but is unable to adhere to normal stroma. This interaction is inhibited by soluble EGF receptor ligands. Further, the hematopoietic progenitor cells replicate their DNA while they are attached to the stromal cell layer and become foci of sustained cell proliferation. Thus, pro-TGF-alpha and the EGF receptor can function as mediators of intercellular adhesion and this interaction may promote a mitogenic response. We propose the term "juxtacrine" to designate this form of stimulation between adjacent cells.     

Presence of epidermal growth factor, platelet-derived growth factor, and their receptors in human myometrial tissue and smooth muscle cells: their action in smooth muscle cells in vitro.

Immunohistochemical observations indicate that human myometrial smooth muscle cells express epidermal growth factor (EGF) and platelet-derived growth factor (PDGF)-AB and contain EGF and PDGF-beta receptors with no variation in intensity with phases of the menstrual cycle. Furthermore, immunofluorescent microscopic studies revealed that primary myometrial smooth muscle cell cultures also express EGF, PDGF-AB, and contain EGF and PDGF-beta, but not alpha-receptor. Incubation of subconfluent smooth muscle cells in serum-free medium leads to quiescence within 48 h as demonstrated by 3H-thymidine incorporation and labeling index. Exposure of quiescent cells to 10% fetal bovine serum stimulates resumption of DNA synthesis and proliferation in a time-dependent manner with a doubling time of 41.6 h. EGF (1.5-50 ng/ml) and PDGF-AB (1-10 ng/ml) in a dose- and time-dependent manner significantly stimulated 3H-thymidine incorporation by quiescent myometrial smooth muscle cells (P less than 0.05). Combinations of EGF (15 ng/ml) and PDGF-AB (10 ng/ml) significantly increased 3H-thymidine incorporation induced by either growth factor alone (P less than 0.05). PDGF-BB at 10 ng/ml also stimulated 3H-thymidine incorporation and its effect was similar to that induced by PDGF-AB at the same concentration. 17 beta-Estradiol (E2) at 1 microM inhibited 3H-thymidine incorporation by the smooth muscle cells (P less than 0.05). E2 also reduced the stimulatory effect of EGF (15 ng/ml) and PDGF (3 ng/ml). Progesterone at 1 microM either alone or in combination with E2 did not have any effect on 3H-thymidine incorporation or alter the mitogenic action of EGF and PDGF. The effect of EGF and PDGF on cell growth and 3H-thymidine incorporation by myometrial smooth muscle cells was independent of phases of the menstrual cycle. In summary, the results of present studies indicate that human myometrial tissue and myometrial smooth muscle cells in primary culture locally produce EGF and PDGF-AB and contain EGF and PDGF-beta, but not alpha-receptors. Moreover, the myometrial smooth muscle cells in culture respond to the mitogenic action of EGF and PDGF.     

Location of epidermal growth factor receptors on porcine thyroid follicle cells and receptor regulation by thyrotropin

By using a direct electron microscopic autoradiographical technique, we were able to demonstrate that the epidermal growth factor (EGF) receptor is asymmetrically located on polarized porcine thyroid follicle cells cultured on a collagen gel matrix. More than 80% of autoradiographical grains from [125I]EGF were associated with the basolateral cell surface compared to only about 2.5% at the apical cell margin. EGF stimulated growth only when the collagen gels were floating, indicating a basolateral location of functional EGF receptors. Preincubation with TSH or another stimulator of cAMP synthesis, forskolin, increased binding of [125I]EGF to the cells. Moreover, the subsequent mitogenic response to EGF was potentiated by such pretreatment. The results are in accordance with the hypothesis that TSH potentiates the response to EGF in the stimulation of thyroid growth.     

Exposure to platelet-derived growth factor modulates the porcine aortic smooth muscle cell response to somatomedin-C

Platelet-derived growth factor (PDGF) is a potent mitogen for smooth muscle cells, but to detect maximal stimulation by PDGF, the cells must be incubated with plasma. Somatomedin-C (Sm-C), a peptide growth factor that is present in plasma, has been shown to interact with PDGF synergistically to stimulate DNA synthesis in cultured fibroblasts. These studies were designed to test the hypothesis that PDGF interacted with Sm-C to stimulate smooth muscle cell replication and to compare the response of this cell type to that of fibroblasts. When PDGF or Sm-C was added individually to smooth muscle cell cultures, each growth factor induced only minimal increases in [3H]thymidine incorporation into DNA (i.e. PDGF, 3,400 +/- 1,120 to 54,900 +/- 1,550 cpm; Sm-C, 3,400 +/- 1,120 to 10,950 +/- 980 cpm). In contrast, addition of increasing concentrations of Sm-C to cultures that were continuously exposed to PDGF in the presence of Sm-C-deficient plasma resulted in a synergistic increase in [3H]thymidine incorporation (3,400 +/- 1,120 to 54,500 +/- 1,800 cpm; P less than 0.001). To determine if Sm-C was required for smooth muscle cell replication, cultures were sequentially exposed to PDGF, followed by Sm-C-deficient plasma. The rate at which the non-Sm-C-exposed cells synthesized DNA was retarded compared to that of cells exposed to Sm-C-containing plasma; however, 68% nuclear labeling was present after 44 h of incubation. To exclude the possibility that some cellular secretory product was substituting for Sm-C, the medium was changed every 2 h and replaced by fresh Sm-C-deficient medium. Using these test conditions, exposure to PDGF and Sm-C-deficient plasma induced only 11% labelling. Readdition of pure Sm-C to this medium restored nuclear labeling to 82% at 44 h. Other variables that appeared to modulate the cellular response to Sm-C were culture density and simultaneous PDGF exposure. Sm-C and PDGF both appear to be potent mitogens for porcine aortic smooth muscle cells, and when added together to quiescent cultures, their effects are synergistic. Smooth muscle cells appear to require Sm-C to initiate DNA synthesis, and in its absence produce a Sm-like factor that can partially compensate for Sm-C deficiency and allow replication.     

Transforming growth factor beta reverses the glucocorticoid-induced wound-healing deficit in rats: possible regulation in macrophages by platelet-derived growth factor.

Transforming growth factor beta (TGF-beta) and the platelet-derived growth factor (PDGF) are potent mitogenic polypeptides which enhance rates of wound healing in experimental animals; in contrast, glucocorticoids inhibit wound repair. The potential of TGF-beta and PDGF to reverse this inhibition in healing was tested in methylprednisolone-treated rats with deficits in skin wound strength of 50%. Single applications of TGF-beta (10-40 pmol per wound, 0.25-1 micrograms) applied locally at the time of wounding fully reversed this deficit in a concentration-dependent and highly reproducible manner. Wounds in glucocorticoid-treated animals were characterized by a near total absence of neutrophils and macrophages and by a delayed influx and reduced density of fibroblasts; however, such wounds treated with TGF-beta showed significant increases in wound fibroblasts and in intracellular procollagen type I. PDGF did not reverse the deficit in wound breaking strength in glucocorticoid-treated rats; there were more fibroblasts in the PDGF-treated wounds, but these fibroblasts lacked the enhanced expression of procollagen type I found in TGF-beta-treated wounds. The wound macrophages, required for normal tissue repair, remained absent from both PDGF- and TGF-beta-treated wounds in glucocorticoid-treated animals. This result suggested that macrophages might normally act as an intermediate in the induction of procollagen synthesis in fibroblasts of PDGF-treated wounds and that TGF-beta might bypass the macrophage through its capacity to stimulate directly new synthesis of procollagen type I in fibroblasts. Whereas PDGF does not stimulate procollagen synthesis, in a rodent macrophage cell line, PDGF induced a highly significant, time-dependent enhancement of expression of TGF-beta.