Biphasic effects of type beta transforming growth factor on epidermal growth factor receptors in NRK fibroblasts. Functional consequences for epidermal growth factor-stimulated mitosis

Periodontal wound healing with and without platelet-rich plasma: histologic observations and assessment of flap tensile strength

BACKGROUND

Platelet-rich plasma (PRP) has been promoted as a surgical adjunct to enhance hard and soft tissue wound healing. Although anecdotally reported to be of value, the results of controlled studies examining the added effects of PRP on surgical procedures have been mixed. The purpose of this study was to test the effect of PRP on flap strength at various post-surgical time points in a minipig animal model.

METHODS

Twelve Yucatan minipigs provided four sites per animal. PRP was prepared from each animal at the time of surgery. Following reflection of a mucoperiosteal flap in each quadrant, subgingival plaque and calculus were removed. Each surgical site was irrigated with sterile saline; prior to suturing, one randomly selected test quadrant in each arch was treated with PRP. Four animals were euthanized at day 14, and two animals were euthanized at 2, 7, 10, and 28 days. The flap strength in each quadrant was tested by attaching to a loop of 3-0 silk suture through the tissue; the force required to separate the flap from the tooth/bone interface was recorded for each site. A separate portion of each flap site was prepared for descriptive histologic examination, including inflammation, hemorrhage, and new bone growth.

RESULTS

Flap strength was significantly less on day 2 compared to later time points, and there were no significant differences between the test and control groups. No histologic differences in healing between test and control sites were seen at any time point.

CONCLUSIONS

PRP did not seem to contribute to greater flap strength at any post-surgical time point, nor was it associated with any histologic differences in wound healing in this Yucatan minipig model. The time points chosen for observation post-surgery, as well as the variability in the PRP platelet count, may have contributed to the lack of positive findings in this study.

Treatment of periodontal intrabony defects with demineralized freeze-dried bone allograft in combination with platelet-rich plasma: a comparative clinical trial

BACKGROUND

The aim of the present randomized, double-masked, clinical trial was to compare platelet-rich plasma (PRP) combined with a demineralized freeze-dried bone allograft (DFDBA) to DFDBA mixed with a saline solution in the treatment of human intrabony defects.

METHODS

Sixty interproximal intrabony osseous defects in 60 healthy, non-smoking subjects diagnosed with chronic periodontitis were treated in this study. Thirty subjects each were randomly assigned to the test group (PRP + DFDBA) or the control group (DFDBA + saline). Clinical and radiographic measurements were made at baseline and at the 12-month evaluation.

RESULTS

Compared to baseline, the 12-month results indicated that both treatment modalities resulted in significant changes in all clinical parameters (gingival index, bleeding on probing, probing depth, clinical attachment level, and gingival recession; P <0.001) and radiographic parameters (hard tissue fill and bone depth reduction; P <0.001). However, the test group exhibited statistically significantly greater changes compared to the control group in probing depth reduction (4.3 +/- 1.7 mm versus 2.6 +/- 2.2 mm; P <0.05) and clinical attachment gain (3.5 +/- 2.1 mm versus 2.3 +/- 2.4 mm; P <0.001).

CONCLUSIONS

Treatment with a combination of PRP and DFDBA led to a significantly greater clinical improvement in intrabony periodontal defects compared to DFDBA with saline. No statistically significant differences were observed in the hard tissue response between the two treatment groups, which confirmed that PRP had no effect on hard tissue fill or gain in new hard tissue formation.

Modulated release of bioactive protein from multilayered blended PLGA coatings

The objective of this study was to develop a poly(D,L-lactic-co-glycolic acid) (PLGA)-based coating system for producing biologically-inspired delivery profiles. Protein-loaded microspheres were made from PLGA (50:50) terminated with carboxylic acid groups (PLGA-2A) blended either with more hydrophobic PLGA (50:50) having lauryl ester endcaps (PLGA-LE) or with the more hydrophilic Pluronic F-127 (PF-127). Dense coatings were formed by pressure-sintering the microspheres. Altering hydrophobicity changed the water concentration within coatings, and consequently the time to onset of polymer degradation and protein release was modulated. After blending up to 8% Pluronic, degradation by-products began accumulating immediately upon incubation in saline, whereas, degradation was delayed for up to 14 days with blending of up to 30% PLGA-LE. Primary protein release peaks from one-layer coatings could be created from 7 to 20 days using 8% PF-127 or 30% PLGA-LE blends, respectively. Multilayered coatings of different blends generated several release peaks, with their temporal occurrence remaining approximately the same when layers of other hydrophobicity were added above or below. To allow design of coatings for future use, results were used to construct a model based on Fourier analysis. This polymer blend system and model can be used to mimic temporally varying profiles of protein expression.

Regenerative potential of platelet-rich plasma added to xenogenic bone grafts in peri-implant defects: a histomorphometric analysis in dogs

BACKGROUND

The purpose of this investigation was to evaluate the regenerative influence of platelet-rich plasma (PRP) added to xenogenic bone grafts on bone histomorphometric parameters in a dog model.

METHODS

Ninety endosseous dental implants were inserted in the mandibles of nine hound dogs. Mesial and distal 3-wall peri-implant defects were surgically created adjacent to the implants. Defects were randomly assigned to three groups: demineralized freeze dried bone with platelet-rich plasma (DFDB + PRP), DFDB alone, and no treatment (NT). Animals were sacrificed at 1, 2, and 3 months according to a previously established randomization schedule, and specimens were subjected to histomorphometric analysis. Percentages of bone area inside the implant threads (BiIT), bone-to-implant contact (BIC), and bone area outside implant threads (BoIT) were recorded. Treatment effects were evaluated using analysis of variance models.

RESULTS

The effect of the three treatments on the outcome measures did not differ significantly by healing time (P > 0.05 for the healing time by treatment interaction). However, the average (standard deviation) percentage of BIC and BoIT was significantly different between the treatment groups. In particular, the average percentage of BIC differed between peri-implant defects treated with DFDB + PRP (33.8% [11.0]) and those treated with DFDB alone (28.5% [10.8]; P = 0.042), as well as those in the NT group (27.9% [11.0]; P = 0.024). Furthermore, the average percentage of BoIT differed significantly between defects treated with DFDB + PRP compared to defects in the NT group (51.6% [12.2] versus 43.3% [10.3]; P = 0.005). There was borderline evidence to suggest that the average percentage of BiIT and BIC was significantly different depending on the length of the healing time (P = 0.054 and P = 0.085, respectively).

CONCLUSION

This study found that the addition of PRP to xenogenic bone grafts demonstrated a low regenerative potential in this animal model.

Cell responses to BMP-2 and IGF-I released with different time-dependent profiles

During wound healing, growth factors are expressed in time-dependent amounts. Constant delivery of biomolecules, however, is often used to influence cell and tissue behavior. In the present studies, a crosslinked gelatin-coating system was used to deliver bone morphogenetic protein 2 (BMP-2) or insulin-like growth factor (IGF-I) to three types of mesenchymal cells with three temporally varying release profiles. The "early" delivery profile released most of the growth factor within the first 2 days. The "pseudo-zero-order" profile approximated constant rate of delivery for about 5 days. The "late" delivery profile released most of the growth factor after about 5 days. Early delivery of IGF-I had the greatest effect on mitogenesis of SaOS-2 human osteosarcoma cells with a secondary effect noted nearly 5 days after delivery was completed. Late delivery of BMP-2 resulted in greatest alkaline phosphatase (AP) activity in mouse pluripotent C3H10T1/2 cells. Rat bone marrow stromal cells (BMCs) responded to all delivery profiles of BMP-2, with the duration of elevated AP activity increasing as the amount of BMP-2 delivered increased. In addition to an early increase in AP activity, late release also stimulated BMCs over a longer portion of the culture period. BMCs responded similarly to SaOS-2 cells when seeded on early IGF-I delivery coatings, increasing AP activity after delivery had ended. Overall, these studies further show the importance of delivery profile, specifically the characteristics of time and concentration, on cell and tissue responses.

Controls of EGF-induced morphological transformation of human bronchial epithelial cells

Human bronchial epithelial cells, both normal primary (NHBE) and the BEAS-2B line, respond to epidermal growth factor (EGF) by extruding lengthy filaments, or filapodia. The morphological transformation of BEAS-2B cells maximized at 48 h using 1-10 nM EGF. EGF-induced filapodia extension was inhibited by co-exposure to transforming growth factor beta, which did not affect tyrosine phosphorylation of the EGF receptor (EGFR). Inhibition was also effected by phorbol myristoyl acetate (PMA), which reduced the rate of EGFR tyrosine phosphorylation. Dibutyryl-cAMP had no effect, whereas the protein kinase inhibitor H-89 stimulated the EGF response. The ability to regulate cellular responses to EGF by hormonal and chemical approaches has implications for current investigations into the roles of EGF in lung growth, differentiation, and wound repair.

Phenotypic transformation of normal rat kidney fibroblasts by endothelin-1. Different mode of action from lysophosphatidic acid, bradykinin, and prostaglandin f2alpha

In the present study, we compared the effects of endothelin (ET)-1 on cell proliferation and second messenger induction in normal rat kidney (NRK) fibroblasts, with those of other activators of G-protein-coupled receptors such as prostaglandin (PG)-F2alpha, bradykinin (BK), and lysophosphatidic acid (LPA). LPA is mitogenic by itself, while the other factors require the presence of EGF. In density-arrested NRK cells, ET-1 and LPA induce phenotypic transformation rapidly, with similar kinetics as retinoic acid (RA) and transforming growth factor (TGF)-beta, while BK and PGF2alpha only do so with delayed kinetics. ET-1 and PGF2alpha are strong inducers of anchorage-independent growth, with a similar level of induction as TGFbeta, in contrast to LPA and BK. When investigating the second messenger generation, we found that ET-1 is the strongest activator of arachidonic acid release and phosphatidylinositol diphosphate hydrolysis. Only in the case of ET-1 the cell depolarization is not reversible upon removal of the factor. Similarly, only the ET-1-induced transient enhancement of intracellular calcium concentration is paralleled by both homologous and heterologous desensitization. In conclusion, these data show that ET-1 is a potent inducer of second messengers and phenotypic transformation in NRK cells, with characteristics that clearly differ from those of other activators of G-protein-coupled receptors, most likely as a result of prolonged receptor activation.

Characterization of a newly established human acinic cell adenocarcinoma cell line (HACC) originating from the salivary gland: morphological features and role of various growth factors on the growth of the HACC cell line

Human acinic cell adenocarcinoma cell (HACC) line was established from the pleural effusion that contains metastatic tumor cells of acinic cell adenocarcinoma of papillary and microcystic type originating from the parotid gland. The HACC cells grew in an adherent monolayer with a doubling time of 66 h. Implanted tumor of SCID mice revealed similar histological findings to that of the primary tumor. The HACC cells produced mucin and expressed epithelial markers as well as alpha1-antitrypsin and lysozyme, whereas salivary peptide P-C was expressed in cultured HACC cells but not in the primary and implanted HACC cell tumors. S-100 protein was also expressed in both the primary tumor and HACC cell line. Neither amplification of common oncogenes nor expression of p53 was observed. The receptor for epidermal growth factor (EGF) was expressed, indicating EGF and transforming growth factor-alpha (TGF-alpha) enhanced the growth of the HACC line. Unexpectedly, tumor necrosis factor-a (TNF-alpha) also enhanced the growth of the HACC line significantly. However, there was no evidence of autocrine growth using these growth factors. In contrast, TGF-beta1 inhibited the growth of the HACC cell line through apoptosis. The HACC cell line has features similar to both acinar and intercalated ductal cells of the salivary gland. Epidermal growth factor, TGF-alpha and TNF-alpha are potential growth factors for the HACC cell line. The HACC cell line may be a good model for studying the biological behavior of salivary gland neoplasms.

Oxygen dependency of epidermal growth factor receptor binding and DNA synthesis of rat hepatocytes

BACKGROUND/AIMS

Changes in oxygen availability modulate replicative responses in several cell types, but the effects on hepatocyte replication remain unclear. We have studied the effects of transient nonlethal hypoxia on epidermal growth factor receptor binding and epidermal growth factor-induced DNA synthesis of rat hepatocytes.

METHODS

Lactate dehydrogenase activity in culture supernatant, intracellular adenosine triphosphate content, 125I-epidermal growth factor specific binding, epidermal growth factor receptor protein expression, and 3H-thymidine incorporation were compared between hepatocytes cultured in hypoxia and normoxia.

RESULTS

Hypoxia up to 3 h caused no significant increase in lactate dehydrogenase activity in the culture supernatant, while intracellular adenosine triphosphate content decreased time-dependently and was restored to normoxic levels by reoxygenation (nonlethal hypoxia). Concomitantly, 125I-epidermal growth factor specific binding to hepatocytes decreased time-dependently (to 54.1% of normoxia) and was restored to control levels by reoxygenation, although 125I-insulin specific binding was not affected. The decrease in 125I-epidermal growth factor specific binding was explained by the decrease in the number of available epidermal growth factor receptors (21.37+/-3.08 to 12.16+/-1.42 fmol/10(5) cells), while the dissociation constant of the receptor was not affected. The change in the number of available receptors was not considered to be due to receptor degradation-resynthesis, since immunodetection of the epidermal growth factor receptor revealed that the receptor protein expression did not change during hypoxia and reoxygenation, and since neither actinomycin D nor cycloheximide affected the recovery of 125I-epidermal growth factor binding by reoxygenation. Inhibition of epidermal growth factor-induced DNA synthesis after hypoxia (to 75.4% of normoxia by 3 h hypoxia) paralleled the decrease in 125I-epidermal growth factor binding.

CONCLUSIONS

Transient hypoxia, which caused no increase in lactate dehydrogenase leakage but affected intracellular adenosine triphosphate levels, did, however, modulate the number of available epidermal growth factor receptors without affecting the receptor protein expression, and inhibit the epidermal growth factor-induced DNA synthesis of hepatocytes. This suggests that even transient nonlethal hypoxia affects the epidermal growth factor-induced DNA synthesis of rat hepatocytes through reversible changes in the epidermal growth factor receptor molecule, which depends on oxygen availability.

Synergistic enhancement of EGF, but not HGF, stimulated hepatocyte motility by TGF-beta 1 in vitro

The ability of TGF-beta 1 (transforming growth factor-beta 1) to suppress growth factor induced proliferation of many cell types in vitro is well documented; however, TGF-beta 1 increases within a similar time frame as the hepatocyte mitogens HGF (hepatocyte growth factor), EGF (epidermal growth factor), and TGF-alpha (transforming growth factor-alpha) prior to hepatocyte proliferation during liver regeneration. This has raised the issue that TGF-beta 1 may have effects on hepatocytes additional to mito-inhibition and that these effects may be relevant to the regenerative process. To this end, we examined the effect of TGF-beta 1 on both the mitogenesis and the motility of growth factor stimulated primary rat hepatocytes and the hepatoblastoma cell line HepG2 in vitro. TGF-beta 1 significantly enhanced the chemotactic motility of EGF or TGF-alpha, and not HGF, stimulated hepatocytes on a collagen I substratum. TGF-beta 1 was not chemotactic when added alone and decreased the DNA synthesis of all hepatocyte cultures to near control levels. HepG2 cells were chemotactic toward HGF, EGF, and TGF-beta 1 alone and displayed an additive chemotactic response when TGF-beta 1 was added to either HGF or EGF. Additionally, HepG2 cells were refractory to the growth stimulatory effects of HGF or EGF and the growth inhibitory effects of TGF-beta 1. Hepatocytes plated onto other collagen-containing substrates (collagen IV, Matrigel, or ECL, an entactin-collagen IV-laminin matrix), but not on fibronectin or laminin alone, also displayed enhanced EGF stimulated motility by TGF-beta 1. The data indicate that an additional, novel role for TGF-beta 1 during liver tissue remodeling following PHx may include the synergistic enhancement EGF stimulated hepatocyte motility responses, and this enhancement is observed only on collagen-containing extracellular matrices.

Stimulation of protracted connective tissue repair in normal mice by transforming growth factor beta 1

The repair and contraction during connective tissue repair of mesenteric perforations is prolonged in mice compared with rats. In the present study the stimulating effect of transforming growth factor beta 1 (TGF-beta 1) on different aspects of such repair of the mouse mesentery was assessed. The number of closed mesenteric perforations were counted on different days after operation and the free peritoneal cells were counted, the mitotic index was assessed, and actin distribution of fibroblasts around the perforation was studied with laser scanning confocal microscopy. TGF-beta 1 significantly increased the speed of closure and seemed to induce more actin in fibroblasts at the wound margin. It did not significantly influence the mitotic index, but fewer free peritoneal cells were obtained in mice treated with TGF-beta 1. We conclude that TGF-beta 1 is a potent stimulator of connective tissue repair and contraction in mice. The different methods of closure in rats and mice implicate different molecular responses in wounds and further studies on the stimulating effect of TGF-beta 1 may indicate basic fibroblastic cellular mechanisms that are active during contraction in connective tissue repair.

Expression of transforming growth factor beta 1 (TGF beta 1), -beta 2, and- beta 3 by cultured human prostate cells

Transforming growth factor beta s (TGF beta s) are members of a superfamily of polypeptides that control cell cycle progression and a variety of other cellular activities. TGF beta family members, -beta 1, -beta 2, and -beta 3, have been identified in prostate. The levels of expression of these TGF beta isotypes have been reported to vary with the pathologic state of the prostate. While the significance of these observations remains to be elucidated there is little doubt that TGF beta s play an important role in controlling growth of the prostate. The prostatic cells expressing TGF beta s have not been identified. This information would provide insight into the physiologic role of TGF beta s and suggest ways that growth control may be altered in prostate disease. We used stromal (PS) and epithelial (PE) cells, cultured from normal human prostate and benign prostatic hyperplasia (BPH), to study the effect of TGF beta s on cell proliferation and TGF beta transcript and protein expression. The proliferation of PS and PE was inhibited by pM quantities of TGF beta 1, -beta 2, and -beta 3. Both cell types expressed transcripts for all three TGF beta isotypes, but PS primarily secreted TGF beta 1, whereas PE secreted more TGF beta 2 than TGF beta 1. These observations suggest that TGF beta s are antiproliferative agents in vivo, and that the stroma is the source of TGF beta 1 while the epithelium is the major source of TGF beta 2 in prostate. There were no significant differences in the growth response to TGF beta s, the TGF beta-isotype expressed, or the amount of TGF beta secreted by cells cultured from normal prostate or BPH.

EGF receptor expression and growth of psoriatic and normal human keratinocytes are modulated by 1.25 (OH)2-vitamin D3 ex vivo

Calcitriol or 1.25 (OH)2-vitamin D3 is used in the treatment of psoriasis as an inhibitor of cell proliferation. We studied the action of calcitriol ex vivo on the growth of psoriatic and normal human keratinocytes, and on the expression of the EGF receptor. Third passaged normal and psoriatic keratinocytes were seeded (10(4)/cm2) in 24-well dishes in serum-free medium (MCDB supplemented with amino acids, with either 0.1 or 1.1 mM of calcium) and 10(-9) M calcitriol. When subconfluence was reached, cell counts and 125I-EGF binding studies were performed. Cell counts showed at least a 50% decrease in growth under all conditions studied (normal or psoriatic keratinocytes; 0.1 or 1.1 mM calcium) when calcitriol was added. 125I-EGF binding studies showed a decrease in total receptor numbers in the presence of calcitriol with acceleration of binding at low concentrations of 125I-EGF. Scatchard plot analysis showed only one type of high affinity receptor. Receptor sites were decreased (30% to 40% of controls) in the presence of calcitriol together with a decrease in the dissociation constant. In conclusion, at almost physiological concentrations ex vivo, calcitriol strongly decreased normal and psoriatic keratinocyte growth. This potent antiproliferative effect could in part be explained by the capacity of calcitriol to downregulate EGF receptor expression.

Mechanism of action of epidermal growth factor-induced porcine oocyte maturation

EGF has been reported to promote oocyte maturation in several species, although the mechanism of action is not yet known. The present study is designed to determine the pathway used by EGF to enhance porcine oocyte maturation. Oocytes were aspirated from 2-5 mm follicles and cultured with various treatments in Medium-199 at 37 degrees C, 100% relative humidity, and 5% CO2 for 48 hr for the maturation study and 3 hr for intracellular cAMP measurement. Although treatment with 100 IU/ml hCG stimulated both intracellular cAMP formation and oocyte maturation, 10 ng/ml EGF stimulated oocyte maturation only. Dibutyryl cAMP (dbcAMP) inhibited oocyte maturation at 10(-5), 10(-4), and 10(-3) M concentration s in the control medium. However, in the presence of 10 ng/ml EGF, dbcAMP inhibited oocyte maturation only at a concentration of 10(-3) M. Increasing concentrations of EGF (i.e., 25 and 50 ng/ml) were ineffective in overcoming the inhibitory effect of dbcAMP at 10(-3) M. In contrast, EGF reversed the decreased maturation rate caused by transforming growth factor-beta. Phorbol myristate acetate (PMA), a tumor-promoting phorbol ester, enhanced the spontaneous maturation rate; 4 alpha-phorbol dideconoate, an inactive phorbol ester, did not show this effect. PMA- and EGF-stimulated porcine oocyte maturation is reversed by calphostin-C, a PKC inhibitor. In conclusion, EGF's promotional activity on porcine oocyte maturation is independent of the cAMP pathway and probably mediated by the PKC pathway.

Tenascin-C induction by the diffusible factor epidermal growth factor in stromal-epithelial interactions

Tenascin-C, a six-armed extracellular matrix glycoprotein, is expressed in a temporally and spatially restricted pattern during carcinogenesis and invasion or metastasis of carcinoma cells in association with stromal-epithelial interactions. The human epidermoid carcinoma-derived cell lines, A431 and HEp-2, which do not express tenascin-C by themselves in vitro, do express tenascin-C after transplantation into nude mice, and transforming growth factor beta 1 (TGF-beta 1) induces them to express tenascin-C in vitro. Epidermal growth factor (EGF) induced tenascin-C in these cells more effectively (about 3.5-fold greater) than did TGF-beta 1. Hepatocyte growth factor (HGF) and platelet-derived growth factor (PDGF) had little effect on the induction of tenascin-C. EGF also induced other extracellular matrix components, fibronectin and laminin. Tenascin-C was also induced when the carcinoma cells were co-cultured with embryonic fibroblasts from mice which were homozygous for a null mutation in the tenascin-C gene, or when the conditioned medium from these cells was added. The induction of tenascin-C in the co-culture was reduced by treating the cells with antibodies against EGF or its receptor. The addition of EGF caused both cell types to disrupt their cytoskeleton and focal contacts as evidenced by the loss of stress fibers and vinculin plaques. EGF did neither induce tenascin-C nor affect the morphology in tenascin-C-nonproducing A549 carcinoma cells, which did not produce tenascin-C after transplantation. Thus, EGF induces tenascin-C in tenascin-C-nonproducing human carcinoma cells through EGF receptors. Furthermore, in stromalepithelial interactions, the diffusible factor EGF participates in the induction of human tenascin-C in these cells through EGF receptors.

Lysophosphatidic acid and bradykinin have opposite effects on phenotypic transformation of normal rat kidney cells

The bioactive lipid lysophosphatidic acid is besides a strong mitogen for quiescent fibroblasts, a potent inducer of phenotypic transformation of normal rat kidney cells. The lysophosphatidic acid induced loss of density-arrest is strongly inhibited by bradykinin. Although their effects on normal rat kidney cell proliferation are opposite, bradykinin mimics many of the intracellular effects induced upon lysophosphatidic acid receptor activation, including phosphoinositide turnover, Ca(2+)-mobilization and arachidonic acid release. Bradykinin does not counteract the lysophosphatidic acid induced reduction of cAMP levels in normal rat kidney cells. However, bradykinin inhibits the lysophosphatidic acid and other growth factor induced phenotypic transformation through the induction of a so far uncharacterized prostaglandin G/H synthase product. The growth inhibitory effect of bradykinin is limited to density-arrested cells, while upon prolonged treatment bradykinin itself is capable to induce the loss of density-dependent growth control. It is concluded that bradykinin is a bifunctional regulator of normal rat kidney cell proliferation and that its inhibitory effects are mediated via the induction of a prostaglandin derivative.

The effect of transforming growth factor-beta on fibroblast cell proliferation in intact connective tissue in vitro

Transforming growth factor-beta (TGF-beta) has varying effects on cell proliferation, stimulating some cell types while inhibiting others. Its effect on proliferation has mostly been assessed in cell cultures without consideration for the influence of a tissue matrix. In the present investigation we studied the effect of TGF-beta on fibroblast cell proliferation in intact connective tissue in vitro using the membranous part of the rat mesentery. Mesenteric membranes were spread over the hole of a cytocentrifuge paper, incubated in vitro, and exposed to various concentrations of TGF-beta with or without serum added. At designated times after incubation, the specimens were fixed, spread out on microscope slides, and stained by the Feulgen reaction. Cell proliferation was estimated by counting mitoses in fibroblasts and mesothelial cells and by DNA cytometry of fibroblast nuclei using computer assisted image analyses. Higher concentrations of TGF-beta significantly increased proliferation estimated as either the percentage of cells in the S+G2 phase of the cell cycle or the mitotic index when serum was added. In medium without serum, TGF-beta did slightly, but not significantly, increase proliferation. The results show that TGF-beta stimulates connective tissue cell proliferation dose-dependently in intact connective tissue in vitro and that addition of serum to the medium is a prerequisite for optimal stimulation.

Transforming growth factor beta and the cell surface in tumor progression

Type 1 transforming growth beta (TGF-beta 1) is a multifunctional regulator of cellular differentiation, motility and growth. It is capable of inhibiting or stimulating these processes depending on cell type, cell density, culture conditions and TGF-beta 1 concentration. TGF-beta 1 regulates growth, in part, by inducing the expression and secretion of various types of collagen, which participate in the control of cell adhesion and migration, as well as growth. TGF-beta 1 also regulates cell growth by controlling the response to epidermal growth factor (EGF) and other growth factors, in ways that can either decrease or increase their growth-promoting effects. Alterations in both negative and positive growth responses to TGF-beta 1 play important roles in tumor progression. Loss of sensitivity to growth inhibition by TGF-beta 1 can occur as a result of decreased expression of collagen. Acquisition of sensitivity to growth stimulation, and autocrine transformation by TGF-beta 1, are associated with aberrant EGF receptor regulation. Aberrant growth factor receptor regulation by TGF-beta 1 may be mediated by a protein kinase C (PKC)-dependent pathway which inhibits degradation of growth factor receptor/ligand complexes. The evidence reviewed is consistent with a minimal two-step mechanism for autocrine transformation, which involves production of growth factor and enhanced cellular response as a result of aberrant membrane traffic. Defects in membrane traffic regulation may provide an explanation for common alterations in tumor cell response to both multiple growth inhibitors and growth stimulators, and may also suggest novel approaches to cancer chemotherapy.

Regulation of synovial cell growth. Coexpression of transforming growth factor beta and basic fibroblast growth factor by cultured synovial cells

OBJECTIVE

To demonstrate expression of transforming growth factor beta (TGF beta) and basic fibroblast growth factor (bFGF) by cultured rheumatoid arthritis (RA) synovial cells and to investigate their role as synovial cell mitogens.

METHODS

Polypeptide growth factors were detected and identified by immunocytochemical staining and Western blot analysis. Messenger RNA (mRNA) transcripts encoding TGF beta and bFGF were identified by polymerase chain reaction analysis. The influence of neutralizing growth factor monoclonal antibodies (MAb) on RA synovial cell growth was investigated. TGF beta bioactivity was determined by Mv1Lu assay.

RESULTS

Lysates of RA, as compared with normal, synovial cells contained greater amounts of TGF beta and bFGF. Western blot analysis identified a single TGF beta band (MW approximately 25 kd) in each of the cell lysates examined. Western blot analysis using MAb DE6 identified a doublet of bFGF bands (MW approximately 18.0 kd) in normal synovial cell lysates and 4 bFGF bands (MW approximately 18.0, 22.0, 22.6, and 25.2 kd) in RA synovial cell lysates. RA and normal synovial cells expressed mRNA transcripts encoding TGF beta 1 but not TGF beta 2, and FGF-2 (basic FGF). Additional mRNA transcripts encoding FGF-5 and FGF-7 were expressed by RA, but not normal, synovial cells in culture. In contrast to MAb 1D11.16, which caused a dose-dependent decrease in RA synovial cell growth, MAb DG2 (up to 100 micrograms/ml) had no effect on cell growth.

CONCLUSION

RA and normal synovial cells cultured in serum-free medium express TGF beta 1 and native bFGF. However, only RA synovial cells in culture express higher molecular weight isoforms of bFGF. TGF beta 1 appears to regulate synovial cell growth in vitro through an external autocrine loop. Despite expression of high-affinity bFGF receptors on cultured synovial cells, the mechanisms by which bFGF modulates synovial cell growth are unknown.

Transforming growth factor-beta 1 inhibitory effect of platelet-derived growth factor-induced signal transduction on human bone marrow fibroblasts: possible involvement of protein phosphatases

Transforming growth factor-beta 1 (TGF-beta 1) is a potent growth inhibitor for many cell types. On fibroblasts, TGF-beta 1 has been shown to inhibit human platelet-derived growth factor (PDGF)-induced mitogenicity. The mechanism implicated in this growth inhibition is unknown. In this work, we show on human bone marrow fibroblasts that TGF-beta 1, which inhibited PDGF-BB mitogenicity, was able to block PDGF-BB-induced early events such as polyphosphoinositide (PtdIns 4,5-P2, PtdIns 4-P, and PtdIns) breakdown and Ins 1,4,5-P3 formation. No significant modification by TGF-beta 1 of PDGF-BB binding (n1 = 200,000 vs. n2 = 195,000 sites per cell with TGF-beta 1; Kd1 = Kd2 = 0.5 x 10(-9) M) and of internalization kinetics was observed. In addition, TGF-beta 1 was shown to inhibit PDGF-BB receptor autophosphorylation either in intact cells or in partially isolated membranes and to partially inhibit PDGF-R tyrosine kinase activity. Since a dephosphorylation mechanism through protein phosphatases could be implicated, we used okadaic acid, a potent inhibitor of type 1 and 2A serine/threonine phosphatases and showed that okadaic acid restored PDGF-receptor autophosphorylation on tyrosine residues. Based on these data, we suggest that an alternative regulatory mechanism of PDGF tyrosine phosphorylation seems to involve serine/threonine phosphatase activation.

Regulation of synovial cell growth by polypeptide growth factors

In vitro, rheumatoid arthritis (RA) synovial cells display several of the characteristics of neoplastic and virally transformed cells. The recent observation that synovial cell cultures, derived from collagenase digests of synovial membranes from RA patients, proliferate in serum-free medium suggests that these cells have the capacity to synthesize those factors essential for their growth. Direct immunocytochemical staining and Western analysis have identified transforming growth factor-beta (TGF-beta) band and basic fibroblast growth factor (FGF) in the cytoplasm of RA and normal synovial cells in long-term culture. Greater amounts of each growth factor were found in RA, as compared with normal synovial cell lysates. Western analysis identified a single TGF-beta band in RA and normal synovial cell lysates. Four bands were identified by Western analysis on RA synovial cell lysates probed with monoclonal antibodies recognizing bFGF, whereas only two bands (which co-migrated with human native recombinant bFGF) were identified in normal cell lysates probed with these antibodies. Gene expression analysis using PCR identified mRNA transcripts encoding TGF-beta 1 and FGF-2 (bFGF), but not TGF-beta 2 in all cell cultures studied. Taken together, these data indicate that cultured synovial cells co-express TGF-beta 1 and multiple isoforms of hFGF. These data further strengthen the concept that both polypeptide growth factors are involved in the regulation of synovial cell growth.

TGF-beta stimulation of endometrial and breast-cancer cell growth

Growth of the human endometrial carcinoma Ishikawa cell line was stimulated by transforming growth factor-beta1 when cultured in serum-containing and chemically defined culture medium. This response was not unique to endometrial carcinoma cells, as the breast-cancer cell line, T47-D, was similarly stimulated by TGF-beta 1. TGF-beta 1 stimulated growth of MCF-7 breast-cancer cells in chemically defined medium but inhibited growth of this cell line in serum-containing medium. The data provide a demonstration of a positive growth response to TGF-beta 1 in oestrogen-receptor-positive cells and do not support the hypothesis that this growth factor is simply a negative growth regulator in epithelial-cancer cell lines.

Transforming growth factor beta 1 is a powerful modulator of platelet-derived growth factor action in vascular smooth muscle cells

We have studied the effect of transforming growth factor beta 1 (TGF-beta 1) on vascular smooth muscle cell (SMC) mitogenesis and expression of thrombospondin and other growth related genes. We found that TGF-beta 1 treatment of vascular SMC induced a prolonged increase in steady-state mRNA levels of thrombospondin as well as alpha 1 (IV) collagen. The increase began at approximately 2 h, peaked by 24 h, and remained considerably elevated 48 h after growth factor addition. There was a corresponding increase in thrombospondin protein as well as increased expression of several other secreted polypeptides. The increase in thrombospondin contrasted sharply with that observed for platelet-derived growth factor (PDGF) which induced a rapid and transient increase in thrombospondin mRNA level. Although TGF-beta 1 was able to directly enhance expression of thrombospondin as well as the growth-related genes c-fos and c-myc, and induced c-fos expression with identical kinetics as PDGF, it was unable to elicit [3H]thymidine incorporation into DNA in three independent smooth muscle cell strains. However, TGF-beta 1 was able to strongly increase the mitogenic response of SMC to PDGF. Addition of both TGF-beta 1 and PDGF to SMC also caused a synergistic increase in the expression of thrombospondin as well as c-myc. Interestingly, in one other smooth muscle cell strain, a weak and delayed mitogenic response to TGF-beta 1 alone was observed. Our results strongly suggest that induction of thrombospondin expression by TGF-beta 1 and by PDGF occurs by distinct mechanisms. In addition, that TGF-beta 1 can enhance PDGF-induced mitogenesis may be due to the ability of TGF-beta 1 to directly induce the expression of thrombospondin, c-fos, c-myc, and the PDGF beta-receptor.

Distribution of epidermal growth factor (EGF) receptors in rabbit corneal epithelial cells, keratocytes and endothelial cells, and the changes induced by transforming growth factor-beta 1

Three kinds of rabbit corneal cells (epithelial cells, keratocytes and endothelial cells) were cultured, and the growth promoting effects of epidermal growth factor (EGF) were examined in these cells. It was found that the sensitivity of the epithelial cells to EGF was the highest, that of the endothelial cells was a little lower, and that of the keratocytes was the lowest. Transforming growth factor-beta 1 (TGF-beta 1) did not influence growth of the three kinds of corneal cells. It was found that TGF-beta 1 enhanced the growth promoting effect of EGF in the keratocytes, but not in the epithelial and endothelial cells. EGF receptors in the corneal cells were labelled with [125I]EGF and analysed by Scatchard plot. In the epithelial and endothelial cells, both high and low affinity receptors were found, while the keratocytes had only low affinity receptor. In the epithelial cells, the number and the association constant of the high affinity receptors were, respectively, 2.79 x 10(4) per cell and 0.034 nM, and those of the low affinity receptors were, respectively, 13.4 x 10(4) per cell and 0.700 nM. In the endothelial cells, the number and the association constant of the high affinity receptors were 1.27 x 10(4) per cell and 0.086 nM, respectively, and those of the low affinity receptors were 8.91 x 10(4) per cell and 1.536 nM. In the keratocytes, the number of receptors and the association constant were 9.49 x 10(4) per cell and 1.535 nM, respectively. The corneal cells were treated with TGF-beta 1 for 24 hr and its influence on EGF receptors was examined. The results showed that TGF-beta 1 induced the high affinity receptors in the keratocytes, although TGF-beta 1 did not influence EGF receptors in the epithelial and endothelial cells. The number of high affinity receptors in keratocytes treated with TGF-beta 1 was 1.02 x 10(4) per cell and the association constant was 0.171 nM (this was approximately tenfold higher than that of the receptor of keratocytes not treated with TGF-beta 1).

Regulation of amphiregulin mRNA by TGF-beta in the human lung adenocarcinoma cell line A549

Transforming growth factor beta is a strong growth inhibitor for many types of normal and transformed cells, although little is known on the mechanism of this anti-proliferative effect. The human lung adenocarcinoma cell line A549 is growth arrested by TGF-beta 1 and serves as a model for studying this effect. We describe that, concurrent with the inhibition of A549 cell growth, TGF-beta 1 treatment causes a dramatic reduction in the level of expression of the amphiregulin (AR) gene, a recently identified member of the EGF/TGF alpha family. Similar results were also observed with TGF-beta 2. Peak inhibition occurred at 24 hr of treatment and was reversible upon removal of TGF-beta 1. The level of AR protein secreted by A549 cells was also decreased by TGF-beta 1. In contrast, TGF-alpha mRNA was not detected in these cells regardless of TGF-beta 1 treatment. Another TGF-beta inhibited cell line, PC-3 (human prostatic adenocarcinoma) also exhibited a decrease in AR message levels following exposure to TGF-beta 1. The growth inhibitory effects of TGF-beta may in part be mediated by modulation of AR expression.

Altered response to growth factors or retinoic acid in phenotypic transformation of normal rat kidney cells expressing human c-fos gene

Anchorage-independent growth of normal rat kidney (NRK) fibroblast in soft agar depends on both transforming growth factor beta (TGF beta) and epidermal growth factor (EGF). To examine whether c-fos protein is involved in phenotypic transformation of NRK cells, we have transfected and isolated several NRK cell lines that carry the human c-fos gene fused to the metallothionein IIA promoter. A transfectant, Nf-1, had constitutive levels of the human c-fos expression. Anchorage-independent growth of Nf-1 was already stimulated by EGF alone, and the colony sizes of Nf-1 were comparable to those of the parental NRK in the presence of both EGF and TGF beta. Anchorage-independent growth of NRK could be observed in the presence of TGF beta or retinoic acid or platelet derived growth factor (PDGF) and EGF. No growth of NRK in soft agar appeared when basic fibroblast growth factor (bFGF) and EGF were present. By contrast, anchorage-independent growth of Nf-1 was surprisingly enhanced by EGF and TGF beta or retinoic acid or PDGF or bFGF. Expression of the human c-fos gene may compensate the signal to phenotypic transformation induced by TGF beta as well as retinoic acid or PDGF or bFGF.

Hepatocyte growth inhibitory factor derived from HTLV-I(+) T cell lines: effect on the epidermal growth factor-dependent proliferation of rat hepatocytes

A human T cell leukemia virus-I infected T cell line, ATL-2, produces an interleukin-2 receptor inducing factor, adult T cell leukemia (ATL)-derived factor (ADF). In the conditioned medium (CM) of ATL-2, we found an inhibitory activity on the epidermal growth factor (EGF)-dependent proliferation of primary cultured rat hepatocytes, measured by cell number and [3H]thymidine incorporation. ATL-2 CM dose-dependently inhibited hepatocyte proliferation. This activity was fractionated by gel filtration at a molecular size of 15,000 to 40,000 and was tentatively called hepatocyte growth inhibitory factor (HGI). Further fractionation with the ion-exchange column indicated that HGI was separable from ADF. Nevertheless, there was a positive correlation between HGI and ADF production, because the HGI activity was also detected in the CM of another ADF producer cell line (HUT102), while no significant HGI activity was detected in the CM of low ADF producer cell lines, ED and MOLT4.

Transforming growth factor-beta receptor profiles of human and murine embryonic palate mesenchymal cells

Cell signalling in the developing mammalian palate appears to involve various growth factors and hormones. An important developmental role for the transforming growth factor-beta (TGF-beta) class of growth factors is suggested by the immunolocalization of TGF-beta 1 in the palate during its ontogeny. This study examined the effects of TGF-beta stimulation of, as well as TGF-beta receptor profiles in, murine embryonic palate mesenchymal (MEPM) and human embryonic palate mesenchymal (HEPM) cells. Results showed that TGF-beta 1 (1 ng/ml) stimulated proliferation of HEPM cells and inhibited proliferation of MEPM cells in a dose-dependent manner. The time course of 125I-TGF-beta 1 binding to specific receptors was determined by incubating cells in the presence of 170 pM 125I-TGF-beta 1 for up to 4 h. In both cell types, at 37 degrees C, the binding of 125I-TGF-beta decreased linearly over 4 h, while at 4 degrees C, binding increased with time of incubation. Incubation of both cell types at 4 degrees C for 4 h, with increasing concentrations of 125I-TGF-beta 1, resulted in binding which demonstrated saturation kinetics. Scatchard analyses revealed one class of receptors for HEPM (K 32.3 pM) and MEPM (K 26.3 pM). However, SDS-PAGE analyses of 125I-TGF-beta chemically crosslinked to specific receptor sites revealed that both cell types contained the types I (65,000 Mr) and III (230,000 Mr) TGF-beta receptors while MEPM also contained the type II (86,000 Mr) receptor. Binding studies further demonstrated the ability of platelet-derived growth factor to transmodulate TGF-beta binding. These results indicate that the HEPM cell line and primary cultures of MEPM cells, although obtained from palates at similar developmental stages, are dramatically different in their responsiveness to TGF-beta and have disparate TGF-beta receptor profiles.

Transforming growth factor (TGF)-beta like activity of intracranial meningioma and its effect on cell growth

Polypeptides, characterized by their ability to confer a transformed phenotype on an untransformed indicator cell have been isolated directly from surgical specimens of intracranial meningioma by using an acid/ethanol extraction procedure. Transforming activity in meningeal cells was based on the ability to induce NRK 49F rat kidney fibroblasts to form colonies in soft agar. This polypeptide was separated by gel filtration into two fragments of 15 and 40 kilodalton (kDa) molecular weight. Among other cases of brain neoplasms, one case of glioblastoma multiforme had moderate TGF-beta activity, but medulloblastoma and neurinoma had no activity. Purified TGF-beta also stimulated DNA synthesis in primary cultured meningioma cells, but no effect was seen in U 251MG human glioma cells. While the physiological function of TGF-beta is still ill-defined and the molecular character of its receptor has not been analyzed, intracranial meningiomas are noted to have TGF-beta-like activity. TGF-beta also induces the DNA synthesis of cultured meningioma cells. From these results, TGF-beta would be considered one of the growth promoting factors in meningioma.

Bifunctional effects of transforming growth factor-beta (TGF-beta) on endothelial cell growth correlate with phenotypes of TGF-beta binding sites

Transforming growth factor-beta (TGF-beta) is a bifunctional, dose-dependent regulator of endothelial cell proliferation induced in vitro by heparin-binding growth factor 1 (HBGF-1, acidic FGF). Here we have examined the relationship between endothelial cell growth and the expression of cell surface binding sites for TGF-beta and HBGF-1. Fetal bovine heart endothelial cell (FBHEC) growth was stimulated by low concentrations of TGF-beta and inhibited by high concentrations of TGF-beta while expressing two distinct classes of TGF-beta binding sites with binding constants of 24 pM (6300 sites/cell) and 900 pM (12,000 sites/cell). In contrast, human umbilical vein endothelial cells (HUVEC), whose growth was slightly promoted by TGF-beta, exhibited a single class of high-affinity TGF-beta binding sites (Kd = 45 pM, 4500 sites/cell). Affinity crosslinking using [125I]TGF-beta showed that FBHEC expressed two distinct low molecular weight TGF-beta binding sites (Mr 85,000 and 58,000), while HUVEC expressed a single type of low molecular weight TGF-beta binding site (Mr 85,000). As detected by binding of [125I]HBGF-1, preincubation of FBHEC with high concentrations of TGF-beta transmodulated the expression of high-affinity HBGF-1 receptors. In contrast, no transmodulation of HBGF-1 receptors occurred in FBHEC during preincubation with low concentrations of TGF-beta. Furthermore, preincubation of HUVEC with TGF-beta did not transmodulate the expression of HBGF-1 receptors. The data suggest that the ability of TGF-beta to stimulate or inhibit endothelial cell proliferation in a dose-dependent manner correlated with the expression of specific TGF-beta binding site subtypes and involved the transmodulation of HBGF-1 receptors.

Transforming growth factor beta enhances parathyroid hormone stimulation of adenylate cyclase in clonal osteoblast-like cells

The effects of transforming growth factor beta (TGF beta) on parathyroid hormone (PTH)-responsive adenylate cyclase were examined in clonal rat osteosarcoma cells (UMR-106) with the osteoblast phenotype. Purified TGF beta incubated with UMR-106 cells for 48 hr produced a concentration-dependent increase in PTH stimulation of adenylate cyclase, with maximal increase in PTH response (37%) occurring at 1 ng/ml TGF beta. TGF beta also enhanced receptor-mediated activation of adenylate cyclase by isoproterenol and prostaglandin E2 (PGE2) and nonreceptor-mediated enzyme activation by cholera toxin and forskolin. In cells in which PTH-stimulated adenylate cyclase activity was augmented by treatment with pertussis toxin, the incremental increase in PTH response produced by TGF beta was reduced by 33%. However, TGF beta neither mimicked nor altered the ability of pertussis toxin to catalyze the ADP-ribosylation of a 41,000-Da protein, presumably the alpha subunit of the inhibitory guanine nucleotide-binding regulatory component (Gi) of adenylate cyclase, in cholate-extracted UMR-106 cell membranes. TGF beta also had no effect on the levels of alpha or beta subunits of Gi, as assessed by immunotransfer blotting. In time course studies, brief (less than or equal to 30 min) exposure of cells to TGF beta during early culture was sufficient to increase PTH response but only after exposed cells were subsequently allowed to grow for prolonged periods. TGF beta enhancement of PTH and isoproterenol responses was blocked by prior treatment of cells with cycloheximide but not indomethacin. The results suggest that TGF beta enhances PTH response in osteoblast-like cells by action(s) exerted at nonreceptor components of adenylate cyclase. The effect of TGF beta may involve Gi, although in a manner unrelated to either pertussis toxin-catalyzed ADP-ribosylation of the alpha subunit of Gi or changes in levels of Gi subunits. The regulatory action of TGF beta on adenylate cyclase is likely to be mediated by the rapid generation of cellular signals excluding prostaglandins, followed by a prolonged sequence of events involving protein synthesis. These observations suggest a mechanism by which TGF beta may regulate osteoblast responses to systemic hormones.

Human relaxin inhibits division but not differentiation of 3T3-L1 cells

For the first time, we demonstrate here the ability of human relaxin to block cell division. During the induction of differentiation of 3T3-L1 fibroblasts to adipocytes, the cells typically undergo two rounds of cell division followed by accumulation of lipid droplets and expression of insulin-stimulated glucose transport as the cells attain the adipocyte phenotype. Human relaxin added during induction had no effect on the development of the adipocyte phenotype or insulin-stimulated glucose transport. However, it blocked cell division at a half-maximal concentration of 1.25 nM, well within physiological range. This could be reversed by the addition of antibodies specific for human relaxin. Thus relaxin joins a select number of hormones with growth inhibitory properties such as transforming growth factor-beta (TGF beta) and mammastatin. Potentially, this is an important but until now unidentified function of relaxin. Unlike other inhibitory polypeptides, like TGF beta, relaxin does not prevent differentiation but rather uncouples it from cell division.

neu oncogene protein and epidermal growth factor receptor are independently expressed in benign and malignant breast tissues

The neu oncogene protein, p185, and epidermal growth factor receptor (EGFR) were localized immunohistochemically in benign and malignant human breast tissues using monoclonal antibodies. Both benign and malignant epithelial cells were positive for these oncogene proteins in acetone-postfixed frozen sections. Stromal cells were negative for p185, but occasionally positive for EGFR. Myoepithelial cells were consistently positive for EGFR, and p185 was localized predominantly in duct-lining cells, where the basolateral plasma membrane was the normal expression site of both substances. Paraformaldehyde-prefixed frozen sections were less sensitive for antigen demonstration. Based on the intensity of immunoreactivity, 11 of 37 acetone-postfixed breast carcinomas (30%) were judged neu overexpressors, while none of 24 benign tissues overexpressed neu. Epidermal growth factor receptor was demonstrated in 18 of 36 acetone-postfixed cancer tissues (50%) and was overexpressed in three (8%). At the cellular level, heterogenous expression of p185 and EGFR was occasionally observed in both benign and malignant tissues, and a single case of cancer overexpressing both neu and EGFR showed reciprocal patterns of staining, indicating their independent expression. In some carcinomas, EGFR was localized only in stromal cells. Our findings confirmed mutually independent expression of the two closely related protooncogenes in benign and malignant breast tissues.

Differential effects of transforming growth factor-beta and epidermal growth factor on the cell cycle of cultured rabbit articular chondrocytes

We examined the effect of transforming growth factor (TGF-beta) on the proliferative rate and cell cycle of cultured rabbit articular chondrocytes using cell counting, cytofluorometry, and [3H]-thymidine incorporation. In the presence of 2% or 10% FCS (fetal calf serum), TGF-beta at 0.01, 0.1, 1, and 10 ng/ml had an inhibitory effect on cell proliferation after 24 h exposure with a dose dependence only for 2% FCS. Flow cytometric analysis of cell DNA content at that time showed that a high proportion of cells were arrested in late S-phase (SQ or G2Q) in either 2% or 10% FCS-containing medium. In both cases, a disappearance of the cell blockage occurred between 24 and 48 h after TGF-beta addition. However, whereas a stimulation of cell proliferation rate was observed at that time in cultures containing 10% FCS, a dose-dependence inhibition of cell growth was detected, in contrast, for 2% FCS-treated cells. Presence of TGF-beta during the last 24 h was not necessary to release the arrested cells. Furthermore, platelet-poor plasma at 10% produced the same effects as FCS, suggesting that platelet-derived factors, such as platelet-derived growth factor (PDGF), could not be responsible for the release of blocked cells in this case. We compared the effect of TGF-beta to that of epidermal growth factor (EGF), used at an optimal concentration (10 ng/ml). In both slowly growing (2% FCS) and proliferating chondrocytes (10% FCS), EGF caused a significant increase of cell proliferation as early as 24 h. No arrest in late S-phase but an augmentation of the percentage of cells in S- and G2M-phases were observed. When combined, TGF-beta and EGF did not induce synergistic effect on the chondrocyte proliferation, as estimated by cell counting. [3H]-thymidine labeling showed that the factors induced identical maxima of incorporation but the peak occurred earlier for TGF-beta than for EGF (approximately 6 h versus 12 h, respectively). Although both factors induce similar cell-number increases at 48 h in 10% FCS-containing medium, these proliferative effects were due to different actions on the cell cycle. The present study indicates that TGF-beta induces first a recruitment of chondrocytes in noncycling SQ- or G2Q-blocked cells. The, the release of these cells may produce either apparent stimulation of cell proliferation if sufficient levels of an unknown serum factor are present (10% FCS) or an inhibition of growth rate when only reduced amounts of this factor are available (2% FCS).(ABSTRACT TRUNCATED AT 400 WORDS)

Cellular mechanisms of TGF-beta action

Transforming growth factor beta (TGF-beta), initially identified in platelet extracts by virtue of its ability to confer anchorage-independent growth and a neoplastic phenotype on mesenchymal cells, has subsequently been identified as a potent inhibitor of proliferation in most cells of epithelial origin. Our laboratory has investigated the role of specific second messengers in mediating the transcriptional responses of fibroblasts following addition of TGF-beta 1. Our studies indicate that TGF-beta 1, alone and in conjunction with epidermal growth factor (EGF), is capable of stimulating increases in both phosphoinositide metabolism and calcium influx, leading to significant increases in intracellular levels of Ca++ and inositol trisphosphate (IP3). Our data indicated that Ca++ influx and inositol phosphate release are coupled in Rat-1 cells, and suggested that influx of Ca++ from the extracellular medium is required for the change in IP3 accumulation observed in response to both EGF and TGF-beta 1. Using nuclear run-on analysis of the transcription of rat transin, a secreted metalloproteinase homologous to human stromelysin, we have also demonstrated a significant inhibition of transin transcription within 10 min of TGF-beta 1 treatment. The ability of TGF-beta 1 to inhibit transin gene transcription was not related to the TGF-beta 1-induced influx of Ca++ or to an increase in intracellular inositol phosphates, since inhibiting production of these second messengers failed to inhibit repression of the transin gene.

Density-induced down regulation of epidermal growth factor receptors

Previous studies have shown that cell density can regulate the binding of several growth factors. To determine whether cell density exerts a uniform effect on the expression of epidermal growth factor (EGF) receptors, seven cell lines were examined in detail. For each cell line, EGF binding was found to decrease as cell density increases. Scatchard analysis of the binding data reveals that decreases in EGF binding are due to reductions in the number of cell surface EGF receptors. The only apparent exception is the effect of cell density on the binding of EGF to A-431 cells. For these cells, increases in cell density lead to two effects: decreases in the number of high affinity EGF receptors and increases in the total number of EGF receptors. In addition to the effects of cell density on EGF receptors, it was determined that increases in cell density can coordinately down-regulate receptors for as many as four different growth factors. Overall, the findings described in this report for EGF and those previously described for transforming growth factor type-beta (TGF-beta) and fibroblast growth factor (FGF) demonstrate the existence of a common mechanism for down-regulating growth factor receptors.

Control of rat glomerular epithelial cell growth in vitro

The interaction of cultured rat GEC1 with several growth factors was explored in order to obtain a better understanding of in vivo factors which might stimulate GEC proliferation. GEC proliferated in response to EGF but not IGF-1, MSA or PDGF. Specific, saturable receptors for EGF were detected in saturation and competition binding studies utilizing 125I-EGF with an approximate Kd of 1.7 nM and 86,000 binding sites per cell. TGF-beta inhibited GEC growth in a time and dose dependent manner with a brief early exposure resulting in prolonged growth inhibition which was not reversible by EGF. Exposure to TGF-beta sufficient to maximally inhibit growth had no effect on EGF binding to GEC. More prolonged exposure to TGF-beta, however, did result in an increase in the apparent number of EGF receptors on GEC but no change in Kd. These studies suggest that EGF and TGF-beta released by inflammatory cells or platelets during the course of glomerular injury may play a role in modulating glomerular cell proliferation.

Alpha-transforming growth factorlike activities and bifunctional regulators of cell growth in human malignant neoplasms

Multiple transforming growth factors (TGFs) capable of conferring the neoplastic phenotype on NRK-49F cells without the addition of any other exogenous growth factor in the soft agar assay, were purified from two human solid malignant neoplasms: a squamous lung carcinoma and a pectoral rhabdomyosarcoma. In both tumors, low-molecular-weight transforming activities (4000-6000) that were not potentiated by epidermal growth factor (EGF), competed for binding to the EGF receptor, possessed mitogenic activity on NRK fibroblasts arrested in serum-deprived medium, and did not show inhibitory effects on DNA synthesis induced by EGF and insulin in NRK cells. Other TGFs with molecular weights 9000 to 48,000, were also found in the malignant tissues examined; these TGFs, were not potentiated by EGF, did not compete for binding to the EGF receptor, were not mitogenic for NRK cells, and acted as potent inhibitors of DNA synthesis induced by EGF and insulin in NRK cells. These results demonstrate that growth-promoting activities, and modulating agents that can act as either enhancers or inhibitors of cell proliferation, are present in neoplastic tissues of different embryologic origin and histologic type.

Inhibition of 125I-epidermal growth factor binding to cultured keratinocytes by antiproliferative molecules gamma interferon, cyclosporin A, and transforming growth factor-beta

The growth of cultured human keratinocytes (KC) is inhibited by gamma interferon (IFN-gamma), cyclosporin A and transforming growth factor-beta, but not by tumor necrosis factor. When these antiproliferative molecules were added to KC they induced a concentration and time-dependent inhibition of 125I-epidermal growth factor (I-EGF) binding. These anti-proliferative molecules primarily reduced the number of binding sites by approximately 25%-50% without affecting the binding affinity. Tumor necrosis factor did not influence the ligand binding by I-EGF. In parallel with the ability of the antiproliferative molecules to inhibit I-EGF binding, there was an increase in transforming growth factor-alpha production. These results suggest that several different antiproliferative molecules may share a common mechanism to inhibit cell growth by reducing I-EGF binding to KC.

Stimulation by transforming growth factor-beta of epidermal growth factor-dependent growth of aged human fibro-blasts: recovery of high affinity EGE receptors and growth stimulation by EGF

The stimulatory effects of transforming growth factor beta (TGF-beta) on epidermal growth factor (EGF)-dependent growth of adult and newborn human fibroblasts were investigated. EGF-stimulated growth in low serum of dermal fibroblasts from a 41 year-old adult (HSF-41) was less than half that of newborn foreskin fibroblasts (HFF). The EGF-stimulated growth of HFF after 55 population doublings (HFF-55) was similarly reduced. The decreased growth response to EGF of fibroblasts aged in vivo and in vitro appeared to result principally from a decreased sensitivity to EGF due to a decreased number and affinity of high affinity EGF receptors (H-EGFR). Pre-incubation of HSF-41 and HFF-55 with 25 pM TGF-beta enhanced the growth responses of these cells to EGF and increased the levels of high affinity EGF-binding by these cells. Thus, the stimulation by TGF-beta of EGF-dependent growth of human fibroblasts aged in vivo or in vitro is mediated by increased levels of high affinity EGF binding.

Effects of transforming growth factor beta and epidermal growth factor on cell proliferation and the formation of bone nodules in isolated fetal rat calvaria cells

When cells enzymatically isolated from fetal rat calvaria (RC cells) are cultured in vitro in the presence of ascorbic acid and Na beta-glycerophosphate, discrete three-dimensional nodules form with the histologic, immunohistochemical, and ultrastructural characteristics of bone (Bellows et al; Calcified Tissue International 38:143-154, 1986; Bhargava et al., Bone, 9:155-163, 1988). Quantitation of the number of bone nodules that forms provides a colony assay for osteoprogenitor cells present in the RC population (Bellows and Aubin, Develop. Biol., 133:8-13, 1989). Continuous culture with either epidermal growth factor (EGF) or transforming growth factor beta (TGF-beta) results in dose-dependent inhibition of bone nodule formation; however, the former causes increased proliferation and saturation density, while the latter reduces both parameters. Addition of EGF (48 h pulse, 2-200 ng/ml) to RC cells at day 1 after plating results in increased proliferation and population saturation density and an increased number of bone nodules formed. Similar pulses at confluence and in postconfluent multilayered cultures when nodules first begin forming (approx. day 11) inhibited bone nodule formation and resulted in a smaller stimulation of cell proliferation. Forty-eight hour pulses of TGF-beta (0.01-1 ng/ml) reduced bone nodule formation and proliferation at all times examined, with pulses on day 1 causing maximum inhibition. The effects of pulses with TGF-beta and EGF on inhibition of nodule formation are independent of the presence of serum in the culture medium during the pulse. The data suggest that whereas EGF can either stimulate or inhibit the formation of bone nodules depending upon the time and duration of exposure, TGF-B inhibits bone nodule formation under all conditions tested. Moreover, these effects on osteoprogenitor cell differentiation do not always correlate with the effects of the growth factors on RC cell proliferation.

Transforming growth factor-beta inhibits the growth of renal cell carcinoma in vitro

Transforming growth factor-beta (TGF-beta) is a bifunctional growth regulatory hormone which inhibits the growth of many normal and neoplastic epithelial cell lines in monolayer culture. Endogenous and exogenous TGF-beta may influence cell proliferation through autocrine and paracrine binding to specific TGF-beta receptors. Growth effects of TGF-beta on human renal cell carcinoma cell lines have not been thus far described. We have studied the effects of TGF-beta on one renal tumor-derived (UOK-39) and one established (SKRC-7) renal cell carcinoma cell line. Exogenous addition of biologically active TGF-beta to cell cultures at concentrations between two and five ng./ml. inhibited the anchorage-dependent growth of UOK-39 by 75% and SKRC-7 by 44%, relative to controls. Low numbers of high affinity TGF-beta receptors were identified on both cell lines in 125I-TGF-beta binding assays. UOK-39 cells bound radiolabeled TGF-beta with higher affinity than SKRC-7 cells, but had fewer receptor sites, by Scatchard analysis of binding data. These results suggest that TGF-beta inhibits proliferation of renal carcinoma cells in vitro which may be mediated through binding of exogenous TGF-beta to functional TGF-beta receptors on the cell surface.

Increased epidermal growth factor receptor level in breast cancer cells treated by 1,25-dihydroxyvitamin D3

The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on epidermal growth factor receptor (EGF-R) level regulation was investigated on a human breast cancer cell line (BT-20). These cells display a great number of EGF-R (1 +/- 0.4 x 10(6) sites per cell). Scatchard analysis of binding data indicates the presence of two classes of sites: one of high affinity (Kd = 0.48 +/- 0.2 nM), the other of low affinity and higher capacity (Kd = 2.24 +/- 0.93 nM). Treatment of cells by 1,25(OH)2D3 for several days induces a progressive increase of the EGF-R number of sites per cell. This effect is dose and time dependent and results in a 3-fold enhancement of EGF-R binding in cells treated for 15 days, which involves the two classes of binding sites in the same proportion. This effect is not due to modifications of the EGF internalization and degradation processes. Inhibition of the effect of 1,25(OH)2D3 by cycloheximide suggests that it is dependent on new protein synthesis. There are no data in favor of a reduced occupancy of EGF-R sites by EGF-like substance accounting for the increase of unoccupied sites. Analysis of 125I binding by quantitative transmission electron microscope autoradiography illustrates the observation of a higher number of sites on the plasma membrane in treated than in control cells.

Transforming growth factor beta modulates proliferation of osteoblastic cells: relation to its effect on receptor levels for epidermal growth factor

The effect of transforming growth factor beta (TGF-beta) on cellular proliferation of osteoblastic MC3T3-E1 cells was studied with particular emphasis on its effect on modulation of epidermal growth factor (EGF) receptors. In other cells, TGF-beta has been reported to augment EGF receptors. Exposure of MC3T3-E1 cells to TGF-beta initially increased cell surface EGF receptor levels and decreased the rate of DNA synthesis. The initial elevation of EGF receptor levels was due to increased receptor number per cell, not to changes in binding affinity. On the contrary, prolonged exposure (longer than 40 h) resulted in a decrease in EGF receptor and an increase in the rate of DNA synthesis. Thus, the effects of TGF-beta on these cells appears to be biphasic, reflecting complex mechanisms of action; the early effects of TGF-beta may be consistent with cellular differentiation to the osteoblastic phenotype with decreased cellular proliferation, whereas chronic exposure of these cells to TGF-beta stimulated cellular proliferation and inhibited osteoblastic phenotype expression. It is not likely that stimulation of cellular proliferation was through elevation of EGF receptor levels, because TGF-beta did not enhance the stimulatory effect of EGF on cellular proliferation. Thus, we conclude that TGF-beta possesses a stimulatory effect on the cellular proliferation of osteoblastic MC3T3-E1 cells independent of its modulative effect on EGF receptor level.