PDGF-like growth factor induces EGF-potentiated phenotypic transformation of normal rat kidney cells in the absence of TGF beta

Silencing CD36 gene expression results in the inhibition of latent-TGF-beta1 activation and suppression of silica-induced lung fibrosis in the rat

Background

The biologically active form of transforming growth factor-β1 (TGF-β1) plays a key role in the development of lung fibrosis. CD36 is involved in the transformation of latent TGF-β1 (L-TGF-β1) to active TGF-β1. To clarify the role of CD36 in the development of silica-induced lung fibrosis, a rat silicosis model was used to observe both the inhibition of L-TGF-β1 activation and the antifibrotic effect obtained by lentiviral vector silencing of CD36 expression.

Methods

The rat silicosis model was induced by intratracheal injection of 10 mg silica per rat and CD36 expression was silenced by administration of a lentiviral vector (Lv-shCD36). The inhibition of L-TGF-β1 activation was examined using a CCL-64 mink lung epithelial growth inhibition assay, while determination of hydroxyproline content along with pathological and immunohistochemical examinations were used for observation of the inhibition of silica-induced lung fibrosis.

Results

The lentiviral vector (Lv-shCD36) silenced expression of CD36 in alveolar macrophages (AMs) obtained from bronchoalveolar lavage fluid (BALF) and the activation of L-TGF-β1 in the BALF was inhibited by Lv-shCD36. The hydroxyproline content of silica+Lv-shCD36 treated groups was significantly lower than in other experimental groups. The degree of fibrosis in the silica+Lv-shCD36-treated groups was less than observed in other experimental groups. The expression of collagen I and III in the silica+Lv-shCD36-treated group was significantly lower than in the other experimental groups.

Conclusion

These results indicate that silencing expression of CD36 can result in the inhibition of L-TGF-β1 activation in a rat silicosis model, thus further preventing the development of silica-induced lung fibrosis.

Role of the prostanoid FP receptor in action potential generation and phenotypic transformation of NRK fibroblasts

By using an shRNA approach to knockdown the expression of the prostaglandin (PG)-F(2alpha) receptor (FP-R), the role of PGF(2alpha) in the process of phenotypic transformation of normal rat kidney (NRK) fibroblasts has been studied. Our data show that PGF(2alpha) up-regulates Cox-2 expression both at the mRNA and protein level, indicating that activation of FP-R in NRK fibroblasts induces a positive feedback loop in the production PGF(2alpha). Knockdown of FP-R expression fully impaired the ability of PGF(2alpha) to induce a calcium response and subsequent depolarization in NRK cells. However, these cells could still undergo phenotypic transformation when treated with a combination of EGF and retinoic acid, but in contrast to the wild-type cells, this process was not accompanied by a membrane depolarization to -20 mV. Knockdown of FP-R expression also impaired the spontaneous firing of calcium action potentials by density-arrested NRK cells. These data show that a membrane depolarization is not a prerequisite for the acquisition of a transformed phenotype. Furthermore, our data provide the first direct evidence that activity of PGF(2alpha) by putative pacemaker cells underlies the generation of calcium action potentials in NRK monolayers.

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.

Differential effects of PDGF isoforms on proliferation of normal rat kidney cells

The effects of the PDGF isoforms AA, AB and BB have been studied on the proliferation of normal rat kidney cells, a non-tumorigenic fibroblast cell line which contains both type alpha and type beta PDGF receptors. On monolayer cells made quiescent by serum deprivation, PDGF-AA is a relatively poor mitogen compared to PDGF-AB and PDGF-BB. When these cells are made density-arrested following continuous incubation with epidermal growth factor, however, they can be restimulated to proliferate by all three PDGF isoforms with similar activity when added at sufficiently high concentration, resulting in phenotypic cellular transformation. Binding of radiolabelled isoforms to confluent NRK monolayers obeys the predictions of an induced receptor dimerisation model, and increases in the order AA < AB < BB. Upon preincubation of the cells with PDGF-AA, the dose-response curve for mitogenic activity of PDGF-AB is shifted to higher concentrations, indicating that PDGF-AA can partly antagonize the growth stimulating activity of PDGF-AB, as has also been observed in ligand binding studies. This observation has subsequently been confirmed using fluorescence cytometric analysis. PDGF-AB is highly active in inducing anchorage-independent proliferation of NRK cells, but in all such assays PDGF-AA is at least as potent as PDGF-BB. Intriguingly, PDGF-BB is almost devoid of activity in inducing soft agar growth of these cells, in contrast to PDGF-AA. When compared to substrate-attached cells, enhanced expression of the type alpha PDGF receptor was observed under anchorage-independent conditions. These results show that the relative potency of the three PDGF isoforms to stimulate proliferation of NRK cells is different for quiescent cells in monolayer, density-arrested cells and anchorage-independent cells. Moreover it is shown that the biological activity of PDGFs can be impaired by the additional presence of other isoforms.

Growth in serum-free medium of NIH3T3 cells transformed by the EJ-H-ras oncogene: evidence for multiple autocrine growth factors

Rodent fibroblastic cells transformed by ras oncogenes can grow in serum-free (S-) medium. We have studied clonal lines of mouse NIH3T3 fibroblasts transfected with the EJ-H-ras oncogene, and observed that practically all become independent of exogenous growth and attachment factors shortly after transfection. Moreover, all the clones tested soon form anchorage-independent (AI) colonies in S- medium, and most give rise to spheroids able to grow in suspension. The cell-conditioned S- medium of the transformed (TR) cells stimulates autocrinally the AI and anchored growth of these cells, in the absence of serum, and it contains growth factors related to TGF-alpha (or EGF), PDGF and bFGF, and other uncharacterized factors. Some of these factors are not found, or are found only in very small amounts, in the S- medium of non-transformed NIH3T3 cells, which also stimulates the growth of the TR cells, in the absence of serum. In addition, the TR cells contain 4-6 times more cell-associated bFGF than the non-transformed cells and release more latent TGF-beta activatable by acid treatments. However, no active TGF-beta is secreted by either cell type. Activated TGF-beta and pure TGF-beta 1 stimulate the growth of the anchored TR and NIH3T3 cells, but inhibit the AI growth of the TR cells. Another inhibitor of this growth is also found in the concentrated medium of the NIH3T3 cells.

Maturation-associated changes in the cellular composition of mouse calvariae and in the biochemical characteristics of calvarial cells separated into subclasses on Percoll density gradients

The effects of tissue maturation on the cellular composition and biochemical characteristics of bone were studied in neonatal, young adult, and aging mice. Osteoblast subclasses were isolated on Percoll density gradients. Neonatal calvariae consisted almost exclusively of cells banding at low and intermediate buoyant density. High buoyant density cells constituted 5-10% of total cells at 10 days of age but increased to 50-60% by 5 weeks of age. These latter cells were released late during collagenase digestion. This indicates that they arise from the deeper layer of bone. For this reason, we consider them putative osteocytes. We established that constitutive secretion of IGF-I and TGF-beta and activities of cellular alkaline phosphatase paralleled those of the tissue of origin in all cell groups and was highest in cells of intermediate buoyant density. These activities declined rapidly after cessation of growth at 5 weeks of age in both bone and isolated cells. Between 5 and 8 weeks of age, the hormonal response to PTH also declined dramatically. The maximum cAMP induced by PTH declined by about 70% in highly responsive cells of intermediate buoyant density and fell to insignificant levels in cells of high buoyant density. We found that a cyclic AMP response to PTH was positively correlated with stimulated secretion of IGF-I by this hormone in cells from animals of all ages. Despite their inability to respond to PTH with increases in cAMP and IGF-I, adult bone cells of high buoyant density continued to respond to PTH with increases in the secretion of TGF-beta.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor beta stimulates mitogenically mouse NIH3T3 fibroblasts and those cells transformed by the EJ-H ras oncogene

TGF-beta 1 stimulates thymidine incorporation and the growth rate of mouse NIH3T3 fibroblasts and of those cells transformed by the EJ-H-ras oncogene (TR15 cells), in the presence and the absence of serum. Thymidine incorporation, in serum-deprived cells, is stimulated to a higher degree by 0.1-1 ng/ml of TGF-beta in NIH3T3 than in TR15 cells, which have a 10-fold higher basal level of incorporation. In both cell types TGF-beta 1 is as active, or more active than other mitogens (TGF-alpha, PDGF-AB, bFGF) at the same concentration. The growth rate of NIH3T3 cells, in low serum or serum-free (S-) medium, is stimulated by only 10 picograms/ml of TGF-beta 1, and that of TR15 cells, in S- medium, by only 1 picogram/ml. In contrast, TGF-beta 1 inhibits mitogenically unestablished mouse embryo fibroblasts and these fibroblasts immortalized spontaneously and able to grow in S- medium. It also inhibits the anchorage-independent growth of TR15 cells. NIH3T3 and TR15 cells respond, similarly, to TGF-beta activated by acification of their culture medium. The kinetics of thymidine incorporation and of activation of the c-myc proto-oncogene, observed already after 1 hr, in treated NIH3T3 and TR15 cells, suggests a direct mitogenic stimulation. The level of activated c-myc RNA is 2-fold higher at 2 hr, and subsequently decreases relatively less in the TR15 cells.

Characterization of polyclonal anti-peptide antibodies specific for transforming growth factor beta 2

An antiserum was prepared against a synthetic peptide corresponding to the first 29 N-terminal amino acid residues of transforming growth factor beta type 2 (TGF beta 2) from porcine platelets. The anti-TGF beta 2 peptide antiserum appeared to be completely specific for TGF beta 2 in several immunological assays, including enzyme-linked immunosorbent assays, immunoblotting and immunofluorescence experiments. Furthermore, this antiserum completely neutralized the growth inhibitory effect of TGF beta 2 on mink lung carcinoma (ML-CC164) cells and the transforming capacity of this factor on quiescent monolayers of NRK cells in the presence of epidermal growth factor. These data indicate that the N-terminal region of TGF beta 2 may be involved in the biological activity of this growth factor. TGF beta 1 was not recognized by the anti-TGF beta 2 peptide antiserum. The specificity of the anti-TGF beta 2 peptide antiserum for TGF beta 2 appeared to be useful in identifying TGF beta 2 produced by different cell systems and will be helpful in determining possible functional differences between TGF beta 1 and TGF beta 2.

Transcriptional activation by TGF beta 1 mediated by the dyad symmetry element (DSE) and the TPA responsive element (TRE)

Transforming growth factor beta 1 (TGF beta 1) is a multifunctional regulator of growth and differentiation. However, both cytoplasmatic and nuclear signal transduction mechanisms leading to the biological effects of TGF beta 1 are largely unknown. In this report we show, that TGF beta 1 induces the expression of the immediate early genes c-jun and jun B, that encode trans-acting factors regulating transcription of a variety of genes in response to growth factors and phorbol esters. The jun genes are induced by TGF beta 1 in a protein synthesis independent fashion both in quiescent mouse 3T3 fibroblasts, which are growth stimulated by TGF beta 1, as well as in mink lung CCL64 (ML-CCL64) epithelial cells, which are growth inhibited by TGF beta 1. The PDGF inducible JE gene was induced by TGF beta 1 in 3T3, but not in ML-CCL64 cells. Furthermore, we show that chimaeric reporter-CAT constructs containing the TPA responsive element (TRE) or the dyad symmetry element (DSE) are activated by TGF beta 1 in transient transfection assays in both growth inhibited and growth stimulated cells. These results show that the early genomic responses to TGF beta 1 resemble changes in gene expression induced by serum, growth factors and phorbol esters, suggesting common mechanisms of transcriptional activation.

Effects of cell heterogeneity on production of polypeptide growth factors and mesoderm-inducing activity by Xenopus laevis XTC cells

The Xenopus laevis XTC cell line has been analyzed for the production of polypeptide growth factors and mesoderm-inducing activity. By the use of specific biological assays, it is shown that XTC cells produce a growth factor functionally related to the platelet-derived growth factor (PDGF) and two transforming growth factor (TGF) beta-like activities. Mesoderm-inducing activity, as measured on X. laevis ectodermal explants from stage 10 embryos, was found to coelute on a Bio-Gel P-100 column with one of the TGF beta-like activities at an apparent molecular weight of 6-10 kDa. Analysis of the DNA content from XTC cells by flow cytometry demonstrated that the cell line is heterogeneous and consists of both tetraploid and diploid cells. Cloning of the XTC cells and selecting single-cell colonies on the basis of their ability to grow in soft agar resulted in the isolation of several homogeneous, morphologically different clonal derivatives. Analysis of conditioned medium from these clonal derivatives showed that only one of them, the only diploid line among six investigated, produced a strong heat- and acid-stable mesoderm-inducing activity that induced notochord and muscle formation in stage 10 X. laevis ectodermal explants. The relation between this activity and a recently described TGF beta-like mesoderm-inducing factor obtained from XTC-conditioned medium will be discussed. In conclusion, a clonal cell line derived from X. laevis XTC cells which provides a good source for further characterization of mesoderm-inducing factors has been established.

Expression of transforming growth factor beta 2 during the differentiation of murine embryonal carcinoma and embryonic stem cells

Transforming growth factor beta 2 (TGF beta 2) mRNA expression was studied by Northern blot analysis in a range of feeder-independent murine embryonal carcinoma (EC) cells and in feeder-dependent EC and embryonic stem (ES) cells. TGF beta 2 transcripts were not detected in any undifferentiated cells including P19, F9, PC13, C1003, PSA-1, P10, and ES. Following induction of differentiation, however, TGF beta 2 became expressed, independently of the cell type formed. Retinoic acid (RA) addition and/or deprivation of the differentiation inhibiting activity of feeder cells resulted in the appearance of TGF beta 2 transcripts within 2 days. These kinetics correlated entirely with the first appearance of the protein; an anti-peptide antibody specifically recognizing TGF beta 2 did not stain P19 EC cells by immunofluorescence but 2-3 days after RA addition, a significant proportion of the population was strongly labeled. In addition, primitive endoderm cells emerging from the inner cell mass of substrate attached blastocysts stained brightly with anti-TGF beta 2, while the undifferentiated inner cell mass cells did not. Although all trophectoderm cells at the mid-blastocyst stage were stained, few had detectable levels of TGF beta 2 after plating on a substrate. Neither TGF beta 1 nor TGF beta 2 affected the growth of EC cells, but a range of differentiated derivatives were all inhibited, with TGF beta 2 being marginally more effective than TGF beta 1 at the same concentration.

The use of biological assays for detection of polypeptide growth factors

Polypeptide growth factors can be identified and quantified with high accuracy by the use of specific biological assays. In general these bioassays are highly sensitive for detection of growth factor activity, and enhanced specificity can be obtained by a proper choice of selective culture conditions for the target cells involved. In this paper sensitive and selective bioassays are described for growth factors acting on substrate-attached cells, in particular members of the epidermal growth factor, transforming growth factor beta, platelet-derived growth factor, insulin-like growth factor, and heparin-binding growth factor families. A cross-reactivity scheme has been worked out to identify possible contaminations in growth factor preparations.

Transforming growth factor-beta and its receptor are differentially regulated in human embryonal carcinoma cells

The human embryonal carcinoma cell lines Tera-2 clone 13 and NTera-2 clone D1 can be induced by retinoic acid to differentiate in vitro into neuroectodermal derivatives. The undifferentiated cells are rapidly proliferating and tumorigenic, whereas retinoic-acid-treated cells possess a decreased growth rate, lose their transformed phenotype and show a finite lifespan. Differentiation is accompanied by a marked increase in the levels of mRNA for TGF-beta 1 and TGF-beta 2 and the production of TGF-beta activity. Just like murine embryonal carcinoma cells the growth of Tera-2 clone 13 cells is not affected by the addition of either TGF-beta 1 or TGF-beta 2 to the culture medium. In contrast to published data on murine embryonal carcinoma cells, Tera-2 clone 13 and NTera-2 clone D1 cells bind TGF-beta 1 with high affinity, which is due to the presence of type-III TGF-beta receptors. Furthermore, and again in contrast to murine embryonal carcinoma cells, treatment of the human embryonal carcinoma cells with retinoic acid causes a nearly complete loss of TGF-beta 1 binding sites. These results are discussed in the light of similarities and differences in the regulation of growth and differentiation of human and murine embryonal carcinoma cell lines.

Identification and characterization of polypeptide growth factors secreted by murine embryonal carcinoma cells

Undifferentiated P19 and PC13 murine embryonal carcinoma (EC) cells have been analyzed for their ability to secrete polypeptide growth factors. This has been carried out by a combination of specific bioassays and the use of biochemical and immunological detection methods. Both P19 and PC13 EC cells secrete a platelet-derived growth factor (PDGF)-like growth factor, a type beta transforming growth factor, and insulin-like growth factors. In addition, PC13 EC cells secrete a heparin-binding growth factor functionally related to fibroblast growth factor, while P19 EC cells secrete transforming growth factor-alpha. This is the first demonstration for secretion of transforming growth factor-alpha by an equivalent of early embryonic cells. The possible paracrine growth stimulating effects of these growth factors have been tested on differentiated derivatives of P19 EC cells, corresponding to all three germ layers. The differences in growth factor production by various embryonal carcinoma cells are discussed in relation to the developmental origin of these cell lines.

Purification of a growth factor related to platelet-derived growth factor and a type beta transforming growth factor secreted by mouse neuroblastoma cells. A general strategy for the purification of basic polypeptide growth factors

A general strategy was developed for the purification of basic polypeptide growth factors. This method is a combination of gel filtration, weak-cation-exchange h.p.l.c. and reverse-phase h.p.l.c., separating the proteins according to size, charge and hydrophobicity respectively. All steps are carried out at low pH with exclusively volatile acidic buffer solutions. The sterile conditions and easy removal of salt by freeze-drying facilitate the detection of the growth factors by biological assays. By using this method, homogeneous preparations of two basic growth factors were purified in high yield from mouse-neuroblastoma-Neuro-2A-cell-conditioned medium. It is shown that these purified factors are biochemically and immunologically related to platelet-derived growth factor and type beta transforming growth factor from human platelets.

A new method for high yield purification of type beta transforming growth factor from human platelets

A new method was developed for the purification of type beta transforming growth factor from human platelets. This method is a three-step procedure including gel filtration, weak cation exchange HPLC and reverse phase HPLC. All steps are carried out at low pH using exclusively volatile acidic buffer solutions. The sterile conditions and easy removal of salt by lyophilization facilitate the quantification of the growth factor in biological assays. Based on immunological characterization the purified acid-stable, highly basic transforming growth factor beta is the beta 1 form. Using the present method pure platelet TGF beta 1 is obtained in very high yield. 40 units of outdated human platelets yield 800 micrograms pure TGF beta 1, which is about a 10-20 fold higher yield than reported for other purification procedures.

Differentially regulated production of platelet-derived growth factor and of transforming growth factor beta by a human teratocarcinoma cell line

The human teratocarcinoma stem cell line Tera-2 clone 13 is induced by retinoic acid to differentiate in vitro into endodermal or neuroectodermal cell types. In the absence of externally added growth factors, Tera-2 clone 13 cells proliferated at the same rate as in the presence of serum growth factors. Analysis of serum-free medium conditioned by Tera-2 clone 13 cells showed the presence of a polypeptide immunologically and biochemically related to platelet-derived growth factor (PDGF). In addition transforming growth factor beta (TGF-beta), but no TGF-alpha production could be detected. Tera-2 clone 13 cells specifically expressed high levels of the A-chain mRNA, but not the B-chain mRNA of PDGF. During retinoic acid induced differentiation the level of A-chain mRNA became markedly reduced. In contrast the TGF-beta mRNA levels increased significantly upon differentiation. The implications of these findings are discussed in terms of regulation of growth and differentiation in early embryos as well as in (human) teratocarcinomas.