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

Maternal hypothyroidism prolongs gestation period and impairs glucose tolerance in offspring of Wistar rats

OBJECTIVES

Pregnancy is a critical period keenly regulated by both maternal and foetal factors and a shift in these factors could result in severe complications manifesting in foetal and adult life. However, maternal hypothyroidism before and/or during pregnancy is a critical factor. This study investigated the effect of maternal hypothyroidism on glucose tolerance and thyroid function in male and female offspring.

METHODS

Fifteen adult female Wistar rats were divided into three groups: Group 1 (sham-control), Group 2 (thyrodectomized) and Group 3 (thyroidectomised + L-thyroxine treated). Blood thyroxine (T4) level was measured on the day 10 after thyroidectomy in Groups 1 and 2, and day 35 in Group 3. Males were introduced to the female rats after T4 measurement. At PND-112, T4 levels of their offspring were measured. Oral Glucose Tolerance Test (OGTT) was measured in offspring at PND-133.

RESULTS

Thyroxine reduced significantly in Group 2 and their offspring (male and female) compared to Group 3 while gestation period was prolonged significantly in Group 2 compared to Group 1. Hypothyroid male offspring showed depressed glucose tolerance, however, no effect was observed in female offspring.

CONCLUSIONS

This study suggests that maternal hypothyroidism prolonged gestation period, induced foetal hypothyroidism in both genders and depressed glucose tolerance in male offspring.

Fibronectin is the major fibroblast chemoattractant in rabbit anti-glomerular basement membrane disease

The mechanism for fibroblast recruitment in renal fibrosis due to anti-glomerular basement membrane (anti-GBM) disease is unknown. Since fibroblast recruitment can occur via chemotaxis, assessment of the possible production of fibroblast chemotactic activity by affected renal tissue and its identification could provide important clues. Anti-GBM disease was induced by injection of guinea pig anti-rabbit GBM immunoglobulin G into rabbits previously sensitized to guinea pig immunoglobulin G. On days 4, 7, and 14 after induction, renal tissue was harvested and glomeruli isolated. Overnight serum-free conditioned media from whole cortex and glomeruli were prepared and assayed for fibroblast chemotactic activity. The results show low level activity in both conditioned media from control animals. In contrast, conditioned media from anti-GBM-treated animals at all time points showed significantly elevated fibroblast chemotactic activity peaking on day 4 with subsequent reduction thereafter. The magnitude of increase in cortical conditioned media was significantly higher than that for glomerular conditioned media, suggesting that most of the activity was derived from extraglomerular sources. Gel filtration analysis revealed the activity to be heterogeneous, consisting of at least four major species with estimated molecular weights ranging from 10 to > 100 kd. Acidification of conditioned media failed to increase chemotactic activity significantly, whereas protease digestion abolished it. Treatment of conditioned media with antifibronectin inhibited > 85% of the chemotactic activity, whereas antibodies to platelet-derived growth factor and transforming growth factor-beta did not have a significant effect. These findings taken together suggest that fibronectin-derived peptides represent the predominant fibroblast chemoattractant produced by renal cortex in anti-GBM disease.

Bradykinin-induced growth inhibition of normal rat kidney (NRK) cells is paralleled by a decrease in epidermal-growth-factor receptor expression

Normal rat kidney fibroblasts, grown to density arrest in the presence of epidermal growth factor (EGF), can be induced to undergo phenotypic transformation by treatment with transforming growth factor beta or retinoic acid. Here we show that bradykinin blocks this growth-stimulus-induced loss of density-dependent growth arrest by a specific receptor-mediated mechanism. The effects of bradykinin are specific, and are not mimicked by other phosphoinositide-mobilizing agents such as prostaglandin F2 alpha. Northern-blot analysis and receptor-binding studies demonstrate that bradykinin also inhibits the retinoic acid-induced increase in EGF receptor levels in these cells. These studies provide additional evidence that EGF receptor levels modulate EGF-induced expression of the transformed phenotype in these cells.

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.

Transforming growth factor beta as a neuronoglial signal during peripheral nervous system response to injury

In contrast to the central nervous system (CNS), the peripheral nervous system (PNS) displays an important regenerative ability which is dependent, at least in part, on Schwann cell properties. The mechanisms which stimulate Schwann cells to adapt their behavior after a lesion to generate adequate conditions for PNS regeneration remain unknown. In this work, we report that adult rat dorsal root ganglion (DRG) neurons are able, after a lesion performed in vivo or when they are dissociated and cultured in vitro, to synthesize transforming growth factor beta (TGF beta), a pleiotropic growth factor implicated in wound healing processes and in carcinogenesis. This TGF beta is tentatively identified as the beta-1 isoform. Adult rat DRG neurons release a biologically active form of TGF beta which is able to elicit multiple Schwann cell responses including a stimulation to proliferate. Moreover, purified TGF beta-1 produces a Schwann cell morphology alteration and decreases the secretion of tissue-type plasminogen activator (tPA) and enhances the secretion of plasminogen activator inhibitor (PAI) by Schwann cells. This generates conditions which are thought to favor a successful neuritic regrowth. Furthermore, purified TGF beta-1 stimulates type IV collagen mRNA expression in Schwann cells. This subtype of collagen is associated with the process of myelinization. Finally, TGF beta-1 decreases nerve growth factor (NGF) mRNA expression by Schwann cells, an effect which could participate in the maintenance of a distoproximal NGF gradient during nerve regeneration. We propose that neuronal TGF beta plays an essential role as a neuronoglial signal that modulates the response of Schwann cells to injury and participates in the successful regeneration processes observed in the PNS.

Phenotypic transformation of normal rat kidney cells by transforming growth factor beta is not paralleled by enhanced production of a platelet-derived growth factor

Phenotypic transformation of normal rat kidney (NRK) cells requires the concerted action of multiple polypeptide growth factors. Serum-deprived NRK cells cultured in the presence of epidermal growth factor (EGF) become density-inhibited at confluence, but they can be restimulated by a number of defined polypeptide growth factors, resulting in phenotypic cellular transformation. Kinetic data show that restimulation by transforming growth factor beta (TGF-beta) and retinoic acid is delayed when compared to induction by platelet-derived growth factor (PDGF), indicating that both TGF beta and retinoic acid may exert their growth-stimulating action by an indirect mechanism. Northern blot analysis shows that NRK cells express the genes for various polypeptide growth factors, including TGF beta 1, PDGF A-chain and basic fibroblast growth factor, but that the levels of expression are not affected by TGF beta or retinoic acid treatment. NRK cells also secrete low amounts of a PDGF-like growth factor into their extracellular medium, but the levels of secretion are insufficient to induce mitogenic stimulation and are unaffected by agents inducing phenotypic transformation. In combination with studies on the effects of anti-PDGF antibodies, it is concluded that phenotypic transformation of NRK cells by TGF beta and retinoic acid is not the result of enhanced production of a PDGF-like growth factor.

Colorectum cell-derived growth factor (CRDGF) is homologous to amphiregulin, a member of the epidermal growth factor family

We have previously shown that an autocrine factor (CRDGF) of molecular weight 25,000 is produced by the HT29 human colon cancer cell line. Although CRDGF was shown to inhibit the binding of epidermal growth factor (EGF) to its receptor, several lines of evidence suggested that it was distinct from EGF or transforming growth factor-alpha (TGF-alpha). In order to check the possibility that CRDGF represents a new member of the EGF family, a four-step purification protocol involving acid gel filtration, cation-exchange high-performance liquid chromatography (HPLC), C18 reversed-phase HPLC and gel permeation HPLC was used to purify this protein to homogeneity. The purified material exhibited a 22 kDa molecular mass on SDS-PAGE. Partial N-terminal amino acid sequence of CRDGF showed identity to amphiregulin (AR), an EGF-related protein. Western blotting experiments using AR-specific antiserum confirmed that CRDGF and AR are identical proteins. In addition, we showed that AR, like EGF or TGF-alpha stimulated the phosphorylation of the epidermal growth factor receptor (EGF-R) on tyrosine residues. This indicates that the AR intracellular signalling pathway involves the activation of EGF-R kinase.

Transforming growth factor-beta production in anti-glomerular basement membrane disease in the rabbit

The purpose of this study was to assay for the presence of collagen synthesis stimulatory activity in the kidney during immune-induced renal injury that results in severe fibrosis in both glomerular and interstitial compartments. A model of antiglomerular basement (anti-GBM) disease in the rabbit was induced on day 0 by the injection of anti-GBM antibody and renal cortex tissues were then sampled at various time points. Only conditioned media prepared from diseased renal cortical samples showed collagen synthesis stimulatory activity when tested on rabbit mesangial cells. The activity had an estimated molecular weight range of 16 to 25 kd and was neutralized by antibody to transforming growth factor-beta (TGF-beta). A standard assay for TGF-beta using a mink lung epithelial cell line confirmed the increase in TGF-beta activity in conditioned media of diseased cortex from day 7 and day 14 animals, which was not significantly activated by previous acidification. This suggests that most of the TGF-beta present in renal conditioned media was in the active form. The increase in renal cortical secretion of active TGF-beta was accompanied by increases in renal cortical TGF-beta mRNA content on days 4 and 7 after induction, with subsequent return to control levels. A similar increase in TGF-beta activity was present in nonacidified conditioned media of purified glomeruli from diseased days 7 and 14 animals, which was also accompanied by significant increases in TGF-beta mRNA. However with acidification no significant differences were noted between control and diseased samples, suggesting the presence of substantial latent TGF-beta activity in control glomerular conditioned media. These same control-conditioned media contained inhibitor activity for added exogenous TGF-beta. These results support the conclusion that the association between increased TGF-beta secretion and increased renal cortical collagen synthesis in this model is consistent with a role for this cytokine in directing fibrogenesis in the kidney.

Stimulation of rat endothelial cell transforming growth factor-beta production by bleomycin

This study examines the hypothesis that mediators from lung endothelial cells could promote lung collagen synthesis in pulmonary fibrosis. Since bleomycin induces pulmonary fibrosis in humans and animals, the effects of this drug on endothelial cells were examined. Endothelial cell conditioned media were prepared in the presence of various doses of bleomycin, and tested for their ability to stimulate lung fibroblast collagen synthesis. The results show a dose-dependent stimulation of endothelial cell secretion of collagen synthesis stimulatory activity by bleomycin, which peaked at a dose greater than or equal to 100 ng/ml. Stimulation was selective for collagenous protein synthesis. Gel filtration analysis showed most of the activity to reside in fractions with an estimated molecular mass range of 10-27 kD. The activity was inhibited by anti-transforming growth factor-beta (TGF-beta)antibody, but not by nonimmune control IgG. The presence of TGF-beta was confirmed using the mink lung epithelial cell assay. Northern blotting revealed significant increases in TGF-beta mRNA in bleomycin-stimulated endothelial cells. Thus in vitro stimulation of endothelial cells by bleomycin upregulates TGF-beta production, presumably by increased transcription. In view of the chemotactic and matrix synthesis stimulatory properties of this cytokine, such an increase in TGF-beta production may play an important role in bleomycin-induced pulmonary fibrosis.

Immunomodulatory properties of platelet factor 4: prevention of concanavalin A suppressor-induction in vitro and augmentation of an antigen-specific delayed-type hypersensitivity response in vivo

The immunomodulatory properties of platelet factor 4 (PF4) have been examined in vitro and in vivo. This agent prevented the induction of concanavalin A (Con A)-induced suppressor cells in vitro in a dose-dependent manner but it did not affect the function of established Con A suppressor cells. This effect was not due to an enhanced production of interleukin-2 (IL-2) by lymphocytes exposed to PF4. The delayed-type hypersensitivity (DTH) reaction to sheep erythrocytes (SRBC) was used as a model for the generation of antigen-specific suppression in vivo. PF4 enhanced the magnitude of the swelling following SRBC challenge 10 days after sensitization by the i.p. route or following sensitization by both the s.c. and i.p. routes. These studies show that PF4 has immunomodulatory activities in well-defined models of cell-mediated immunity and suggest that this agent has a potential use in the dissection of events in antigen-specific suppression.

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.

Cultured neurons release an inhibitor of astroglia proliferation (astrostatine)

Using in vitro techniques, we looked for a possible downregulation of rat astroglia proliferation by neuronal cells. We demonstrate that medium conditioned by 7-day-old rat cerebellar granule neurons or by 16-day-old rat embryo hippocampal neurons strongly inhibits the proliferation of cultured astroglial cells. Two neuronal cell lines, the PC12 rat pheocromocytoma and the neuro 2A (N2A) murine neuroblastoma also release such an activity. This release in N2A-conditioned medium (CM) occurs when the cells are at high density and show a low proliferation rate. This activity is present in media conditioned by neuronal cells, but not in media conditioned by normal astrocytes, by two glioma cell lines, or by one fibroblastic cell line. This proliferation inhibitor addresses normal astrocytes: the proliferation of two glioma cell lines, of a fibroblastic cell line, and of the two neuronal cell lines (PC12, N2A) is not inhibited by N2A CM. Moreover, this activity is directed against type 1 astrocytes, but not against type 2. Using three different assays, we demonstrate that DNA synthesis by astroglial cells is inhibited. N2A CM has no cytotoxic effect on astrocytes and does not modify their overall protein synthesis. Using affinity and gel filtration chromatography, we show that this activity is associated with a protein whose molecular weight ranges between 15 and 20 kDa. The possible relationship between this N2A cell-derived astroglia proliferation inhibitor and other types of potential glial proliferation inhibitors has been investigated. A brain glycoprotein immunologically related to epidermal growth factor receptor (EGFR) was reported to inhibit astroglial cell proliferation in vitro. Using polyclonal and monoclonal antibodies against EGFR, we were unable to immunoprecipitate the astrocyte proliferation inhibitor in N2A CM or to demonstrate by immunoblotting the presence of an EGFR-like immunoreactivity in the N2A CM or in the active chromatographic fractions of N2A CM. Transforming growth factor beta (TGF beta) is a well-known modulator of the proliferation of various cell types and was shown to be present in N2A CM. Using a polyclonal anti-TGF beta antibody that recognizes TGF beta on Western blots of N2A CM, we were unable to immunoprecipitate the astrocyte proliferation inhibitor of N2A CM. It seems thus far that the neuronal astroglia proliferation inhibitor is a new protein for which we propose the name astrostatine.

Direct effects of estrogen on c-fos and c-myc protooncogene expression and cellular proliferation in human breast cancer cells

Estrogen induces DNA synthesis to a lesser degree, but with similar kinetics compared to insulin-like growth factors when added to quiescent MCF7 human breast cancer cells. Moreover, this steroid rapidly induces expression of the growth-related c-fos and c-myc protooncogenes. The induction was shown to be a direct effect, independent of protein synthesis. These results demonstrate that no growth factor production is involved in estrogen-induced protooncogene expression, and that these direct effects on gene expression may be an important step in estrogen-induced mitogenesis.

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.