Transforming growth factor beta modulates the expression of collagenase and metalloproteinase inhibitor

Exposure of quiescent MRC-5 human fibroblasts to growth factors such as epidermal growth factor, basic fibroblast growth factor or embryonal carcinoma-derived growth factor resulted in the induction of mRNA transcripts encoding the metalloproteinases collagenase and stromelysin and the specific metalloproteinase inhibitor TIMP, whilst expression of collagen and fibronectin was relatively unaffected. Exposure of quiescent cells to growth factors in the presence of transforming growth factor beta (TGF-beta) resulted in inhibition of collagenase induction and a synergistic increase in TIMP expression. TGF-beta alone did not significantly induce metalloproteinase or TIMP expression. These effects on mRNA transcripts were reflected in increased secretion of TIMP protein and collagenase activity. Nuclear run-off analysis of growth factor-induced transcription revealed that the TGF-beta modulation of TIMP and collagenase expression was due to transcriptional mechanisms. The observations suggest that TGF-beta exerts a selective effect on extracellular matrix deposition by modulating the action of other growth factors on metalloproteinase and TIMP expression.

Mesoderm induction in early Xenopus embryos by heparin-binding growth factors

In early embryonic development the basic body plan arises because cells in different regions become programmed to follow different developmental pathways. We have proposed that in the early amphibian embryo this process of regional specification arises from the action of three different inducing factors, or morphogens, but we have not until now had any idea of their chemical nature. In this paper we report that pure basic fibroblast growth factor (bFGF), at very low concentrations and with high specificity, closely mimics the effect of the ventrovegetal (VV) signal and that the transmission of the natural VV signal can be blocked by heparin, suggesting that it may be a heparin-binding factor such as bFGF.

The role of EGF receptor transmodulation in embryonal carcinoma-derived growth factor-induced mitogenesis

Exposure of quiescent 10T1/2 fibroblast cells to embryonal carcinoma-derived growth factor (ECDGF) results in a rapid temperature and ECDGF concentration-dependent inhibition of [125I]EGF binding to the epidermal growth factor (EGF) receptor (transmodulation). ECDGF predominantly inhibits the association of [125I]EGF with a high affinity subclass of EGF receptors, and induces increased phosphorylation of the EGF receptor on serine and threonine residues. No mitogenic effect of EGF can be detected in the presence of ECDGF concentrations which induce maximal EGF receptor transmodulation. ECDGF-induced EGF receptor transmodulation is sensitive to phorbol ester-induced desensitization whereas ECDGF-induced DNA synthesis is unaffected by prolonged pre-treatment with biologically active phorbol ester. These findings suggest that EGF receptor transmodulation is not essential for ECDGF mitogenicity but may inhibit EGF-induced DNA synthesis.

Developmentally regulated expression of insulin-like growth factors by differentiated murine teratocarcinomas and extraembryonic mesoderm

The expression of plasma membrane receptors for insulin-like growth factors (IGFs) by PC13 embryonal carcinoma (EC) cells, and their immediate differentiated progeny PC13END was examined by binding radiolabelled IGF-I to cell monolayers. Both cell types express high-affinity IGF receptors, but the apparent number of unoccupied receptors sites falls by about 60% upon differentiation. Crosslinking studies reveal that both type 1 and type 2 IGF receptors are expressed by PC13EC cells. PC13END-cell-conditioned medium contains developmentally regulated, separable activities, one of which reacts directly with IGF-II, and the other with IGF for plasma membrane receptors. The former activity represents a soluble secreted IGF-binding protein. The latter activity is structurally and functionally similar to rat IGF-II. Polyclonal antibodies raised against purified rat IGF-II specifically recognize multiple forms of IGF in radiolabelled culture supernatants and material which closely resembles the soluble IGF-binding protein. Immunoprecipitation of radiolabelled culture supernatants with anti-rat IGF-II reveals that the differentiation of PC13EC cells is accompanied by the coexpression of IGF-like molecules and the soluble binding protein, and that IGF-like molecules are expressed by extraembryonic tissues of mesodermal origin in the early postimplantation mouse embryo. These findings show that IGF-like molecules are expressed in early mammalian development and may act in an autocrine fashion in vivo.

Advances in understanding cell interactions in tissue resorption. Relevance to the pathogenesis of periodontal diseases and a new hypothesis

Much of the connective tissue degradation that takes place in periodontal diseases is mediated by proteolytic enzymes. Previous studies have focused on the action of proteinases released by invading polymorphonuclear neutrophils and macrophages, and bacterial enzymes. In view of recent work establishing that resident connective tissue cells can be induced by cytokines to bring about the destruction of their own matrix, we propose a new hypothesis. In this we envisage that a critical step is the interaction of bacterial antigens with inflammatory cells, resulting in the production of a cytokine, interleukin-1. Our interpretation of in vitro evidence is that the loss of connective tissue attachment and bone matrix resorption in periodontal diseases is mediated by metalloproteinases such as collagenase and stromelysin released by cells of the periodontium. Such proteolytic destruction can be induced by interleukin-1, whose production may not be dependent on a specific microbial flora but may be triggered by a number of organisms. It is now clear that interleukin-1 has multiple actions on both immune and non-immune cells; these include the induction of lymphocyte differentiation and proliferation and the stimulation of bone and cartilage resorption, and prostaglandin and metalloproteinase synthesis by connective tissues. It seems likely that further knowledge about the production and function of this cytokine will have an increasing impact in many diseases that involve resorption, particularly since interleukin-1-like molecules can be produced by cell types other than monocytes/macrophages, including keratinocytes and fibroblasts.

Antioxidant systems in tumour cells: the levels of antioxidant enzymes, ferritin, and total iron in a human hepatoma cell line

The human hepatoma cell line Hep 3B, which has the hepatitis B virus genome, shows over 80% decrease of copper/zinc superoxide dismutase activity, over 90% decrease of manganese superoxide dismutase activity, over 70% decrease of catalase activity, absence of glutathione peroxidase and glutathione S-transferase activities, over 270-fold increase of ferritin content and 25-fold increase of total iron compared to normal autopsy liver. These conditions of low antioxidant enzyme activities and iron overload are those which support the accumulation of oxygen free-radicals and DNA damage commonly considered to be carcinogenic mechanisms.

Proliferation of a human embryonal carcinoma-derived cell line in serum-free medium: inter-relationship between growth factor requirements and membrane receptor expression

Substantial multiplication in vitro of cloned cells from a human embryonal carcinoma cell line, Tera 2, has been obtained in a basal medium (DMEM/Ham's F12,50:50, v/v) supplemented with 10 micrograms low density lipoprotein/ml, 100 micrograms high density lipoprotein/ml, 100 ng multiplication stimulating activity/ml, 100 ng insulin/ml and 1 microgram transferrin/ml. The growth rate appears to be similar to that obtained in 10% serum. Furthermore, studies on the expression of cell surface receptors revealed that cloned Tera 2 cells express high-affinity receptors for IGF-II but not for insulin. The cells also express receptors for Epidermal Growth Factor (EGF) even though the addition of EGF does not stimulate their proliferation in serum-free medium. These results suggest that the expression of specific growth factor receptors is not an absolute determinant of hormone responsiveness.

Pig interleukin 1 (catabolin) is a potent stimulator of bone resorption in vitro

A homogeneous form of pig interleukin 1 (catabolin) stimulates the resorption of mouse bones in culture. Concentrations as low as 25 pM are effective, demonstrating that it is more potent than 1,25-dihydroxy-vitamin D3 in our assay system. Catabolin was originally defined by its ability to stimulate glycosaminoglycan release from cartilage in culture and purified from pig mononuclear leucocyte supernatants. It also augments lectin-induced thymocyte proliferation, indicating that it is a form of pig interleukin 1. Bone resorbing factors are synthesized by other cell types, including fibroblasts and osteoblasts; we suggest that such cytokines are important in mediating the action of systemic hormones on bone.

PC13 embryonal carcinoma-derived growth factor

A potent growth factor, PC13 embryonal carcinoma-derived growth factor (ECDGF), has been isolated from serum-free medium conditioned by PC13 murine embryonal carcinoma cells. ECDGF is a single chain, cationic hydrophobic molecule of 17 500 daltons. ECDGF will induce DNA synthesis in established fibroblast cell lines and the immediate differentiated progeny of PC13 EC cells in vitro, and consequently appears to differ from other well characterised growth factors both in structure and action.

Pig catabolin is a form of interleukin 1. Cartilage and bone resorb, fibroblasts make prostaglandin and collagenase, and thymocyte proliferation is augmented in response to one protein

Homogeneous catabolin from pig leucocytes induced proteoglycan breakdown, but not collagen breakdown, in explants of articular cartilage. It augmented lectin-induced proliferation of mouse thymocytes, stimulated production of prostaglandin E2 and collagenase by fibroblasts and chondrocytes, and increased Ca2+ release from mouse calvarial explants, all at concentrations down to 50 pM. In view of these effects it was concluded that pig catabolin is a form of interleukin 1.

Mouse osteoblasts synthesize collagenase in response to bone resorbing agents

Bone cells isolated from mouse calvariae by a sequential digestion procedure have many osteoblast characteristics: they respond to PTH and prostaglandin E2 by activation of adenylate cyclase but not to calcitonin, they stain for alkaline phosphatase and they make only type I collagen. In confluent monolayer culture, they do not secrete collagenase in appreciable quantities, unless stimulated with resorptive substances such as PTH, prostaglandin E2, 1,25(OH)2 vitamin D-3 and monocyte-conditioned medium. This suggests they play a direct role in bone resorption.

A factor synthesized by rabbit periosteal fibroblasts stimulates bone resorption and collagenase production by connective tissue cells in vitro

Unstimulated monolayer cultures of confluent rabbit periosteal fibroblasts synthesize a factor that stimulates bone resorption in vitro. Furthermore it stimulates rabbit chondrocytes and mouse osteoblasts to synthesize collagenase. The factor has no effect on dead bone in culture, and its activity on live bone is mediated principally by osteoclasts, since it is 75% inhibited by salmon calcitonin. Characterization of the factor by gel filtration and isoelectric focusing indicates an Mr in the range 15000-25000 and a pI corresponding to approx. pH 4.7. These biological and physiochemical properties are similar to those reported for a factor released by peripheral blood monocytes. However, whereas human monocyte factor in both the crude and partially-purified state exhibits interleukin-1 activity, crude and fractionated periosteal fibroblast-conditioned medium does not. This is the first report of a conditioned medium containing a molecule like the monocyte-factor which appears to have no interleukin 1 activity. The factor may be synthesized by a wide range of cell types, and could have an important role in mediating connective tissue degradation during both physiological and pathological resorption.

Most highly repeated dispersed DNA families in the mouse genome

The construction of a small library of mouse repetitive DNA has been previously reported (Pietras et al., Nucleic Acids Res. 11:6965-6983, 1983). Here we report that the 35 plasmids in this library corresponding to highly repeated (greater than 30,000 copies per genome) dispersed DNA sequences can be grouped into no more than 5 distinct families. These families together comprise 8 to 10% of the mouse genome. They include the previously described small elements B1, B2, and R and the large MIF-1 element. Twelve of the 35 clones contain evolutionarily conserved (EC) sequences. One EC clone in our library mostly consists of alternating dCdT residues; another consists of tandem repeats of the sequence CCTCT. The majority of B1s and B2s in the genome appear to be homogeneous, whereas R sequences, ECs, and MIF-1s are heterogeneous. Two earlier reports showed highly repeated mammalian DNA sequences in the herpesvirus genome (Peden et al., Cell 31:71-80, 1982; Puga et al., Cell 31:81-87, 1982). We show that sequences homologous to our EC clones are present in the herpesvirus genome, although these polypyrimidine stretches are not detected in poxvirus, adenovirus, and simian virus 40 genomes. We detect transcripts containing homology to all of these sequences in a nuclear transcription assay. Also, we show that small, polyadenylated RNA molecules homologous to B2 sequences are expressed in undifferentiated embryonal carcinoma cells but not in their differentiated derivatives. The significance of these findings is discussed.

Apolipoprotein expression by murine visceral yolk sac endoderm

Apolipoprotein expression was examined in the postimplantation mouse embryo. Antibodies directed against murine Apolipoprotein AI and human low-density lipoprotein (LDL) particles specifically immunoprecipitated metabolically labelled radioactive apolipoproteins from the culture supernatant of 10.5 days post coitum (days p.c.) yolk sac visceral endoderm cultured in vitro. No evidence for apolipoprotein expression by other embryonic or extraembryonic tissues at this stage was obtained. Immunohistochemical staining at sectioned 10.5 days p.c. embryos with anti-Apolipoprotein AI antibodies revealed specific localization of immunoreactive material in the yolk sac visceral endoderm. We conclude that the yolk sac visceral endoderm is a source of lipoproteins during postimplantation embryonic development.

The use of in vitro models for investigating the response of fibrous joints to tensile mechanical stress

To clarify the role of mechanical deformation in the remodeling of fibrous joints, organ culture systems have been developed to apply mechanical stress to cranial sutures under controlled experimental conditions. Tensile mechanical stress applied to cranial sutures from newborn rabbits produces a two- to threefold increase in protein synthesis and a twofold increase in collagen synthesis that can be detected within 6 hours. There is also a threefold increase in the DNA content of the sutures after 48 hours. Under normal conditions sutural fibroblasts synthesize type I collagen but respond to tensile deformation by synthesizing significant amounts of type III collagen. This suggests that the biomechanical environment of a connective tissue cell is an important determinant of the collagen type synthesized. However, the effect is likely to be an indirect one by virtue of its influence on the metabolic activity of the cells. Mechanically activated cells do not preferentially synthesize structural proteins, since mechanical stress stimulates the synthesis not only of structural macromolecules but also of the enzymes responsible for their specific hydrolysis. This is not accompanied by increased degradation, however, perhaps because the metalloproteinase inhibitor TIMP synthesized by the tissues is also increased. Confluent rabbit and mouse periosteal fibroblasts synthesize and release into the culture medium factors that can inhibit bone cell proliferation and stimulate bone resorption in vitro. It seems likely that further investigation of the interaction between fibroblasts and osteoblasts at the bone--fibrous tissue interface will require a reassessment of current thinking concerning the mechanisms regulating sutural osteogenesis.

Consequences of parental exposure to epidermal growth factor for progeny cell division

The consequences of parental exposure to epidermal growth factor (EGF), for progeny cell cycle times was investigated. Slowly dividing mouse 3T3 fibroblasts were exposed to EGF for 8 hr, the EGF was withdrawn, and the cell cycle times of parental and progeny cells were measured by time-lapse video microscopy. It was observed that exposure to EGF induced a round of cell division following a lag phase of approximately 8 hr. The progeny of these cells exhibited accelerated cell cycle times compared to cells that had not been exposed to EGF. Parental cell division time was significantly correlated with progeny cell cycle time. Sibling progeny cell cycle times were also significantly correlated. EGF can therefore apparently exert an effect on the cell cycle times of more than one generation of cells.

Serum-free culture of PC13 murine embryonal carcinoma cells

The requirements for the serum-free culture of PC13 murine embryonal carcinoma cells were determined. Supplementation of a 50:50 mixture of Dulbecco's modified Eagles medium and MCDB104 with transferrin (5 micrograms/ml), human high-density lipoprotein (HDL) (100 micrograms/ml), and human low-density lipoprotein (LDL) (50 micrograms/ml) supported growth comparable to that observed with 5% foetal calf serum. Media supplementation with lipoproteins apparently substitutes for the effects of insulin, desoctapeptide insulin, (DOP), or multiplication-stimulating activity (MSA) on EC cell multiplication. Clonal growth of PC13 EC cells in this serum-free medium could only be achieved in the presence of suitable feeder cell monolayers. These observations demonstrate that PC13 EC cells do not have an absolute requirement for exogenous mitogens to support multiplication.

A monoclonal antibody which detects a cell surface antigen on murine embryonal carcinoma and early mouse embryo stages may recognize a carbohydrate determinant involving alpha-linked galactose

A rat monoclonal antibody (5D4) apparently specific for murine embryonal carcinoma cells and cells of the pre-implantation embryo is described. It does not react with differentiated cells from a variety of different tumours and tissues of the mouse. Biochemical studies show that the molecules that carry 5D4 antigen are resistant to protease digestion on the cell surface but susceptible to procedures which affect carbohydrate structure. It is likely that this antibody detects a carbohydrate bearing determinant which may include an alpha-linked galactose residue.

Modulation of dexamethasone receptor expression in embryonal carcinoma cells and their differentiated derivatives

The dexamethasone binding capacity of embryonal carcinoma cells and their differentiated derivatives was investigated. Manipulation of the embryonal carcinoma cell-culture conditions resulted in an unstable reversible expression of the glucocorticoid receptors. Stable expression of the receptors is observed when these cells are induced to differentiate. Cells grown under identical conditions were assayed for their ability to bind epidermal growth factor.

Anterior mandibular displacement and condylar growth. An experimental study in the rat

Anterior displacement of the mandible was produced in twenty-eight 1-month-old female rats by two methods: (1) cast-gold splints cemented to the maxillary incisor teeth and (2) a removable stainless steel mesh appliance worn 6 hours each day, during which time the animals were sedated. The controls were littermates without appliances and in the mesh group were also sedated. Animals in the splint group were killed after 24 hours, 1 week, and 1 month; those in the mesh group were killed after 24 hours and after 1 week. the condyles were removed and cultured for 24 hours in medium containing 3H-thymidine. One condyle from each animal was processed for routine histologic and autoradiographic study. The other was digested in phosphate-buffered saline containing RNA-ase and pronase, and the specific activity of 3H-thymidine incorporation expressed as dpm/microgramDNA. Anterior mandibular displacement produced by both methods failed to result in a significant increase in the incorporation of 3H-thymidine into explant DNA. In the 7-day mesh experiment, however, there was a significant increase in the DNA content of the condylar explants from the displacement group, suggesting an increase in the cell population. This finding should be treated with caution because of the small numbers of animals involved, but it indicates an important area for further study. Changes in the distribution of labeled cells within the proliferative zone (PZ) were also observed autoradiographically in the mesh group, but there was little to suggest that mandibular displacement was accompanied by a significant increase in cell division within the PZ. Remodeling changes affecting both the articular tissue and the subchondral bone were a characteristic feature of the 1-month bit plane group.

Rabbit cranial suture fibroblasts under tension express a different collagen phenotype

We present evidence that cells in fibrous joints respond to tensile mechanical stress by synthesizing significant quantities of type III collagen. Under normal conditions sutural fibroblasts synthesize type I collagen. Type III comprised some 20 per cent of the newly synthesized collagen in stressed joints, a level that was achieved within 24 h of the onset of tension and remained unchanged throughout a 4-day experimental period. These findings suggest that the biomechanical environment of a connective tissue cell is an important determinant of the type of collagen synthesized. However, we propose that the effect is likely to be an indirect one by virtue of its influence on the metabolic activity of the cells.

A cell surface antigen, TER, expressed by embryos and germ cells

An antiserum prepared in rabbits against the C3HeB/FeJ mouse ovarian teratocarcinoma E6496 was absorbed in vivo in C3HeB/FeJ mice. This absored antiserum identified an antigen, denoted TER, that is present on sperm, ova, embryonic germ cells, and cells of the early mouse embryo. TER was absent from all adult somatic cells tested, but found on several murine tumors.

Characterization of a xenogeneic antiserum raised against the fetal germ cells of the mouse: cross-reactivity with embryonal carcinoma cells

A xenogeneic antiserum (PG-1) raised against the germ cells of the 13.5d p.c. mouse conceptus reacts with the fetal germ cells of both sexes and adult male germ cells, but not with any nongerminal tissue that has been tested. PG-1 can also react with the EC cells of four different teratocarcinoma cell lines. There are, however, marked differences in the absorptive capacity of the different EC cell lines. The antigen(s) recognized by the antiserum are confined to only a proportion of cells in some EC lines. This antiserum has a number of potential applications in studies of the origin and development of the mouse germ cell lineage.