Isolation of the oncogene and epidermal growth factor-induced transin gene: complex control in rat fibroblasts

Mechanisms of matrix degradation in rheumatoid arthritis

In the inflammatory synovium production of collagenase is probably responsible for the degradation of collagen in the extracellular matrix and distortion of the architecture and function of the joints. Major collagenase-producing cells are mesenchymal cells such as fibroblasts and chondrocytes, which synthesize and secrete the enzyme influenced by the action of cytokines produced by adjacent mononuclear cells. The cytokines act primarily through cell-surface receptors, whose signal is probably then mediated by complexes of nuclear oncoproteins, to activate transcription of the procollagenase gene. The increased production of collagenase ultimately is the result of a cascade of cellular effects involving complex interactions of different ligands in a system characterized by amplification and feedback loops.

Regulation of gene expression by tumor promoters

Tumor promoters change the program of genes expressed in cells in culture and in the multicellular organism. The growing list of genes that are induced or repressed includes protooncogenes, transcription factors, secreted proteases and viruses. Most of the regulation is at the level of transcription. Several of the cis-acting promoter elements mediating regulation, the transcription factors binding to these elements and their post-translational activation, as well as some of the initial steps of the interaction of cells with tumor promoters have been characterized. The components of the signal transduction chain to the nucleus are, however, still unknown. Mutant and inhibitor studies suggest that the activation or inactivation of certain genes constitute the basis for the development of the tumor promotion phenotype.

Molecular oncogenetics of metastasis

Metastasis is a complex non-stochastic process that is most likely the result of genetic and epigenetic interactions of a wide variety of genes. The search for a single gene which can encompass such a pleiotropic response as to account for the observed phenotypic characteristics of metastatic tumour populations has been unsuccessful. Particular studies involving gene transfection, subtractive hybridisation and cell fusion are beginning to identify specific genes which contribute to metastasis in some cell types. However, such analyses are complicated by the inherent genetic instability and phenotypic heterogeneity present in tumour populations. A more detailed understanding of the metastatic process may require an abandoning of current generalised approaches to metastasis in favour of concentrating on key components of the metastatic cascade such as adhesion and invasion.

Transforming growth factor-ßs as modulators of pericellular proteolytic events

Since the discovery of transforming growth factor-ß:s an increasing number of different biological effects have been attributed to this group of proteins. Analysis of the cellular responses to TGFß stimulation at the molecular level has indicated that TGFß acts as an activator of transcription of several genes. This may in part explain the plethora of various functions that have been ascribed to TGFß. In addition to the TGFß family of polypeptides there is an increasing number of related factors, whose major roles appear to be involved in developmental processes. A distinct feature of TGFß is its ability to regulate pericellular proteolysis of cultured cells. As yet this property has not been associated with other members of this group of polypeptides. Depending on the target cell type TGFß may either increase or decrease pericellular proteolytic activity. Proteolytic activation of latent TGFß and its possible inhibition by TGFß-induced protease inhibitors could be a physiological feed-back mechanism in the control of proteolytic activity in the vicinity of cells.

Transin/stromelysin expression in rheumatoid synovium. A transformation-associated metalloproteinase secreted by phenotypically invasive synoviocytes

Transin is a neutral metalloproteinase whose mRNA was first isolated from rat fibroblasts that had undergone malignant transformation. The protein is highly expressed in malignant rather than benign animal tumors. Its human analog is stromelysin, a 51-kd metalloproteinase initially isolated from cultured human synoviocytes. Northern blot analysis demonstrated that rheumatoid arthritis synovial tissue contained significantly higher levels of stromelysin mRNA than did osteoarthritis synovial tissue. Cultured synoviocytes were also shown to express stromelysin mRNA, and an affinity-purified anti-peptide antiserum to stromelysin specifically immunoprecipitated the stromelysin protein from the conditioned medium of cultured explant rheumatoid synoviocytes. Immunohistochemical staining of rheumatoid synovium demonstrated specific cytoplasmic staining of cells of the synovial lining layer, stromal fibroblasts, and endothelial cells. Osteoarthritic synovia showed significantly less stromelysin staining. Similarly, rheumatoid synovia demonstrated marked nuclear staining for the proliferation- and transformation-associated Myc oncoprotein. In contrast, osteoarthritic synovia showed negligible staining. These results support the belief that the proliferative, invasive behavior of rheumatoid synoviocytes reflects the expression of biochemical features generally associated with phenotypically transformed, malignant tumors. Clearly not a malignancy, the rheumatoid synovium appears to be paracrine driven by mediators generated in local inflammatory milieu.

Sulfation of two tyrosine-residues in human complement S-protein (vitronectin)

Human S-protein (vitronectin) and hemopexin, two structurally related plasma proteins of similar molecular mass and abundance, were analyzed for tyrosine sulfation. Both proteins were synthesized and secreted by the human hepatoma-derived cell line Hep G2, as shown by immunoprecipitation from the culture medium of [35S]methionine-labelled cells. When Hep G2 cells were labelled with [35S]sulfate, S-protein, but not hemopexin, was found to be sulfated. Half of the [35S]sulfate incorporated into S-protein was recovered as tyrosine sulfate. The stoichiometry of tyrosine sulfation was approximately two mol tyrosine sulfate/mol S-protein. Examination of the S-protein sequence for the presence of the known consensus features for tyrosine sulfation revealed three potential sulfation sites at positions 56, 59 and 401. Tyrosine 56 is the most probable site for stoichiometric sulfation, followed by tyrosine 59 which appears more likely to become sulfated than tyrosine 401. Tyrosines 56 and 59 are located in the anionic region of S-protein which has no homologous counterpart in hemopexin. We discuss the possibility that tyrosine sulfation of the anionic region of S-protein may stabilize the conformation of S-protein in the absence of thrombin-antithrombin III complexes and may play a role in its binding to thrombin-antithrombin III complexes during coagulation.

Cloning of the genes for human stromelysin and stromelysin 2: differential expression in rheumatoid synovial fibroblasts

Stromelysin is a member of a gene family of metalloproteinases involved in extracellular matrix remodeling in normal and diseased processes. Primary cultures of rheumatoid synovial cells produce large amounts of metalloproteinase mRNA and proteins. We cloned a cDNA for human stromelysin from a rheumatoid synovial cell cDNA library, and we used the cDNA to isolate the gene for human stromelysin and a related gene, stromelysin 2. We sequenced parts of the genes and found that both are contained on approximately 14 kilobase pairs of DNA. Using an exon-containing fragment of the stromelysin 2 genomic clone as a specific probe in Northern blot analysis, we demonstrate the differential expression of stromelysin and stromelysin 2 in rheumatoid synovial cells, human foreskin fibroblasts, and rabbit synovial fibroblasts. In addition, using chimeric constructs of the stromelysin promoter linked to the bacterial gene chloramphenicol acetyltransferase (CAT), we show that the elements required for the tumor promoter phorbol myristate acetate (PMA), epidermal growth factor (EGF), and interleukin 1 beta (IL-1 beta) induction are contained on a 307 base pair fragment which includes approximately 270 base pairs (bp) of 5'-flanking DNA. The cloning of the human stromelysin and stromelysin 2 genes, the documentation of their differential expression, and the identification of transcriptional regulatory regions in the stromelysin gene will facilitate the study of metalloproteinase gene expression in normal processes and in diseases such as rheumatoid arthritis.

Transforming growth factor-beta causes partial inhibition of interleukin 1-stimulated cartilage degradation in vitro

We show that purified human transforming growth factor-beta (1-10ng/ml) inhibits interleukin 1-stimulated loss of proteoglycan from cartilage in vitro. Inhibition is incomplete, as interleukin 1 retains the ability to cause a dose dependent stimulation of proteoglycan release in the presence of high levels of transforming growth factor-beta (100ng/ml) although both basal and interleukin 1-stimulated levels can be reduced by up to 50 per cent. This observation, together with its ability to stimulate proteoglycan synthesis and to stimulate proteinase inhibitor production, suggests a possible role for transforming growth factor-beta in limiting cartilage proteoglycan loss in inflammatory conditions such as rheumatoid arthritis.

NGF induction of the gene encoding the protease transin accompanies neuronal differentiation in PC12 cells

Various proteases have been found to be released by the growth cones of developing neurons in culture and have been hypothesized to play a role in the process of axon elongation. We report here that nerve growth factor (NGF) induced the gene encoding the metalloprotease transin in PC12 cells with a time course coincident with the initial appearance of neurites by these cells. Acidic and basic fibroblast growth factors also stimulated transin mRNA expression and neurite outgrowth, whereas various other agents had no effects on either of these phenomena. In contrast, dexamethasone was found to inhibit the induction of transin mRNA when added with, or following, NGF treatment. Finally, we show that sequences contained within 750 bp of the 5' untranscribed region of the transin gene confer responsiveness to NGF and dexamethasone.

Collagenase is expressed by rabbit VX2 tumour cells in syngeneic and xenogeneic hosts

Specific antisera for the connective tissue metalloproteinases, collagenase, gelatinase (type IV collagenase) and stromelysin were used to study their respective localizations in both rabbit primary VX2 tumours and in lung metastatic deposits (frozen immediately after excision). Collagenase was found within some cells of the primary tumour and also bound to the extracellular matrix at discrete sites. Previous studies suggest that this matrix staining represents active enzyme. Stromelysin and gelatinase had a more limited distribution, particularly the latter, but both showed cell and matrix staining. In the lung metastases collagenase and stromelysin occurred less frequently, although both cell and matrix staining were observed; gelatinase was not seen. When rabbit VX2 cells were transplanted into nude mice they grew as a discrete nodule. Cells within this nodule stained with the antiserum to collagenase, which recognizes rabbit but not mouse enzyme, and thus demonstrated that cells of tumoural origin synthesize collagenase in vivo. Stromelysin was also co-localized with collagenase in some tumour cells.

Urokinase-type plasminogen activator biosynthesis is induced by the EJ-Ha-ras oncogene in CL26 mouse colon carcinoma cells

CL26 murine colon carcinoma cells express urokinase-type plasminogen activator (u-PA) mRNA and activity after transfection with the activated c-Ha-ras-I (EJ-ras) oncogene cloned from the EJ bladder carcinoma. PA activity and mRNA in control cells transfected with the non-mutated c-Ha-ras-I (CO-ras) gene remained negative. Ras mRNA was detected in EJ-ras- and CO-ras-transfected cells, but not in untransfected or pSV2-neo-transfected cells. These results indicate that u-PA biosynthesis can be modulated by EJ-Ha-ras-dependent pathways of signal transduction.

Transforming growth factor-beta regulation of collagenase, 72 kDa-progelatinase, TIMP and PAI-1 expression in rat bone cell populations and human fibroblasts

Quiescent cultures of normal fetal rat calvarial bone cell populations (RC I and RC IV) and human fibroblasts were incubated with 1.0 ng/ml TGF-beta and the conditioned culture media were processed individually to separate collagenase and 72 kDa-progelatinase from TIMP, the tissue inhibitor of matrix metalloendoproteinases, using mini-columns of heparin- and gelatin-Sepharose. Collagenase synthesis was decreased progressively by TGF-beta in fibroblasts despite a 1.6-fold increase in secreted protein levels and a approximately 1.8-fold increase in 72 kDa-progelatinase synthesis. The human fibroblasts and the osteoblast-enriched RC IV cells showed a greater TGF-beta-induced stimulation in 72 kDa-progelatinase levels over controls compared with the RC I cells. In contrast to RC IV cells, in which TIMP mRNA levels were increased 2.9-fold by TGF-beta, the constitutive level of TIMP transcripts in the RC I cells was greater than 20-fold over that of the RC IV cells, but was not elevated by TGF-beta. TGF-beta also increased TIMP expression in fibroblasts approximately 1.7-fold and PAI-1 levels approximately 5-fold in RC IV cells, and greater than 10-fold in fibroblasts.

Phorbol ester-responsive H-ras1 gene promoter contains multiple TPA-inducible/AP-1-binding consensus sequence elements

We have constructed recombinant DNA plasmids which carry both the aminoglycoside phosphotransferase (aph) gene and the chloramphenicol acetyl-transferase (CAT) gene linked to the human normal or mutant T24 H-ras1 promoter. We have transfected these plasmids into rat 208F fibroblasts using the calcium phosphate technique and selected for stable transformants by geneticin resistance. These transformants expressed CAT activity at low levels. However, when treated with the phorbol ester TPA, CAT levels increased substantially. Cells transfected with recombinant plasmids carrying a promoterless CAT gene did not respond to TPA. We have noted four motifs in the H-ras1 promoter region which resemble TPA-inducible and AP-1-binding consensus sequences. We suggest that AP-1-like proteins may play a role in control of H-ras1 transcription.

Effect of cytokines and growth factors on the expression of elastase activity by human synoviocytes, dermal fibroblasts and rabbit articular chondrocytes

Human synoviocytes, rabbit articular chondrocytes and human skin fibroblasts in culture were examined for their ability to express elastase activity. Latent enzyme activity degrading insoluble elastin was detected in the culture media of the three cell types and was completely abolished by metal chelating agents. Triton X-100 cell extracts were found to degrade a synthetic elastase substrate, N Succinyl-(Ala)3p-nitroanilide (SANA). The SANA-degrading activity of cell extracts could be attributed to a metalloprotease for fibroblasts and synoviocytes (100%) and to a metalloprotease associated with a cysteine protease for chondrocytes (70 and 30% respectively). This SANA-degrading activity was partly due to the combined action of an endo and an exopeptidase. Tumor Necrosis Factor-alpha (TNF-alpha) and Interferon-gamma (IFN-gamma) significantly enhanced the elastin degrading activity present in the culture media of both synoviocytes and chondrocytes. Interleukin-1 beta significantly increased the secretion of elastase by chondrocytes. By contrast, Transforming Growth Factor-beta (TGF-beta) reduced by 80 per cent the secretion of elastinolytic activity by chondrocytes but had not effect on other cell types.

Transforming growth factor beta in the control of epidermal proliferation

Transforming growth factor beta is a polypeptide growth factor with a multiplicity of diverse biologic effects. Increasingly, data support a role for TGF beta in the autocrine regulation of normal epithelial cell growth (Figure 1). Definition of the normal pathways for growth stimulation and inhibition of epithelial cell growth by autocrine peptides like TGF beta and TGF alpha undoubtedly will increase understanding of normal growth and development, embryogenesis, wound repair, and tumorigenesis.

Transforming growth factor-beta stimulates the expression of fibronectin by human keratinocytes

Transforming growth factor beta (TGF-beta) is a 25-kD protein which has regulatory activity over a variety of cell types. It is distinct from epidermal growth factor (EGF) and EGF analogs, and exerts its action via a distinct receptor. Its effect on proliferation or differentiation can be positive or negative depending on the cell type and the presence of other growth factors. It also modulates the expression of cellular products. TGF-beta causes fibroblasts to increase their production of the extracellular matrix components, fibronectin and collagen. Human keratinocytes (HK) are known to have TGF-beta receptors. We wished to study the effect of TGF-beta on the production of extracellular matrix proteins by human keratinocytes in culture. Human keratinocytes were grown in serum-free defined medium (MCDB-153) to about 70% confluence. Following a 16-h incubation in medium lacking EGF and TGF-beta, cells were incubated for 12 h in medium containing varying concentrations of EGF and TGF-beta. Cells were then labeled with 35S-methionine for 10 h in the same conditions. Labeled proteins from the medium were analyzed by SDS-PAGE and autoradiography. TGF-beta at 10 ng/ml induced a sixfold increase in the secretion of fibronectin, as well as an unidentified 50-kD protein. Thrombospondin production was also increased, but not over a generalized twofold increase in the production of all other proteins. EGF, at 10 ng/ml, caused a smaller additive effect. TGF-beta may be an important stimulator of extracellular matrix production by human keratinocytes.

Epidermal growth factor stimulates transcription of the c-jun proto-oncogene in rat fibroblasts

Some growth factor-induced genes, such as the c-fos gene, are activated rapidly and transiently without intervening protein synthesis. Others, like the rat transin gene, are activated more slowly but more durably and their activation requires prior protein synthesis. It is tempting to speculate that certain rapidly-activated genes code for transcription factors which interact directly with promoter regions of genes like the transin gene to trigger their expression. Unfortunately, little is known about the majority of primary response genes to support this hypothesis. The proto-oncogene c-jun codes for the transcription factor AP-1 or a closely related protein. We show that epidermal growth factor stimulates transcription of the c-jun gene in fibroblasts as a primary response. This supports the notion that increased expression of genes encoding transcription factors is an important element of the signal transduction mechanism, assuring the long-term transcriptional response of cells to growth factors.

Requirement for fos gene expression in the transcriptional activation of collagenase by other oncogenes and phorbol esters

Transcription from the c-fos promoter and from minimal promoter constructs carrying the phorbol ester-responsive element [12-O-tetradecanoylphorbol-13-acetate (TPA) responsive element (TRE)] corresponding to the sequence in the human collagenase gene is activated by elevated levels of the oncogene products v-src, c-Ha-ras, activated c-Ha-ras, and v-mos, as well as by phorbol ester. Elevated c- or v-fos expression stimulates TRE-dependent transcription but represses the c-fos promoter. Antisense fos sequences abolish basal and induced transcription from TRE constructs and derepress the c-fos promoter. These results establish a key role for fos in signal transduction and implicate the fos protein as a trans-activating and -repressing molecule.

TGF-beta inhibits growth factor-induced DNA synthesis in hamster fibroblasts without affecting the early mitogenic events

Transforming growth factor beta (TGF-beta) was found to inhibit (IC50 = 0.1 ng/ml) alpha-thrombin or FGF-induced mitogenicity in G0-arrested Chinese hamster lung fibroblasts. Growth factor-stimulated cells became rapidly insensitive to TGF-beta addition during their progression through G0/G1 suggesting that an early step of the mitogenic response was the target of TGF-beta action. Surprisingly, none of the well characterized early mitogenic events commonly triggered by growth factors was found to be affected by TGF-beta addition. These responses included: phosphoinositide breakdown, activation of protein kinase C as determined by EGF receptor down-modulation, subsequent rises in pHi, c-fos, and c-myc mRNA levels, ribosomal protein S6 phosphorylation, the increase in RNA and protein synthesis, induction of ornithine decarboxylase. Only the induction of thymidine kinase, a marker of entry in the S phase, was found to be repressed by TGF-beta, with maximal inhibition when TGF-beta was added early in G1. These results indicate that the inhibitory action of TGF-beta does not affect the growth factors signalling pathways but touches an early event different from those so far analyzed.

Restriction fragment length polymorphism analysis and assignment of the metalloproteinases stromelysin and collagenase to the long arm of chromosome 11

Collagenase and stromelysin are two metalloproteinases produced mainly by connective tissue cells and involved in the breakdown of the extracellular matrix. cDNA clones for both of these genes have been isolated and sequencing has shown them to be closely related. The collagenase and stromeylsin cDNA clones have been used to assign these genes to the long arm of chromosome 11 in the regions 11q21-22.1 and 11q22.2-22.3, respectively. This has been achieved using somatic cell hybrids and in situ hybridization. In addition a Taq1 restriction fragment length polymorphism has been demonstrated using the stromelysin cDNA.

Cloning of a complementary DNA for rabbit proactivator. A metalloproteinase that activates synovial cell collagenase, shares homology with stromelysin and transin, and is coordinately regulated with collagenase

Rabbit proactivator is a neutral metalloproteinase that activates another metalloproteinase, procollagenase, and degrades noncollagenous matrix. We describe the construction of an activator complementary DNA (cDNA) clone, which is 1.9 kb, that selects a 2.1-kb messenger RNA (mRNA) in Northern blot hybridizations. Nucleic acid sequence studies of the activator cDNA indicate 1) that it encodes protein Mr 53,881, 2) that this protein exhibits approximately 80% homology with rat transin, an oncogene-induced protein with a previously unknown function, and 3) that, in the first 172 residues, it is virtually identical to the rabbit metalloproteinase, stromelysin. Homology between rabbit activator and human skin collagenase is approximately 50%. Activator and collagenase mRNA are coordinately regulated; untreated cultures of rabbit synovial fibroblasts produce low levels of each protein, but addition of phorbol myristate acetate (10(-8)M) results in an increase in mRNA for both proteins by 2.5-5 hours. Adding all-trans-retinoic acid (10(-6)M) or dexamethasone (10(-7)M) to phorbol-stimulated cells coordinately suppresses both activator and collagenase mRNA. Our data suggest the existence of coordinately regulated metalloproteinases that are important in the modulation of connective tissue metabolism.

Transforming growth factor type beta can act as a potent competence factor for AKR-2B cells

Transforming growth factor type beta (TGF beta) is a pleiotropic regulator of cell growth with specific high-affinity cell-surface receptors on a large number of cells; its mechanism of action, however, is poorly defined. In this report, we utilized the mouse fibroblast line AKR-2B to explore the question of the temporal requirements during the cell cycle in regard to both the growth inhibitory and the growth stimulatory action of TGF beta. The results indicate that AKR-2B cells are most sensitive to the inhibitory action of TGF beta during early to mid-G1. In addition, TGF beta need be present only briefly (as little as 1 min) in order to exert its inhibitory effect on EGF-induced DNA synthesis. Likewise, the stimulatory effect of TGF beta in the absence of EGF requires only an equally brief exposure to TGF beta. Use of homogeneous 125I-labeled TGF beta in a cell-binding assay demonstrates that TGF beta bound to cell-surface receptors can readily exchange into the culture medium T1/2 = 120 min), helping to rule out the possibility that persistent receptor-bound TGF beta is the source of a continuous stimulus. The data indicate that TGF beta exposure induces a stable state in the cell (T1/2 = 20 h) similar to but distinct from the state of "competence" induced by platelet-derived growth factor (PDGF).

Expression of cell-cycle-dependent genes in serum stimulated cells whose entry into S phase is blocked by cytochalasin D

A low concentration (0.6 micrograms/ml) of cytochalasin D inhibits the initiation of DNA synthesis after serum stimulation of growth-arrested GC-7 cells. Since actin-containing structures are suggested to be involved in the transfer of the growth signal to nuclei and in the synthesis and transport of nascent RNA, the effect of cytochalasin D on the expression of cell-cycle-regulated genes after serum stimulation was studied by Northern blot analysis. Cytoplasmic accumulation of such mRNAs as or c-fos, c-myc, beta-actin an ornithine decarboxylase occurred in serum-stimulated cells regardless of the presence of cytochalasin D, whereas that of thymidine kinase and histone H3 was blocked by the drug.

Phorbol ester-inducible genes contain a common cis element recognized by a TPA-modulated trans-acting factor

The promoter regions of several phorbol diester-(TPA-) inducible genes (collagenase, stromelysin, hMT IIA, and SV40) share a conserved 9 bp motif. Synthetic copies of these closely related sequences conferred TPA inducibility upon heterologous promoters. Footprinting analysis indicated that these TPA-responsive elements (TREs) are recognized by a common cellular protein: the previously described transcription factor AP-1. A point mutation that eliminated the basal and induced activity of the TRE also interfered with its ability to bind AP-1. Treatment of cultured cells with TPA led to a rapid 3- to 4-fold increase in TRE binding activity, by a posttranslational mechanism. These results strongly suggest that AP-1 is at the receiving end of a complex pathway responsible for transmitting the effects of phorbol ester tumor promoters from the plasma membrane to the transcriptional machinery.

Transformation by Rous sarcoma virus induces a novel gene with homology to a mitogenic platelet protein

A cDNA clone, designated 9E3, was isolated from a chick embryo fibroblast (CEF) cDNA library. 9E3 mRNA was 20-fold higher in CEF following transformation by Rous sarcoma virus because of increased transcription rate. In CEF infected with temperature-sensitive mutants, increased 9E3 mRNA was found within 2 hr of a shift to permissive temperature. Nucleotide sequence and in vitro translation results indicate that 9E3 mRNA encodes an 11 kd polypeptide that is homologous to human connective tissue activating peptide III (CTAP-III), a mitogenic platelet alpha-granule protein, and to beta-thromboglobulin and platelet factor 4. The reported biological activities of CTAP-III suggest that elevated expression of 9E3 may play a role in producing some of the phenotypic features of RSV-transformed cells.