Enhanced jun gene expression is an early genomic response to transforming growth factor beta stimulation

Cytoskeleton regulates expression of genes for transforming growth factor-beta 1 and extracellular matrix proteins in dermal fibroblasts

Cytoskeleton not only controls cell morphology but also regulates cell growth, migration, differentiation, and gene expression, events which are fundamental to embryogenesis, carcinogenesis, and wound healing. We have recently reported that reorganization of cytoskeleton induces expression of mRNA for transforming growth factor-beta 1 (TGF-beta 1), collagenase, and tissue inhibitor of metalloproteinase-I (TIMP-I) in dermal fibroblasts. In this report we have examined the role of gene transcription in this induction. As judged by nuclear run-on assay, trypsin, EGTA (ethylene glycol-bis (beta-aminoethyl ether) N, N, N', N', tetra-acetic acid), or cytochalasin C (Chs) increased the rate of transcription of the TGF-beta 1 gene by 2.0, 2.7, and 1.6 fold, respectively, and of the collagenase gene by 5.3, 6.2, and 3.3 fold. The rate of transcription of the TIMP-I gene was increased by trypsin (4.3 fold) or EGTA (3.8 fold) but unaffected by Chs. Cytochalasin induced an increase in the rate of transcription of procollagen I (alpha 1), procollagen I (alpha 2), and fibronectin genes by 1.4, 1.5, and 1.9 fold respectively, while trypsinization or EGTA treatment had no or little effects on these gene. Since transcription of the TGF-beta 1 gene is believed to be largely governed by the activating protein 1 (AP1) complex, we also examined the expression of mRNA for c-fos and c-jun protoon-coproteins. Trypsinization induced rapid (within 30 min) and transient expression of c-fos mRNA. A 2.4 fold increase in c-jun mRNA was apparent after 4 hr and persisted for at least 24 hr. Actinomycin D (Act D) suppressed the induction of TGF-beta 1 mRNA by Chs but had less effect on the TGF-beta 1 mRNA in trypsinized cells which had been replated for 4 hr, suggesting that the half life of TGF-beta 1 mRNA is reduced in cells with a disassembled cytoskeleton. Simultaneous treatment with Chs and cycloheximide (Cxm) resulted in a superinduction of TGF-beta 1 mRNA by 88 +/- 23% (n = 4, P < 0.05), which was abrogated by preexposure to Act D. In contrast, the induction of collagenase mRNA by Chs was totally blocked by Cxm, indicating that the Cxm-mediated superinduction is selective and that protein synthesis is required for induction of this mRNA. Our results suggest that the activities of genes for proteins involved in the structure (Type I collagen and fibronectin), turnover (collagenase and TIMP-1) and regulation (TGF-beta 1) of extracellular matrix (ECM), are all governed at least in part by the status of the cytoskeleton. Since the cytoskeleton is reorganized during cell division, migration, and differentiation, these results may have implications for the regulation of ECM during such processes as embryogenesis, carcinogenesis, and wound healing.

Transforming growth factor-beta: the breaking open of a black box

Transforming growth factor-beta (TGF-beta) and its related proteins regulate broad aspects of body development, including cell proliferation, differentiation, apoptosis and gene expression, in various organisms. Deregulated TGF-beta function has been causally implicated in the generation of human fibrotic disorders and in tumor progression. Nevertheless, the molecular mechanisms of TGF-beta action remained essentially unknown until recently. Here, we discuss recent progress in our understanding of the mechanism of TGF-beta signal transduction with respect to the regulation of gene expression, the control of cell phenotype and the potential usage of TGF-beta for the treatment of human diseases.

Effect of transforming growth factor-beta1 on expression of aryl hydrocarbon receptor and genes of Ah gene battery: clues for independent down-regulation in A549 cells

An inhibitory effect on both constitutive and inducible expression of cytochrome P450 isoenzymes has been shown for different cytokines and growth factors. We previously described an inhibition of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced CYP1A1 mRNA and enzyme activity by transforming growth factor-beta1 (TGF-beta1) in human lung cancer A549 cells. In the present study, we report that not only TCDD-induced expression of CYP1A1 but also basal mRNA expression of CYP1A1, CYP1B1, and aryl hydrocarbon receptor (AHR) was down-regulated by TGF-beta1 in cells not treated with TCDD. In contrast, mRNA expression of the AHR partner protein Arnt (aryl hydrocarbon receptor nuclear translocator) was not influenced. Furthermore, TCDD-induced expression of CYP1B1 and NMO-1 was inhibited, and the IC50 values of 5-10 pM TGF-beta1 were in the same range as observed for inhibition of CYP1A1 and AHR mRNA expression. Transfection studies with a plasmid containing a luciferase reporter gene under control of two dioxin-responsive elements indicate an effect on AHR protein expression. Results of time-course studies revealed a parallel inhibition of AHR and CYP1 mRNA expression, indicating that TGF-beta1 is a direct negative regulator of transcription of these genes. The treatment of cells with cycloheximide led to a superinduction of TCDD-induced CYP1A1 and CYP1B1 mRNA expression and abolished the inhibitory effect of TGF-beta1 on basal as well as TCDD-induced CYP1 and AHR mRNA expression. TGF-beta1 seems not to influence the stability of AHR mRNA. The results suggest that TGF-beta1 induces rapid transcription and translation of an as-yet-unknown negative regulatory factor or factors that may directly regulate expression of AHR and genes of Ah gene battery.

Expression of c-fos and jun protooncogenes in ovine trophoblasts in relation to interferon-tau expression and early implantation process

Expression of c-fos and jun protooncogenes was analyzed in the ovine extraembryonic trophoblast from days 14-18 of gestation, using Northern and Western blotting and immunohistochemistry. This study was carried out in relation to the early implantation process and the expression of interferon-tau, which is secreted in large amounts for a few days before implantation. Our results demonstrated that c-fos, c-jun, and junB were differently expressed in the ovine trophoblast around the time of implantation. The c-fos mRNA and protein were detected at high levels prior to attachment and decreased thereafter, following the pattern of expression of interferon-tau, whereas c-jun expression was maintained at relatively high levels during the implantation process. By contrast, the levels of junB mRNA and protein decreased prior to attachment. Immunohistochemical studies indicated that JunB, like C-Fos and interferon-tau, was no longer expressed in the trophoblastic cells which had established cellular contacts with the uterine epithelium. A striking finding in this study is the temporal correlation between the accumulation of c-Fos and c-Jun proteins and the expression of the interferon-tau (days 14 and 15 of gestation). We also showed by gel-retardation assays that an AP-1-like site present in the promoter of one interferon-tau gene was functional in vitro, as judged by its ability to bind day-15 trophoblast nuclear protein extracts. Nuclear proteins binding to this site had the characteristics of AP-1, as judged by the ability to be competed efficiently by a consensus TRE (12.0-tetradecanoyl phorbol 13-acetate-responsive element)-site oligonucleotide and by antibodies to c-Fos and Jun proteins. These results suggest that Fos and Jun could form regulatory complexes of interferon-tau expression and/or are regulated by common mechanisms which are still unknown.

Effects of transforming growth factor-beta 1 and phorbol ester on PAI-1 and PA genes in human lung cells

Transforming growth factor-beta (TGF-beta) mediates the production of extracellular matrix proteins, proteases and protease inhibitors in epithelial cells. Both TGF-beta and phorbol-12-myristate-13-acetate (PMA) exert both positive and negative effects on mitogenesis in these as well as other cell types. Phorbol esters act through stimulation of protein kinase C (PKC) and are among the most potent tumor promoters known. The present study was conducted to determine whether the effect of TGF-beta in human non-small cell lung cancer (NSCLC) and normal human bronchial epithelial (NHBE) cells parallels that of the phorbol esters and whether this effect of TGF-beta involves PKC. TGF-beta 1 and PMA increased expression of TGF-beta 1 mRNA 24 hr after their addition to both NSCLC and NHBE cells. The effects of these agents on expression of the mRNAs for TGF-beta 2 and TGF-beta 3 were more complex; while TGF-beta 2 and TGF-beta 3 mRNAs increased transiently in response to TGF-beta 1 in NHBE cells and TGF-beta 3 mRNA increased transiently in some NSCLC cells, expression of these mRNAs decreased in most of these cells in response to PMA with the exception of the carcinoid NCI-H727 where TGF-beta 2 mRNA increased dramatically, TGF-beta 1 and PMA both caused a persistent increase in expression of the mRNAs for both plasminogen activator inhibitor-1 (PAI-1) and plasminogen activator (PA) up to 24 hr in most NSCLC cells, with the increase in PAI-1 mRNA beginning several hours before that of PA mRNA. In contrast, while TGF-beta 1 also increased expression of PAI-1 mRNA in NHBE cells, the expression of PA mRNA decreased simultaneously. The effect of PMA on PAI-1 and PA mRNAs was opposite of TGF-beta 1 in these cells, with expression of PAI-1 mRNA decreasing and PA mRNA increasing after addition of PMA. These data show that there is parallel regulation of the genes for TGF-beta 1, PAI-1 and PA by TGF-beta 1 and PMA in NSCLC, but differential regulation of the genes for PAI-1 and PA by these agents in NHBE cells. The responses of the mRNAs and proteins of TGF-beta 1, PAI-1 and PA to TGF-beta 1 and PMA were inhibited by the serine/ threonine kinase inhibitor H7 in NSCLC cells. Treatment of NSCLC cells with TGF-beta 1 and PMA resulted in a persistent increase in the expression of fibronectin mRNA and protein. This response was blocked by the addition of H7. Inhibition of these effects by H7 in NSCLC cells suggests that H7 blocks TGF-beta responses by inhibiting a protein serine/threonine kinase(s). Because the effects of TGF-beta and PMA on the different TGF-beta isoforms, PA, PAI and fibronectin in NHBE and NSCLC cells are complex, our data suggest that there are distinct mechanisms for controlling the different TGF-beta isoforms, PA, PAI and extracellular matrix proteins in normal lung and lung cancer cells.

Regulation of tissue inhibitor of metalloproteinases-3 gene expression by transforming growth factor-beta and dexamethasone in bovine and human articular chondrocytes

Physiological and pathological degradation of cartilage extracellular matrix (ECM) is regulated by the balance between tissue inhibitors of metalloproteinases (TIMPs) and matrix metalloproteinases (MMPs). We examined the potential of chondrocytes from normal bovine or human osteoarthritic (OA) cartilage to express RNA for the new inhibitor TIMP-3 and studied its regulation by an inducer of matrix synthesis, transforming growth factor-beta (TGF-beta). Freshly released chondrocytes constitutively expressed three transcripts of TIMP-3 that are induced by serum factors. In primary cultures of chondrocytes, one of these factors, TGF-beta, increased TIMP-3 mRNA in a dose-dependent fashion that required de novo protein synthesis and transcription. TGF-beta did not alter stability of the TIMP-3 transcripts in RNA decay time-courses, suggesting a transcriptional control. Nuclear run-on assays confirmed increased rate of TIMP-3 gene transcription by TGF-beta. An antiinflammatory glucocorticoid, dexamethasone, inhibited the basal, and suppressed partially the TGF-beta-inducible, TIMP-3 expression in primary bovine and human chondrocytes. DNA sequencing of bovine TIMP-3 cDNA revealed an open reading frame of a 211-amino-acid protein containing signal peptide and 12 conserved cysteines. The encoded protein differed from human TIMP-3 at four positions. The constitutive expression and evolutionary conservation of TIMP-3 imply its important function. TIMP-3 induction by TGF-beta suggests the role of this factor and TIMP-3 in cartilage remodeling with important implications for arthritis.

Role of c-Jun and proximal phorbol 12-myristate-13-acetate-(PMA)-responsive elements in the regulation of basal and PMA-stimulated plasminogen-activator inhibitor-1 gene expression in HepG2

Experiments were designed to clarify the role of c-Jun/c-Fos and of putative phorbol 12-myristate-13-acetate-(PMA)-responsive elements (TREs) in the induction of plasminogen-activator inhibitor 1 (PAI-1) gene transcription in the human hepatoma cell line HepG2 by activators of protein kinase C (PKC). Treatment of HepG2 cells with the phorbol ester PMA or serum rapidly and transiently increased c-Jun and c-Fos mRNA and protein levels prior to PAI-1 induction. This induction of PAI-1 gene transcription was found to be dependent on ongoing protein synthesis. An essential role of c-Jun and c-Fos in basal and PMA-stimulated transcription of the PAI-1 gene is demonstrated by our finding that antisense c-jun and c-fos oligodeoxynucleotides both strongly reduced basal and PMA-stimulated PAI-1 synthesis. Since it has already been shown that two TREs between positions -58 and -50 and between -79 and -72 of the PAI-1 promoter are essential for basal and PMA-induced PAI-1 promoter activity ([16]), we examined binding of nuclear proteins to these elements. The protein-binding activity to the TRE between positions -79 and -72 shows very strong PMA induction of an unknown factor, which is not related to c-Jun or c-Fos. The TRE binding between positions -58 and -50 forms two complexes, both containing c-Jun protein. The faster migrating complex primarily contains c-Jun homodimers. The amount of the faster migrating complex is enhanced more than 30-fold in PMA-treated cells, due to a strongly increased binding of c-Jun homodimers and, to a minor extent, to binding of c-Jun/c-Fos heterodimers. Dissociation experiments suggest that the c-Jun/c-Fos heterodimers bind with much lower affinity compared to binding of c-Jun homodimers. Together with the finding that both antisense c-jun and antisense c-fos oligodeoxynucleotides reduced the amount of c-Jun homodimer, we conclude that binding of c-Jun homodimer to the TRE at positions -58 to -50 is important in the basal activity and PMA activation of the PAI-1 promoter in HepG2 cells.

Cell-specific induction of distinct oncogenes of the Jun family is responsible for differential regulation of collagenase gene expression by transforming growth factor-beta in fibroblasts and keratinocytes

Transforming growth factor-beta (TGF-beta) plays a major role in regulating connective tissue deposition by controlling both extracellular matrix production and degradation. In this study, we show that TGF-beta transcriptionally represses both basal and tumor necrosis factor-alpha-induced collagenase (matrix metalloprotease-1) gene expression in dermal fibroblasts in culture, whereas it activates its expression in epidermal keratinocytes. We demonstrate that this differential effect of TGF-beta on collagenase gene expression is due to a cell type-specific induction of distinct oncogenes of the Jun family, which participate in the formation of AP-1 complexes with different trans-activating properties. Specifically, our data indicate that the inhibitory effect of TGF-beta in fibroblasts is likely to be mediated by jun-B, based on the following observations: (a) TGF-beta induces high levels of jun-B expression and (b) over-expression of jun-B mimics TGF-beta effect in inhibiting basal collagenase promoter activity and preventing tumor necrosis factor-alpha-induced trans-activation of the collagenase promoter. In contrast, TGF-beta induction of collagenase gene expression in keratinocytes is preceded by transient elevation of c-jun proto-oncogene expression. Over-expression of c-jun leads to trans-activation of the collagenase promoter in both cell types, suggesting that c-jun is a ubiquitous inducer of collagenase gene expression. Transfection of keratinocytes with an antisense c-jun construct together with a collagenase promoter/reporter gene construct inhibits basal and TGF-beta-induced up-regulation of the collagenase promoter activity, implying that c-jun mediates TGF-beta effect in this cell type. Collectively, our data suggest differential signaling pathways for TGF-beta in dermal fibroblasts and epidermal keratinocytes, leading to cell type-specific induction of two AP-1 components with opposite transcriptional activities.

Signal transduction and TGF-beta superfamily receptors

The TGF-beta superfamily includes a large number of related growth and differentiation factors expressed in virtually all phyla. Superfamily members bind to specific cell surface receptors that activate signal transduction mechanisms to elicit their effects. Candidate receptors fall into two primary groups, termed type I and type II receptors. Both types are serine/threonine kinases. Upon activation by the appropriate ligand, type I and type II receptors physically interact to form hetero-oligomers and subsequently activate intracellular signaling cascades, ultimately regulating gene transcription and expression. In addition, TGF-beta binds to a third receptor class, type III, a membrane-anchored proteoglycan lacking the kinase activity typical of signal transducing molecules. Type III receptors appear to regulate ligand availability to type I and type II receptors. Although a number of transduction mechanisms may be available to TGF-beta superfamily members, evidence gathered through the use of specific kinase and G-protein inhibitors and through assays measuring activation and levels of signaling intermediates suggests that at least one signaling pathway interacts with Ras and Raf proteins via a G-protein intermediate. Raf begins the cytoplasmic kinase cascade that leads to gene regulation. The myriad responses regulated by TGF-beta superfamily members makes the understanding of signal transduction mechanisms utilized by these proteins of great interest to a wide range of biological disciplines.

Regulation of primary response and specific genes in adrenal cells by peptide hormones and growth factors

Using cultured bovine adrenal fasciculata cells (BAC), we investigated the effects of two hormones, corticotropin (ACTH) and angiotensin II (Ang-II) and two growth factors, insulin-like growth factors I (IGF-I) and transforming growth factor beta 1 (TGF beta 1), on the mRNA levels of nuclear proto-oncogenes of the Fos and Jun families and on the mRNA levels of genes expressed in BAC coding for ACTH and AT1 receptors, cytochrome P450scc and P450 17 alpha and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD). ACTH and IGF-1 increased c-fos and jun-B mRNA levels early with later increases in the levels of mRNA for the ACTH receptor and the three steroidogenic enzymes, and enhanced steroidogenic responses to both ACTH and Ang-II. In contrast, Ang-II increased mRNA coding for the three proto-oncogenes (cfos, c-jun, and jun-B), decreased those for P450 17 alpha and 3 beta-HSD, and caused marked homologous and heterologous steroidogenic desensitization. TGF beta 1 increased only jun-B mRNA and markedly reduced BAC-differentiated functions and steroidogenic responsiveness to both ACTH and Ang-II. The long-term effects of ACTH on human adrenal fasciculata cells were comparable with those observed in BAC, whereas the long term effects of Ang-II and TGF beta 1 were different from those observed in BAC. Whether these species-specific differences are related to a different effect of these factors on proto-oncogene expression is not yet known.

Transforming growth factor-beta system and its regulation by members of the steroid-thyroid hormone superfamily

TGF-beta s and their receptors are expressed ubiquitously, and they act as key regulators of many aspects of cell growth, differentiation, and function. Steroid action on target tissues is often associated with increase in TGF-beta isoforms. Regulation of TGF-beta expression and activation is crucial for normal development and growth control. The loss of responsiveness of different tumor cells to the antiproliferative effects of TGF-beta is a common feature in carcinogenesis. Multiple changes are required for the cells to gain complete resistance to TGF-beta growth inhibition (Fynan and Reiss, 1993; Kimchi et al., 1988; Samuel et al., 1992). Although many tumor cells are not growth inhibited by TGF-beta, they respond to TGF-beta treatment by changes in the expression of matrix components and enhanced proteolytic activity (KeskiOja et al., 1988). Agents that induce TGF-beta production in target tissues can have a chemopreventive or chemotherapeutic value for the management of epithelial malignancies. Conversely, data supporting a positive role for TGF-beta in established tumor progression are beginning to emerge (Arteaga et al., 1993a,b; Barrett-Lee et al., 1990; Arrick et al., 1992 ; E. A. Thompson et al., 1991). In later stages of tumor development, cell proliferation is often not inhibited by TGF-beta, and tumor cells secrete large amounts of this growth factor (Fynan and Reiss, 1993). In vivo TGF-beta secreted by tumor or stromal cells can influence host responses such as a natural killer cell function and thus indirctly support tumor cell viability (Arteaga et al., 1993b). TGF-beta may also affect tumor growth indirectly by stromal effects and promotion of angiogenesis. TGF-beta may also be involved in the progression of breast tumors from the steroid-sensitive to steroid-insensitive state (King et al., 1989). Understanding of the net effect of TGF-beta in different stages of tumor development is critical for the evaluation of its therapeutic value in cancer treatment.

Expression of vascular endothelial growth factor in renal vascular disease and renal allografts

Vascular endothelial growth factor (VEGF) is a dimeric glycoprotein that exerts a proliferative effect specifically on endothelial cells. VEGF can increase vascular permeability and collagenase activity, is chemotactic for monocytes, and may dilate blood vessels. It can be induced by phorbol ester and cAMP in both mesenchymal and epithelial cells. In vitro cell culture experiments suggest that VEGF is upregulated by oxygen deprivation. In this study we tested whether in vivo acute and/or chronic reduction of renal blood flow by vascular obstruction would result in increased expression of VEGF mRNA and protein. Three normal kidneys, five human kidneys with narrowing of preglomerular vessels by vascular rejection or by vasculitis, and eight kidneys with nephrosclerosis and/or diabetic nephropathy were examined. In situ hybridization with 35S-labelled riboprobes showed a pronounced expression of VEGF mRNA in acutely hypoxic proximal and distal tubules of both the cortex and medulla; VEGF protein was demonstrated in the epithelia of these tubules by immunohistochemistry. In kidneys with chronically reduced blood flow, the majority of atrophic tubules were negative for VEGF mRNA and protein, although interstitial cells expressed VEGF mRNA. In arcuate arteries showing intimal and adventitial fibrosis, some medial smooth muscle cells were positive for VEGF mRNA. In glomeruli with segmental sclerosis, viable podocytes showed a prominent signal for VEGF mRNA. Mesangial cells did not express VEGF in the cases studied. It is possible that hypoxia itself led to the upregulation of VEGF in tubular epithelia and vascular smooth muscle cells. The vasodilatory and permeability-promoting effects of the endothelial growth factor produced by damaged tubular epithelia may constitute a mechanism to alleviate a decrease in blood flow and substrate availability and to re-establish vascular integrity.

Expression of transforming growth factor-beta 1 in mouse skin during the acute phase of radiation damage

Transforming growth factor-beta (TGF beta 1) plays a central role in wound healing, so its perturbation by radiation may contribute to the acute and late effects seen in irradiated skin. TGF beta 1 mRNA expression was measured by PCR, in the skin of the CD1 and CBA mouse, exposed to Sr-90 beta from an 11-mm diameter source. TGF beta 1 mRNA expression increased sharply after doses between 1 and 10 Gy and plateaued at approximately 200% above controls after doses between 20 and 50 Gy. Immunohistochemistry showed that the TGF beta 1 protein was confined to the dermis and suprabasal cells with none in basal cells. A dose of 50 Gy produces an acute desquamative reaction in 100% of mice that is resolved in 30 days. After the same dose, TGF beta 1 mRNA expression fell below the controls at 3 h (-9.4% in the CD1 and -44% in the CBA mouse); rose sharply at 6-12 h (+124% CD1, +230% CBA), returned to control levels by 24-48 h, then rose progressively to approximately 200% above the controls between days 7 and 14. TGF beta 1 mRNA expression remained elevated at 100-200% above controls until the end of the experiment at 55 days. The significance of these changes in TGF beta 1 is discussed in the context of the early stress response reaction to radiation, the acute inflammatory and the later chronic fibrosis of the skin.

Shortsighted acts in the decapentaplegic pathway in Drosophila eye development and has homology to a mouse TGF-beta-responsive gene

Differentiation in the Drosophila eye imaginal disc traverses the disc as a wave moving from posterior to anterior. The propagation of this wave is driven by hedgehog protein secreted by the differentiated cells in the posterior region of the disc. Hedgehog induces decapentaplegic expression at the front of differentiation, in the morphogenetic furrow. We have identified a gene, shortsighted, which is expressed in a hedgehog-dependent stripe in the undifferentiated cells just anterior to the furrow and which appears to be involved in the transmission of the differentiation-inducing signal; a reduction in shortsighted function leads to a delay in differentiation and to a loss of photoreceptors in the adult. shortsighted is also required for a morphogenetic movement in the brain that reorients the second optic lobe relative to the first. shortsighted encodes a cytoplasmic leucine zipper protein with homology to a mouse gene, TSC-22, which is transcriptionally induced in response to TGF-beta.

Early gene responses associated with transforming growth factor-beta 1 growth inhibition and autoinduction in MCF-7 breast adenocarcinoma cells

In the human breast carcinoma cell line (MCF-7), exogenous TGF-beta 1 induces a dose-dependent inhibition of cell proliferation. In a MCF-7 cell subline [MCF-7(-)], which has an undetectable level of type II TGF-beta receptor, exogenous TGF-beta 1 does not inhibit cell proliferation but is still able to induce its own message. In both cell lines, TGF-beta 1 stimulates expression of c-jun, whereas a rapid, transient and marked increase in c-fos mRNA is only observed in the MCF-7 cells sensitive to the growth inhibitory effect of TGF-beta 1. Depletion of protein kinase C abolishes the c-fos but not the c-jun response to TGF-beta 1. Our results suggest that growth inhibition and autoinduction by TGF-beta 1 are mediated by different signalling pathways. In addition, a PKC-dependent increase in c-fos expression seems to be associated with the growth inhibitory effect of TGF-beta 1.

Beta IG-H3, a novel secretory protein inducible by transforming growth factor-beta, is present in normal skin and promotes the adhesion and spreading of dermal fibroblasts in vitro

We have previously identified a gene, beta ig-h3, which is highly induced in A549 cells (human lung adenocarcinoma) after growth arrest by transforming growth factor-beta. The beta ig-h3 gene encodes a 683-amino-acid secretory protein termed beta IG-H3, and treatment of several cell lines with transforming growth factor-beta results in increased secretion of beta IG-H3 into cell culture supernatants. In this report, we further characterize beta IG-H3 with respect to its synthesis and function. Primary human foreskin fibroblasts grown in monolayer culture produced beta IG-H3 mRNA and secreted beta IG-H3 protein into the growth media. Treatment of these cells with transforming growth factor-beta led to an increase in beta IG-H3 mRNA and protein. Cells grown on three-dimensional scaffolds secreted beta IG-H3 into the extracellular matrix, as judged by immunostaining with anti-beta IG-H3 antibodies. beta IG-H3 was also detected in normal human skin, especially in the papillary dermis. Finally, we show that recombinant beta IG-H3 supported attachment and spreading of dermal fibroblasts, suggesting that beta IG-H3 may function as an extracellular attachment protein in skin.

Transforming growth factor beta 1 modulates angiotensin II-induced calcium influx in vascular smooth muscle

The modulatory effects of transforming growth factor beta 1 (TGF beta 1) on the angiotensin II (Ang II)-induced increase in cytosolic free calcium concentration ([Ca2+]i) were investigated in vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). [Ca2+]i in VSMC was measured using the fluorescent dye fura-2. When TGF beta 1 was applied 30s prior to Ang II, the Ang II-induced [Ca2+]i increase was significantly enhanced in VSMC from SHR (P < 0.05 compared to control), whereas after the preincubation with TGF beta 1 for 30 min, the Ang II-induced [Ca2+]i increase was significantly reduced in VSMC from both strains. Using the manganese-quenching technique, it was confirmed that short-term exposure to TGF beta 1 enhanced the Ang II-induced trans-plasma-membrane calcium influx in SHR. The inhibition of protein kinase C by calphostin C abolished the stimulatory effect of TGF beta 1 on the Ang II-induced [Ca2+]i increase. It is concluded that TGF beta 1 modulates the Ang II-induced calcium handling in VSMC.

Transforming growth factor beta activation of p44mapk in proliferating cultures of epithelial cells

Transforming growth factor-beta (TGF-beta) is a potent growth inhibitor of a variety of epithelial cell types. The primary signaling mechanism involved in mediating this and other cellular effects of TGF-beta is still unknown. We report here that both TGF-beta 1 and TGF-beta 2 resulted in a rapid activation of mitogen-activated protein kinase (MAPK) p44mapk, occurring within 5-10 min of growth factor addition. This effect occurred in exponentially proliferating cultures of intestinal epithelial (IEC) 4-1 cells under conditions in which DNA synthesis was inhibited by 95% to 98%. Furthermore, TGF-beta 2 induced a sustained activation of p44mapk under these conditions, lasting for at least 90 min after initial growth factor treatment. Another TGF-beta-sensitive epithelial cell line (CCL 64) displayed a similar rapid increase in p44mapk activity when treated with TGF-beta 1. In contrast, in IEC 4-6 cells that are resistant to TGF-beta effects on growth and DNA synthesis, TGF-beta 2 treatment did not result in an activation of p44mapk. In contrast to the results in proliferating cultures, treatment of quiescent cultures of IEC 4-1 cells with TGF-beta 2 resulted in no significant change in either DNA synthesis or p44mapk activity within 15 min of TGF-beta addition. In contrast, addition of the growth-stimulatory combination of factors (epidermal growth factor + insulin + transferrin = EIT) to quiescent and proliferating IEC 4-1 cells stimulated DNA synthesis and resulted in a sustained activation of p44mapk. Together, our results suggest an association between activation of p44mapk and both TGF-beta-mediated growth inhibition and EIT-mediated growth stimulation. This suggests that the specificity for the cellular effects of growth factors may not occur at the level of MAPK activation per se, but rather at downstream events that include phosphorylation of distinct transcriptional complexes and activation of a select assortment of genes. With regard to TGF-beta specifically, we have proposed a model to explain how activation of p44mapk may be associated with a growth-inhibitory response.

Requirements for transforming growth factor-beta regulation of the pro-alpha 2(I) collagen and plasminogen activator inhibitor-1 promoters

Experiments were designed to clarify the role of several proteins, junB, retinoblastoma protein (RB), and the transforming growth factor-beta (TGF-beta) receptors that are potential intermediates in TGF-beta activation of the alpha 2(I) collagen promoter. Treatment of NIH-3T3 cells with TGF-beta increased the activity of a transiently transfected murine alpha 2(I) collagen promoter (nucleotides -350 to +54) fused to a luciferase reporter gene 9-fold. Cotransfection of a junB stimulated the basal activity of the alpha 2(I) collagen promoter 93-fold, respectively. Expression of antisense junB RNA attenuated the effect of TGF-beta. Simian virus 40 large T antigen, an inhibitor RB function, did not prevent TGF-beta effects on the alpha 2(I) collagen promoter. A chimeric receptor containing the extracellular domain of the colony-stimulating factor-1 receptor and the intracellular domain of the type I TGF-beta receptor enhanced alpha 2(I) collagen promoter activity 4.8-fold, whereas a similar chimera containing the type II receptor intracellular domain had much weaker effects. Similar results were obtained with a plasminogen activator inhibitor-1 promoter, previously shown to be activated by TGF-beta through AP-1 elements. We conclude that TGF-beta activates the alpha 2(I) collagen and plasminogen activator inhibitor-1 promoters in NIH-3T3 cells through junB and the type I TGF-beta receptor kinase domain.

Malignant transformation by H-ras results in aberrant regulation of ribonucleotide reductase gene expression by transforming growth factor-beta 1

Ribonucleotide reductase is a key rate-limiting and regulatory step in DNA synthesis and plays a crucial role in the coordination of DNA synthesis, DNA repair, and cell proliferation. The present study demonstrates a link between alterations in TGF-beta 1 regulation during malignant conversion and the expression of ribonucleotide reductase. H-ras-transformed mouse 10T1/2 cell lines exhibiting malignant potential were examined for possible TGF-beta 1-mediated alterations in ribonucleotide reductase expression. Selective induction of ribonucleotide reductase gene expression occurred, since only H-ras-transformed highly metastatic cells exhibited marked elevations in ribonucleotide reductase expression, whereas nontransformed normal 10T1/2 cells were unaffected by TGF-beta 1 treatment. These changes occurred without any detectable modifications in DNA synthesis rates, suggesting that these changes were regulated by a novel mechanism independent of the S-phase of the cell cycle. Furthermore, this TGF-beta 1-mediated regulation of ribonucleotide reductase expression was shown to occur through an autocrine mechanism. TGF-beta 1-modulated regulation of ribonucleotide reductase expression requires de novo protein synthesis and involves, at least in part, transcriptional and post-transcriptional events. Furthermore, evidence is presented to suggest a possible role for protein kinase C-mediated events, protein phosphatases, and G-protein-coupled events in the TGF-beta 1-mediated regulation of ribonucleotide reductase expression in H-ras-transformed malignant cells. TGF-beta 1 regulation of ribonucleotide reductase in highly malignant cells appears to be complex and multifaceted and constitutes an integral part of an altered growth regulatory program.

Activin A and retinoic acid synergize in cyclooxygenase-1 and thromboxane synthase induction during differentiation of J774.1 macrophages

The murine macrophage cell line J774.1 was used to study the development of prostanoid biosynthesis under the influence of activin A and retinoic acid. Treatment of cells with 3 nM activin A for 48 h increased the biosynthesis of the prostaglandins E2, D2, F2 alpha and thromboxane A2 more than fourfold due to an induction of cyclooxygenase-1 while cyclooxygenase-2 was unaffected. Transforming growth factor-beta acted in a similar way. Retinoic acid, when present alone, was without effect on the total cyclooxygenase products and only slightly changed the pattern of prostanoids. However, when coincubated with activin A, retinoic acid specifically induced the synthesis of thromboxane-A-synthase-specific mRNA and induced an increase in enzyme activity with a synergistic effect on cyclooxygenase-1 protein and mRNA. JunB, but not c-jun, mRNA expression was found under these conditions in addition to a transient c-fos mRNA increase. The combination of activin A and retinoid acid may be regarded as a differentiation model to study the development of cell-specific prostanoid patterns in macrophages and possibly other differentiating cells.

Regulation of the expression of the VEGF/VPS and its receptors: role in tumor angiogenesis

Vascular endothelial growth factor (VEGF)/vascular permeability factor (VPS) plays a crucial role for the vascularization of tumors including breast cancers. Tumors produce ample amounts of VEGF, which stimulates the proliferation and migration of endothelial cells (ECs), thereby inducing tumor vascularization by a paracrine mechanism. VEGF receptors (VEGF-Rs) are highly expressed by the ECs in tumor blood vessels. VEGF expression can be induced in various cell types by a number of stimuli including hypoxia, differentiation, growth factors and tumor promoters of the phorbol ester class, such as TPA. The VEGF inductive pathways comprise kinases, oncogenes, tumor suppressor genes, and steroid hormone transcription factors, many of which seem to converge on the activator protein (AP-1) transcription factor. Much less is known about the regulation of VEGF-R expression, which is restricted to ECs. This expression is greatly enhanced in diseased tissue such as solid tumors. So far, it appears that growth factors, cytokines, and tumor promoters are involved in the control of VEGF-R expression. Here we review current knowledge about the regulation of the expression of VEGF and its receptors.

TGF-beta regulation of nuclear proto-oncogenes and TGF-beta gene expression in normal human osteoblast-like cells

Transforming growth factor-beta (TGF-beta) is present in high levels in bone and plays an important role in osteoblast growth and differentiation. In order to dissect the molecular mechanisms of action of TGF-beta on osteoblasts, the effects of TGF-beta on the steady state mRNA levels of c-fos, c-jun, and jun-B proto-oncogenes on normal human osteoblast-like cells (hOB) and a transformed human osteoblast cell line (MG-63) were measured. Treatment of hOBs with 2 ng/ml of TGF-beta 1 resulted in a rapid increase in c-fos mRNA levels as early as 15 min post-treatment. A maximum (10-fold) increase was observed at 30 min after TGF-beta treatment followed by a decrease to control values. Similar responses were measured whether the cells were rapidly proliferating or quiescent. TGF-beta 1 induced jun-B mRNA levels more gradually with steady increase initially observed at 30 min and a maximum induction measured at 2 h post-TGF-beta treatment. In contrast, TGF-beta treatment caused a time dependent decrease in the c-jun mRNA levels, an opposite pattern to that of jun-B mRNA. Treatment of hOBs with TGF-beta 1 in the presence of actinomycin-D abolished TGF-beta 1 induction of c-fos mRNA, suggesting that TGF-beta action is mediated via transcription. In the presence of cycloheximide, TGF-beta causes super-induction of c-fos mRNA at 30 min, indicating that the c-fos expression by TGF-beta is independent of new protein synthesis. Further, transfection of 3 kb upstream region of jun-B promoter linked to a CAT reporter gene into ROS 17/2.8 cells was sufficient to be regulated by TGF-beta 1. Interestingly, TGF-beta treatment also increased the mRNA levels of TGF-beta 1 itself at 4 h post TGF-beta treatment, with a maximum increase observed at 14 h of treatment. TGF-beta 1 treatment for 30 min were sufficient to cause a delayed increase in TGF-beta protein secretion within 24 h. These data support that TGF-beta has major effects on hOB cell proto-oncogene expression and that the nuclear proto-oncogenes respond as rapid, early genes in a cascade model of hormone action.

Regulation of connective tissue synthesis in systemic sclerosis

Excessive connective tissue deposition in the skin and other organs is the pathologic hallmark of systemic sclerosis (SSc), and fibrosis accounts for much of the chronic morbidity of this disease. Unregulated production of collagen in SSc skin fibroblasts has been demonstrated both in vivo and in vitro, and is considered to be a critical process in the development of fibrosis. In addition to collagen, other components of the extracellular matrix are also overexpressed in SSc fibroblasts, and may be important in the functional alterations of connective tissue. The transcriptional activity of several genes coding for matrix macromolecules is upregulated in SSc fibroblasts. The pleiotropic signaling molecule transforming growth factor-beta (TGF beta) is likely to be intimately involved in initiating and perhaps perpetuating the fibrotic response in SSc. TGF beta, a potent profibrotic cytokine, is highly expressed in endothelial cells, in fibroblasts near blood vessels, and in perivascular inflammatory cells in involved tissues in SSc. The apparent failure of SSc fibroblasts to down-regulate their collagen synthesis when cultured in a three-dimensional matrix suggest an additional mechanism for the maintenance of unregulated collagen production in these cells. Finally, subpopulations of fibroblasts with an activated biosynthetic phenotype may become dominant in SSc. Therefore, persistent elevation of extracellular matrix gene expression in SSc tissues may be the result of a series of events representing the interaction of genetic and hormonal factors. A precise delineation of the mechanisms of fibroblast activation is needed for understanding the pathogenesis of SSc, and for the rational design of therapeutic interventions aimed at interfering with the fibrotic process.

Initiation of growth inhibition by TGF beta 1 is unlikely to occur in G1

Type beta transforming growth factors represent a family of polypeptides that modulate growth and differentiation. They exert their effect on target cells through interaction with multiple cell surface receptors. Transforming growth factor-beta 1 has a strong inhibitory action on cell division in mink lung CC164 cells, a process that is initiated by immediate induction of junB and phosphorylation of nuclear protein followed by a reduced expression of cdk4. However, its signal transduction pathways are still unresolved. In this study we report a detailed analysis of cell kinetic events following addition of transforming growth factor-beta 1 to mink lung CCL64 cells. We show that transforming growth factor-beta 1 reduces [3H]thymidine incorporation after a delay of 8 hours, which reaches its nadir at 16 hours. The reduced growth rate is maintained for at least 48 hours as shown by flow cytometric analysis of DNA content. Using time-lapse video microscopy it was shown that control cells double on average every 14.4 hours, whereas the transforming growth factor-beta 1-treated cells have a doubling time of on average 20.3 hours. The difference in intermitotic time is a consequence of a prolonged G1 phase (a shift from 7.5 to 13.5 hours on average). However, changes in intermitotic times occur only after cells have undergone division in the presence of transforming growth factor-beta 1 and treated cells finish the ongoing cell cycle exactly like control cells. From these findings we conclude that transforming growth factor-beta 1 may change cell cycle parameters by interfering with cellular events prior to G1.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and partial characterization of the c-jun oncogene in Xenopus laevis

Sequencing analysis of a 275-nt cDNA fragment encoding the DNA-binding region at the carboxyl terminal of the Xenopus c-jun protein product shows that this region exhibits 77-79% nucleotide homology and 93% amino acid homology with the DNA-binding region of mouse and human c-jun, and contains an intact leucine zipper motif and a basic DNA-binding region. Xenopus c-jun mRNA is induced in quiescent Xenopus A6 kidney cells by 12-O-tetradecanoylphorbol-13-acetate, PDGF and cycloheximide. This 'immediate early' response suggests that Xenopus c-jun may be similar in both structure and function to that observed for its mammalian counterpart.

Peptide hormone and growth factor regulation of nuclear proto-oncogenes and specific functions in adrenal cells

Among the large number of immediate early genes, nuclear proto-oncogenes of the Fos and Jun families, have been postulated to be involved in the long-term effects of several growth factors on cell differentiation and/or multiplication. Since adrenal cell differentiated functions appear to be regulated by specific hormones and growth factors, the effects of these factors on proto-oncogene mRNA levels were analysed in bovine adrenal fasciculata cells (BAC) in culture. Corticotropin (ACTH) and insulin-like growth factor I increased c-fos and jun-B mRNA, but had no effect on c-jun mRNA and these early changes were associated with a later increase in BAC specific function [ACTH receptors, cytochrome P450 17 alpha) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD)] and an enhanced steroidogenic responsiveness to both ACTH and angiotensin-II (A-II). On the other hand, A-II increased the three proto-oncogene (c-fos, c-jun and jun-B) mRNAs, induced a decrease of P450 17 alpha and 3 beta-HSD and caused a marked homologous and heterologous (ACTH) densitization. Transforming growth factor beta 1 which only increased jun-B mRNA, markedly reduced BAC differentiated functions and the steroidogenic responsiveness to both ACTH and A-II. Thus, it is postulated that the proto-oncoproteins encoded by the immediate early genes may play a role in the long-term effects of peptide hormones and growth factors on BAC differentiated functions.

Transforming growth factor beta 1-mediated induction of junB is selectively inhibited by expression of Ad.12-E1A

Transforming growth factor beta (TGF-beta), a multifunctional polypeptide growth factor, regulates the expression of many genes critical to cell cycle progression, such as members of the jun gene family which encode components of the transcription factor complex AP-1. The transforming proteins encoded by the early region 1A of adenovirus12 (Ad.12-E1A) abrogate some of the cellular responses to TGF-beta as well as affecting, differentially, the expression of cellular jun genes. Our data demonstrate that expression of Ad.12-E1A in rat 3Y1 fibroblast cells inhibits induction of junB by TGF-beta 1 while not altering the regulation of junB by phorbol ester or serum. Regulation of c-jun gene expression by TGF-beta 1, phorbol ester, and serum is not appreciably altered by the expression of Ad.12-E1A. Inhibition of TGF-beta induced junB expression is not due to a defect in TGF-beta/receptor interaction on Ad.12-E1A transformed cells and is not observed in other isotypic fibroblast cells transformed by SV40 or polyomavirus. These data suggest that multiple, independent, intracellular signal transduction pathways exist which mediate genomic responses to TGF-beta. Cellular expression of Ad.12-E1A-12S gene products results in selective disruption of some TGF-beta 1 signaling cascades and not those activated by phorbol ester or serum. These data further suggest that some cellular targets which mediate TGF-beta 1 action may also be unique targets of action for the E1A-12S transforming protein of adenovirus12.

TGF beta alters growth and differentiation related gene expression in proliferating osteoblasts in vitro, preventing development of the mature bone phenotype

This study examines the mechanism by which TGF-beta 1, an important mediator of cell growth and differentiation, blocks the differentiation of normal rat diploid fetal osteoblasts in vitro. We have established that the inability for pre-osteoblasts to differentiate is associated with changes in the expression of cell growth, matrix forming, and bone related genes. These include histone, jun B, c-fos, collagen, fibronectin, osteocalcin, alkaline phosphatase, and osteopontin. Morphologically, the TGF-beta 1-treated osteoblasts exhibit an elongated, spread shape as opposed to the characteristic cuboidal appearance during the early stages of growth. This is followed by a decrease in the number of bone nodules formed and the amount of calcium deposition. These effects on differentiation can occur without dramatic changes in cell growth if TGF-beta 1 is given for a short time early in the proliferative phase. However, continuous exposure to TGF-beta 1 leads to a bifunctional growth response from a negative effect during the proliferative phase to a positive growth effect during the later matrix maturation and mineralization phases of the osteoblast developmental sequence. Extracellular matrix genes, fibronectin, osteopontin and alpha 1(I) collagen, are altered in their expression pattern which may provide an aberrant matrix environment for mineralization and osteoblast maturation and potentiate the TGF-beta 1 response throughout the course of osteoblast differentiation. The initiation of a TGF-beta 1 effect on cell growth and differentiation is restricted to the proliferative phase of the culture before the cells express the mature osteoblastic phenotype. Second passage cells that are accelerated to differentiate by the addition of dexamethasone or by seeding cultures at a high density are refractory to TGF-beta 1. These in vitro results indicate that TGF-beta 1 exerts irreversible effects at a specific stage of osteoblast phenotype development resulting in a potent inhibition of osteoblast differentiation at concentrations from 0.1 ng/ml.

Transforming growth factor beta 1 inhibits interleukin-1-induced but enhances ionomycin-induced interferon-gamma production in a T cell lymphoma: comparison with the effects of rapamycin

Transforming growth factor beta 1 (TGF-beta 1) is a multifunctional cytokine whose potent immunomodulatory activity is well documented. To explore the mechanisms of this activity we examined the effect of TGF-beta 1 on the production of IFN-gamma measured at the mRNA and protein levels in the YAC-1 T cell lymphoma. In previous studies, this model proved useful to characterize the mode of action of the immunosuppressant rapamycin (RAP). Here, we found that when induced by IL-1 or IL-1 + PMA, the production of IFN-gamma is suppressed by both TGF-beta 1 (ED50 = 1.9 pM) and RAP (ED50 = 0.2 nM). In contrast, when induced by the calcium ionophore ionomycin, in the absence or in the presence of PMA, this production is enhanced up to 10-fold by TGF-beta 1 (ED50 = 1.8 pM) and 1.5-3-fold by RAP. Therefore, in YAC-1 cells, TGF-beta 1 exerts opposite effects on IFN-gamma production depending on the mode of activation, and these effects parallel those of RAP. To further analyze the mode of action of TGF-beta 1 in this system, we used okadaic acid (OA), an inhibitor of serine/threonine protein phosphatases. Treatment with OA rendered the expression of IFN-gamma mRNA induced by IL-1 insensitive to TGF-beta 1 or RAP, indicating that activation of a phosphatase may play a role in the suppressive effect of both agents. However, OA did not prevent the augmentation of ionomycin-mediated induction of IFN-gamma mRNA by either TGF-beta 1 or RAP. Hence, the up-regulation of IFN-gamma production by TGF-beta 1 and RAP may involve a different biochemical mechanism than that mediating their suppressive action. These observations also favor the hypothesis that the two agents act on the same regulatory pathways. This was further supported by the finding that TGF-beta 1 and RAP modulate IFN-gamma production in an additive rather than synergistic fashion. However, their effects could be dissociated in mutants of YAC-1 cells selected for resistance to the inhibition of IL-1-mediated IFN-gamma induction by RAP. Moreover, the IFN-gamma modulatory action of RAP in YAC-1 cells was accompanied by an antiproliferative effect, whereas TGF-beta 1 failed to alter the growth of these cells. Therefore, the immunomodulatory action of TGF-beta 1 may result from the disruption of biochemical processes related to, although distinct from, those affected by RAP.

Regulation of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in human vascular smooth muscle cells

Vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and E-selectin are inducible proteins involved in cell-cell adhesion. Immunohistochemical studies have indicated that human atherosclerotic plaques contain smooth muscle cells (SMCs) that express ICAM-1 and VCAM-1. Recently, we demonstrated that SMCs in culture express a functionally active cytokine-inducible ICAM-1. SMCs and mononuclear cells participate in the local accumulation of cytokines and related growth factors in atherosclerotic lesions. Therefore, we determined the effects of different cytokines and growth factors on mRNA content and cell surface expression of VCAM-1, ICAM-1, and E-selectin in cultured human aortic SMCs by Northern blotting, quantitative polymerase chain reaction amplification, and immunofluorescence flow cytometry. Under basal conditions of cultivation, both VCAM-1 mRNA and membrane expression of VCAM-1 were low and were induced very little by interleukin-1 beta (100 U/mL). Platelet-derived growth factor or transforming growth factor-beta decreased VCAM-1 mRNA basal expression. Treatment of SMCs with tumor necrosis factor-alpha (TNF-alpha) led to an increase in both VCAM-1 mRNA and cell surface expression for VCAM-1 in a dose- and time-dependent manner. Interferon-gamma induced a weak increase in VCAM-1 mRNA expression, with no synergistic effect on the stimulation by TNF-alpha. Various differences were noted between the expression of ICAM-1 and VCAM-1 genes, because interleukin-1 beta induced substantial amounts of ICAM-1 but not VCAM-1. The addition of interferon-gamma delays the time at which peak expression of ICAM-1 in response to TNF-alpha stimulation occurs. Under our conditions, we did not detect any expression of E-selectin by SMCs. These results suggest that cytokines regulate VCAM-1 and ICAM-1 expression on arterial SMCs and could play an important role in the pathophysiology of inflammatory and immune processes in atherosclerosis.

Transforming growth factor-beta inhibits rat intestinal cell growth by regulating cell cycle specific gene expression

Transforming growth factor-beta 1 (TGF-beta 1) inhibits the growth of intestinal cells, but the mechanisms involved are unknown. Using a rat intestinal crypt cell line (IEC-6), we determined the site of action in the cell cycle that TGF-beta 1 acts to suppress proliferation. We also examined the effect of TGF-beta 1 on the expression of proliferation-associated "immediate early" genes (zif268, jun-B, c-myc) during the early G1 phase and the cdc2 gene during the transition from the G1 phase to the S phase of the cell cycle. Cell cycle progression was determined by incorporation of 3H-thymidine, and gene expression was analyzed by Northern blot analysis. We found that TGF-beta 1 acts to inhibit proliferation of rat intestinal crypt cells by blocking cell cycle progression at the middle G1 phase. The genes activated during G1 can be divided into TGF-beta 1 insensitive (zif268, jun-B, and c-myc) and TGF-beta 1 sensitive (the cdc2 gene). TGF-beta 1 suppresses the induction of the cdc2 gene during the G1/S transition without inhibiting the activation of immediate early genes during the early G1 phase.

Cloning from a mouse osteoblastic cell line of a set of transforming-growth-factor-beta 1-regulated genes, one of which seems to encode a follistatin-related polypeptide

Transforming growth factor(TGF)beta 1 is a potent inhibitor of growth in mouse osteoblastic MC3T3-E1 cells. To isolate genes that are induced by TGF beta 1, the differential screening method was adopted using a cDNA library constructed from cells treated with TGF beta 1 for 4 h. Six independent cDNA clones were isolated (TGF beta-stimulated clone, TSC-5, TSC-36, TSC-115, TSC-128, TSC-160 and TSC-161), the expression of which was increased by TGF beta 1-treatment with maximal expression at 6-10 h. The steady-state levels of TSC-36, TSC-128 and TSC-160 increased almost tenfold, whereas those of TSC-5, TSC-115 and TSC-161 were elevated at most threefold. From partial nucleotide sequences, TSC-160 was found to be identical to rrg (ras-recision gene, lysyl oxidase), and TSC-115 had 80% similarity with tropomyosin cDNA, whereas other genes seemed novel. Expression of TSC-36 and TSC-160 was dramatically decreased in v-Ki-ras-transformed MC3T3 cells or in transformed NIH 3T3 cells (DT), and was recovered to normal levels in a flat revertant (C11). A nearly full-length copy of TSC-36 cDNA was isolated, and an open reading frame indicated that it encodes a protein of 35 kDa. An antiserum was raised against the C-terminal peptide predicted from the nucleotide sequence, and a polypeptide with an approximate molecular mass of 38 kDa was detected in cultured medium of MC3T3-E1 cells. The amino acid sequence of TSC-36 protein was found to have some similarity with follistatin, an activin-binding protein, and a limited similarity with the secreted protein rich in cysteine (SPARC).

General inhibition by transforming growth factor beta 1 of thyrotropin and cAMP responses in human thyroid cells in primary culture

Transforming growth factor beta 1 (TGF beta 1) mRNA has previously been identified in human thyroid cells and this agent has been shown to inhibit DNA synthesis in thyroid cells of some other species. In normal human thyroid cells in primary culture, TGF beta 1 inhibited inconstantly the low basal DNA synthesis and strongly the stimulation of DNA synthesis by epidermal growth factor (EGF) and serum, and by thyroid-stimulating hormone (TSH) acting through cAMP. This inhibition, by TGF beta 1, of the TSH and cAMP-dependent DNA synthesis was associated with an inhibition of PCNA (proliferating cell nuclear antigen) synthesis. TGF beta 1 almost completely abolished the cAMP induced stimulation of iodide uptake and thyroperoxidase synthesis. It thus, like EGF, also acts as a dedifferentiating agent. Investigation of the pattern of protein synthesis by two-dimensional gel electrophoresis revealed that while TGF beta 1, by itself, increased the synthesis of only one protein, a tropomyosin isoform, it inhibited most of the effects of cAMP on protein synthesis (35 out of 45 cAMP-regulated proteins were affected). It also reversed the effect of cAMP on the morphology of the thyrocytes. The fact that TGF beta 1 did not affect the increase in cAMP provoked by TSH in human thyroid cells while inhibiting most of the effects of dibutyryl cAMP in these cells suggests an action at a step distal to cAMP generation.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor beta 1 selectively regulates ornithine decarboxylase gene expression in malignant H-ras transformed fibrosarcoma cell lines

Negative growth regulators such as the transforming growth factor beta (TGF-beta) family appear to be important inhibitors in most tissue types. However, inhibition of DNA synthesis and cell proliferation is frequently lost during malignant transformation, and in some cases, tumor cell proliferation is actually stimulated by TGF-beta. The present study demonstrates a novel link between alterations in TGF-beta regulation during malignant conversion, and the expression of ornithine decarboxylase, a key rate-limiting activity in the biosynthesis of polyamines, and an enzyme that plays an important role in cell growth and differentiation. A panel of radiation and H-ras transformed mouse 10T1/2 cell lines exhibiting increasing malignant potential was investigated for possible TGF-beta 1 mediated changes in ornithine decarboxylase gene expression. Selective induction of gene expression was observed since only H-ras transformed cell lines with malignant potential exhibited marked elevations in ornithine decarboxylase message levels. Ornithine decarboxylase gene expression in nontransformed 10T1/2 cells and cell lines capable of only benign tumor formation was unaffected by TGF-beta 1 treatment. H-ras transformed cells were transfected with a plasmid placing the TGF-beta 1 coding region under the control of a zinc sensitive metallothionein promoter. When these cells were cultured in the presence of zinc an elevation of TGF-beta 1 mRNA was observed within 30 min. This increase in TGF-beta 1 message closely coincided with an elevation in ornithine decarboxylase message, and preceded an induction of jun-B, an early response gene in cells sensitive to TGF-beta 1 stimulation. Evidence for regulation of ornithine decarboxylase gene expression by TGF-beta 1 at both transcription and posttranscription was found. Actinomycin D pretreatment of malignant cells prior to TGF-beta 1 exposure prevented the increase in ornithine decarboxylase message. Marked differences in the rates of ornithine decarboxylase message decay were observed when cells treated with TGF-beta 1 were compared to untreated controls, with the half-life of ornithine decarboxylase mRNA increasing from 2.5 h in untreated cells to 17.5 h in cells exposed to TGF-beta 1. In addition, evidence was obtained for a cycloheximide sensitive regulator of ornithine decarboxylase gene expression, since the presence of this protein synthesis inhibitor increased the levels of ornithine decarboxylase message, and this effect was synergistically augmented by exposure of cells to cycloheximide and induction of TGF-beta 1 gene expression together.(ABSTRACT TRUNCATED AT 400 WORDS)

Transforming growth factor beta 1-induced delay of cell cycle progression and its association with growth-related gene expression in mouse fibroblasts

TGF beta-induced cell cycle progression is relatively slower than that induced by EGF or PDGF-BB. Further, TGF beta delays EGF or PDGF-induced 5-phase entry in C3H 10T1/2 mouse fibroblasts. In accordance with this delay, the induction of mRNA level of 'immediate early genes' such as c-myc, c-fos, c-jun and junB by TGF beta has slower kinetics compared with those of EGF. TGF beta induces c-sis gene, suggesting possible involvement of secondary growth stimulation by PDGF-like proteins. However, anti-PDGF-AB antibody, which was inhibitory to FDGF-BB-induced [3H]thymidine incorporation, did not block TGF beta-induced DNA synthesis. These results first demonstrate that the delay of cell cycle progression by TGF beta is closely associated with the altered regulation of growth-related gene expression in fibroblasts.

Activation of the jun-D gene during treatment of human myeloid leukemia cells with 1-beta-D-arabinofuranosylcytosine

The jun-D gene is a member of the c-jun family of early response genes that code for DNA binding proteins. The present studies demonstrate that 1-beta-D-arabinofuranosylcytosine (ara-C) increases jun-D expression in HL-525 myeloid leukemia cells. This induction by ara-C was maximal at 6 hr and transient. In contrast, ara-C had no detectable effect on the gene coding for the cAMP-responsive element binding protein 1. Nuclear run-on assays demonstrated that ara-C treatment is associated with an increased rate of jun-D transcription. The results also show that jun-D transcripts are stabilized at a posttranscriptional level in ara-C-treated cells. Taken together, these results demonstrate that ara-C induces expression of the jun-D gene and that this effect is regulated by transcriptional and posttranscriptional mechanisms.

Early response gene induction following DNA damage in astrocytoma cell lines

Early response genes (ERGs) are a group of genes with low or absent expression in quiescent cells that can be induced rapidly by a variety of proliferation and differentiation stimuli. c-jun and c-fos are prototypes for this group of genes. Recent evidence suggests that DNA damaging agents such as cytotoxic drugs and ionizing radiation can elicit strong ERG induction, suggesting that these genes may be involved in DNA damage repair and/or cell death. Paralleling this interest in drug-induced ERG expression is a growing body of evidence implicating ERG expression as important to the intrinsic function of the central nervous system. We therefore set out to explore the pattern of chemotherapeutic drug- and radiation-induced c-jun and c-fos expression in neuroectodermally (astrocytic) derived cell lines. We have demonstrated that various chemotherapeutic agents and ionizing radiation can induce c-jun in a time- and concentration-dependent manner. Furthermore, this induction can be prevented by pretreatment of the cells with agents that protect against DNA damage. Finally, we have demonstrated that c-fos and c-jun expression and induction are discoordinately regulated, reflecting a difference in astrocytic cell lines compared to hematopoietic cell lines. The possible relevance of these observations to the clinical resistance of astrocytic tumors to standard chemotherapy and radiation is discussed.

Regulation of chicken Hsp70 and Hsp90 family gene expression by transforming growth factor-beta 1

Transforming growth factor-beta 1 (TGF beta) is a regulator of protein synthesis in cultured chicken embryo cells (CEC). Preceding a gradual increase in overall protein synthesis, members of the Hsp70 family (Hsp70, Hsc70, and Grp78) and the Hsp90 family (90-2 and 90-3) of molecular chaperones are induced rapidly and represent a new class of TGF beta-inducible proteins (I.M. Takenaka and L.E. Hightower, J. Cell. Physiol., 152:568-577, 1992). Herein, 32P-labeled cDNA probes encoding Hsc70 and Hsp90 were used to show that levels of the corresponding mRNAs increased as a fraction of total RNA and in polysomes within five hours of treatment of CEC with TGF beta. This cytokine did not increase rates of hsc70 and hsp90 gene transcription as measured by run-on transcription assays of isolated nuclei. However, the Hsp RNA inductions were inhibited by dactinomycin, indicating a requirement for newly synthesized RNA. Both Hsc70 and Hsp90 mRNAs had relatively short half-lives, measured by Northern blot analyses of dactinomycin chases, which were not altered substantially in TGF beta-treated cells. In contrast, Hsp mRNA half-lives increased in heat shocked CEC exposed to dactinomycin during recovery, revealing a difference in regulation of these genes in stressed cells compared with TGF beta-treated cells. Our results support the conclusion that hsc70 and hsp90 gene expression is regulated posttranscriptionally in TGF beta-treated CEC, and the mechanism likely involves a nuclear event such as increasing the half-lives of nuclear RNA transcripts, processing, or transport into the cytoplasm.

Characteristics of protooncogene expression in A5 cells

Stimulation of beta-adrenergic receptors by isoproterenol or addition of 8-BrcAMP rapidly and transiently induces the expression of the protooncogenes, c-fos, and jun B, but not that of c-jun in A5 cells. These results indicate that different intracellular pathways may operate within the same cell for the induction of this group of early response genes. The inducibility of c-fos and jun B genes by either isoproterenol of 8-BrcAMP is transcriptionally regulated and accompanied by increases in their respective products. Furthermore, both c-fos and jun B mRNA levels are elevated at G0/G1 phase of the A5 cell cycle and are inducible by isoproterenol or 8-BrcAMP at the different phases of the cell cycle. These data further suggest a possible role of c-fos and jun B in A5 cell cycle.

Localization of Fos and Jun proteins in rat aortic smooth muscle cells after vascular injury

The availability of specific reagents to measure gene activity has provided important tools and potential new directions for the study of smooth muscle cell (SMC) proliferation in vivo. In this report, we have measured steady-state mRNA levels of several fos and jun family members in aortic tissue by Northern blotting after vascular injury. In addition, protein products of these genes were analyzed by immunocytochemistry. Within 15 minutes of balloon injury, mRNA levels of c-fos, fosB, c-jun, junB, and junD were elevated severalfold. In contrast, fos-related antigen (fra-1) mRNA showed a delayed onset of expression. The expression kinetics of these immediate early genes was similar to those in cultured cells stimulated to undergo proliferation by growth factors, suggesting that such SMC gene activation in vivo reflects permeation of blood-derived growth factors into the vessel wall or intravascular release of preformed growth factors. Translation of fos and jun genes into immunoreactive products was demonstrated 2 hours after balloon injury with antisera to Fos and Jun proteins. Treating rats with cycloheximide abolished this immunoreactivity. The distribution of Fos and Jun products was concentrated in SMC nuclei at the luminal border of the rat aorta. Such focal expression may have consequences for the initiation of SMC DNA synthesis and migration after vascular injury. Furthermore, the expression of Fos and Jun proteins in SMC after vascular balloon injury may be used as an index of SMC activation under a variety of experimental settings.

Modulation of the synthesis and glycosylation of the glucose transporter protein by transforming growth factor-beta 1 in Swiss 3T3 fibroblasts

Transforming growth factor-beta 1 (TGF-beta 1) stimulated growth and glucose uptake in Swiss mouse fibroblasts. DNA synthesis was increased 2-3-fold after 48 h incubation of growing 3T3 cells with TGF-beta 1 in calf serum-containing medium. Glucose transport activity in the cells was increased within 3 h after addition of TGF-beta 1 and this stimulation continued during incubation for 48 h. TGF-beta 1 also increased the levels of a brain type-glucose transporter (GLUT1) mRNA and the GLUT1 protein (55 kDa) in the membranes, consistent with the increase in glucose uptake. Furthermore, a longer exposure of TGF-beta 1 for 24-48 h induced a marked increase in the 65 kDa GLUT1 in 3T3 cell membranes. Other growth factors such as epidermal growth factor, fibroblast growth factor, transforming growth factor-alpha, and insulin did not elevate glucose uptake and the levels of 55 and 65 kDa GLUT1 proteins. Adding tunicamycin or deoxymannojirimycin to the TGF-beta 1-treated and untreated cells caused these 55 and 65 kDa glucose transporters to migrate as one band at 40-43 kDa. In addition, treating membrane proteins with glycopeptidase F, which removes N-linked oligosaccharides, also generated a glucose transporter of 40 kDa, suggesting that the 55 and 65 kDa GLUT1 proteins have a similar or identical core polypeptide but with different N-linked oligosaccharides. These results indicate that TGF-beta 1 modulates the synthesis of GLUT1 protein as well as its glycosylation in Swiss 3T3 cells, and that these changes may contribute to the control of cell proliferation by TGF-beta 1.

Enhanced bFGF gene expression in response to transforming growth factor-beta stimulation of AKR-2B cells

Treatment of quiescent cultures of mouse embryo-derived AKR-2B cells with transforming growth factor beta resulted in an induction of basic fibroblast growth factor (bFGF) mRNA and bFGF protein in the stimulated cells. In contrast to bFGF, acidic fibroblast growth factor (aFGF) was not induced by TGF beta. The mitogenic effect of transforming growth factor beta on AKR-2B cells may be mediated by the induction of bFCF in these cells.

Consecutive silver staining and autoradiography of 35S and 32P-labeled cellular proteins: application for the analysis of signal transducing pathways

The methodology for the simultaneous analysis of protein synthesis concomitant with protein phosphorylation/dephosphorylation is described. The technique consists of metabolic labeling of rat liver epithelial (RLE) cells with [32P]orthophosphate and [35S]methionine, performing two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) of the mixed samples, followed by silver staining and subsequent autoradiography of the dried silver stained 2-D PAGE electrophoretograms using two films placed back-to-back. The first film, which is positioned in direct contact with the dried silver-stained gel, visualized both exposure to 35S and 32P while the second film recorded exposure to only 32P due to the differential energy levels of the two isotopes. The juxta-positioning of the silver-stained images with the two autoradiographic film images permits the unambiguous mapping of the phosphorylated polypeptides back to their corresponding silver-stained and methionine-labeled counterparts. This strategy provides quantitative information utilizing both silver staining (measure of constitutive levels of protein expression) and metabolic labeling to measure rates of protein synthesis and/or degradation and phosphorylation and/or dephosphorylation using [35S]methionine and [32P]orthophosphate, respectively. We have utilized this methodology for the in vitro analysis of transforming growth factor type beta 1 (TGF-beta 1)-mediated signal transduction in RLE cells and have identified three nuclear polypeptides, 1 (pI 4.95/M(r) 97 kDa), 2 (5.00/85 kDa) and 3 (4.90/84 kDa) whose phosphorylation status is rapidly and transiently modulated by TGF-beta 1. The methodology described should have wide applications in studies where it is desirous to measure protein synthesis and/or degradation concomitant with signal transduction pathways involving protein phosphorylation.