Showing papers by "Michael B. Sporn published in 1988"
TL;DR: The data suggest that these two adjacent conserved amino acids in positions 47 and 48 play different roles in defining the structure and/or biological activity of TGF-alpha and that the carboxy terminus of T GF-alpha is involved in interactions with cellular TGF -alpha receptors.
Abstract: To study the relationship between the primary structure of transforming growth factor alpha (TGF-alpha) and some of its functional properties (competition with epidermal growth factor (EGF) for binding to the EGF receptor and induction of anchorage-independent growth), we introduced single amino acid mutations into the sequence for the fully processed, 50-amino-acid human TGF-alpha. The wild-type and mutant proteins were expressed in a vector by using a yeast alpha mating pheromone promoter. Mutations of two amino acids that are conserved in the family of the EGF-like peptides and are located in the carboxy-terminal part of TGF-alpha resulted in different biological effects. When aspartic acid 47 was mutated to alanine or asparagine, biological activity was retained; in contrast, substitutions of this residue with serine or glutamic acid generated mutants with reduced binding and colony-forming capacities. When leucine 48 was mutated to alanine, a complete loss of binding and colony-forming abilities resulted; mutation of leucine 48 to isoleucine or methionine resulted in very low activities. Our data suggest that these two adjacent conserved amino acids in positions 47 and 48 play different roles in defining the structure and/or biological activity of TGF-alpha and that the carboxy terminus of TGF-alpha is involved in interactions with cellular TGF-alpha receptors. The side chain of leucine 48 appears to be crucial either indirectly in determining the biologically active conformation of TGF-alpha or directly in the molecular recognition of TGF-alpha by its receptor.
1,129 citations
TL;DR: Transforming growth factor-β (TGF-β) as mentioned in this paper is the cytokine with the broadest range of activities in repair of injured tissue, based both on the variety of cell types that produce and/or respond to it and on the spectrum of its cellular responses.
Abstract: Transforming growth factor-β (TGF-β) is generally acknowledged to be the cytokine with the broadest range of activities in repair of injured tissue, based both on the variety of cell types that produce and/or respond to it and on the spectrum of its cellular responses (Roberts and Sporn, 1990). TGF-β is released from degranulating platelets and secreted by all of the major cell types participating in the repair process, including lymphocytes, macrophages, endothelial cells, smooth muscle cells, epithelial cells, and fibroblasts (see Fig. 1). A unique feature of this molecule is that its autoinduction results in sustained expression at the site of a wound and extends the effectiveness of both the initial burst of endogenous TGF-β released upon injury and exogenous TGF-β that might be applied to a wound. The ability of TGF-β to improve and/or accelerate tissue repair has been studied extensively in a variety of animal models of both normal and impaired healing. A limited number of clinical trials are in progress, but it is anticipated that many new applications for TGF-β will ultimately be found, once problems with appropriate timing and formulation can be solved.
1,032 citations
TL;DR: Among 11 polypeptide growth factors that regulate angiogenesis, fibrogenesis and other aspects of tissue repair, two proteins that are 71% similar proved to be potent macrophage deactivators: these are transforming growth factor-β1 (TGF- β1) and TGF-β2.
Abstract: Macrophage activation—enhanced capacity to kill, in a cell that otherwise mostly scavenges—is essential for host survival from infection and contributes to containment of tumours. Both microbes and tumour cells, therefore, may be under pressure to inhibit or reverse the activation of macrophages. This reasoning led to the demonstration of macrophage deactivating factors from both microbes1,2 and tumour cells3–5. In some circumstances the host itself probably requires the ability to deactivate macrophages. Macrophages are essential to the healing of wounds and repair of tissues damaged by inflammation. Yet the cytotoxic products of the activated macrophages can damage endothelium, fibroblasts, smooth muscle and parenchymal cells (reviewed in ref. 6). Thus, after an inflammatory site has been sterilized, the impact of macrophage activation on the host might shift from benefit to detriment. These concepts led us to search for macrophage deactivating effects among polypeptide growth factors that regulate angiogenesis, fibrogenesis and other aspects of tissue repair. Among 11 such factors, two proteins that are 71% similar proved to be potent macrophage deactivators: these are transforming growth factor-β1 (TGF- β1) and TGF- β2.
846 citations
TL;DR: The actions of many peptide growth factors include both stimulation and inhibition of cell proliferation, as well as effects unrelated to the control of cell growth.
Abstract: The actions of many peptide growth factors include both stimulation and inhibition of cell proliferation, as well as effects unrelated to the control of cell growth. One peptide can have both stimulatory and inhibitory activity in a single cell, depending on the context of the other signal molecules present.
815 citations
TL;DR: The latent TGF-beta secreted by platelets may be a cellular delivery complex, whereas the latent form found in serum may represent a clearance complex, and alpha 2M may scavenge excess T GF-beta that is released when the platelet latent form is activated, possibly by the clotting process.
569 citations
TL;DR: It is reported that TGF-beta 1 increases steady-state levels of its own message in six different normal and transformed cells in culture.
568 citations
TL;DR: Medium conditioned by Xenopus XTC cells (XTC-CM), known to have powerful mesoderm-inducing activity, was shown to contain TGF-beta-like activity as measured by a radioreceptor binding assay, colony formation in NRK cells, and growth inhibition in CCL64 cells.
Abstract: Mesoderm induction in the amphibian embryo can be studied by exposing animal region explants (destined to become ectoderm) to appropriate stimuli and assaying the appearance of mesodermal products like alpha-actin messenger RNA. Transforming growth factor beta 2 (TGF-beta 2), but not TGF-beta 1, was active in alpha-actin induction, while addition of fibroblast growth factor had a small synergistic effect. Medium conditioned by Xenopus XTC cells (XTC-CM), known to have powerful mesoderm-inducing activity, was shown to contain TGF-beta-like activity as measured by a radioreceptor binding assay, colony formation in NRK cells, and growth inhibition in CCL64 cells. The activity of XTC-CM in mesoderm induction and in growth inhibition of CCL64 cells was inhibited partially by antibodies to TGF-beta 2 but not by antibodies to TGF-beta 1. Thus, a TGF-beta 2-like molecule may be involved in mesoderm induction.
414 citations
TL;DR: It is demonstrated that activated human alveolar macrophages express the gene for transforming growth factor-α (TGF-α) in an inducible manner and secrete a factor into the culture medium that is functionally and immunologically identical to TGF- α.
342 citations
TL;DR: Using a human transforming growth factor beta 1 (TGF beta) cDNA probe, an RNA species migrating at about 1.7 kilobases in cultured primary chicken embryo chondrocytes is detected that is distinct from chicken TGF beta 1.
Abstract: Using a human transforming growth factor beta 1 (TGF beta) cDNA probe, we have detected an RNA species migrating at about 1.7 kilobases in cultured primary chicken embryo chondrocytes that is distinct from chicken TGF beta 1. The cloning and sequencing of cDNAs corresponding to this chondrocyte RNA demonstrate that it represents a new member of the TGF beta family, which we have named TGF beta 4. Unlike previously described TGF beta which are 390 to 414 amino acids long, the predicted precursor protein of TGF beta 4 is only 304 amino acids and does not appear to contain a signal peptide. Also unique to this new TGF beta is an insertion of two amino acids near the N-terminus of the processed peptide which would result in a 114 amino acid mature protein after cleavage from the precursor at a tetrabasic arg-arg-arg-arg site. The nine cysteine residues characteristic of all TGF beta are conserved. TGF beta 4 shows 82%, 64%, and 71% identity with the amino acid sequences of processed TGF beta 1, 2, and 3, respectively.
224 citations
TL;DR: A significant role for TGF-beta in the response of the heart to injury is indicated, as shown by the results of immunohistochemical staining and Northern blot analysis of mRNA.
Abstract: TGF-β1 has been examined in the heart during myocardial infarction caused by ligation of the left coronary artery. Infracted and uninfected myocardium have been compared by immunohistochemical staining of TGF-β1 and by Northern blot analysis of mRNA. Normal ventricular myocytes are strongly stained by an antibody to TGF-β1. Progressive loss of staining of these myocytes begins within 1 hr after coronary ligation. However, by 24-48 hr after ligation, intense staining of myocytes at the margin of infracted areas is seen. Northern blots of infracted myocardium 48 hr after ligation show a 3to 4-fold increase in the principal 2.4 kb TGF-β1 mRNA; there is also a marked increase in a minor 1.9 kb transcript. In the same tissue samples, there is a 2-fold decrease in the mRNA for the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase. The results indicate a significant role for TGF-β in the response of the heart to injury.
219 citations
TL;DR: It is proposed that TGF-beta, secreted by tumour cells, can augment tumour growth indirectly by effects on the stromal elements, which include suppression of the immune response, and enhancement of both angiogenesis and formation of connective tissue.
Abstract: TGF-beta is the prototype of a large family of multifunctional regulatory proteins. The principal sources of the peptide, platelets and bone, suggest that it plays a role in healing and remodeling processes. In vitro, TGF-beta is chemotactic for monocytes and fibroblasts and can greatly enhance accumulation of extracellular matrix components by fibroblasts. Its ability to stimulate the formation of granulation tissue locally and the demonstration of specific time- and tissue-dependent expression in embryogenesis suggest that similar mechanisms are operative in vivo. By analogy to its effects in wound healing and embryogenesis, it is proposed that TGF-beta, secreted by tumour cells, can augment tumour growth indirectly by effects on the stromal elements. These effects include suppression of the immune response, and enhancement of both angiogenesis and formation of connective tissue. Many tumour cells have escaped from direct growth inhibitory effects of TGF-beta by a variety of mechanisms including inability to activate the latent form of the peptide, loss of cellular receptors for TGF-beta, and loss of functional intracellular signal transduction pathways.
TL;DR: Using a human TGF beta 1 cDNA probe, two distinct TGF Beta RNAs are detected in cultured primary chick embryo chondrocytes and one of these RNAs shows similarity to mammalian TGFbeta 1.
Abstract: Transforming growth factor beta 1 (TGF beta 1) has been purified and the mRNA cloned from a number of mammalian species including human, murine, bovine, porcine, and simian. Using a human TGF beta 1 cDNA probe, we have detected two distinct TGF beta RNAs in cultured primary chick embryo chondrocytes. One of these RNAs, migrating at about 1.7 kilobases, shows similarity to mammalian TGF beta 1. The second RNA, migrating at about 3 kilobases, is a novel TGF beta mRNA which we have named TGF beta 3. Clones corresponding to each of these RNAs were isolated from a cultured primary chick embryo chondrocyte cDNA library. Two cDNA clones for TGF beta 3, pTGFB-ChX17 and pTGFB-ChX25, contained a 39 nucleotide-long 5'-untranslated region, a 1236 nucleotide-long coding region, and a 911 nucleotide-long 3'-untranslated region. The predicted protein includes a signal peptide of 20-23 amino acids as in human TGF beta 1 and 2, and a precursor protein consisting of 412 amino acids, which can be cleaved at a lys-arg site to produce a 112 amino acid processed peptide containing nine cysteine residues in the same positions as in human TGF beta 1 and 2. At the nucleotide level, the processed coding region of TGF beta 3 shows 72% and 76% identity with the processed coding regions of human TGF beta 1 and TGF beta 2, respectively; at the amino acid level, TGF beta 3 shows 76% identity with TGF beta 1 and 79% identity with TGF beta 2.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: It is demonstrated that the peptide TGF-beta is a potent inhibitor of LAK cell and CTL generation in vitro.
Abstract: The effect(s) of purified transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF) on the induction and function of lymphokine-activated killer (LAK) cells and cytotoxic T lymphocytes (CTL) was examined. The addition of TGF-beta, but not PDGF, to cultures containing fresh C57BL/6 mouse splenocytes or human peripheral blood lymphocytes plus recombinant interleukin-2 markedly inhibited the development of mouse and human LAK cell activity (measured after 3 days for cytotoxicity against cultured or fresh tumor targets in 4-h 51Cr release assays). The addition of TGF-beta, but not PDGF, to a one-way, C57BL/6 anti-DBA/2, mixed lymphocyte reaction effectively blocked the generation of allospecific CTL as well. However, TGF-beta did not inhibit the effector function of LAK cells or of allospecific CTL when added directly to the short-term cytolytic assay. A second form of homodimeric TGF-beta, type 2, was also found to be suppressive on the development of murine LAK cells and allospecific CTL. Collectively, these data demonstrate that the peptide TGF-beta is a potent inhibitor of LAK cell and CTL generation in vitro.
TL;DR: Most eukaryotic cells encode principally a 2.5-kilobase (kb) transforming growth factor (TGF)-beta 1 mRNA, but two major TGF-beta 1 RNA species are found in porcine tissues, one of which has a longer 3'-untranslated sequence generated by the selection of an alternate polyadenylation site.
TL;DR: Stimulation of growth by PDGF and TGF‐β1 is unusual for an epithelial cell type, and indicates that mesothelial cells have growth regulatory properties similar to connective tissue cells.
Abstract: Monolayer cultures of human mesothelial cells made quiescent by serum deprivation are induced to undergo one round of DNA synthesis by platelet-derived growth factor (PDGF), epidermal growth factor (EGF), or transforming growth factor type beta 1 (TGF-beta 1). This one-time stimulation is independent of other serum components. The kinetics for induction of DNA synthesis observed for PDGF, EGF, and TGF-beta 1 are all similar to one another, with a peak of DNA synthesis occurring 24-36 h after the addition of the growth factors. Repetitive rounds of DNA synthesis and cell division do not ensue after addition of PDGF, EGF, or TGF-beta 1 alone or in combination; however, in media supplemented with chemically denatured serum, each of these factors is capable of sustaining continuous replication of mesothelial cells. Stimulation of growth by PDGF and TGF-beta 1 is unusual for an epithelial cell type, and indicates that mesothelial cells have growth regulatory properties similar to connective tissue cells.
Journal Article•
TL;DR: It is reported here that Harvey sarcoma virus-transformed NIH-3T3 cells and Moloney sarcomA virus- transformed NRK cells show increased expression of the mRNAs for TGF-alpha, T GF-beta, PDGF A-chain and nerve growth factor compared to their untransformed counterparts.
Abstract: Transforming growth factors-alpha and beta (TGF-alpha and -beta) and platelet-derived growth factor (PDGF), three distinct peptide hormones, acting together, are able to potentiate the phenotypic transformation of normal rat kidney (NRK) cells. Cells transformed by retroviruses have been shown to secrete increased levels of TGF-alpha, TGF-beta and PDGF. We report here that Harvey sarcoma virus-transformed NIH-3T3 cells and Moloney sarcoma virus-transformed NRK cells show increased expression of the mRNAs for TGF-alpha, TGF-beta, PDGF A-chain and nerve growth factor (NGF) compared to their untransformed counterparts. No amplification or rearrangement in the genomic DNA is seen in the transformed cells. In tumor tissue formed by subcutaneous injection of Ha-3T3 cells, this enhanced level of TGF-beta mRNA returns to the control level of the untransformed cells. The increase in TGF-beta mRNA in the transformed cells is paralleled by an increase in the level of TGF-beta protein as shown by immunoprecipitation and Western blotting procedures using specific TGF-beta antibodies.
TL;DR: Although TGF-/3 was initially discovered and named in the context of a transformation assay, the ubiquitous distribution of the molecule suggests that it must play a fundamental regulatory role in normal cell physiology.
Abstract: Transforming growth factor-/3 (TGF-/3) is the founder member of a growing family of structurally related peptides that are involved in the regulation of cell growth and development in organisms as phylogenetically distant as flies and man. TGF-/3 itself is a multifunctional molecule whose biological effects are highly context-dependent. Thus, depending on the cell type and the cell environment, TGF-/3 in vitro can stimulate or inhibit proliferation, promote or block differentiation, and modulate cellular function.’.’ Two closely related forms of TGF-/3 have been identified. Type 1 and type 2 TGF-/3 share 70% sequence identity and are indistinguishable in most biological assay systems. However, activities unique to cach type are emerging2 and it can be anticipated that the two types may be differentially regulated. Structurally, the active form is a disulfide-linked homodimer of 25 kDa and the monomeric unit is encoded as the C-terminal 112 amino acids of a 390-residue p r e c ~ r s o r . ~ With 2 mg extractable TGF-p/kg, platelets are the most concentrated source of TGF-/3 1 in the body, probably reflecting an important role for the molecule in wound healing4 Bone is also a major source (0.1 mg/kg), and all other tissues examined have detectable, though lower (0.01-0.03 mg/kg) TGF-/3 levels. Thus, although TGF-/3 was initially discovered and named in the context of a transformation assay, the ubiquitous distribution of the molecule suggests that it must play a fundamental regulatory role in normal cell physiology.
TL;DR: It is determined that the 350 nucleotide RNA band may be composed of multiple species of RNA which are related to the anti-sense DNA strand that is opposite to the strand that codes for the 4800 nucleotide TGF alpha mRNA.
Abstract: Human transforming growth factor α (TGFα) is coded for by an mRNA of about 4800 nucleotides. The cDNA sequence demonstrates that the 50 amino acid TGFα is embedded in a larger 160 amino acid precursor protein. We report here that in addition to the 4800 nucleotide TGFα mRNA, there is a novel second RNA species of about 350 nucleotides that hybridizes to a human TGFα cDNA probe. This small RNA species has been found in the RNA of several human tumor cells including HT1080, A549, A431, A2058, and A673. We have demonstrated an inverse relationship between the amounts of the 4800 nucleotide TGFα mRNA and the 350 nucleotide novel RNA in these human cells. Restriction enzyme cleavage of a human TGFα cDNA probe into three separate domains consisting of a processed coding region and 5′- and 3′-preprocessed coding and untranslated regions showed that only the 3′-untranslated region hybridized to the 350 nucleotide RNA. Using sense and anti-sense single-stranded 3′-untranslated region probes, we determined that the...