Amino acid sequence of the BSC-1 cell growth inhibitor (polyergin) deduced from the nucleotide sequence of the cDNA

Advances and Challenges in Targeting TGF-β Isoforms for Therapeutic Intervention of Cancer: A Mechanism-Based Perspective

The TGF-β family is a group of 25 kDa secretory cytokines, in mammals consisting of three dimeric isoforms (TGF-βs 1, 2, and 3), each encoded on a separate gene with unique regulatory elements. Each isoform plays unique, diverse, and pivotal roles in cell growth, survival, immune response, and differentiation. However, many researchers in the TGF-β field often mistakenly assume a uniform functionality among all three isoforms. Although TGF-βs are essential for normal development and many cellular and physiological processes, their dysregulated expression contributes significantly to various diseases. Notably, they drive conditions like fibrosis and tumor metastasis/progression. To counter these pathologies, extensive efforts have been directed towards targeting TGF-βs, resulting in the development of a range of TGF-β inhibitors. Despite some clinical success, these agents have yet to reach their full potential in the treatment of cancers. A significant challenge rests in effectively targeting TGF-βs' pathological functions while preserving their physiological roles. Many existing approaches collectively target all three isoforms, failing to target just the specific deregulated ones. Additionally, most strategies tackle the entire TGF-β signaling pathway instead of focusing on disease-specific components or preferentially targeting tumors. This review gives a unique historical overview of the TGF-β field often missed in other reviews and provides a current landscape of TGF-β research, emphasizing isoform-specific functions and disease implications. The review then delves into ongoing therapeutic strategies in cancer, stressing the need for more tools that target specific isoforms and disease-related pathway components, advocating mechanism-based and refined approaches to enhance the effectiveness of TGF-β-targeted cancer therapies.

The Discovery and Early Days of TGF-β: A Historical Perspective

Transforming growth factors (TGFs) were discovered as activities that were secreted by cancer cells, and later by normal cells, and had the ability to phenotypically and reversibly transform immortalized fibroblasts. TGF-β distinguished itself from TGF-α because it did not bind to the same epidermal growth factor (EGF) receptor as TGF-α and, therefore, acted through different cell-surface receptors and signaling mediators. This review summarizes the discovery of TGF-β, the early developments in its molecular and biological characterization with its many biological activities in different cell and tissue contexts and its roles in disease, the realization that there is a family of secreted TGF-β-related proteins with many differentiation functions in development and activities in normal cell and tissue physiology, and the subsequent identification and characterization of the receptors and effectors that mediate TGF-β family signaling responses.

Inhibition of compensatory renal growth by the N-terminus of a sheep-derived peptide

The N-terminal sequence of a novel sheep-derived peptide with growth inhibitory activity has been obtained. The N-terminal fragment was chemically synthesised and designated EPL001. The kidney was chosen as the first mammalian system in which to study EPL001 since kidney growth can be accurately quantified following a surgical reduction in renal mass. Cell proliferation was measured in mouse collecting duct kidney (MCDK) cells stimulated with insulin-like growth factor I (IGF-I). Compensatory renal growth (CRG) was induced in Wistar rats and either EPL001 or an EPL001 antibody delivered by continuous renal tissue infusion. Mouse monoclonal antibodies to EPL001 were generated for immunoneutralisation, rabbit polyclonal antibodies were generated for immunohistochemistry. EPL001 had no apparent effect on IGF-I stimulated cell proliferation in MCDK cells in vitro, yet provoked a dose-dependent inhibition of CRG in vivo. An EPL001 antibody potentiated CRG, in the absence of exogenous EPL001, consistent with an inhibitory role in kidney growth for an endogenous peptide containing the EPL001 sequence. Tubular staining for epitopes to the EPL001 sequence was detected in normal human kidney sections and enhanced in renal cell carcinoma. Results support the presence of growth inhibitory activity in the N-terminus of a sheep-derived peptide with evidence for both its presence and endogenous activity in the kidney. Attempts to further characterise its structure and activity are ongoing.

Regulation of epithelial proliferation by TGF-beta

The closely related mammalian TGF-betas (TGF-beta 1, TGF-beta 2 and TGF-beta 3) are potent inhibitors of proliferation of many cell types in vitro. TGF-beta 1 has been demonstrated to be growth inhibitory in vivo for epithelial, endothelial, myeloid and lymphoid cells. Utilizing skin keratinocytes as a model system for studying the mechanism of TGF-beta 1-induced growth inhibition, it has been demonstrated that TGF-beta 1 rapidly inhibits transcription of the c-myc gene. Antisense c-myc oligonucleotides inhibit proliferation of keratinocytes as effectively as does TGF-beta 1, indicating that TGF-beta 1 suppression of c-myc expression is an important component of this growth inhibition. Studies utilizing DNA tumour virus transforming gene constructs have shown that the retinoblastoma gene product, pRb, or a related protein, is needed for TGF-beta 1 suppression of c-myc transcription. Thus, TGF-beta 1 may act through a tumour suppressor gene product, pRb, to suppress transcription of a proto-oncogene, c-myc, and subsequently inhibit cell proliferation.

Latent TGF-beta binding proteins: extracellular matrix association and roles in TGF-beta activation

Transforming growth factor betas (TGF-betas) are multifunctional and pleiotropic growth factors. Their major effects include inhibition of cell proliferation and enhancement of extracellular matrix production. TGF-betas are secreted from cells as latent complexes, consisting of mature dimeric growth factor, the latency-associated propeptide (LAP), and a distinct gene product, latent TGF-beta binding protein LTBP. The secreted complex is targeted to specific locations in the extracellular matrix by the appropriate LTBP. The latent complex needs subsequently to be activated. Most studies describing biological effects of TGF-beta have been carried out in cell cultures using high concentrations of active, soluble TGF-beta, where appropriate targeting of the growth factor is missing. However, TGF-beta is produced and secreted in vivo as a latent complex in a specific and targeted manner. Various experimental approaches have convincingly shown the importance of the activation of latent TGF-beta, as well as the importance of LTBPs as targeting molecules of the effects of TGF-beta. Essential steps in the activation appear to be cellular recognition of extracellular matrix-associated LTBPs and subsequent recognition of the associated latent TGF-beta. Cell recognition by specific molecules like integrins and proteolytic events involving plasminogen activation evidently play multifaceted roles in the regulation of TGF-beta activation.

Latent transforming growth factor-beta binding proteins (LTBPs)--structural extracellular matrix proteins for targeting TGF-beta action

Growth factors of the transforming growth factor-beta family are potent regulators of the extracellular matrix formation, in addition to their immunomodulatory and regulatory roles for cell growth. TGF-beta s are secreted from cells as latent complexes containing TGF-beta and its propeptide, LAP (latency-associated peptide). In most cells LAP is covalently linked to an additional protein, latent TGF-beta binding protein (LTBP), forming the large latent complex. LTBPs are required for efficient secretion and correct folding of TGF-beta s. The secreted large latent complexes associate covalently with the extracellular matrix via the N-termini of the LTBPs. LTBPs belong to the fibrillin-LTBP family of extracellular matrix proteins, which have a typical repeated domain structure consisting mostly of epidermal growth factor (EGF)-like repeats and characteristic eight cysteine (8-Cys) repeats. Currently four different LTBPs and two fibrillins have been identified. LTBPs contain multiple proteinase sensitive sites, providing means to solubilize the large latent complex from the extracellular matrix structures. LTBPs are now known to exist both as soluble molecules and in association with the extracellular matrix. An important consequence of this is LTBP-mediated deposition and targeting of latent, activatable TGF-beta into extracellular matrices and connective tissues. LTBPs have a dual function, they are required both for the secretion of the small latent TGF-beta complex as well as directing bound latent TGF-beta to extracellular matrix microfibrils. However, it is not known at present whether LTBPs are capable of forming microfibrils independently, or whether they are a part of the fibrillin-containing fibrils. Most LTBPs possess RGD-sequences, which may have a role in their interactions with the cell surface. At least LTBP-1 is chemotactic to smooth muscle cells, and is involved in vascular remodelling. Analyses of the expressed LTBPs have revealed considerable variations throughout the molecules, generated both by alternative splicing and utilization of multiple promoter regions. The significance of this structural diversity is mostly unclear at present.

C-CAM1 expression: differential effects on morphology, differentiation state and suppression of human PC-3 prostate carcinoma cells

Studies in rat prostate and liver have suggested that C-CAM1 is involved in the formation and maintenance of histotypic associations in tissues and possibly tumors. Most recently, C-CAM1 has been shown to suppress tumorigenicity of prostate and colon carcinoma cells. However, the mechanisms whereby C-CAM1 suppresses growth and the relationship of this activity to its proposed role in histotypic interactions remain largely unknown. In the present study, we have analysed the growth, phenotypic, morphological and ultrastructural characteristics of four human PC-3 prostate carcinoma cell lines transduced with C-CAM1 retrovirus. We report that three of four lines regained their tumorigenic phenotype in vivo while maintaining high levels of C-CAM1 expression and a growth retarded phenotype in vitro. These findings suggested that high levels of C-CAM1 expression were negatively influencing recovery during reconstitution after freezing or during the latency period after subcutaneous injection and that loss of suppression resulted from changes in expression of other molecules required for full disclosure of C-CAM1 mediated growth inhibition. Results from Northern blot and immunofluorescence analyses of tumor nodules demonstrated that C-CAM1 decreased rather than enhanced phenotypic differentiation and induced ultrastructural and morphological changes that occurred independently of tumor suppression.

Distinct functional domains of TGF-beta bind receptors on endothelial cells

Transforming growth factor-beta (TGF-beta) is a multi-functional regulator of cell growth and differentiation. Three distinct isoforms of TGF-beta exist having similar, but not identical actions. TGF-beta 1, but not TGF-beta 2, binds to T beta RII and also to endoglin, a cell surface protein abundant on endothelial cells. In contrast, the affinity constant of TGF-beta 2 for alpha 2-macroglobulin is 10-fold greater than that of TGF-beta 1. TGF-beta 2 also binds better than TGF-beta 1 to a glycosyl phosphatidylinositol (GPI)-linked binding protein expressed on vascular endothelial cells. Using chimeric TGF-beta molecules, in which selected regions of TGF-beta 1 have been exchanged for the corresponding region of TGF-beta 2, we demonstrate here that amino acids 92-95 or 94-98 of TGF-beta determine isoform specific binding to endoglin. In contrast, exchange of only amino acids 95 and 98 did not alter TGF-beta specificity. Isoform specific binding to a GPI-linked protein on EJG endothelial cells was modulated by a region containing amino acids 40-68, although exchange of only amino acids 40-47 did not confer isoform specific binding. Significantly, the 92-98 region also modulates binding of TGF-beta to the type II receptor whereas isoform specific binding to alpha 2-macroglobulin requires concerted exchange of amino acids 45 and 47. Taken together, these results show that at least three different functional domains are important modulators of TGF-beta interaction with binding proteins and receptors.

Extracellular matrix-associated transforming growth factor-beta: role in cancer cell growth and invasion

Growth factors of the transforming growth factor-beta (TGF-beta) family inhibit the proliferation of epithelial, endothelial, and hematopoietic cells, and stimulate the synthesis of extracellular matrix components. TGF-beta s are secreted from cells in high-molecular-mass protein complexes that are composed of three proteins, the mature TGF-beta-dimer, the TGF-beta propeptide dimer, or latency-associated protein (LAP), and the latent TGF-beta binding protein (LTBP). Mature TGF-beta is cleaved from its propeptide during secretion, but the proteins remain associated by noncovalent interactions. LTBP is required for efficient secretion and processing of latent TGF-beta and it binds to LAP via disulfide bond(s). LTBP is a component of extracellular matrix microfibrils, and it targets the latent TGF-beta complex to the extracellular matrix. TGF-beta signaling is initiated by proteolytic cleavage of LTBP that results in the release of the latent TGF-beta complex from the extracellular matrix. TGF-beta is activated by dissociation of LAP from the mature TGF-beta. Subsequent signaling involves binding of active TGF-beta to its type II cell surface receptors, which phosphorylate and activate type I TGF-beta receptors. Type I receptors, in turn, phosphorylate cytoplasmic transcriptional activator proteins Smad2 and Smad3, inducing their translocation to the nucleus. Recent evidence suggests that acquisition of resistance to TGF-beta growth inhibition plays a major role in the progression of epithelial and hematopoietic cell malignancies. The role of secretion of TGF-beta in tumorigenesis is more complex. The secretion of TGF-beta s by tumor cells may contribute to autocrine growth inhibition, but on the other hand, it may also promote invasion, metastasis, angiogenesis, and even immunosuppression. Tumor cells may also fail to deposit LTBP:TGF-beta complexes to the extracellular matrix. The elucidation of the mechanisms of the release of TGF-beta from the matrix and its subsequent activation aids the understanding of the pathophysiologic roles of TGF-beta in malignant growth, and allows the development of therapeutic agents that regulate the activity of TGF-beta.

Mutational analysis of a transforming growth factor-beta receptor binding site

Transforming growth factor-beta s (TGF-beta 1, -beta 2, -beta 3) are important regulators of cell growth and differentiation which share approximately 70% identical amino acids. Using LS513 colorectal cells, which are growth inhibited by TGF-beta 1 (ED50 of 100 pM), but are refractory to TGF-beta 2 (ED50 of 50,000 to 100,000 pM), we have determined that amino acids 92-98 of TGF-beta specify growth inhibition. The chimeric protein TGF-beta 1/beta 2(92-98), in which amino acids 92-98 of TGF-beta 1 were exchanged for the corresponding amino acids of TGF-beta 2, was indistinguishable from TGF-beta 2 at inhibiting growth of LS513 cells. In contrast, both TGF-beta 1/beta 2(92-95) and TGF-beta 1/beta 2(94-98) inhibited the growth of LS513 cells with an ED50 of approximately 1000 pM. TGF-beta 1/beta 2(95-98), in which amino acids 95-98 of TGF-beta 1 have been replaced with the corresponding amino acids of TGF-beta 2, had full activity and was indistinguishable from TGF-beta 1. Receptor cross-linking experiments demonstrated that binding of the chimeras to the type I and type II receptors of LS513 cells was consistent with their biological activity. TGF-beta 1/beta 2(95-98), TGF-beta 1/beta 2(92-95) and TGF-beta 1/beta 2(94-98) were each similar to TGF-beta 2 in that they failed to bind to the soluble Type II receptor in a solid-phase assay. These results demonstrate that amino acids 92-98 are involved in the interaction between TGF-beta and its signaling receptors and they show that modest changes within this region can substantially alter biological response.

Neurons promote macrophage proliferation by producing transforming growth factor-beta2

The infiltration of bone marrow-derived macrophages into the CNS contributes to growth and reactions of microglia during development or after brain injury. The proliferation of microglial cells is stimulated by colony-stimulating factor 1 (CSF-1), an astrocyte-produced growth factor that acts on mononuclear phagocytes. In the present study, we have shown, using an in vitro model system, that rodent neurons obtained from the developing cerebral cortex produce a soluble factor that strongly enhances the proliferation of macrophages cultured in the presence of CSF-1. Both macrophages isolated from the developing brain and those from the adult bone marrow were stimulated. Kinetic analyses of [3H]thymidine incorporation into macrophages indicated that their response to the neuron-derived factor involved a shortening of the cycle of proliferating cells. The effect of neurons on macrophages was blocked in the presence of antibodies neutralizing transforming growth factor-beta2 (TGF-beta2), whereas recombinant TGF-beta2 stimulated macrophage proliferation in the presence of CSF-1. Neuronal secretion of TGF-beta2 was confirmed by reverse transcription-PCR detection of TGF-beta2 transcripts and immunodetection of the protein within neurons and in their culture medium. In situ hybridization and immunohistochemical experiments showed neuronal expression of TGF-beta2 in sections of cerebral cortex obtained from 6-d-old rats, an age at which extensive developmental recruitment of macrophages occurs in this cerebral region. Altogether, our results provide direct evidence that neurons have the capacity to promote brain macrophage proliferation and demonstrate the role of TGF-beta2 in this neuronal function.

Neurons promote macrophage proliferation by producing transforming growth factor-beta2

The infiltration of bone marrow-derived macrophages into the CNS contributes to growth and reactions of microglia during development or after brain injury. The proliferation of microglial cells is stimulated by colony-stimulating factor 1 (CSF-1), an astrocyte-produced growth factor that acts on mononuclear phagocytes. In the present study, we have shown, using an in vitro model system, that rodent neurons obtained from the developing cerebral cortex produce a soluble factor that strongly enhances the proliferation of macrophages cultured in the presence of CSF-1. Both macrophages isolated from the developing brain and those from the adult bone marrow were stimulated. Kinetic analyses of [3H]thymidine incorporation into macrophages indicated that their response to the neuron-derived factor involved a shortening of the cycle of proliferating cells. The effect of neurons on macrophages was blocked in the presence of antibodies neutralizing transforming growth factor-beta2 (TGF-beta2), whereas recombinant TGF-beta2 stimulated macrophage proliferation in the presence of CSF-1. Neuronal secretion of TGF-beta2 was confirmed by reverse transcription-PCR detection of TGF-beta2 transcripts and immunodetection of the protein within neurons and in their culture medium. In situ hybridization and immunohistochemical experiments showed neuronal expression of TGF-beta2 in sections of cerebral cortex obtained from 6-d-old rats, an age at which extensive developmental recruitment of macrophages occurs in this cerebral region. Altogether, our results provide direct evidence that neurons have the capacity to promote brain macrophage proliferation and demonstrate the role of TGF-beta2 in this neuronal function.

Eradication of established intracranial rat gliomas by transforming growth factor beta antisense gene therapy

Like human gliomas, the rat 9L gliosarcoma secretes the immunosuppressive transforming growth factor beta (TGF-beta). Using the 9L model, we tested our hypothesis that genetic modification of glioma cells to block TGF-beta expression may enhance their immunogenicity and make them more suitable for active tumor immunotherapy. Subcutaneous immunizations of tumor-bearing animals with 9L cells genetically modified to inhibit TGF-beta expression with an antisense plasmid vector resulted in a significantly higher number of animals surviving for 12 weeks (11/11, 100%) compared to immunizations with control vector-modified 9L cells (2/15, 13%) or 9L cells transduced with an interleukin 2 retroviral vector (3/10, 30%) (P < 0.001 for both comparisons). Histologic evaluation of implantation sites 12 weeks after treatment revealed no evidence of residual tumor. In vitro tumor cytotoxicity assays with lymph node effector cells revealed a 3- to 4-fold increase in lytic activity for the animals immunized with TGF-beta antisense-modified tumor cells compared to immunizations with control vector or interleukin 2 gene-modified tumor cells. These results indicate that inhibition of TGF-beta expression significantly enhances tumor-cell immunogenicity and supports future clinical evaluation of TGF-beta antisense gene therapy for TGF-beta-expressing tumors.

Modulation of murine EL-4 thymic lymphoma cell proliferation and cytokine production by vitamin E succinate

RRR-alpha-tocopheryl succinate (VES) was studied for effects on murine EL-4 cell proliferation and production of interleukin-2 (IL-2) and transforming growth factor-beta (TGF-beta). VES was biphasic in its actions: 0.1 microgram/ml enhanced EL-4 cell proliferation, whereas 10-20 microgram/ml inhibited cellular proliferation. Cell-conditioned media (CM) from EL-4 cells treated with 0.2 ng/ml phorbol myristate acetate (PMA) + 0.1 microgram/ml VES contained increased amounts of IL-2, as determined by the murine cytotoxic T cell IL-2-dependent CTLL-2 bioassay. VES at 0.1 microgram/ml or 0.1 microgram/ml VES + 0.2 ng/ml PMA induced the expression of IL-2 mRNA by EL-4 cells three to nine hours after treatment. CM from EL-4 cells treated with VES at 10-20 microgram/ml exhibited potent antiproliferative activity when tested in the TGF-beta-responsive mink lung cell (Mv1Lu) bioassay and showed reduced inhibitory effects when tested on TGF-beta receptor-negative mink lung (DRA-27) cells. CM from control-treated EL-4 cells exhibited no antiproliferative activity. The VES-induced antiproliferative activity was characterized as TGF-beta by neutralization analyses and immunoprecipitation of metabolically labeled proteins with TGF-beta-specific reagents. VES treatment of EL-4 cells had no effect on TGF-beta 1 mRNA expression while downregulating TGF-beta 3 mRNA expression. In summary, these studies showed that 0.1 microgram/ml VES enhanced cellular proliferation, in part, via increased IL-2 production, whereas 10-20 micrograms/ml VES inhibited cellular proliferation, in part, via the secretion of biologically active TGF-beta.

Inhibition of purified CD34+ hematopoietic progenitor cells by human immunodeficiency virus 1 or gp120 mediated by endogenous transforming growth factor beta 1

Human CD34+ hematopoietic progenitor cells, stringently purified from the peripheral blood of 20 normal donors, showed an impaired survival and clonogenic capacity after exposure to either heat-inactivated human immunodeficiency virus (HIV) 1 (strain IIIB) or cross-linked envelope gp120. Cell cycle analysis, performed at different times in serum-free liquid culture, showed an accumulation in G0/G1 in HIV-1- or gp120-treated cells and a progressive increase of cells with subdiploid DNA content, characteristic of apoptosis. In blocking experiments with anti-transforming growth factor (TGF) beta 1 neutralizing serum or TGF-beta 1 oligonucleotides, we demonstrated that the HIV-1- or gp120-mediated suppression of CD34+ cell growth was almost entirely due to an upregulation of endogenous TGF-beta 1 produced by purified hematopoietic progenitors. Moreover, by using a sensitive assay on the CCL64 cell line, increased levels of bioactive TGF-beta 1 were recovered in the culture supernatant of HIV-1/gp120-treated CD34+ cells. Anti-TGF-beta 1 neutralizing serum or TGF-beta 1 oligonucleotides were also effective in inducing a significant increase of the plating efficiency of CD34+ cells, purified from the peripheral blood of three HIV-1-seropositive individuals, suggesting that a similar mechanism may be also operative in vivo. The relevance of these findings to a better understanding of the pathogenesis of HIV-1-related cytopenias is discussed.

Differential gene expression in migrating renal epithelial cells after wounding

An in vitro model of wound healing was used to study cell migration that is independent of proliferation during renal regeneration after acute tubular necrosis. Monolayer cultures of high-density, quiescent renal epithelial cells of the BSC-1 line were subjected to scrape wounding and then Northern blot analysis was employed to identify genes that mediate cell migration. After wounding the monolayer, there is maximal induction of the immediate-early genes Egr-1, c-fos, NAK-1, and gro at 1 hour, followed by peak induction of connective tissue growth factor (CTGF) and c-myc at 4 hours. Message levels of urokinase-type plasminogen activator (u-PA) and its inhibitor (PAI-1) and heat shock protein (HSP)-70 are markedly raised 4-8 hours after wounding. Constitutive expression is repressed at 1 hour for transcripts that encode receptors for fibronectin (FN), epidermal growth factor, and hepatocyte growth factor (c-met), and the secreted proteins FN and osteopontin. Expression of genes encoding transforming growth factor (TGF)-beta 1 and -beta 2, retinoic acid receptor alpha, int-1, int-2, and gap junction protein which can play a role in cell movement, appeared unchanged after wounding. Differential expression of genes was a function of cell location relative to the wound; NAK-1, PAI-1, and HSP-70 were induced or stimulated only in cells at the wound edge, u-PA was stimulated in cells away from the wound, and CTGF was induced in each of these populations suggesting that cell-to-cell communication may regulate gene expression after wounding. Adenosine diphosphate, a potent stimulator of cell migration which enhances expression of u-PA and PAI-1 in nonwounded cultures, additively stimulates these genes after wounding and may thereby potentiate wound healing. Thus scrape wounding of renal epithelial cells is followed by induction, stimulation, or repression of specific genes with distinct responses in different populations of cells.

Calcium oxalate monohydrate crystals stimulate gene expression in renal epithelial cells

Primary or secondary hyperoxaluria is associated with calcium oxalate nephrolithiasis, interstitial fibrosis and progressive renal insufficiency. Monolayer cultures of nontransformed monkey kidney epithelial cells (BSC-1 line) and calcium oxalate monohydrate (COM) crystals were used as a model system to study cell responses to crystal interactions that might occur in the nephrons of patients during periods of hyperoxaluria. To determine if COM crystals signal a change in gene expression, Northern blots were prepared from total renal cellular RNA after the cells were exposed to crystals. The immediate early genes c-myc, EGR-1, and Nur-77 were induced at one hour. At two to six hours stimulated expression of the genes encoding plasminogen activator inhibitor (PAI-1) and platelet-derived growth factor (PDGF)-A chain was detected, but constitutive expression of urokinase-type plasminogen activator (u-PA) was not altered. Expression of connective tissue growth factor (CTGF) was induced at one hour and persisted up to 24 hours. The stimulation of gene expression by COM crystals was relatively crystal- and renal cell-type specific. Thus the interaction of kidney epithelial cells with COM crystals alters expression of genes that encode three classes of proteins: transcriptional activators, a regulator of extracellular matrix (ECM), and growth factors. Activation of PAI-1 gene expression without a change in u-PA favors accumulation of ECM proteins, as does increased expression of PDGF and CTGF which can also stimulate fibroblast proliferation in a paracrine manner. These results suggest that COM crystal-mediated stimulation of specific genes in renal tubular cells may contribute to the development of interstitial fibrosis in hyperoxaluric states.

A human keratinocyte cell line produces two autocrine growth inhibitors, transforming growth factor-beta and insulin-like growth factor binding protein-6, in a calcium- and cell density-dependent manner

Two growth inhibitors were identified in culture medium conditioned by a human keratinocyte cell line, HaCat. TGF-beta was detected in media conditioned by growing or confluent HaCat cells, as well as in media conditioned at physiological (1 mM) or low (0.03 mM) Ca2+ concentrations. However, a considerable part of transforming growth factor beta (TGF-beta) in media conditioned at a physiological Ca2+ concentration was in active form, whereas most TGF-beta in media conditioned at a low Ca2+ concentration was latent. The other growth-inhibitory activity, which was detected only in media conditioned by confluent cells at a physiological Ca2+ concentration, was purified to homogeneity by a four-step procedure. The N-terminal amino acid sequence of the 33-kDa protein was identical with that of insulin-like growth factor binding protein-6 (IGFBP-6). Purified IGFBP-6 inhibited the growth of HaCat and Balb/MK keratinocyte cell lines, as well as Mv1Lu cells. The growth activity was also demonstrated by human recombinant IGFBP-6. In summary, HaCat cells secrete at least two possible autocrine growth inhibitors: TGF-beta which is secreted constitutively, but activated in a Ca(2+)-dependent manner, and IGFBP-6 which is secreted in a cell density- and Ca(2+)-dependent manner.

beta ig-h3: a transforming growth factor-beta-responsive gene encoding a secreted protein that inhibits cell attachment in vitro and suppresses the growth of CHO cells in nude mice

beta ig-h3 is a novel gene first discovered by differential screening of a cDNA library made from A549 human lung adenocarcinoma cells treated with transforming growth factor-beta 1 (TGF-beta 1). It encodes a 683-amino-acid protein containing a secretory signal sequence and four homologous internal domains. Here we show that treatment of several types of cells, including human melanoma cells, human mammary epithelial cells, human keratinocytes, and human fibroblasts, with TGF-beta resulted in a significant increase in beta ig-h3 RNA. A portion of the beta ig-h3 coding sequence was expressed in bacteria, and antisera against the bacterially produced protein was raised in rabbits. This antisera was used to demonstrate that several cell lines secreted a 68-kD beta IG-H3 protein after treatment with TGF-beta. Transfection of beta IG-H3 expression plasmids into Chinese hamster ovary (CHO) cells led to a marked decrease in the ability of these cells to form tumors in nude mice. The beta IG-H3 protein was purified from media conditioned by recombinant CHO cells, characterized by immunoblotting and protein sequencing and shown to function in an anti-adhesion assay in that it inhibited the attachment of A549, HeLa, and WI-38 cells to plastic in serum-free media. Sequencing of cDNA clones encoding murine beta ig-H3 indicated 90.6% conservation at the amino acid level between the murine and human proteins. Finally, the beta ig-h3 gene was localized to human chromosome 5q31, a region frequently deleted in preleukemic myelodysplasia and leukemia. The corresponding mouse beta ig-h3 gene was mapped to mouse chromosome 13 region B to C1, which confirms a region of conservation on human chromosome 5 and mouse chromosome 13. We suggest that this protein be named p68 beta ig-h3.

Expression of TGF-beta during in vitro differentiation of hamster tracheal epithelial cells

The control of growth and differentiation of tracheal epithelial cells is poorly understood. Retinoic acid seems to be essential for the growth and secretory cell differentiation of hamster tracheal epithelial (HTE) cells in culture. In this study, we tested the hypothesis that one way by which retinoic acid (RA) stimulates growth is by decreasing transforming growth factor beta (TGF beta) expression or activity or both. HTE cells were very sensitive to TGF beta-induced growth inhibition. TGF beta 1 was more potent than TGF beta 2 with 50% inhibition of growth achieved at a concentration less than 0.1 ng/ml. A single TGF beta 1 transcript of 2.4 kb was expressed in HTE cells, and the amount increased by fourfold as cell proliferation decreased and differentiation increased. No TGF beta 2 mRNA could be detected in proliferating undifferentiated HTE cells, but two distinct mRNAs (5.1 and 3.5 kb) were observed to be induced in a transient fashion in RA-treated cells which correlated with the onset of differentiation. The amount of biologically active TGF beta in conditioned media from HTE cells at different stages of growth and differentiation in primary culture was determined by the mink lung epithelial cell growth inhibition assay and the use of neutralizing antibodies. These assays indicated a large increase in the total amount of TGF beta at the time the cells slowed their growth and started to differentiate. The activity was due primarily to TGF beta 1. Interestingly, cells treated with RA had a major component of "preactivated" (non-latent) TGF beta 1 compared to control cells.(ABSTRACT TRUNCATED AT 250 WORDS)

A GC-rich domain with bifunctional effects on mRNA and protein levels: implications for control of transforming growth factor beta 1 expression

Chimeric plasmids containing selected reporter coding domains and portions of the transforming growth factor beta 1 (TGF-beta 1) 3' untranslated region (UTR) were prepared and used to identify potential mechanisms involved in regulating the biosynthesis of TGF-beta 1. Transient transfections with core and chimeric constructs containing the chloramphenicol acetyltransferase (CAT) reporter showed that steady-state CAT mRNA levels were decreased two- to threefold in response to the TGF-beta 1 3' UTR. Interestingly, CAT activity was somewhat increased in the same transfectants. Thus, production of CAT protein per unit of mRNA was stimulated by the TGF-beta 1 3' UTR (approximately fourfold in three cell lines of distinct lineage). The translation-stimulatory effect of the TGF-beta 1 3' UTR suggested by these studies in vivo was confirmed in vitro by cell-free translation of core and chimeric transcripts containing the growth hormone coding domain. These studies showed that production of growth hormone was stimulated threefold by the TGF-beta 1 3' UTR. A deletion analysis in vivo indicated that the GC-rich domain in the TGF-beta 1 3' UTR was responsible for both the decrease in mRNA levels and stimulation of CAT activity-mRNA. We conclude that this GC-rich domain can have a bifunctional effect on overall protein expression. Moreover, the notable absence of this GC-rich domain in TGF-beta 2, TGF-beta 3, TGF-beta 4, and TGF-beta 5 indicates that expression of distinct TGF-beta family members can be differentially controlled in cells.

A GC-rich domain with bifunctional effects on mRNA and protein levels: implications for control of transforming growth factor beta 1 expression

Chimeric plasmids containing selected reporter coding domains and portions of the transforming growth factor beta 1 (TGF-beta 1) 3' untranslated region (UTR) were prepared and used to identify potential mechanisms involved in regulating the biosynthesis of TGF-beta 1. Transient transfections with core and chimeric constructs containing the chloramphenicol acetyltransferase (CAT) reporter showed that steady-state CAT mRNA levels were decreased two- to threefold in response to the TGF-beta 1 3' UTR. Interestingly, CAT activity was somewhat increased in the same transfectants. Thus, production of CAT protein per unit of mRNA was stimulated by the TGF-beta 1 3' UTR (approximately fourfold in three cell lines of distinct lineage). The translation-stimulatory effect of the TGF-beta 1 3' UTR suggested by these studies in vivo was confirmed in vitro by cell-free translation of core and chimeric transcripts containing the growth hormone coding domain. These studies showed that production of growth hormone was stimulated threefold by the TGF-beta 1 3' UTR. A deletion analysis in vivo indicated that the GC-rich domain in the TGF-beta 1 3' UTR was responsible for both the decrease in mRNA levels and stimulation of CAT activity-mRNA. We conclude that this GC-rich domain can have a bifunctional effect on overall protein expression. Moreover, the notable absence of this GC-rich domain in TGF-beta 2, TGF-beta 3, TGF-beta 4, and TGF-beta 5 indicates that expression of distinct TGF-beta family members can be differentially controlled in cells.

Selective growth arrest and phenotypic reversion of prostate cancer cells in vitro by nontoxic pharmacological concentrations of phenylacetate

Differentiation therapy may provide an alternative for treatment of cancers that do not respond to cytotoxic chemotherapy or hormonal manipulations. This hypothesis led us to evaluate the effect of a nontoxic differentiation inducer, sodium phenylacetate (NaPA), on hormone-refractory prostate cancer, the second most common cause of cancer deaths in men. NaPA treatment of androgen-independent PC3 and DU145 prostate cell lines, like that of hormone-responsive LNCaP cultures, resulted in dose-dependent inhibition of cell proliferation. Similar treatments were not significantly inhibitory to replicating normal endothelial cells and skin fibroblasts. In addition to the selective cytostatic effect, NaPA induced reversion of the prostatic cells to a nonmalignant phenotype, evidenced by their reduced invasiveness and loss of tumorigenicity in athymic mice. Phenotypic reversion was accompanied by alterations in gene expression, including selective reduction in tumor growth factor-beta 2 mRNA levels and increased amounts of class I major histocompatibility complex HLA transcripts. Furthermore, there was a decrease in tumor-associated proteolysis mediated by urokinase plasminogen activator, a molecular marker of disease progression in humans. When tumor cells were treated with NaPA together with suramin, a drug with demonstrable activity in patients, there was complete abrogation of cell growth under conditions in which each treatment alone produced only a partial effect. The in vitro antineoplastic activity was observed with drug concentrations that have been achieved in humans with no significant toxicities, suggesting that PA, used alone or in combination with other antitumor agents, warrants evaluation in the treatment of advanced prostatic cancer.

A factor derived from chick embryo retina which inhibits DNA synthesis of retina itself

Chick embryo retinas contain a peptide factor that inhibits DNA synthesis in explants of chick embryo retina. The inhibitory factor, obtained by acid/ethanol extraction from 15-day-old chick embryo retinas, was partially purified by affinity chromatography on heparin-sepharose CL-6B and gel filtration on Sephadex G-100. The inhibitor reduced DNA synthesis with maximal effects observed in retinal explants from 7 to 8-day-old chick embryos. The inhibitory effect became apparent after 10 h of incubation and reached the maximum levels after 16 h. DNA-inhibiting activity was heat and acid-stable and was destroyed by trypsin and alkaline treatments. The inhibitory effect was observed in retinal explants incubated in a medium free from L-glutamine, and the addition of this compound to the medium reduced the inhibitory effect in a concentration-dependent manner.

cDNA cloning and sequence analysis of beta ig-h3, a novel gene induced in a human adenocarcinoma cell line after treatment with transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) is capable of affecting the proliferation of many cell types. To identify novel genes whose protein products may mediate cellular responses to this factor, a cDNA library was made from mRNA isolated from a human lung adenocarcinoma cell line (A549) that had been treated for 3 days with TGF-beta. The library was screened by differential hybridization and a cDNA clone, beta ig-h3, was isolated. This gene was induced up to 20-fold in A549 cells after 2 days of treatment with TGF-beta 1. It was also induced in several other cell lines, including PC-3 and H2981. DNA sequence analysis of beta ig-h3 indicated that it encoded a novel protein, beta IG-H3, of 683 amino acids, which contained an amino-terminal secretory sequence and a carboxy-terminal Arg-Gly-Asp (RGD) sequence that can serve as a ligand recognition site for several integrins. beta IG-H3 also contained short amino acid regions homologous to similar regions in Drosophila fasciclin-I and four homologous internal domains, which can be folded into a potential bivalent structure and could act as a bridge between cells expressing the appropriate ligand. beta ig-h3 RNA was detected in several cell lines and tissues. COS cells transfected with plasmids encoding beta IG-H3 secreted a major 68-kD protein that was detected by immunoblotting using antipeptide antibodies. Since beta ig-h3 is induced in several cell lines whose proliferation is affected by TGF-beta 1, it may be involved in mediating some of the signals of this multifunctional growth modulator.

Evolutionary origins of the transforming growth factor-beta gene family

A molecular phylogeny for the transforming growth factor-beta (TGF-beta) gene family based on a comparison of nucleotide sequences is proposed. A phylogenetic tree constructed from these sequences shows that the family evolved from a common ancestral gene that came into existence at about the time of arthropod and chordate divergence. This model suggests that the present day TGF-beta gene family consists of four members: TGF-beta 1 (= TGF-beta 4), TGF-beta 2, TGF-beta 3, and TGF-beta 5. The molecular phylogeny and Southern hybridization data also suggest that the proteins for mammalian TGF-beta 1 and chicken TGF-beta 4 are the products of homologous rather than duplicated genes. If the gene duplication event that produced the ancestral gene for TGF-beta 1 occurred before the divergence of birds and mammals, then sufficient time would have elapsed to generate these quite distinct avian and mammalian TGF-beta 1 proteins. Therefore, the TGF-beta family contains four distinct proteins, TGF-beta 1, 2, 3, and 5.

Crystal structure of transforming growth factor-beta 2: an unusual fold for the superfamily

The transforming growth factors-beta (TGF-beta 1 through -beta 5) are a family of homodimeric cytokines that regulate proliferation and function in many cell types. Family members have 66 to 80% sequence identity and nine strictly conserved cysteines. A crystal structure of a member of this family, TGF-beta 2, has been determined at 2.1 angstrom (A) resolution and refined to an R factor of 0.172. The monomer lacks a well-defined hydrophobic core and displays an unusual elongated nonglobular fold with dimensions of approximately 60 A by 20 A by 15 A. Eight cysteines form four intrachain disulfide bonds, which are clustered in a core region forming a network complementary to the network of hydrogen bonds. The dimer is stabilized by the ninth cysteine, which forms an interchain disulfide bond, and by two identical hydrophobic interfaces. Sequence profile analysis of other members of the TGF-beta superfamily, including the activins, inhibins, and several developmental factors, imply that they also adopt the TGF-beta fold.

Identification of a structural domain that distinguishes the actions of the type 1 and 2 isoforms of transforming growth factor beta on endothelial cells

A chimeric transforming growth factor beta (TGF-beta) molecule has been synthesized to map the amino acids responsible for the substantially greater activity of TGF-beta 1 than TGF-beta 2 on growth and migration of endothelial cells. This chimera consists of a dimer of a monomeric unit composed of amino acids 1-39 of TGF-beta 2, 40-82 of TGF-beta 1, and 83-112 of TGF-beta 2. Structural identity of the purified recombinant protein has been confirmed by immunoblotting and NH2-terminal sequencing. The biological potency of the TGF-beta 2-1-2 chimera was equal to that of TGF-beta 1 in inhibition of growth of both fetal bovine heart endothelial cells and rat epididymal fat pad microvascular endothelial cells. Similarly, the TGF-beta 2-1-2 chimera was nearly equivalent to TGF-beta 1 and at least 10-fold more active than TGF-beta 2 in inhibiting migration of bovine aortic endothelial cells. These results identify the sequence between amino acids 40-82 as an important region within TGF-beta that functions to specify a TGF-beta 1- or TGF-beta 2-like activity.

Adenine nucleotides stimulate migration in wounded cultures of kidney epithelial cells

Adenine nucleotides speed structural and functional recovery when administered after experimental renal injury in the rat and stimulate proliferation of kidney epithelial cells. As cell migration is a component of renal regeneration after acute tubular necrosis, we have used an in vitro model of wound healing to study this process. High density, quiescent monkey kidney epithelial cultures were wounded by mechanically scraping away defined regions of the monolayer to simulate the effect of cell loss after tubular necrosis and the number of cells that migrated into the denuded area was counted. Migration was independent of cell proliferation. Provision of adenosine, adenine nucleotides, or cyclic AMP increased the number of migrating cells and accelerated repair of the wound. Other purine and pyrimidine nucleotides were not effective. Arginine-glycine-aspartic acid-serine peptide, which blocks the binding of extracellular fibronectin to its cell surface receptor, completely inhibited migration in the presence or absence of ADP. Very low concentrations of epidermal growth factor (K0.5 approximately 0.3 ng/ml) stimulated migration, whereas transforming growth factor-beta 2 was inhibitory (Ki approximately 0.2 ng/ml). Thus, adenosine and/or adenine nucleotides released from injured or dying renal cells, or administered exogenously, may stimulate surviving cells in the wounded nephron to migrate along the basement membrane, thereby rapidly restoring tubular structure and function.

Crystallization and preliminary X-ray analysis of recombinant human transforming growth factor beta 2

Recombinant human transforming growth factor beta 2 (TGF-beta 2) was cloned and expressed in E. coli. The protein was isolated from inclusion bodies, renatured and purified to a single component as judged by reversed-phase HPLC. The recombinant TGF-beta 2 was shown to have a biological activity equal to that of native TGF-beta 2 in a fibroblast migration assay. Pure, active recombinant TGF-beta 2 has been crystallized from polyethylene glycol 400. The trigonal crystals of spacegroup P3(1)21 or P3(2)21 have unit cell dimensions of a=b=60.6 A, c=75.2 A and diffract beyond 2.0 A.

Effect of the expression of transforming growth factor-beta 2 in primary human glioblastomas on immunosuppression and loss of immune surveillance

Glioblastomas are malignant brain tumors that are attended by an immunosuppressed state. The authors have studied the expression of transforming growth factor-beta 2, which is known to have potent immunosuppressive and angiogenic properties. Transforming growth factor-beta 2 messenger ribonucleic acid and its protein product are both found to be greatly overexpressed in these tumors and are absent from normal brain tissue. The overexpression of this growth factor may contribute to the escape of neoplastic astrocytes from immune surveillance and, furthermore, to the immunosuppressed state that is characteristic of many of these patients.

Cyclic AMP induces transforming growth factor beta 2 gene expression and growth arrest in the human androgen-independent prostate carcinoma cell line PC-3

The standard therapy for advanced prostate cancer is androgen ablation. Despite transitory responses, hormonally treated patients ultimately relapse with androgen-independent disease that is resistant to further hormonal manipulation and cytotoxic chemotherapy. To develop an additional approach to the treatment of advanced prostate cancer, we have been studying the signal transductions controlling the growth of human androgen-independent prostate carcinoma cell lines. We report here that elevation of intracellular cAMP markedly inhibits the growth of the hormone-refractory cell line PC-3. To examine the mechanism of cAMP action in PC-3 cells, we tested the effect of the cAMP analog dibutyryl cAMP (Bt2-cAMP) on the regulation of the potent negative growth factor transforming growth factor beta (TGF-beta). Bt2-cAMP selectively induced the secretion of TGF-beta 2 and not TGF-beta 1 by PC-3 cells. This TGF-beta 2 was shown to be bioactive by using the CCL-64 mink lung cell assay. TGF-beta 1 was not activated despite being present at 3-fold higher concentrations than TGF-beta 2. Northern analysis showed that Bt2-cAMP induced an increase in the five characteristic TGF-beta 2 transcripts and had no effect on the level of TGF-beta 1 or TGF-beta 3 transcripts. TGF-beta 2 induction was only weakly enhanced by cycloheximide and was completely inhibited by actinomycin D. These data show that Bt2-cAMP induces the expression of active TGF-beta 2 by PC-3 prostate carcinoma cells, suggesting a new approach to the treatment of prostate cancer and a new molecular mechanism of cAMP action.

Expression of activins and TGF beta 1 and beta 2 RNAs in early postimplantation mouse embryos and uterine decidua

The expression of the mesoderm inducing factors, activins and TGF beta s, was characterized in 5 1/2-9 1/2 day mouse embryos and implantation sites by in situ hybridization. Activin beta A RNA was not detected within the embryo, but is expressed in nearby decidual cells from 5 to 7 days. Thus activin A could play a role within the embyro during gastrulation. Activin beta A is also expressed in more mesometrially located decidual cells from 6 to 9 1/2 days. Activin beta B and inhibin alpha RNAs were not detected, while a control tissue was highly positive. TGF beta 1 is expressed in the secondary decidual zone and in developing endothelial cells in the decidua and embryo. TGF beta 2 is expressed in the mesometrial decidua at 6 1/2 days and in the midline of the cranial neural plate.

Regulation of expression of transforming growth factor-beta 2 by transforming growth factor-beta isoforms is dependent upon cell type

The effect of three different isoforms of transforming growth factor-beta (TGF-beta) on the expression of TGF-beta 2 mRNA was studied in several continuous tumor cell lines. As previously reported for the mouse fibroblast cell line AKR-2B, the expression of TGF-beta 2 mRNA transcripts of 5.4, 4.7, 3.7 and 3.0 kb was decreased after a 24 hr treatment with 5 ng/ml of TGF-beta 1, TGF-beta 2 or TGF-beta 3. In A549, HBL-100 and BSC-1 epithelial cell lines, five distinct TGF-beta 2 mRNA transcripts of 5.8, 5.1, 4.0, 3.8 and 2.8 kb were detected by Northern blot analysis. Treatment of these cells with TGF-beta 1, TGF-beta 2 or TGF-beta 3 for 24 hr resulted in a 2-3 fold increase in the 5.8, 4.0 and 3.8 kb transcripts, with little detectable change in abundance of the 5.1 and 2.8 kb transcripts. The effect of the TGF-beta proteins was dose (5 ng/ml) and time (3-6 hr) dependent. A similar 2-3 fold increase in the level of secreted TGF-beta 2 was observed following treatment of A549 cells with TGF-beta 1. Basal level and induced expression of TGF-beta 2 mRNA in response to TGF-beta isoforms was decreased in the presence of actinomycin D. In all cell lines studied, the expression of the 2.5 kb TGF-beta 1 mRNA was relatively unchanged or markedly increased in response to treatment with TGF-beta.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning and primary structure of the chicken transforming growth factor-beta 2 gene

The chicken transforming growth factor-beta 2 (TGF-beta 2) gene and its flanking regions were cloned and characterized. The gene contains 7 exons and 6 introns spanning about 70 kb. Primer extension analysis identified one major and two minor starts of transcription. A comparison of the 5'-flanking regions for human and chicken TGF-beta 2 genes revealed limited sequence homology around the start of transcription, including conserved TATA-box, CRE, and AP-2 sequence motifs. A species comparison of the 5' untranslated region did not reveal any sequence homology beyond the coding region. In contrast, the 3' untranslated region was highly conserved, suggesting that this region may play an important role in the expression of the TGF-beta 2 gene.

Identification and analysis of discrete functional domains in the pro region of pre-pro-transforming growth factor beta 1

A series of site-specific insertion and deletion mutants was prepared in the pro domain of transforming growth factor beta 1 (TGF beta 1) encoded by simian TGF beta 1 cDNA. These mutants were transiently expressed in COS-1 cells and the ability of each to be properly processed, folded correctly, and secreted was determined by immunoblot analysis of cells and culture supernatants. Insertions in regions corresponding to amino acid residues 50, 154, and 170 blocked secretion; culture supernatants from COS-1 cells showed no immunologically reactive proteins, whereas intact cells contained high levels of the mutant polypeptides. Insertions in the middle portion of the pro domain at residues 81, 85, and 144 affected disulfide maturation of the mature TGF beta 1. An insertion at residue 110, on the other hand, appeared to destabilize the mature TGF beta 1 polypeptide, resulting in degraded growth factor. Relatively small (10 amino acids) to large (125 amino acids) deletion mutations in the pro domain of TGF beta 1, when expressed as the full-length pre-pro-TGF beta 1, appeared to block secretion. By contrast, if the pro domain (designated beta 1-latency-associated peptide [beta 1-LAP]) was expressed independently, deletion mutants in the region 40-110 were readily secreted by the COS-1 cells, whereas deletions in residues 110-210 either destabilized the structure of the protein or blocked its intracellular transport. Cross-linking assays employing radioiodinated TGF beta 1 and biological assays indicate that residues 50-85 of beta 1-LAP are required for association with mature TGF beta 1.

Signals that release growth factors from renal epithelial cells

Monkey kidney epithelial cells of the nontransformed BSC-1 line have been used as a model system to investigate growth control. Renal growth in K depletion nephropathy was studied in culture by reducing the K concentration of the medium, which accelerated cell proliferation. This response appeared to be mediated by release of a growth-promoting activity that has an apparent molecular weight of 12,000 to 30,000. Growth stimulation was also observed when the Na concentration of the medium was reduced and was associated with the appearance of two growth-promoting factors (apparent molecular weight, 6,200 and 9,000) that exhibited cell-type specificity. Thus, modest reductions in the extracellular concentration of K or Na result in rapid appearance of autocrine factors that could modulate cell function along the nephron. The most powerful mitogen for BSC-1 cells is adenosine diphosphate (ADP). This nucleotide stimulates expression of several cell cycle-specific genes and proto-oncogenes, and induces secretion of a platelet-derived growth factor-like protein that is not mitogenic for BSC-1 cells. Release of this growth factor by renal epithelial cells in vivo would represent a paracrine mechanism to initiate proliferation of neighboring stromal or vascular cells.

Isolation and characterisation of milk growth factor, a transforming-growth-factor-beta 2-related polypeptide, from bovine milk

A strategy was developed for the purification of a biologically active polypeptide growth and migration factor from skimmed bovine milk. This 25-kDa dimeric molecule, termed milk growth factor (MGF), was isolated by a method consisting of a combination of strong cation-exchange chromatography, low-pressure hydrophobic-interaction chromatography, hydrophobic-interaction HPLC and size-exclusion HPLC steps, which separated the protein according to its properties of charge, hydrophobicity and size, respectively. On average, a total purification of 10(6)-10(7)-fold and a yield of approximately 115 +/- 78 ng/MGF/milk was obtained using the method described. All purification steps were performed with novel combinations of ethanol and volatile acidic salt (ammonium acetate) solutions in order to retain biological activity of the protein. These conditions, together with the easy removal of salt by lyophilization, facilitated the detection of biological activity in fractions collected at each step of the purification by means of a sensitive in vitro fibroblast-migration assay in which the half-maximal activity was obtained at a concentration of approximately 17 +/- 4 pg/ml (i.e. approximately 1 pM) of the pure protein. Biological activity of the dimeric protein was unaffected by heat treatment or exposure to acid (pH 2.0), but was lost upon reduction to its monomeric form. Amino acid composition and sequence analyses demonstrate that MGF is related to transforming growth factor type beta 2.

Molecular cloning and structure of the human transforming growth factor-beta 2 gene promoter

Genomic DNA extending over 10 kb 5' of the transforming growth factor-beta 2 (TGF-beta 2) coding region was isolated from a human lung fibroblast lambda phage library. A 5.6 kb Hind III fragment containing the 5'-untranslated region and flanking sequences was subcloned and sequenced. S1 nuclease protection analysis identified a transcriptional initiation site 1357 nucleotides 5' of the methionine initiation codon (ATG). A "TATA box" consensus sequence was identified 30 bp from this transcriptional start site; however, consensus "CAT box" sequences were not observed. Approximately 50 nucleotides of homopurine-pyrimidine [d(GA.CT)50] sequence were identified in the 5'-untranslated region, as well as two short open reading frames of 5 and 45 amino acids. Several AP-1, AP-2, CRE and SP1-like DNA consensus sequence elements were also identified surrounding the transcription initiation site. 5'-deletion mutants of the promoter region were fused to the chloramphenicol acetyl transferase (CAT) gene and promoter activity of the isolated genomic DNA was demonstrated in several cell lines. DNA constructs containing nucleotides between -508 to +63 demonstrated high levels of promoter activity. However, sequences between -778 and -508 nucleotides modulated this promoter activity in a manner which was dependent upon the cell line utilized, suggesting that regulation of TGF-beta 2 gene transcription may be dependent upon the cellular background. The TGF-beta 2 promoter is markedly different from the promoters that have been recently characterized for TGF-beta 1 and TGF-beta 3.

Expression of recombinant TGF-beta 2(442) precursor and detection in BSC-40 cells

Analysis of cDNA clones encoding transforming growth factor (TGF)-beta 2 predicts two different precursor proteins derived by alternative mRNA splicing; a 414 amino acid precursor [TGF-beta 2(414)] and a 442 amino acid precursor [TGF-beta 2(442)]. The two proteins differ by a 28 amino acid insertion within the pro-region of TGF-beta 2(442). In order to characterize the TGF-beta 2-related proteins encoded by the TGF-beta 2(442) cDNA and determine whether it could, in fact, direct the synthesis of active growth factor, we have expressed this gene in Chinese hamster ovary (CHO) cells and, after amplification with methotrexate, obtained stable clones secreting TGF-beta 2(442). The TGF-beta 2 secreted by these cells was latent as acidification was necessary to detect optimal biological activity. In addition to mature TGF-beta 2, high molecular weight pro-region containing proteins were also secreted as analyzed by immunoblotting using site-specific anti-peptide antibodies. These proteins migrated differently than those secreted by CHO cells transfected with cDNA encoding TGF-beta 2(414), indicating that structural differences exist between the two complexes. An anti-peptide antiserum was produced in rabbits against the 28 amino acid insert region of TGF-beta 2(442). This sera was then used to detect the presence of TGF-beta 2(442) in serum-free media conditioned by BSC-40 cells. Since the TGF-beta 2(442) precursor is produced and secreted by a non-recombinant cell line, this suggests that it may play a physiological role in regulating the activity of TGF-beta 2.

Characterization of latent recombinant TGF-beta 2 produced by Chinese hamster ovary cells

Latent recombinant transforming growth factor-beta 2 (LrTGF-beta 2) complex has been purified from serum-free media conditioned by Chinese hamster ovary cells transfected with a plasmid encoding the TGF-beta 2 (414) precursor. Under neutral conditions, LrTGF-beta 2 had an apparent molecular weight of 130 kDa. The complex contained both mature and pro-region sequences. Acidification of LrTGF-beta 2 resulted in the release of mature 24 kDa TGF-beta 2 from the high molecular weight pro-region-containing complex, suggesting that TGF-beta 2 was non-covalently associated with this complex. These results were confirmed by crosslinking experiments performed on partially purified LrTGF-beta 2. Protein sequence analysis of the purified TGF-beta 2 pro-region indicated that signal peptide cleavage occurred between ser(20) and leu(21). The pro-region, which previously was found to contain mannose-6-phosphate, bound to the mannose-6-phosphate receptor. Proteolytic cleavage of mature TGF-beta 2 from pro-TGF-beta 2 was inhibited by monensin and chloroquine suggesting that binding to this receptor and subsequent transport to acidic vesicles may be involved in the processing of rTGF-beta 2 precursor.

Expression of transforming growth factor-beta 1 and beta 2 in rat glomeruli

The transforming growth factors-beta are potent modulators of cell growth and extracellular matrix metabolism in most types of cultured cells. The distribution and functions of TGF-beta in vivo are less well known. We utilized several different techniques including northern blots, a CCl-64 cell growth inhibition assay, and sandwich enzyme-linked immunosorbent assays (SELISA) to examine the expression of TGF-beta 1 and TGF-beta 2 in rat glomeruli. High levels of TGF-beta 1 mRNA and protein were found in glomeruli (56 +/- 22 ng TGF-beta 1/g tissue). These levels were several-fold higher than those present in whole kidney (10 +/- 5 ng/g). TGF-beta 2 mRNA was present in glomeruli but was not detected in whole kidney. TGF-beta 2 concentrations by SELISA were 19 +/- 8 ng TGF-beta 2/g in glomeruli and less than 5 ng/g in whole kidney. Since TGF-beta has such marked effects on cell growth, we also examined whether alterations in TGF-beta expression were associated with the renal hypertrophy which follows unilateral nephrectomy. Expression of TGF-beta 1 mRNA decreased in glomeruli following nephrectomy. However, this was not associated with a significant fall in glomerular TGF-beta 1 protein concentration. Whole kidney levels of TGF-beta 1 and its mRNA were unchanged following nephrectomy. Similar results were obtained for TGF-beta 2. Our data document the presence of high concentrations of TGF-beta 1 and beta 2 and their corresponding mRNAs in normal rat glomeruli. These results suggest that TGF-beta may play important regulatory roles in the normal glomerulus.

Regulation and expression of transforming growth factor type-� during early mammalian development

We have examined the effect of differentiation on the expression of different members of the transforming growth factor type-beta (TGF-beta) family using embryonal carcinoma (EC) cells and early mammalian embryos. We determined that TGF-beta activity increases approximately 25-100% when the mouse EC cell line, F9, is induced to differentiate with retinoic acid (RA). Interestingly, the increased TGF-beta activity reflects the induction of TGF-beta 2 secretion following differentiation of both F9 EC cells and the human EC cell line, NT2/D1. Using the technique of reverse transcription-polymerase chain reaction (RT-PCR), we have verified that differentiation induces the expression of TGF-beta 2 as well as a distant member of the TGF-beta family, Vgr-1. Transcripts for TGF-beta 2 and Vgr-1 were readily detected in the differentiated cells of F9 and PC-13 but not in their undifferentiated counterparts. Moreover, TGF-beta 2 mRNA was readily detected in NT2/D1 cells following differentiation. In addition, transcripts for TGF-beta 2 were detected by RT-PCR in mouse morulae, preimplantation blastocysts and cultured blastocysts. Based on the data presented, it appears that the expression of both TGF-beta 2 and Vgr-1 is closely associated with the induction of differentiation during early development.

Transforming growth factor beta and noncytopathic mechanisms of immunodeficiency in human immunodeficiency virus infection

This study examines the contribution of transforming growth factor beta (TGF beta), one of the most potent endogenous immunosuppressive factors, to the development of immunodeficiency in human immunodeficiency virus (HIV) infection. Increased titers of TGF beta were found in supernatants of peripheral blood mononuclear cells (PBMCs) from HIV-infected donors as compared to uninfected controls (P less than 0.001). This correlated closely with defective responses of CD4+ lymphocytes to the recall antigens tuberculin purified protein derivative or tetanus toxoid. The addition of TGF beta-neutralizing antibody to PBMCs partially restored these defective T-cell responses. Furthermore, purified TGF beta or HIV+ PBMC culture supernatants preferentially inhibited proliferation of CD4+ lymphocytes as compared to CD8+ cells. The increased expression of the TGF beta protein was associated with increased TGF beta mRNA as determined by a polymerase chain reaction assay. This increase in TGF beta protein and mRNA was due to a selective upregulation of the TGF beta 1 isoform. These results indicate that overexpression of TGF beta 1 occurs in HIV-infected individuals and that this cytokine can contribute to impaired immune functions and to depletion of CD4+ T lymphocytes.