Growth differentiation factor-15 encodes a novel microRNA 3189 that functions as a potent regulator of cell death

According to the latest version of miRBase, approximately 30% of microRNAs (miRNAs) are unique to primates, but the physiological function of the vast majority remains unknown. In this study, we identified miR-3189 as a novel, p53-regulated, primate-specific miRNA embedded in the intron of the p53-target gene GDF15. Antagonizing miR-3189 increased proliferation and sensitized cells to DNA damage-induced apoptosis, suggesting a tumor suppressor function for endogenous miR-3189. Identification of genome-wide miR-3189 targets revealed that miR-3189 directly inhibits the expression of a large number of genes involved in cell cycle control and cell survival. In addition, miR-3189 downregulated the expression of multiple p53 inhibitors resulting in elevated p53 levels and upregulation of several p53 targets including p21 (CDKN1A), GADD45A and the miR-3189 host gene GDF15, suggesting miR-3189 auto-regulation. Surprisingly, miR-3189 overexpression in p53-/- cells upregulated a subset of p53-targets including GDF15, GADD45A, and NOXA, but not CDKN1A. Consistent with these results, overexpression of miR-3189 potently induced apoptosis and inhibited tumorigenicity in vivo in a p53-independent manner. Collectively, our study identified miR-3189 as a novel, primate-specific miRNA whose effects are mediated by both p53-dependent and p53-independent mechanisms. miR-3189 may, therefore, represent a novel tool that can be utilized therapeutically to induce a potent proapoptotic effect even in p53-deficient tumors.

A mutant p53/let-7i-axis-regulated gene network drives cell migration, invasion and metastasis

Most p53 mutations in human cancers are missense mutations resulting in a full-length mutant p53 protein. Besides losing tumor suppressor activity, some hotspot p53 mutants gain oncogenic functions. This effect is mediated in part, through gene expression changes due to inhibition of p63 and p73 by mutant p53 at their target gene promoters. Here, we report that the tumor suppressor microRNA let-7i is downregulated by mutant p53 in multiple cell lines expressing endogenous mutant p53. In breast cancer patients, significantly decreased let-7i levels were associated with missense mutations in p53. Chromatin immunoprecipitation and promoter luciferase assays established let-7i as a transcriptional target of mutant p53 through p63. Introduction of let-7i to mutant p53 cells significantly inhibited migration, invasion and metastasis by repressing a network of oncogenes including E2F5, LIN28B, MYC and NRAS. Our findings demonstrate that repression of let-7i expression by mutant p53 has a key role in enhancing migration, invasion and metastasis.

TGF-beta3 and cancer: a review

With the development of growth factors and growth factor modulators as therapeutics for a range of disorders, it is prudent to consider whether modulating the growth factor profile in a tissue can influence tumour initiation or progression. As recombinant human TGF-beta3 (avotermin) is being developed for the improvement of scarring in the skin it is important to understand the role, if any, of this cytokine in tumour progression. Elevated levels of TGF-beta3 expression detected in late-stage tumours have linked this cytokine with tumourigenesis, although functional data to support a causative role are lacking. While it has proved tempting for researchers to interpret a 'correlation' as a 'cause' of disease, what has often been overlooked is the normal biological role of TGF-beta3 in processes that are often subverted in tumourigenesis. Clarifying the role of this cytokine is complicated by inappropriate extrapolation of the data relating to TGF-beta1 in tumourigenesis, despite marked differences in biology between the TGF-beta isoforms. Indeed, published studies have indicated that TGF-beta3 may actually play a protective role against tumourigenesis in a range of tissues including the skin, breast, oral and gastric mucosa. Based on currently available data it is reasonable to hypothesize that administration of acute low doses of exogenous TGF-beta3 is unlikely to influence tumour initiation or progression.

Heterozygous inactivation of TGF-beta1 increases the susceptibility to chemically induced mouse lung tumorigenesis independently of mutational activation of K-ras

Mice heterozygous for deletion of the transforming growth factor beta1 (TGF-beta1) gene show an enhanced rate of lung tumorigenesis following carcinogen treatment. Since the growth inhibitory activity of TGF-beta1 in epithelial cells is associated with K-ras p21, and K-ras mutations commonly occur in chemically-induced mouse lung tumors, we postulated that tumors in heterozygous TGF-beta1 mice might be more likely to have K-ras mutations compared with tumors in wildtype TGF-beta1 mice. Urethane-induced lung tumors in AJBL6 TGF-beta1 +/- and +/+ mice were examined for K-ras mutations by polymerase chain reaction/single strand conformation polymorphism analysis and sequencing. Mutation frequencies were similar in both genotypes: 12/18 +/- tumors (67%) and 10/16 +/+ tumors (62%). Mutations occurred in 80% +/- and 75% +/+ carcinomas, but in only 50% of the adenomas of both TGF-beta1 genotypes. Codon 61 A-->G transition mutations were predominant, occurring in 61% +/- and 44% +/+ tumors. Three +/- (17%) and three +/+ (19%) tumors showed codon 12 mutations, mostly G-->A transitions. Two +/- tumors had both codon 61 and codon 12 mutations. Interestingly, carcinomas with mutations in codon 61 were larger than those with codon 12 changes. It appears that the mechanism of enhanced susceptibility of TGF-beta1+/- mice to urethane-induced lung carcinogenesis does not involve selective development of tumors with K-ras mutations.

TGF-beta signaling in mammary gland development and tumorigenesis

Ligands of the TGF-beta superfamily are unique in that they signal through transmembrane receptor serine-threonine kinases, rather than tyrosine kinases. The receptor complex couples to a signal transduction pathway involving a novel family of proteins, the Smads. On phosphorylation, Smads translocate to the nucleus where they modulate transcriptional responses. However, TGF-betas can also activate the mitogen-activated protein kinase (MAPK)4 pathway, and the different biological responses to TGF-beta depend to varying degrees on activation of either or both of these two pathways. The Smad pathway is a nexus for cross-talk with other signal transduction pathways and for modulation by many different interacting proteins. Despite compelling evidence that TGF-beta has tumor suppressor activity in the mammary gland, neither TGF-beta receptors nor Smads are genetically inactivated in human breast cancer, though receptor expression is reduced. Possible reasons are discussed in relation to the dual role of TGF-beta as tumor suppressor and oncogene.

Transforming growth factor-beta 1 and its receptors in human lung cancer and mouse lung carcinogenesis

The transforming growth factor-betas (TGF-beta s) are multifunctional proteins that inhibit the proliferation of many epithelial cells through a set of cell protein receptors that includes the TGF-beta type I (RI) and type II (RII) receptors. Loss of growth inhibition by TGF-beta is thought to contribute to the development of many types of tumors. In the present study, we have examined expression of the proteins and mRNAs for TGF-beta 1, TGF-beta RI, and TGF-beta RII in normal human lung, well-characterized non-small cell lung cancer (NSCLC) cell lines, and primary NSCLC specimens. Immunohistochemical staining for TGF-beta 1, TGF-beta RI, and TGF-beta RII using specific antibodies in normal human lung showed expression of the 3 proteins in the epithelium of bronchi and bronchioles as well as in alveoli. Differential expression of TGF-beta RI and TGF-beta RII proteins was detected in 5 NSCLC cell lines using Western blot analysis, with reduced levels in 3 cell lines. A panel of 45 formalin-fixed and paraffin-embedded NSCLC specimens showed positive immunostaining for TGF-beta 1, TGF-beta RI, and TGF-beta RII, with reduced TGF-beta RII in poorly differentiated adenocarcinomas and squamous cell carcinomas and some moderately differentiated adenocarcinomas. In situ hybridization studies conducted with specific riboprobes for TGF-beta 1, TGF-beta RI, and TGF-beta RII showed corresponding localization of expression of the mRNAs in the specimens that showed positive immunostaining for the proteins. To investigate the roles of TGF-beta 1, TGF-beta RI, and TGF-beta RII in chemically induced mouse lung tumorigenesis, we examined the expression of their proteins and mRNAs in 2 mouse model systems. Whereas expression of the proteins and mRNAs for TGF-beta 1 and TGF-beta RI was comparable in lung adenomas and bronchioles of A/J mice treated with benzo(alpha)pyrene, decreased immunostaining and hybridization for TGF-beta RII protein and mRNA was detected in 50% of lung adenomas in these mice. Interestingly, expression of TGF-beta 1 and the TGF-beta receptor proteins was similar to that of bronchioles in C57B1/6 mice and their littermates heterozygous for deletion of the TGF-beta 1 gene treated with diethylnitrosamine. These data show that reduced levels of expression of TGF-beta RII occur in some, but not all, human and mouse lung tumors. This suggests that different mechanisms of action, some of which may involve the TGF-beta signaling pathway, may contribute to the progression of lung tumorigenesis.

Enhanced tumorigenesis and reduced transforming growth factor-beta type II receptor in lung tumors from mice with reduced gene dosage of transforming growth factor-beta1

To elucidate the role of transforming growth factor-beta1 (TGF-beta1) and the TGF-beta type II receptor (TGF-beta RII) as tumor-suppressor genes in lung carcinogenesis, we mated C57BL/6 mice heterozygous (HT) for deletion of the TGF-beta1 gene with A/J mice to produce AJBL6 TGF-beta1 HT progeny and their wild-type (WT) littermates. Immunohistochemical staining, in situ hybridization, and northern blot analyses showed lower staining and hybridization for TGF-beta1 protein and mRNA, respectively, in the lungs of normal HT mice versus WT mice. Competitive reverse transcription-polymerase chain reaction (CRT-PCR) amplification showed the level of TGF-beta1 mRNA in the lungs of HT mice to be fourfold lower than the level in WT lung. When challenged with ethyl carbamate, lung adenomas were detected in 55% of HT mice by 4 mo but only in 25% of WT littermates at this time. Whereas all HT mice had adenomas by 6 mo, it was not until 10 mo before all WT mice had adenomas. After 12 mo, the average number of adenomas was fivefold higher in HT lungs than in WT lungs. Most dramatic was the appearance of lung carcinomas in HT mice 8 mo before they were visible in WT mice. Thus, the AJBL6 TGF-beta1 HT mouse provides an excellent model system to examine carcinogen-induced lung tumorigenesis by increasing progressive lesion incidence and multiplicity relative to their WT littermates. Immunohistochemical staining showed expression of the TGF-beta type I receptor (TGF-beta RI) at moderate to strong levels in lung adenomas and carcinomas in HT and WT mice. In contrast, whereas weak immunostaining for TGF-beta RII was detected in 67% of HT carcinomas at 12 mo, only 22% of WT carcinomas showed weak staining for this protein. Individual lung carcinomas showing reduced TGF-beta RII expression and adjacent normal bronchioles were excised from HT lungs using laser capture microdissection, and CRT-PCR amplification of the extracted RNA showed 12-fold less TGF-beta RII mRNA in these carcinomas compared with bronchioles. Decreasing TGF-beta RII mRNA levels occurred with increasing tumorigenesis in lung hyperplasias, adenomas, and carcinomas, with carcinomas having fourfold and sevenfold lower levels of TGF-beta RII mRNA than adenomas and hyperplasias, respectively. These data show enhanced ethyl carbamate-induced lung tumorigenesis in AJBL6 HT mice compared with WT mice, suggesting that both TGF-beta1 alleles are necessary for tumor-suppressor activity. Reduction of TGF-beta RII mRNA expression in progressive stages of lung tumorigenesis in HT mice suggests that loss of TGF-beta RII may play an important role in the promotion of lung carcinogenesis in mice with reduced TGF-beta1 gene dosage when challenged with carcinogen.

The mammary pathology of genetically engineered mice: the consensus report and recommendations from the Annapolis meeting

NIH sponsored a meeting of medical and veterinary pathologists with mammary gland expertise in Annapolis in March 1999. Rapid development of mouse mammary models has accentuated the need for definitions of the mammary lesions in genetically engineered mice (GEM) and to assess their usefulness as models of human breast disease. The panel of nine pathologists independently reviewed material representing over 90% of the published systems. The GEM tumors were found to have: (1) phenotypes similar to those of non-GEM; (2) signature phenotypes specific to the transgene; and (3) some morphological similarities to the human disease. The current mouse mammary and human breast tumor classifications describe the majority of GEM lesions but unique morphologic lesions are found in many GEM. Since little information is available on the natural history of GEM lesions, a simple morphologic nomenclature is proposed that allows direct comparisons between models. Future progress requires rigorous application of guidelines covering pathologic examination of the mammary gland and the whole animal. Since the phenotype of the lesions is an essential component of their molecular pathology, funding agencies should adopt policies ensuring careful morphological evaluation of any funded research involving animal models. A pathologist should be part of each research team.

Transforming growth factor-beta and breast cancer: Lessons learned from genetically altered mouse models

Transforming growth factor (TGF)-betas are plausible candidate tumor suppressors in the breast. They also have oncogenic activities under certain circumstances, however. Genetically altered mouse models provide powerful tools to analyze the complexities of TGF-beta action in the context of the whole animal. Overexpression of TGF-beta can suppress tumorigenesis in the mammary gland, raising the possibility that use of pharmacologic agents to enhance TGF-beta function locally might be an effective method for the chemoprevention of breast cancer. Conversely, loss of TGF-beta response increases spontaneous and induced tumorigenesis in the mammary gland. This confirms that endogenous TGF-betas have tumor suppressor activity in the mammary gland, and suggests that the loss of TGF-beta receptors seen in some human breast hyperplasias may play a causal role in tumor development.

Loss of responsiveness to transforming growth factor beta induces malignant transformation of nontumorigenic rat prostate epithelial cells

Transforming growth factor (TGF)-betas are multifunctional growth factors, the properties of which include the potent inhibition of epithelial cell growth. Expression patterns of TGF-betas and TGF-beta receptors in the normal prostate indicate that these growth regulators play key roles in prostatic development and proliferative homeostasis. Importantly, TGF-beta receptor levels are frequently diminished in malignant human prostate tissue. To test the hypothesis that loss of TGF-beta responsiveness is causally involved in the tumorigenic process, we have used retroviral transduction to introduce a dominant-negative mutant type II TGF-beta receptor (DNR) into the premalignant rat prostatic epithelial cell line, NRP-152. High-level expression of the DNR abolished the ability of TGF-beta to inhibit cell growth, to promote cell differentiation, and to induce apoptosis, and it partially blocked the induction of extracellular matrix gene expression. When injected into nude mice, NRP-152-DNR cells formed carcinomas at 13 of 34 sites, compared with 0 of 30 sites for parental and control cells (P = 0.0001). We conclude that the type II TGF-beta receptor is an important tumor suppressor in the prostate, and furthermore, that loss of TGF-beta responsiveness can contribute early in the tumorigenic process by causing the malignant transformation of preneoplastic cells.

Identification of the start sites for the 1.9- and 1.4-kb rat transforming growth factor-beta1 transcripts and their effect on translational efficiency

Three distinct transforming growth factor-beta1 (TGF-beta1) transcripts of 2.5, 1.9 and 1.4kb have been described, but the start sites and functional significance of the shorter transcripts are unknown. Here, we have cloned and sequenced a rat genomic fragment encoding approximately 1250 bases upstream of the start of the TGF-beta1 open reading frame. Using a combination of ribonuclease protection and 5' RACE-PCR analysis, we have mapped the start sites for the two shorter TGF-beta1 transcripts in NRP152 cells, a rat prostatic epithelial cell line that expresses all three transcripts at high levels. The 1.4-kb mRNA starts 25 bases upstream of the initiator AUG, whereas the 1.9-kb mRNA has two start sites 366 and 401 bases upstream of the AUG. Polysome analysis of the NRP152 cells indicates that the 1.9-kb transcript is very efficiently translated, whereas the 2.5- and 1.4-kb transcripts appear to be poorly translated. Differential regulation of TGF-beta1 transcript size may therefore represent an important mechanism for regulating TGF-beta1 protein levels.

Transforming growth factor-beta1 is a new form of tumor suppressor with true haploid insufficiency

Components of the transforming growth factor-beta (TGF-beta) signal pathway function as classic tumor suppressors, but the role of the TGF-betas themselves is less clear. Here we show that mice heterozygous for deletion of the TGF-beta1 gene express only 10-30% of wild-type TGF-beta1 protein levels. Although grossly normal, these mice have a subtly altered proliferative phenotype, with increased cell turnover in the liver and lung. Treatment of these mice with chemical carcinogens resulted in enhanced tumorigenesis when compared with wild-type littermates. However, tumors in the heterozygous mice did not lose the remaining wild-type TGF-beta1 allele, indicating that the TGF-beta1 ligand is a new form of tumor suppressor that shows true haploid insufficiency in its ability to protect against tumorigenesis.

Translational control elements in the major human transforming growth factor-beta 1 mRNA

Polysome analysis indicates that the major 2.4 kb transforming growth factor-beta 1 (TGF-beta 1) transcript is poorly translated, both in cultured cells, and in vivo in mouse liver. In contrast, the TGF-beta 2 transcripts are efficiently translated. The contribution of the 5'- and 3'-untranslated regions (UTRs) to the translational inhibition of the full-length TGF-beta 1 transcript was studied by deletion analysis. Despite their high G + C content, both UTRs stimulated translation in vitro. However, polysome analysis of synthetic TGF-beta 1 mRNAs transfected into MCF-7 cells suggests that the cell contains a limited pool of trans-acting factors that interact with the 5'UTR to make it inhibitory in vivo. Further deletion analysis in vitro revealed multiple stimulatory and inhibitory regions in the 5'UTR. This has important implications for the translatability of the naturally occurring shorter TGF-beta 1 transcripts and provides a framework for higher resolution mapping studies. Overall, the poor translational efficiency of the major TGF-beta 1 mRNA in vivo appears to be due to a combination of poor initiation sequence context, and inhibitory interactions of limiting transacting factors with cis-inhibitory elements embedded in an otherwise stimulatory 5'UTR.

Transgenic mice overexpressing a dominant-negative mutant type II transforming growth factor beta receptor show enhanced tumorigenesis in the mammary gland and lung in response to the carcinogen 7,12-dimethylbenz-[a]-anthracene

To test the hypothesis that the transforming growth factor-beta (TGF-beta) system has tumor suppressor activity in the mammary gland, we have generated transgenic mice overexpressing a dominant-negative mutant form of the type II TGF-beta receptor, under the control of the mouse mammary tumor virus-long terminal repeat. High-level expression of the transgene was observed in the mammary and salivary glands, with lower expression in the lung, spleen, and testis. Older nulliparous transgenic mice (9-17 months) showed a marked increase in the incidence and degree of lobulo-alveolar side-branching in the mammary glands when compared to wild-type littermates (24.8% of glands examined histologically versus 14.4%; P = 0.004), suggesting a role for endogenous TGF-betas in regulating development or maintenance of mammary alveoli. Spontaneous tumorigenesis was unchanged in the transgenic mice. However, following initiation with the carcinogen 7,12-dimethylbenz[a]anthracene, the transgenic group showed a significant increase in the incidence and multiplicity of mammary tumors when compared with wild-type littermates (40% incidence in transgenic mice versus 22% for wild-type, with 4 of 25 transgenics developing multiple mammary tumors versus 0 of 27 wild-type; P = 0.03). An early increase in the incidence of lung tumors was also observed in transgenic mice, but no difference between genotype groups was seen in the incidence of tumors in tissues in which the transgene is not expressed. The data show that the endogenous TGF-beta system has tumor suppressor activity in the mammary gland and lung.

Expression of a dominant-negative mutant TGF-beta type II receptor in transgenic mice reveals essential roles for TGF-beta in regulation of growth and differentiation in the exocrine pancreas

Using a dominant-negative mutant receptor (DNR) approach in transgenic mice, we have functionally inactivated transforming growth factor-beta (TGF-beta) signaling in select epithelial cells. The dominant-negative mutant type II TGF-beta receptor blocked signaling by all three TGF-beta isoforms in primary hepatocyte and pancreatic acinar cell cultures generated from transgenic mice, as demonstrated by the loss of growth inhibitory and gene induction responses. However, it had no effect on signaling by activin, the closest TGF-beta family member. DNR transgenic mice showed increased proliferation of pancreatic acinar cells and severely perturbed acinar differentiation. These results indicate that TGF-beta negatively controls growth of acinar cells and is essential for the maintenance of a differentiated acinar phenotype in the exocrine pancreas in vivo. In contrast, such abnormalities were not observed in the liver. Additional abnormalities in the pancreas included fibrosis, neoangiogenesis and mild macrophage infiltration, and these were associated with a marked up-regulation of TGF-beta expression in transgenic acinar cells. This transgenic model of targeted functional inactivation of TGF-beta signaling provides insights into mechanisms whereby loss of TGF-beta responsiveness might promote the carcinogenic process, both through direct effects on cell proliferation, and indirectly through up-regulation of TGF-betas with associated paracrine effects on stromal compartments.

Recharacterization of the start sites for the major human transforming growth factor-beta 1 mRNA

The start sites for the major human TGF-beta 1 transcripts have been reexamined. A comparison of ribonuclease and S1 nuclease protection analyses on native TGF-beta 1 mRNA and in vitro transcribed human TGF-beta 1 transcripts of defined sizes places the most 5' start site for the native TGF-beta 1 message approx. 50 nucleotides upstream from the previously published start site at base +1. Furthermore, the same techniques indicate that the apparent downstream start site at base +271 is an artefact due to the presence of an A + T-rich island in the middle of an otherwise highly G + C-rich sequence. This is not apparent if S1 nuclease protection is used alone, which emphasizes the importance of using the two techniques in combination for this type of analysis. Thus the major 2.5 kb TGF-beta 1 band seen on Northern blots comprises only mRNA transcribed from the more upstream of the two previously characterized promoters. This has important implications both for the transcriptional and translational regulation of this growth factor.

Synthesis and secretion of transforming growth factor beta isoforms by primary cultures of human breast tumour fibroblasts in vitro and their modulation by tamoxifen

Tamoxifen may mediate its effect in early breast cancer in part via an oestrogen receptor (ER)-independent pathway by directly stimulating fibroblasts to produce the negative paracrine growth factor transforming growth factor (TGF)-beta. We have previously shown that secretion of this factor is induced 3-to 30-fold in human fetal fibroblasts in vitro, and by stromal fibroblasts in vivo following tamoxifen treatment of ER-positive and ER-negative breast cancer patients. Primary cultures of breast tumour fibroblasts have been exposed to tamoxifen for 48 h, and rates of secretion of TGF-beta 1 and TGF-beta 2 measured using a quantitative immunoassay. Fibroblast strains derived from malignant and benign tumours produced and secreted similar amounts of TGF-beta 1, but benign breast tumour fibroblasts secreted significantly higher levels of TGF-beta 2 compared with fibroblasts of malignant origin. Tamoxifen did not induce any consistent increase in TGF-beta secretion into the conditioned medium, but immunofluorescence analysis for the intracellular form of TGF-beta 1 revealed evidence of increased immunoreactive protein in tamoxifen-treated fibroblasts, which is localised to the nucleus. Therefore synthesis of TGF-beta 1 appears to be stimulated by tamoxifen, but increased secretion may be abrogated in vitro. Furthermore, using immunocytochemistry and transient transfection with an ER-responsive reporter construct, no ER was demonstrable in these fibroblasts supporting the proposed ER-independent paracrine pathway.

The recombinant proregion of transforming growth factor beta1 (latency-associated peptide) inhibits active transforming growth factor beta1 in transgenic mice

All three isoforms of transforming growth factors beta (TGF-betal, TGF-beta2, and TGF-beta3) are secreted as latent complexes and activated extracellularly, leading to the release of the mature cytokines from their noncovalently associated proregions, also known as latency-associated peptides (LAPs). The LAP region of TGF-beta1 was expressed in a baculovirus expression system and purified to homogeneity. In vitro assays of growth inhibition and gene induction mediated by TGF-beta3 demonstrate that recombinant TGF-beta1 LAP is a potent inhibitor of the activities of TGF-betal, -beta2, and -beta3. Effective dosages of LAP for 50% neutralization of TGF-beta activities range from 4.7- to 80-fold molar excess depending on the TGF-beta isoform and activity examined. Using 125I-labeled LAP, we show that the intraperitoneal application route is effective for systemic administration of LAP. Comparison of concentrations of LAP in tissues shows a homogenous pattern in most organs with the exception of heart and muscle, in which levels of LAP are 4- to 8-fold lower. In transgenic mice with elevated hepatic levels of bioactive TGF-betal, treatment with recombinant LAP completely reverses suppression of the early proliferative response induced by TGF-beta1 in remnant livers after partial hepatectomy. The results suggest that recombinant LAP is a potent inhibitor of bioactive TGF-beta both in vitro and in vivo, after intraperitoneal administration. Recombinant LAP should be a useful tool for novel approaches to study and therapeutically modulate pathophysiological processes mediated by TGF-beta3.

Transforming growth factor-beta1 circulates in normal human plasma and is unchanged in advanced metastatic breast cancer

A method has been developed to determine true plasma transforming growth factor beta (TGF-beta) levels by using the platelet alpha granule-specific marker, platelet factor 4, to correct for the TGF-beta contributed by platelets degranulated ex vivo. TGF-beta levels were measured on acid-ethanol extracts of human plasma using isoform-specific sandwich enzyme-linked immunosorbent assays. Normal human subjects had 4.1 +/- 2.0 ng/ml TGF-beta1 (range, 2.0-12.0; n = 42), <0.2 ng/ml TGF-beta2, and <0.1 ng/ml TGF-beta3 in their plasma. There were no significant changes with age or with hormonal status, but any given individual showed fluctuations of up to 3-fold in measured plasma TGF-beta levels due to unknown factors. Of 28 patients with advanced metastatic breast cancer, 2 had greatly elevated TGF-beta1 levels, while the rest were in the normal range. The presence of physiologically significant levels of TGF-beta1 in the plasmas of normal human subjects may indicate previously unsuspected endocrine roles for this peptide, while TGF-beta2 and TGF-beta3 appear to act only in a local autocrine/paracrine fashion.

Role for autocrine TGF-beta 1 in regulating differentiation of a human leukemic cell line toward osteoclast-like cells

Increasing evidence suggests that transforming growth factor-beta (TGF-beta) is involved in bone formation during remodeling. Using a recently cloned human leukemic cell line (FLG 29.1 cells) we demonstrate that these cells synthesize and secrete TGF-beta 1 and that exogenous or autocrine TGF-beta 1 can induce the same features of osteoclastic-like cells, exerting its effects through the binding to TGF-beta specific receptors. Scatchard analysis of 125I-labeled TGF-beta 1 to FLG 29.1 cells revealed the presence of a single high affinity binding site with a Kd value of approximately 25 pM and a binding capacity of approximately 900 sites/cell. Affinity labeling experiments showed that FLG 29.1 cells express type I and type II TGF-beta receptors. Stimulation of FLG 29.1 cells with low TGF-beta 1 doses reduced cell proliferation and increased cell adhesion and tartrate resistant acid phosphatase (TRAcP) activity. Pretreatment of FLG 29.1 cells with TGF-beta 1 caused a significant and dose-dependent response to calcitonin. Northern blot of total mRNA and analysis of the conditioned media (CM) showed that TGF-beta 1 was synthesized by FLG 29.1 cells. TPA treatment, which induces partial differentiation of these cells, markedly increased TGF-beta 1 mRNA expression and growth factor release. The majority of TGF-beta 1 secreted by TPA-treated cells was in its latent form. However, anti-TGF-beta antibodies inhibited TGF-beta 1 and TPA-induced growth inhibition, calcitonin responsiveness, and TRAcP activity, suggesting that the TPA effect is mediated in part by autocrine TGF-beta 1 and indicating that the cells can activate and respond to the TGF-beta that they secrete. These findings support a potential autocrine role for TGF-beta 1 in osteoclast differentiation.

Inhibition of the chondrocyte phenotype by retinoic acid involves upregulation of metalloprotease genes independent of TGF-beta

Retinoic acid has been identified as a key morphogen governing pattern formation in the developing cartilaginous skeleton. Retinoids have also been implicated in the premature closure of the cartilage growth plate following vitamin A intoxication or administration of retinoids for dermatologic conditions. Previous studies of the mechanism of action of retinoids in non-chondrogenic cells have concluded that retinoic acid is a negative regulator of AP-1 responsive metalloprotease genes. We show that inhibition of expression of the cartilage phenotype by retinoic acid in epiphyseal chondrocytes is associated with positive regulation of AP-1 responsive metalloprotease genes, as well as induction of gene expression for the two components of the transcription factor AP-1, c-fos and c-jun. Despite the similar effects of TGF-beta 1 on expression of cartilage matrix proteins and metalloproteases in this culture system, no appreciable changes in the expression of TGF-beta isoforms were evident in response to retinoic acid treatment. The present investigation demonstrates that regulation of AP-1 responsive genes by retinoic acid can be either positive or negative, depending on the target cell type, and illuminates new mechanisms by which retinoic acid and other retinoids may exert control during development and growth of the limb.

TGF-beta 1 prevents hypertrophy of epiphyseal chondrocytes: regulation of gene expression for cartilage matrix proteins and metalloproteases

Using an in vitro model of rat epiphyseal chondrocyte differentiation in which cells are maintained in a three-dimensional cell pellet, we show that exogenous TGF-beta 1 reversibly prevents terminal differentiation of epiphyseal chondrocytes into hypertrophic cells. Through maintenance of gene expression for the cartilage matrix proteins type II collagen and aggrecan core protein, and with coordinate inhibition of expression of genes encoding the metalloproteases collagenase and stromelysin, TGF-beta 1 stabilizes the phenotype of the prehypertrophic epiphyseal chondrocyte. This ability of TGF-beta 1 to stabilize the cartilage phenotype is critically dependent on culture conditions. Epiphyseal chondrocytes cultured as a subconfluent monolayer of cells dedifferentiate (reduce type II collagen and aggrecan core protein expression, increase metalloprotease expression, and acquire a spindled morphology) in response to short-term TGF-beta 1 treatment. Increasing the initial seeding density and allowing the cells to become multilayered prior to the addition of growth factor reverse the effects of TGF-beta 1 on type II collagen and transin/stromelysin gene expression and maintain a rounded cellular morphology. This finding emphasizes the importance of considering cell density and environmental context in the analysis of the regulatory action of peptide growth factors in general and of the TGF-beta s in particular. We propose that one function of TGF-beta 1 during endochondral ossification is regulation of chondrocyte growth and differentiation through modulation of the relative expression of cartilage matrix proteins and metalloproteases. This function of TGF-beta 1 helps illustrate how the regulation of diverse cellular processes such as matrix synthesis, matrix degradation, and cell growth and differentiation may be coordinated at the molecular level by a single peptide growth factor.

Induction of transforming growth factor beta 1 in human breast cancer in vivo following tamoxifen treatment

We have investigated the ability of tamoxifen to regulate members of the transforming growth factor beta (TGF-beta) family in human breast cancers in vivo. Using immunohistochemical techniques, we find that 3 months of tamoxifen treatment causes a consistent induction of extracellular TGF-beta 1 in breast cancer biopsies, compared with matched pretreatment samples from the same patient. The induced TGF-beta is localized between and around stromal fibroblasts and appears to be derived from these cells. Lower levels of TGF-beta 1,-beta 2, and -beta 3 seen in epithelial cells were not altered by tamoxifen treatment. The increased stromal staining of TGF-beta 1 occurred in estrogen receptor-negative as well as estrogen receptor-positive tumors. These results provide in vivo evidence for a novel, estrogen receptor-independent mechanism of action for tamoxifen, involving the stromal induction of a potent growth inhibitor for epithelial cells.

Post-transcriptional regulation of the human transforming growth factor-beta 1 gene

Since many lines of evidence suggest that expression of the transforming growth factor-beta 1 (TGF-beta 1) gene may be regulated post-transcriptionally, we examined the effect of the 5'-untranslated region (UTR) of this gene on TGF-beta 1 expression. For this purpose, fragments of the 840-nucleotide highly GC-rich TGF-beta 1 5'-UTR were inserted into the 5'-UTR of the structural gene for human growth hormone driven by the simian virus 40 early promoter. A portion of the 5'-UTR of TGF-beta 1 mRNA spanning the sequences from +11 to +147 was shown to inhibit growth hormone expression by as much as 22-fold. This effect was cell-specific; growth hormone production was inhibited in PC-3 human prostate adenocarcinoma and A-549 human lung adenocarcinoma cells, while no effect was seen in rat pheochromocytoma PC12 cells, which show efficient translation of endogenous TGF-beta 1 mRNA. Computer analysis showed that this region of the 5'-UTR contained a stable secondary stem-loop structure spanning sequences +49 to +76. This stem-loop region alone is sufficient to inhibit expression of the growth hormone gene, suggesting that it plays an important role in post-transcriptional regulation of TGF-beta 1 gene expression.

Modulation of monocyte type I transforming growth factor-beta receptors by inflammatory stimuli

The regulatory mechanisms which control the wide array of cellular responses to transforming growth factor beta (TGF beta) are not understood. This report presents evidence that down-regulation of TGF beta receptors on human monocytes may be one mechanism by which the effects of TGF beta are regulated. Treatment of monocytes with interferon gamma (IFN gamma) and lipopolysaccharide for 18 h reduced monocyte receptor number (approximately 400/cell) in a dose-dependent fashion by 89 and 78%, respectively, as determined by 125I-TGF beta binding. Incubation with other cytokines (granulocyte-macrophage colony-stimulating factor, macrophage colony-stimulating factor-1, interleukin-1, tumor necrosis factor alpha) did not alter the amount of TGF beta bound. The decrease in 125I-TGF beta binding could not be attributed to competition for receptor sites by secreted TGF beta. Instead, the decline in binding was due to a loss of type I TGF beta receptors, the subtype primarily expressed by monocytes, with no decrease in receptor affinity. Lipopolysaccharide-induced receptor loss was rapid (1-4 h), in contrast to the prolonged (12 h) decline induced by IFN gamma. Loss of receptors was accompanied by a diminished ability of the cells to respond to TGF beta with an induction of TNF alpha mRNA. Thus, this monocyte system is the first example of a heterologous agent causing the down-regulation of TGF beta receptors with a concomitant decline in a TGF beta-stimulated function.

Addition of a C-terminal extension sequence to transforming growth factor-beta 1 interferes with biosynthetic processing and abolishes biological activity

Transforming growth factor-beta 1 (TGF-beta 1) is synthesized and secreted as a biologically latent complex. It has been proposed that one role of the latent complex is to prevent premature interaction of ligand and receptor intracellularly during biosynthesis (Wakefield et al., J. Cell Biol. (1987) 105, 965-975). To test this hypothesis, the endoplasmic reticulum retention sequence Lys-Asp-Glu-Leu (KDEL) was added to the C-terminus of the wildtype TGF-beta 1 coding sequence, and to a construct in which mutagenesis of two cysteine residues in the precursor pro region results in the synthesis and secretion of active, as opposed to latent, TGF-beta. Addition of either SEKDEL, or the control sequence SEKDVS to the TGF-beta 1 protein abolished biological activity. Western blot analysis indicated that the extended gene products are synthesized, but that the extension sequence partially interferes with the normal dimerization of the protein product, and totally inhibits the normal proteolytic processing and glycosylation of the precursor protein. The data suggest that correct folding of the highly conserved C terminus of TGF-beta 1 is critical for subsequent proteolytic cleavage and glycosylation at sites that are quite distant in the primary sequence. Thus molecular strategies for the generation of TGF-beta antagonists or superagonists should avoid extensive modification of this region of the molecule. Since synthesis of the endogenous TGF-beta 1 is unaffected by the presence of the mutated analog, the data further indicate that transfection with the KDEL-extended TGF-beta 1 sequence cannot be used as a dominant negative mutation to prevent secretion of the endogenous TGF-beta protein.

The growth inhibition of human breast cancer cells by a novel synthetic progestin involves the induction of transforming growth factor beta

Recent experimental work has identified a novel intracellular binding site for the synthetic progestin, Gestodene, that appears to be uniquely expressed in human breast cancer cells. Gestodene is shown here to inhibit the growth of human breast cancer cells in a dose-dependent fashion, but has no effect on endocrine-responsive human endometrial cancer cells. Gestodene induced a 90-fold increase in the secretion of transforming growth factor-beta (TGF-beta) by T47D human breast cancer cells. Other synthetic progestins had no effect, indicating that this induction is mediated by the novel Gestodene binding site and not by the conventional progesterone receptor. Furthermore, in four breast cancer cell lines, the extent of induction of TGF-beta correlated with intracellular levels of Gestodene binding site. No induction of TGF-beta was observed with the endometrial cancer line, HECl-B, which lacks the Gestodene binding site, but which expresses high levels of progesterone receptor. The inhibition of growth of T47D cells by Gestodene is partly reversible by a polyclonal antiserum to TGF-beta. These data indicate that the growth-inhibitory action of Gestodene may be mediated in part by an autocrine induction of TGF-beta.

Recombinant latent transforming growth factor beta 1 has a longer plasma half-life in rats than active transforming growth factor beta 1, and a different tissue distribution

Transforming growth factor beta 1 (TGF-beta 1) is a key regulator of cell growth and differentiation. Under normal physiological conditions, it is made as a biologically latent complex whose significance is unknown. Previous work has indicated that active TGF-beta 1 has a very short plasma half-life in rats (Coffey, R. J., L. J. Kost, R. M. Lyons, H. L. Moses, and N. F. La-Russo. 1987. J. Clin. Invest. 80:750-757). We have investigated the possibility that latent complex formation may extend the plasma half-life of TGF-beta 1 and alter its organ distribution. Radiolabeled latent TGF-beta 1 was formed by noncovalent association of 125I-TGF-beta 1 with the TGF-beta 1 precursor "pro" region from recombinant sources. TGF-beta 1 in this latent complex had a greatly extended plasma half-life (greater than 100 min) in rats compared with active TGF-beta 1 (2-3 min). Whereas active TGF-beta 1 was rapidly taken up by the liver, kidneys, lungs, and spleen and degraded, TGF-beta 1 in the latent complex was largely confined to the circulation, and was less than 5% degraded after 90 min. The pharmacokinetics of TGF-beta 1 in the latent complex were shown to be critically dependent on the degree of sialylation of the complex. The results suggest that formation of latent complexes may switch endogenous TGF-beta 1 from an autocrine/paracrine mode of action to a more endocrine mode involving target organs distant from the site of synthesis.

Anti-oestrogens induce the secretion of active transforming growth factor beta from human fetal fibroblasts

The clinical use of anti-oestrogens in breast cancer therapy has traditionally been restricted to tumours that contain measurable oestrogen receptor protein. However, it is now widely recognised that the clinical response to adjuvant anti-oestrogen therapy appears to be independent of the oestrogen receptor content of the primary tumour. The study reported here was designed to investigate the possibility that human stromal cells can respond to anti-oestrogens by an increased synthesis of the inhibitory growth factor, transforming growth factor beta (TGF-beta). Two established human fetal fibroblast strains were used as models for the breast cancer stromal fibroblasts. These cells were found to respond to the addition of anti-oestrogens by a large increase in their synthesis of biologically active TGF-beta. Despite the application of ligand binding, immunoassay and Northern analysis, no oestrogen receptor or oestrogen receptor mRNA was detected in either of the human fetal fibroblasts strains. These observations may provide a mechanism of action of anti-oestrogens that is independent of the presence of oestrogen receptor in the tumour epithelial cells, and thus provide an explantation for the counter-intuitive results of adjuvant anti-oestrogen action.

Physicochemical activation of recombinant latent transforming growth factor-beta's 1, 2, and 3

Native and recombinant forms of transforming growth factor-beta 1 (TGF-beta 1) are synthesized predominantly as biologically latent complexes. Physicochemical analysis demonstrates that the more recently described TGF-beta 2 and TGF-beta 3 are also latent, and reveals a common series of sharply defined parameters for activation. Human recombinant latent TGF-beta's 1 and 2 show identical profiles of activation by acid and base; the transition from latency occurs between pH 4.1 and 3.1, and between pH 11.0 and 11.9. The profile for chicken recombinant latent TGF-beta 3 is slightly shifted with activation between pH 3.1 and 2.5, and between pH 10.0 and 12.3. Thermal activation of native and recombinant latent TGF-beta 1 occurs over the temperature ranges of 75-100 degrees C and 65-100 degrees C, respectively, with complete activation after 5 min at 80 degrees C. Temperatures above 90 degrees C result in thermal denaturation of TGF-beta 1 itself. Recombinant latent TGF-beta's 2 and 3 are also activated over this temperature range; however, maximum activation occurs at 100 degrees C. These results suggest common elements in latent complex structure despite differences between the TGF-beta subtypes in pro-region primary sequence.

Recombinant TGF-beta 1 is synthesized as a two-component latent complex that shares some structural features with the native platelet latent TGF-beta 1 complex

The entire coding region of the human transforming growth factor beta 1 (TGF-beta 1) precursor cDNA has been stably expressed in a human renal carcinoma cell line. Like platelet TGF-beta 1, the recombinant TGF-beta 1 is secreted in a biologically latent form. Immunoblot analysis and gel-filtration indicate that the recombinant latent TGF-beta 1 is a 100-kDa complex in which active 25-kDa TGF-beta 1 is noncovalently associated with the remaining 75 kDa of the processed precursor. Unlike the platelet latent complex, the recombinant latent complex contains no 135-kDa component. Thus, the processed precursor peptide alone is sufficient to confer latency on active TGF-beta 1, and the 135-kDa platelet component has a different role. The processed precursor is similarly glycosylated in recombinant and platelet complexes, and in both has an exposed heparin binding site that may be involved in targeting of the latent complex. Finally, acid activation of recombinant and platelet complexes is reversible, suggesting that the activation process does not cause major structural modifications in the components of the latent complex.

Latent transforming growth factor-beta from human platelets. A high molecular weight complex containing precursor sequences

Human platelets, when induced to degranulate by thrombin, secrete transforming growth factor-beta (TGF-beta) in a biologically latent form. In this form, TGF-beta cannot bind to its cellular receptor, nor can it be immunoprecipitated by polyclonal antisera to TGF-beta, suggesting that the receptor-binding site and other TGF-beta epitopes may be masked. Western blot analysis of the platelet secretate indicates that the latent form of TGF-beta is a 220-235 kDa complex, in which mature TGF-beta (25 kDa) is noncovalently associated with sequences from the remainder of the precursor (74 kDa), and a third unidentified entity (approximately 135 kDa). The third component is immunologically unrelated to other growth factor binding proteins. The complex is glycosylated, and gel filtration analysis suggests it may exist in solution as higher molecular weight aggregates. Further chromatographic analysis indicates that in its latent form, the platelet TGF-beta cannot bind to alpha 2-macroglobulin (alpha 2M), but that if the platelet latent TGF-beta is activated by transient acidification, the released active TGF-beta will bind to alpha 2M. We have previously identified the latent form of TGF-beta found in serum as an alpha 2M.TGF-beta complex (O'Connor-McCourt, M. D., and Wakefield, L. M. (1987) J. Biol. Chem. 262, 14090-14099). We now propose that 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. Thus alpha 2M may scavenge excess TGF-beta that is released when the platelet latent form is activated, possibly by the clotting process. Finally, we have shown that the latent form of TGF-beta secreted by a variety of cell types in culture is similar, if not identical to that secreted by platelets.

Latent transforming growth factor-beta in serum. A specific complex with alpha 2-macroglobulin

The biological latency of serum transforming growth factor-beta (TGF-beta) was shown to be due to the interaction of TGF-beta with a specific serum binding protein. This binding protein was affinity labeled with 125I-TGF-beta, and its Mr and subunit structure were determined using sodium dodecyl sulfate-gel electrophoresis and gel filtration chromatography. Its Mr is reminiscent of that of the serum protease inhibitor, alpha 2-macroglobulin (alpha 2M). Immunoprecipitation of the 125I-TGF-beta-binding protein complex by a specific anti-alpha 2M antibody, and the formation of identical complexes between 125I-TGF-beta and purified alpha 2M, confirmed that alpha 2M is the TGF-beta-binding protein in serum. Immunoblot analysis showed that endogenous serum TGF-beta is also bound to alpha 2M. However, in contrast to added 125I-TGF-beta, the majority of the endogenous TGF-beta is linked to alpha 2M covalently. Alpha 2M and acid-activated TGF-beta co-eluted from a Superose 6 fast protein liquid chromatography column, confirming that the interaction of TGF-beta with alpha 2M accounts for the latency of serum TGF-beta. It is proposed that alpha 2M may serve an important multifunctional role at sites of inflammation by scavenging both active peptides and proteases that are released by platelets at the site of injury.

Distribution and modulation of the cellular receptor for transforming growth factor-beta

Scatchard analyses of the binding of transforming growth factor-beta (TGF-beta) to a wide variety of different cell types in culture revealed the universal presence of high affinity (Kd = 1-60 pM) receptors for TGF-beta on every cell type assayed, indicating a wide potential target range for TGF-beta action. There was a strong (r = +0.85) inverse relationship between the receptor affinity and the number of receptors expressed per cell, such that at low TGF-beta concentrations, essentially all cells bound a similar number of TGF-beta molecules per cell. The binding of TGF-beta to various cell types was not altered by many agents that affect the cellular response to TGF-beta, suggesting that modulation of TGF-beta binding to its receptor may not be a primary control mechanism in TGF-beta action. Similarly, in vitro transformation resulted in only relatively small changes in the cellular binding of TGF-beta, and for those cell types that exhibited ligand-induced down-regulation of the receptor, down-regulation was not extensive. Thus the strong conservation of binding observed between cell types is also seen within a given cell type under a variety of conditions, and receptor expression appears to be essentially constitutive. Finally, the biologically inactive form of TGF-beta, which constitutes greater than 98% of autocrine TGF-beta secreted by all of the twelve different cell types assayed, was shown to be unable to bind to the receptor without prior activation in vitro. It is proposed that this may prevent premature interaction of autocrine ligand and receptor in the Golgi apparatus.

Transforming growth factor type beta induces monocyte chemotaxis and growth factor production

Recent studies have focused on the potential role of transforming growth factor type beta (TGF-beta) as an immunoregulatory peptide. In this context, we demonstrate that TGF-beta is a potent chemoattractant for human peripheral blood monocytes. At concentrations from 0.1 to 10 pg/ml, TGF-beta induces directed monocyte migration in vitro. Consistent with this observation is the expression of high-affinity TGF-beta receptors on the monocytes with a Kd of 1-10 pM. At higher concentrations of TGF-beta (greater than or equal to 1 ng/ml), monocytes are stimulated to generate biologically active mediator(s) that enhance fibroblast growth. Gene expression for one of these growth factors, interleukin 1, is induced in monocytes within hours after exposure to TGF-beta. Thus, TGF-beta may provide an important signal for monocyte recruitment and for regulation of their synthesis of mediators of fibroblast growth and activity in wound healing.

Evidence that transforming growth factor-beta is a hormonally regulated negative growth factor in human breast cancer cells

The hormone-dependent human breast cancer cell line MCF-7 secretes transforming growth factor-beta (TGF-beta), which can be detected in the culture medium in a biologically active form. These polypeptides compete with human platelet-derived TGF-beta for binding to its receptor, are biologically active in TGF-beta-specific growth assays, and are recognized and inactivated by TGF-beta-specific antibodies. Secretion of active TGF-beta is induced 8 to 27-fold under treatment of MCF-7 cells with growth inhibitory concentrations of antiestrogens. Antiestrogen-induced TGF-beta from MCF-7 cells inhibits the growth of an estrogen receptor-negative human breast cancer cell line in coculture experiments; growth inhibition is reversed with anti-TGF-beta antibodies. We conclude that in MCF-7 cells, TGF-beta is a hormonally regulated growth inhibitor with possible autocrine and paracrine functions in breast cancer cells.

Transforming growth factor beta is an important immunomodulatory protein for human B lymphocytes

The growth and differentiation of B cells to immunoglobulin (Ig)-secreting cells is regulated by a variety of soluble factors. This study presents data that support a role for transforming growth factor (TGF)-beta in this regulatory process. B lymphocytes were shown to have high-affinity receptors for TGF-beta that were increased fivefold to sixfold after in vitro activation. The addition of picogram quantities of TGF-beta to B cell cultures suppressed factor-dependent, interleukin 2 (IL 2) B cell proliferation and markedly suppressed factor-dependent (IL 2 or B cell differentiation factor) B cell Ig secretion. In contrast, the constitutive IgG production by an Epstein Barr virus-transformed B cell line was not modified by the presence of TGF-beta in culture. This cell line was found to lack high-affinity TGF-beta receptors. The degree of inhibition of B cell proliferation observed in in vitro cultures was found to be dependent not only on the concentration of TGF-beta added but also on the concentration of the growth stimulatory substance (IL 2) present. By increasing the IL 2 concentrations in culture, the inhibition of proliferation induced by TGF-beta could be partially overcome. In contrast, the inhibition of Ig secretion induced by TGF-beta could not be overcome by a higher concentration of stimulatory factor, demonstrating that the suppression of B cell differentiation by TGF-beta is not due solely to its effects on proliferation. Furthermore, it was demonstrated that B lymphocytes secrete TGF-beta. Unactivated tonsillar B cells had detectable amounts of TGF-beta mRNA on Northern blot analysis, and B cell activation with Staphylococcus aureus Cowan (SAC) resulted in a twofold to threefold increase in TGF-beta mRNA. Supernatants conditioned by unactivated B cells had small amounts of TGF-beta, SAC activation of the B cells resulted in a sixfold to sevenfold increase in the amount of TGF-beta present in the supernatants. Thus, B lymphocytes synthesize and secrete TGF-beta and express receptors for TGF-beta. The addition of exogenous TGF-beta to cultures of stimulated B cells inhibits subsequent proliferation and Ig secretion. TGF-beta may function as an autocrine growth inhibitor that limits B lymphocyte proliferation and ultimate differentiation.

Transforming growth factor beta is an important immunomodulatory protein for human B lymphocytes

The growth and differentiation of B cells to immunoglobulin (Ig)-secreting cells is regulated by a variety of soluble factors. This study presents data that support a role for transforming growth factor (TGF)-beta in this regulatory process. B lymphocytes were shown to have high-affinity receptors for TGF-beta that were increased fivefold to sixfold after in vitro activation. The addition of picogram quantities of TGF-beta to B cell cultures suppressed factor-dependent, interleukin 2 (IL 2) B cell proliferation and markedly suppressed factor-dependent (IL 2 or B cell differentiation factor) B cell Ig secretion. In contrast, the constitutive IgG production by an Epstein Barr virus-transformed B cell line was not modified by the presence of TGF-beta in culture. This cell line was found to lack high-affinity TGF-beta receptors. The degree of inhibition of B cell proliferation observed in in vitro cultures was found to be dependent not only on the concentration of TGF-beta added but also on the concentration of the growth stimulatory substance (IL 2) present. By increasing the IL 2 concentrations in culture, the inhibition of proliferation induced by TGF-beta could be partially overcome. In contrast, the inhibition of Ig secretion induced by TGF-beta could not be overcome by a higher concentration of stimulatory factor, demonstrating that the suppression of B cell differentiation by TGF-beta is not due solely to its effects on proliferation. Furthermore, it was demonstrated that B lymphocytes secrete TGF-beta. Unactivated tonsillar B cells had detectable amounts of TGF-beta mRNA on Northern blot analysis, and B cell activation with Staphylococcus aureus Cowan (SAC) resulted in a twofold to threefold increase in TGF-beta mRNA. Supernatants conditioned by unactivated B cells had small amounts of TGF-beta, SAC activation of the B cells resulted in a sixfold to sevenfold increase in the amount of TGF-beta present in the supernatants. Thus, B lymphocytes synthesize and secrete TGF-beta and express receptors for TGF-beta. The addition of exogenous TGF-beta to cultures of stimulated B cells inhibits subsequent proliferation and Ig secretion. TGF-beta may function as an autocrine growth inhibitor that limits B lymphocyte proliferation and ultimate differentiation.

Anthropometric measurements and dietary intakes of Cherokee Indian teenagers in North Carolina

Anthropometric measurements, rates of obesity, and food intake practices were investigated among 277 Cherokee Indian youths in North Carolina. Differences in food intake practices between lean and fat individuals were also assessed. Height, weight, and triceps skinfold measurements were taken, along with three dietary recalls. When Cherokee height data were compared with national survey data, no significant differences were found. In contrast, mean body weights and triceps skinfolds of Cherokees were significantly higher than national reference data. Obesity rates were found to be high; almost one-half of the Cherokee boys and one-third of the girls had skinfold thicknesses above the 85th percentile for Ten-State Nutrition Survey reference data. The effects of degree of Cherokee blood on height, weight, and triceps skinfolds were also analyzed. No significant differences existed for triceps skinfolds or weight and degree of Indian blood. However, there was a significant relationship (p less than .001) between height and degree of Indian blood, with a decrease in height with an increase in Indian blood. Mean energy intakes were not significantly different between the lean and fat individuals. Similarly, no differences were found in meal or snacking patterns. It does not appear that the obesity is caused by overeating. The high incidence of obesity among the youth and the prevalence of maturity-onset diabetes in the adult Cherokee population speaks to the need for management of obesity.

Transforming growth factor-beta: biological function and chemical structure

Transforming growth factor-beta (TGF-beta) is a multifunctional peptide that controls proliferation, differentiation, and other functions in many cell types. Many cells synthesize TGF-beta and essentially all of them have specific receptors for this peptide. TGF-beta regulates the actions of many other peptide growth factors and determines a positive or negative direction of their effects. Its marked ability to enhance formation of connective tissue in vivo suggests several therapeutic applications.

Electron transfer across the chromaffin granule membrane. Use of EPR to demonstrate reduction of intravesicular ascorbate radical by the extravesicular mitochondrial NADH:ascorbate radical oxidoreductase

A two-compartment electron paramagnetic resonance system has been developed in which the membrane-impermeable spin probe Ni(en)2+3 is used to selectively eliminate the EPR signal from extravesicular ascorbate radical, such that radicals in intra- and extravesicular compartments can be distinguished. Using this system, we have shown that an increase in ascorbate radical in the extravesicular medium is reflected by an increase in ascorbate radical within resealed chromaffin granule ghosts containing trapped ascorbate but has no effect on radical concentrations inside liposomes containing ascorbate. This indicates that the chromaffin granule membrane contains a component, not present in liposomes, that allows equilibration between the intra- and extravesicular ascorbate/ascorbate radical couples. This component is probably cytochrome b561. We further show that activation of the mitochondrial NADH:ascorbate radical oxidoreductase in the extravesicular medium causes a decrease in intravesicular ascorbate radical in chromaffin granule ghosts but not in liposomes. These data provide direct experimental evidence for the hypothesis that the adrenal medullary mitochondrial NADH:ascorbate radical oxidoreductase could drive the re-reduction of ascorbate free radical generated inside the chromaffin granule by the turnover of dopamine beta-hydroxylase, without the ascorbate radical ever having to leave the granule.

Functional coupling between enzymes of the chromaffin granule membrane

The reactions of cytochrome b561 with other redox-active components of the adrenal chromaffin granule were examined using optical difference spectroscopy. It was shown that there is no direct electron transfer between the cytochrome and dopamine beta-hydroxylase, but that in the presence of ascorbate, turnover of dopamine beta-hydroxylase causes an oxidation of the cytochrome, which is partially reversed by the action of the mitochondrial NADH:A-. oxidoreductase. Thus, these three proteins may be functionally coupled via ascorbate. A quantitative study of the relationship between the redox state of the cytochrome and the ascorbate radical concentration measured by EPR showed that ascorbate reduces the cytochrome in a one-electron transfer reaction. Generation of a proton electrochemical gradient across the granule membrane causes only a small (20 mV) increase in the cytochrome midpoint potential suggesting the cytochrome is not a proton pump. The data are consistent with a model in which cytochrome b561, by reacting with ascorbate or ascorbate free radical on either side of the granule membrane, could couple the ascorbate-consuming reaction of the dopamine beta-hydroxylase inside the chromaffin granule to the ascorbate-regenerating reaction of the NADH:A-. oxidoreductase on the outer mitochondrial membrane. The H+-ATPase of the granule membrane could both drive the flow of electrons in the direction from cytosol to granule and replenish protons consumed by the turnover of dopamine beta-hydroxylase inside the granule.