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Transforming growth factor-beta and breast cancer: Cell cycle arrest by transforming growth factor-beta and its disruption in cancer.

Altered responsiveness to extracellular signals and cell cycle dysregulation are hallmarks of cancer. The cell cycle is governed by cyclin-dependent kinases (cdks) that integrate mitogenic and growth inhibitory signals. Transforming growth factor (TGF)-beta mediates G1 cell cycle arrest by inducing or activating cdk inhibitors, and by inhibiting factors required for cdk activation. Mechanisms that lead to cell cycle arrest by TGF-beta are reviewed. Loss of growth inhibition by TGF-beta occurs early in breast cell transformation, and may contribute to breast cancer progression. Dysregulation of cell cycle effectors at many different levels may contribute to loss of G1 arrest by TGF-beta. Elucidation of these pathways in breast cancer may ultimately lead to novel and more effective treatments for this disease.

Breast Neoplasms↗

Sulforaphane modulates cell cycle and apoptosis in transformed and non-transformed human T lymphocytes.

Isothiocyanates exert chemopreventive effects against chemically induced tumors in animals, modulating enzymes required for carcinogens' activation/detoxification and/or the induction of cell-cycle arrest and apoptosis in tumor cell lines. To investigate the chemopreventive potential of isothiocyanates, we studied proliferation, apoptosis induction and p53, bcl-2 and bax protein expression in Jurkat T-leukemia cells by the isothiocyanate sulforaphane. Sulforaphane caused G(2)/M-phase delay and increase of apoptotic cell fraction in a time- and dose-dependent manner. Necrosis was observed after prolonged exposure to elevated sulforaphane doses. Moreover, it markedly increased p53 and bax protein expression, and slightly affected bcl-2 expression. Since selective targeting and low toxicity for normal host tissues are fundamental requisites for proposed chemopreventive agents such as sulforaphane, we tested sulforaphane on non-transformed phytohemagglutinin-stimulated human T-lymphocytes. We demonstrated that sulforaphane arrested cell-cycle progression in G1 phase by a significant down-modulation of cyclin D3. Moreover, sulforaphane induced apoptosis (and also necrosis), mediated by an increase in the expression of p53, whereas it exerted little effect on bcl-2 and bax levels. These findings indicate that sulforaphane can exert protective effects inhibiting leukemic cell growth. Moreover, sulforaphane is active not only in transformed lymphocytes but also in their normal counterpart. Although in vitro studies do not necessarily predict in vivo outcomes, our findings raise important questions regarding the suitability of sulforaphane for cancer chemoprevention.

Anticarcinogenic Agents↗

Human transforming growth factor-beta 3: recombinant expression, purification, and biological activities in comparison with transforming growth factors-beta 1 and -beta 2.

Recent cDNA characterization has predicted the existence of a new member of the transforming growth factor family, transforming growth factor-beta 3 (TGF beta 3). However, nothing is known about the biological activities of the TGF beta 3 protein, since it has not been purified from any natural sources. We report here the recombinant expression in mammalian cells and the purification to apparent homogeneity of human TGF beta 3. The TGF beta 3 was evaluated in comparison with purified TGF beta 1 and TGF beta 2 in several assays for its effects on stimulation or inhibition of proliferation of mammalian cells. These analyses revealed that TGF beta 3 exerts activities similar to the two other TGF beta species, but that there are distinct differences in potencies between the different TGF beta forms depending on the cell type and assay used.

Animals↗

Interaction of acidic fibroblast growth factor and transforming growth factor-beta in normal and transformed glia in vitro.

The mitogenic and morphological effects of acidic fibroblast growth factor (aFGF) and transforming growth factor-beta (TGF-beta) were assessed on cultured fetal rat astrocytes and C6 rat glioma cells in the presence and absence of serum. Astrocytes incubated with aFGF exhibited an increase in mitotic activity and characteristic morphological changes involving extensive process formation and rounding of cell bodies. Astrocytes incubated with TGF-beta underwent a slight decrease in mitotic activity and remained morphologically unchanged. Cells exposed to a combination of aFGF and TGF-beta demonstrated an attenuation of both the mitogenic and morphological changes observed in the presence of aFGF alone. The C6 glioma cells cultured in the presence of aFGF underwent a characteristic morphological change from a rounded piling cell mass to a more spindle-shaped bipolar cell layer, accompanied by an increase in mitotic activity. In contrast to the astrocyte cultures, increased growth and similar morphological effects were produced by TGF-beta. The combination of aFGF and TGF-beta did not result in attenuation of the mitogenic and morphological changes (as seen in astrocytic cells). These results suggest that, in normal fetal rat astrocytes, TGF-beta is capable of attenuating the mitogenic and morphological changes induced by aFGF in vitro. In the transformed C6 glioma cell line, aFGF and TGF-beta elicit similar mitogenic and morphological changes, without evidence of an antagonistic interaction as seen in normal astrocytes.

Animals↗

A natural musaceas plant extract inhibits proteasome activity and induces apoptosis selectively in human tumor and transformed, but not normal and non-transformed, cells.

Animal studies have demonstrated that a dietary polyphenol known as tannic acid (TA) exhibits anticarcinogenic activity in chemically induced cancers. Most recently, we have reported that TA and ester-bond containing green tea polyphenols are potent proteasome inhibitors in vitro and in vivo. We hypothesize that CellQuest, a patented formula which contains high level of TA obtained from a musaceas (plantain) plant extract, will inhibit the tumor cell proteasome activity. Here, we report that a partially purified CellQuest fraction, S3, potently inhibits the proteasomal chymotrypsin-like activity of Jurkat T cell extracts in a concentration-dependent manner. Inhibition of the proteasome by S3 in leukemia Jurkat T, simian virus 40-transformed and prostate cancer LNCaP cells results in accumulation of ubiquitinated proteins and the natural proteasome substrate p27Kip1, followed by induction of apoptosis. In contrast, non-transformed, immortalized human natural killer cells and normal human fibroblasts are resistant to S3-mediated proteasome inhibition and apoptosis induction. Our present study suggests that CellQuest targets and inhibits the proteasome selectively in tumor cells, which may contribute to the claimed anticancer activity.

Apoptosis↗

Reversible transformation by v-sis: a model cell line for analysis of transformation by antisense methods.

Cellular homologs of v-sis are implicated in numerous human tumor types (Eva et al., 1982; Betsholtz et al., 1984; Johnson et al., 1985; Bronzert et al., 1987; Igarashi et al., 1987; Nister et al., 1988a,b; Versnel et al., 1988; Matsui et al., 1989), but whether tumor growth is maintained by sis expression alone or requires additional changes is unknown. To distinguish these possibilities, we studied reversible transformation of NIH-3T3 cells bearing an inducible v-sis construction. Cells subcultured from 10 of 18 tumors, all less than 0.1 gram and less than or equal to 21 days in age, reverted to a normal phenotype by four criteria, but again exhibited transformation upon induction. Thus, activation of the v-sis autocrine loop alone is sufficient for initiation of tumors. Cells from the remaining and larger, 0.5 +/- 0.7 gram, tumors did not revert by any criteria. This suggests that subsequent tumor growth is maintained by acquisition of irreversible change(s) that occurs at high frequency in vivo.

3T3 Cells↗

Regulation of protein degradation in normal and transformed human cells. Effects of growth state, medium composition, and viral transformation.

In WI-38, a normal human fibroblast, the rates of degradation of short lived and long lived proteins are identical whether the cultures are growing exponentially or are density-inhibited. Replacement of the growth medium with fresh medium does not alter these rates. In VA-13, an SV-40 transformed derivative of WI-38, the rates of protein degradation are also independent of growth rate and fresh medium. However, in both WI-38 and VA-13 the rate of long lived protein degradation increases as the serum concentration is reduced below 5%. After complete serum withdrawal, the rate increases by 60 to 100% in both cell types. Withdrawal of arginine and phenylalanine triples the rate of long lived protein degradation, while addition of 10% dialyzed serum to this amino acid-deficient medium reduces the effect to twice that of the controls. Incubation of both types of cells in phosphate-buffered saline also increases protein degradation. This effect is reduced by glucose, albumin, and dialyzed serum. Therefore, the rate of protein degradation is independent of growth rate in normal and transformed human cells. However, the rate of degradation is closely coupled to certain medium alterations.

Cell Division↗

Failure of cultured chick embryo fibroblasts to incorporate collagen into their extracellular matrix when transformed by Rous sarcoma virus. An effect of transformation but not of virus production.

Whole chick embryo fibroblasts were infected with the Prague wild type Rous sarcoma virus and with a temperature sensitive mutant of this strain, RSVtsLA24. Normal fibroblasts and fibroblasts infected with the temperature-sensitive mutant and cultured at the nonpermissive temperature-sensitive mutant and cultured at the nonpermissive temperature, secreted procollagen into the medium and incorporated collagen into their extracellular matrix. On the other hand, transformed fibroblasts and fibroblasts infected with the temperature-sensitive mutant and cultured at the permissive temperature, were able to secrete procollagen into the medium, but there was no evidence that they were able to convert procollagen to collagen and incorporate collagen into an extracellular matrix. The inability of the infected cells to incorporate collagen into an extracellular matrix was found to be a result of transformation rather than of virus production in these cells.

Animals↗

Human transforming growth factor beta.alpha 2-macroglobulin complex is a latent form of transforming growth factor beta.

125I-Labeled human platelet-derived transforming growth factor beta (125I-TGF-beta) and human alpha 2-macroglobulin (alpha 2M) formed a complex as demonstrated by 5% native polyacrylamide gel electrophoresis. The 125I-TGF-beta.alpha 2M complex migrated at a position identical to that of the fast migrating form of alpha 2M. Most of the 125I-TGF-beta.alpha 2M complex could be dissociated by acid or urea treatment. When 125I-TGF-beta was incubated with serum, the high molecular weight form of 125I-TGF-beta could be immunoprecipitated by anti-human alpha 2M anti-sera as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. alpha 2M purified from platelet-rich plasma also showed the latent transforming growth factor activity and immunoreactivity of TGF-beta. These results suggest that TGF-beta.alpha 2M complex is a latent form of TGF-beta.

Chromatography, Gel↗

Reverse transformation of Harvey murine sarcoma virus-transformed NIH/3T3 cells by site-selective cyclic AMP analogs.

Eighteen site-selective cAMP analogs modified at either the C-8 position or the C-6 position were tested for their growth regulatory effects on the Harvey murine sarcoma virus-transformed NIH/3T3 clone 13-3B-4 cells grown in a serum-free defined medium. All 18 analogs, when tested individually, exhibited an appreciable growth inhibitory effect at micromolar concentrations. The most potent growth inhibitory analogs contained a thio moiety at the C-8 position. In general, C-6 analogs required 5-10-fold greater concentrations than C-8 analogs to produce the same degree of growth inhibition. The growth inhibition induced by these analogs was accompanied by a change in cell morphology; cells treated with the analogs exhibited the morphology characteristic of untransformed fibroblasts, while untreated cells retained a transformed phenotype. The regulatory subunit of cAMP-dependent protein kinase, the cAMP receptor protein, has two different intrachain cAMP binding sites, and cAMP analogs modified at the C-8 position (C-8 analogs) are generally selective for Site 1, while analogs modified at the C-6 position (C-6 analogs) are generally selective for Site 2. Thus, C-8 and C-6 analogs were tested in combination to enhance the growth regulatory effect. Both growth inhibition and morphological change were enhanced synergistically by a combination of the C-6 and C-8 analogs. Two C-6 analogs or two C-8 analogs added together did not cause synergism. For both growth inhibition and phenotypic change, C-8 thio analogs acted far more synergistically than C-8 amino analogs when cells were treated in combination with C-6 analogs, suggesting a response of the RII rather than the RI cAMP receptor protein. DEAE-cellulose chromatography revealed that the growth inhibition, in fact, correlates with an increase of the RII cAMP receptor protein and a decrease of the RI receptor protein. The growth inhibitory effect of the site-selective analogs was not due to the cytotoxic effect of adenosine metabolites as shown by the different behavior of 8-Cl-cAMP compared with 8-Cl-adenosine in 1) cell cycle effects and 2) release from growth inhibition. It is concluded that the observed growth inhibition and phenotypic reversion of 13-3B-4 cells is most likely mediated through the cellular effector, the RII cAMP receptor protein.

Animals↗

Altered signal transduction in erbB-transformed cells. Implication of enhanced inositol phospholipid metabolism in erbB-induced transformation.

To clarify the signal transduction mechanism of the erbB gene (virus oncogene) products leading to cell growth and transformation, the alteration of signal transduction induced by enhanced inositol phospholipid metabolism was studied in chick embryo fibroblast cells (CEF cells) transformed by gag-fused erbB gene-carrying virus (GEV cells). The incorporations of 32P into phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate were markedly increased in GEV cells. In GEV cells, the activities of lipid kinases such as phosphatidylinositol (PI), PIP, and diacylglycerol (DG) kinases were also increased. The activities of other important enzymes involved in inositol phospholipid metabolism, such as CDP-DG:myo-inositol transferase and phospholipase C, were not changed in GEV cells. Increased inositol phospholipid metabolism might lead to the production of second messengers, such as 1,2-DG and inositol 1,4,5-trisphosphate. Indeed, the 1,2-DG content was also increased in GEV cells. Moreover, the activity of protein kinase C (the Ca2+/phospholipid-dependent enzyme), which should be stimulated by 1,2-DG, was elevated in GEV cells; the protein kinase C activity in the membrane fraction of GEV cells was especially high. When CEF cells were treated with tetradecanoylphorbol acetate, protein kinase C activator, plus Ca2+ ionophore, [3H]thymidine incorporation was markedly stimulated, and maximal stimulation was observed with 1 nM Ca2+ ionophore A23187 plus 100 nM TPA. On the other hand, when GEV cells were treated with TPA plus Ca2+ ionophore A23187, [3H]thymidine incorporation was consistently inhibited. Next, studies were made to determine whether the erbB gene product itself had kinase activity on PI, PIP, and DG after membranes were mildly solubilized with Triton X-100 to prevent inactivation of these kinases. Immunoprecipitates of a GEV cell lysate with antisera that reacted with the erbB gene product had PI kinase activity, whereas no activity was detected in those of lysates of uninfected CEF cells. However, the activity was very weak compared with the total cellular activity. No difference in the PIP and DG kinase activities of immunoprecipitates of cell lysates of uninfected CEF cells and GEV cells was observed. These results suggest that the erbB gene product enhances inositol phospholipid metabolism and subsequent signal transduction, but that the erbB gene product is not involved directly in lipid kinases, although it is closely associated with lipid kinase.

1-Phosphatidylinositol 4-Kinase↗

Myc genes linked to viral promoters can collaborate with a transformation-deficient simian virus 40 early gene mutant to transform established rat cells.

Cotransfection of a transformation-deficient and immortalization-positive SV40 early gene mutant with various constructs of viral promoter-linked myc genes induced dense foci in 3Y1 cells, an established cell line derived from rat embryo fibroblasts, whereas transfections with either species alone did not. Four cell clones were isolated from colonies grown in soft agar medium, and found to contain at least a single copy of both DNA species and to express both sequences at relatively high levels. These results indicate that the two immortalizing genes used in the present study collaborate to transform 3Y1 cells.

Animals↗

Transformation of Escherichia coli by R404 factor DNA and properties of the transformants.

Three r-determinants (Cb Cm Cf) out of eight present in R404 factor were transferred in transformation of Escherichia coli by the plasmid DNA isolated from minicells. The r-determinants acquired in this way formed the replicon tr404-1 and were untransferable by conjugation unless another self-transmissible plasmid was present in recipient. The evidences are presented in support of hypothesis that the transfer events consist in infection of transformant cells with sex factor, recombination between tr404-1 replicon and the sex factor and finally transfer of the new formed structure to the host cells of the sex factor.

Anti-Bacterial Agents↗

[Preparation and primary genetic analysis of Drosophila melanogaster transformants line w'lz(b)/XXywf, containing mini-white genes, integrated in the genome during P-element-dependent transformation].

Transformation of Drosophila melanogaster using P-element-based vectors yielded 129 sublines, which carried mini-white gene copies in the different genome regions. Dependence of mini-white gene expression on the location, gene dosage, and sex of the transformed individuals was analyzed. The mutation lzb was shown to suppress mini-white gene expression, the degree of suppression depending on the location and dosage of the mini-white gene.

ATP-Binding Cassette Transporters↗

Detection of transforming growth factor-alpha mRNA and protein in rat lacrimal glands and characterization of transforming growth factor-alpha in human tears.

PURPOSE: To assess whether the lacrimal gland is a possible site of synthesis of transforming growth factor-alpha (TGF-alpha) and to characterize TGF-alpha biochemically in human tears. METHODS: Reverse transcription-polymerase chain reaction (RT-PCR) amplification was used to analyze rat lacrimal glands for the presence of TGF-alpha mRNA. Specific monoclonal antibodies were used to localize TGF-alpha immunohistochemically in lacrimal gland tissue of rats. Human tears were analyzed for immunoreactive TGF-alpha protein using a specific radioimmunoassay, and the molecular weight of TGF-alpha in tears was characterized by Western blot analysis. RESULTS: RT-PCR amplification of rat lacrimal gland RNA generated a band of the predicted 492 base pairs for TGF-alpha mRNA. Immunohistochemical staining of rat lacrimal gland localized TGF-alpha protein to lacrymocytes constituting acini but not to interacinar and intraacinar ducts of lacrimal glands. Western blot analysis of human tears detected a single band at MWt 16,000. Logit transformation of radioimmunoassay data for tears and TGF-alpha standard generated parallel displacement lines, indicating the presence of immunoreactive TGF-alpha levels in human tears with an average concentration of 100 +/- 20 pg/ml (mean +/- SEM). CONCLUSIONS: Rat lacrymocytes synthesize TGF-alpha mRNA and protein, and human tears contain immunoreactive TGF-alpha, suggesting that the lacrimal gland may be an exocrine source for TGF-alpha in tears. The single MWt 16,000 form of TGF-alpha in human tears appears to be generated by an unusual proteolytically processing of the pro-TGF-alpha transmembrane precursor protein.

Adult↗

Transforming growth factor-beta receptor expression on human skin fibroblasts: dimeric complex formation of type I and type II receptors and identification of glycosyl phosphatidylinositol-anchored transforming growth factor-beta binding proteins.

Fibroblasts play a critical role in wound repair and in the development of fibrotic diseases, and transforming growth factor-beta (TGF-beta) has been shown to profoundly modulate fibroblast function. However, there is limited information on the TGF-beta receptor types, isoform specificity, and complex formation in skin fibroblasts. Here, we report that normal adult human skin fibroblasts display two isoform-specific, cell surface glycosyl phosphatidylinositol (GPI)-anchored, TGF-beta binding proteins in addition to the type I, II, and III TGF-beta receptors. The identities of these proteins are confirmed on the basis of their affinity for TGF-beta isoforms, immunoprecipitation with specific antireceptor antibodies, and other biochemical analyses. Immunoprecipitation results also indicated oligomeric complex formation between type I and II and between type II and III TGF-beta receptors. Furthermore, by using affinity labeling and two-dimensional electrophoresis, we demonstrate the occurrence of type I and II heterodimers and type I homodimers of TGF-beta receptors on these cells. Because the type I receptor does not bind TGF-beta in the absence of type II receptor, these results indicate that one molecule of TGF-beta induces the formation of a heterooligomeric complex containing more than one molecule each of type I and II TGF-beta receptors on these cells. These cells respond to TGF-beta by markedly down-regulating all five binding proteins and by potently augmenting DNA synthesis. These results allow the expansion of the proposed heteromeric TGF-beta receptor signaling paradigm using mutant cells that are unresponsive to TGF-beta and cell lines that have been transfected to overexpress these receptors, to include normal TGF-beta-responsive cells. In addition, the definition of TGF-beta receptor profiles in human skin fibroblasts provides important information for studying their alterations in these cells in various skin diseases.

Activin Receptors, Type I↗

Retinoids potentiate transforming growth factor-beta activity in bovine endothelial cells through up-regulating the expression of transforming growth factor-beta receptors.

Retinoic acid (RA) induces the activation of latent transforming growth factor-beta (TGF-beta) in bovine aortic endothelial cells (BAECs) via enhancement of cellular plasminogen activator (PA)/plasmin levels. The resultant TGF-beta suppresses the excessive fibrinolytic activity by decreasing PA expression and stimulating expression of the PA inhibitor, PA inhibitor-1 (PAI-1), and inhibits cell proliferation. Here, we report that, in this regulatory system, RA simultaneously up-regulates the expression of TGF-beta receptor types I and II, resulting in enhancement of TGF-beta activity in the cells. RA increased the numbers of high- and low-affinity binding sites for 125I-TGF-beta1 2.1-fold and 1.5-fold, respectively, without alteration of their Kd values. Affinity labeling and Western and Northern blotting studies showed that, following RA treatment, surface levels of both type I and type II receptors increased due to augmentation in their mRNA levels. The effect was dose- and time-dependent. Treatment with 1 microM RA for 15 hr increased mRNA levels of type I and II receptor threefold and eightfold, respectively. Pretreatment of BAECs with either RA or retinol lowered the concentration of TGF-beta1 required to suppress PA levels, to enhance PAI-1 levels, and to inhibit cell proliferation. Thus, retinoids may regulate cellular functions of BAECs not only by inducing the formation of active TGF-beta but also by stimulating TGF-beta receptor expression. This regulatory mechanism may sustain TGF-beta-mediated regulation of EC function at a focal site where RA is acting.

Actins↗

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.

Animals↗