TGF-beta System Research Articles

RRR-alpha-tocopheryl succinate inhibits the proliferation of human prostatic tumor cells with defective cell cycle/differentiation pathways.

The RRR-alpha-tocopheryl succinate derivative of vitamin E, referred to as vitamin E succinate (VES), inhibits the proliferation of three metastatic human prostatic cancer cell lines, LNCaP, PC-3, and DU-145. LNCaP is a lymph node-derived androgen-sensitive prostate cell line; these cells are defective for response to transforming growth factor-beta (TGF-beta) but are normal for cell cycle-related tumor suppressor genes: p53 and retinoblastoma (Rb). PC-3 is a bone marrow-derived androgen-insensitive prostate cell line; these cells are defective for both p53 alleles but normal for both Rb alleles. DU-145 is a brain-derived androgen-insensitive prostate cell line; these cells are defective for both p53 and both Rb alleles. VES at 5, 10, and 20 micrograms/ml inhibited DNA synthesis in the three cell lines in a dose-dependent manner. Purified TGF-beta 1 at 1 ng/ml inhibited DNA synthesis of PC-3 cells within 24-72 hours and DU-145 cells at 72 hours but did not inhibit DNA synthesis of LNCaP cells. Previous studies in our laboratory showed that VES growth-inhibited tumor cells secrete biologically active antiproliferative factor TGF-beta s, suggesting that VES's mechanism of growth inhibition may involve the TGF-beta system of growth control.(ABSTRACT TRUNCATED AT 250 WORDS)

Human fallopian tube expresses transforming growth factor (TGF beta) isoforms, TGF beta type I-III receptor messenger ribonucleic acid and protein, and contains [125I]TGF beta-binding sites.

Reverse transcription-polymerase chain reaction analysis of total ribonucleic acid (RNA) from human fallopian tubes revealed that transforming growth factor-beta 1 (TGF beta 1), TGF beta 2, and TGF beta 3 as well as TGF beta type I-III messenger RNA (mRNA) are expressed in this tissue. In situ hybridization and immunohistochemical observations using TGF beta isoform-specific [35S]40-mer oligonucleotide probes and polyclonal antibodies indicate that all the tubal cell types express TGF beta isoforms and TGF beta type II receptor mRNA and protein. The tubal epithelial cells appeared to express more TGF beta 1 mRNA and TGF beta 1-3 proteins than other cell types, whereas TGF beta 2 and TGF beta 3 mRNA appeared to be equally expressed in the epithelial and other tubal cell types. In the epithelial lining, both ciliated and nonciliated cells in the ampullary and isthmus regions appeared to express mRNA and protein for TGF beta s and TGF beta type II receptor at a similar level. The intensity of immunostaining of TGF beta s in tubal epithelial cells was lower during the early proliferative and late secretory than the mid- to late proliferative and early to midsecretory phases of the menstrual cycle and reduced during the postmenopausal period. However, the intensity of immunoreactive TGF beta type II receptor in these cells did not vary during the cycle as much as that seen with TGF beta s. Quantitative autoradiography of [125I]TGF beta 1 indicates that fallopian tubes contain specific binding sites for TGF beta 1. Net grain density per 100 microns 2, calculated for different cell types, indicates that the epithelial cells had a significantly higher grain density than other tubal cell types (P < 0.05), with similar densities in the late proliferative and early secretory phases of the cycle. These results provide the first evidence that human fallopian tubes express mRNA and protein and contain specific binding sites for TGF beta system, suggesting an autocrine/paracrine role for TGF beta in a variety of tubal functions.

Absence of transforming growth factor‐β responsiveness in the tamoxifen growth‐inhibited human breast cancer cell line CAMA‐1

Tamoxifen has been an effective antiestrogen in suppressing breast cancer growth which is estrogen-responsive or dependent. Early studies have provided circumstantial evidence that transforming growth factor-beta (TGF-beta) may be an autocrine mediator of tamoxifen action. Therefore, it is both fundamentally important and clinically relevant to investigate the relationship between tamoxifen and TGF-beta. In this study, we demonstrated that CAMA-1 cells, which are sensitive to tamoxifen inhibition, did not respond to TGF-beta growth inhibition. The type I and II TGF-beta receptors were undetectable by the radio-ligand affinity labeling technique. Despite the presence of a normal TGF-beta type II receptor gene, the mRNA transcript of the gene was undetectable by the extremely sensitive Intron-differential RNA/PCR method. The possibility that the lack of TGF-beta receptors might be intimately linked to the absence of normal retinoblastoma (Rb) gene products, as suggested by previous studies of retinoblastoma cells, was further investigated. The lack of TGF-beta receptor expression was found due to reasons other than the absence, deletion or abnormality of the Rb gene because a normal Rb gene and its hyper- and hypo-phosphorylated protein products were detected in CAMA-1 cells. In conclusion, our results suggest that the TGF-beta system is not obligatory for antiestrogen growth inhibition of CAMA-1 cells.

Rat mesangial cell hypertrophy in response to transforming growth factor-β1

Central features of progressive glomerular sclerosis are initial glomerular hypertrophy and subsequent accumulation of extracellular matrix proteins. Since TGF-beta 1 may play a key role in this glomerular response to injury, the present study sought to explore further TGF-beta 1 actions and regulated expression of its receptor in rat mesangial cells. The rat TGF-beta type II receptor (TGF-beta RII) homolog was cloned by screening a rat kidney cDNA library with a human TGF-beta RII cDNA probe, and sequenced. Expression of this receptor subtype in rat mesangial cells was then demonstrated by RNase protection assay, and by Northern blot analysis of poly (A)+ RNA, TGF-beta RII expression was down-regulated in cells treated with exogenous TGF-beta 1. Affinity cross linking studies demonstrated presence of this receptor on cell surface. Rat mesangial cells also expressed TGF-beta 1 and autoinduction by TGF-beta 1 was observed in the same cells, suggesting that this polypeptide may act in an autocrine fashion on mesangial cells, and that it may stimulate a positive autoamplification loop. TGF-beta 1 inhibited mesangial cell proliferation and stimulated significant overall protein and collagen production. Furthermore, mesangial cell size increased in response to chronic TGF-beta 1 treatment. These findings demonstrate that rat mesangial cells express key components of the TGF-beta system and raise the intriguing possibility that in the glomerular mesangium, TGF-beta 1 may not only induce extracellular matrix synthesis, but may also participate in the process of glomerular hypertrophy in response to injury.

Transformed rat tracheal epithelial cells exhibit alterations in transforming growth factor-beta secretion and responsiveness.

The purpose of our studies was to define abnormalities in the transforming growth factor-beta (TGF-beta) system of transformed rat tracheal epithelial (RTE) cells that might cause their abnormal growth behavior. We found that many, but not all, of the transformed cell lines were hyporesponsive or unresponsive to the growth inhibitory effects of TGF-beta 1. Scatchard and receptor cross-linking analyses indicated that loss of TGF-beta 1 responsiveness of transformed cells was probably not due to changes in receptor number or affinity, or to changes in expression of the three TGF-beta-binding protein subtypes. Transformed cells were found to secrete far less TGF-beta-like activity (less than 1/10) than primary cells. Cultured normal and transformed RTE cells expressed three TGF-beta 1 transcripts of 2.5, 1.9, and 1.4 kb. In contrast, rat kidney tissue, a rat embryo fibroblast cell line, and a rat liver cell line expressed only the typical 2.5-kb mRNA transcript commonly reported in the literature. In spite of the marked differences in TGF-beta secretion between normal and transformed cells, their levels of TGF-beta 1 mRNA expression were similar. This suggests a change in the posttranscriptional regulation of TGF-beta 1 expression. TGF-beta 2 message was not detected in either normal or transformed RTE cells in culture. These findings are consistent with the hypothesis that the abnormal growth behavior of transformed RTE cells is at least in part due to disturbances of the TGF-beta system.

Growth factors and oncogenes in human gastrointestinal carcinomas

Multi-autocrine loops of the epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha), platelet-derived growth factor (PDGF) and TGF beta system are expressed in human gastrointestinal carcinomas. In esophageal and gastric carcinomas, they evidently play an important role in tumor progression. Gastrin, one of the major gut hormones, may also act as an autocrine growth factor for gastric and colonic carcinomas. The HST1 and INT-2 genes, belonging to the fibroblast growth factor gene family, are coamplified in approximately 50% of primary tumors and in all the metastatic tumors of esophageal carcinoma. TGF alpha and EGF are the ligands of the tumor cells that overexpress EGF receptor in esophageal carcinomas. The synchronous expression of EGF and its receptor, as well as TGF alpha and ras p21, is evidently correlated with the depth of tumor invasion, metastasis and prognosis of gastric carcinomas. Amplification of c-erbB-2 and EGF receptor genes has been observed in many metastatic sites of gastric carcinomas regardless of histological type. In addition to TGF alpha and EGF, TGF beta and PDGF A chain produced by tumor cells may stimulate collagen synthesis not only by fibroblasts but also by tumor cells themselves, resulting in extensive progression and diffuse fibrosis of scirrhous gastric carcinomas. Moreover, TGF alpha or EGF and estrogen may also play a cooperative role in the development of scirrhous gastric carcinoma. In colorectal carcinoma, it has been shown that the accumulation of several alterations in ras genes and p53 genes is most important for the conversion of adenoma to carcinoma. Critical genetic changes, including activation of oncogenes, mutation and deletion of tumor suppressor genes and disturbances in transcriptional regulatory sequences, may bring about aberrant expression of growth factors and their receptors in gastrointestinal carcinomas. The understanding of the significance of EGF-related growth factors in tumor progression provides a framework for a biological approach to the therapy of human gastrointestinal carcinomas. 8-Cl-cAMP, which inhibits expression of oncogenes and TGF alpha, may be useful not only for cancer therapy but also for the study of cell differentiation.