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

TGF-β1 antisense oligonucleotide ASODN promotes cell proliferation but inhibits apoptosis in human esophageal squamous cell carcinoma cell line EC9706

AIM: To investigate the effects of transforming growth factor-beta 1 antisense oligonucleotide ASODN (TGF-β1-ASODN) on cell proliferation and apoptosis in human esophageal squamous cell carcinoma cell line EC9706.

METHODS: EC9706 cells were transfected with chemically synthesized TGF-β1-ASODN. The expression of TGF-β1 mRNA and protein was detected by reverse transcription-polymerase chain reaction (RT-PCR) and flow cytometry, respectively. Cell morphological changes were observed. The proliferation and apoptosis of EC9706 cells were measured by methyl thiazolyl tetrazolium (MTT) assay and flow cytometry, respectively.

RESULTS: After TGF-β1-ASODN transfection, the expression levels of TGF-β1 mRNA and protein in EC9706 cells were significantly lower than those in untransfected EC9706 cells (0.25 ± 0.07 vs 0.43 ± 0.09 and 35.35% vs 41.38%, respectively; both P < 0.05). TGF-β1-ASODN transfection could stimulate proliferation and inhibit apoptosis of EC9706 cells. After transfection, EC9706 cells lost their normal morphology. Compared with untransfected cells, the survival rate increased (109.4% vs 100.0%, P < 0.05), the percentages of cells in G₁ and S phases decreased (62.9% vs 66.5% and 21.3% vs 23.7%, respectively; both P < 0.05), the percentage of cells in G₂ phase rose (14.8% vs 9.8%, P < 0.05), and the apoptosis rate declined in cells transfected with TGF-β1-ASODN (0.69% vs 0.96%, P < 0.05).

CONCLUSION: TGF-β1-ASODN can silence the expression of the TGF-β1 gene efficiently and specially, and antagonize TGF-β1-mediated proliferation inhibition, cell cycle arrest and apoptosis in EC9706 cells.

Development of gene silencing pyrrole-imidazole polyamide targeting the TGF-beta1 promoter for treatment of progressive renal diseases

Pyrrole-imidazole (Py-Im) polyamides are nuclease-resistant novel compounds that inhibit gene expression by binding to the minor groove of DNA. A Py-Im polyamide that targets rat TGF-beta1 was designed as a gene-silencing agent for progressive renal diseases, and the distribution and the effects of this polyamide on renal injury were examined in Dahl-salt sensitive (Dahl-S) rats. For identification of transcription factor binding elements for activation of the rat TGF-beta1 gene, recombinant TGF-beta1 reporter plasmids were transfected into HEK-293 cells, and promoter activity was measured. Py-Im polyamide was designed to the activator protein-1 binding site of the rat TGF-beta1 promoter. This Py-Im polyamide showed strong, fast, and specific binding to the target DNA in gel mobility shift and Biacore assays. Py-Im polyamide significantly inhibited TGF-beta1 promoter activity and expression of TGF-beta1 mRNA and protein in rat mesangial cells. Intravenously administered fluorescein-labeled polyamide distributed to the kidney of rats. Py-Im polyamide significantly inhibited expression of TGF-beta1 mRNA and protein in the renal cortex of Dahl-S rats and reduced the increase in urinary protein and albumin in Dahl-S rats independent of changes in blood pressure. These results indicate that Py-Im polyamide that targets TGF-beta1 will be a novel gene-silencing agent for the TGF-beta1-associated diseases, including progressive renal diseases.

Synthetic pyrrole-imidazole polyamide inhibits expression of the human transforming growth factor-beta1 gene

Pyrrole-imidazole (Py-Im) polyamides can bind to the predetermined base pairs in the minor groove of double-helical DNA with high affinity. These synthetic small molecules can interfere with transcription factor-DNA interaction and inhibit or activate the transcription of corresponding genes. In the present study, we designed and synthesized a Py-Im polyamide to target -545 to -539 base pairs of human transforming growth factor-beta1 (hTGF-beta1) promoter adjacent to the fat-specific element 2 (FSE2) to inhibit the expression of the gene. Gel mobility shift assay showed that the synthetic Py-Im polyamide binds to its corresponding double-strand oligonucleotides, whereas the mismatch polyamides did not bind. Fluorescein isothiocyanate-labeled Py-Im polyamide was detected in the nuclei of human vascular smooth muscle cells (VSMCs) after 2- to 48-h incubation. Py-Im polyamide significantly decreased the promoter activity of hTGF-beta1 determined by in vitro transcription experiments and luciferase assay. In cultured human VSMCs, Py-Im polyamide targeting hTGF-beta1 promoter significantly inhibited expressions of hTGF-beta1 mRNA and protein. These results indicate that the synthetic Py-Im polyamide designed to bind hTGF-beta1 promoter inhibited hTGF-beta1 gene and protein expression successfully. This novel agent will be used for the TGF-beta-related diseases as a gene therapy.

Independent regulation of transforming growth factor-beta1 transcription and translation by glucose and platelet-derived growth factor

Proximal tubular renal epithelial cells may contribute to the pathogenesis of renal interstitial fibrosis in diabetes by generation of cytokines such as transforming growth factor (TGF)-beta1. We have previously demonstrated that proximal tubular renal epithelial cell TGF-beta1 synthesis may be modulated by elevated glucose concentration and by cytokines such as platelet-derived growth factor (PDGF). The aim of the current study was to characterize the mechanism by which glucose and PDGF synergistically stimulate the generation of TGF-beta1. Addition of either 25 mmol/L of D-glucose or low-dose PDGF increased TGF-beta1 mRNA expression without stimulation of TGF-beta1 protein synthesis. In contrast sequential stimulation with 25 mmol/L of D-glucose for 48 hours followed by low-dose (25 ng/ml) PDGF led to a significant increase in TGF-beta1 synthesis. Elevated glucose concentration stimulated de novo gene transcription as assessed by stimulation of a TGF-beta1 promoter-luciferase construct. This led to induction of a poorly translated TGF-beta1 transcript determined by polysome analysis. PDGF at low dose did not influence TGF-beta1 transcription, but led to alteration in TGF-beta1 mRNA stability and translation. Without a previous glucose-induced increase in the amount of TGF-beta1 transcript, PDGF did not stimulate significant TGF-beta1 protein synthesis. At a high dose (100 ng/ml) PDGF stimulated TGF-beta1 synthesis independent of glucose concentration. This was associated with increased TGF-beta1 gene transcription and alteration in TGF-beta1 mRNA translational efficiency. In conclusion the data suggests that in diabetic nephropathy, the role of glucose is to lower the threshold at which a stimulus such as PDGF stimulates TGF-beta1 protein synthesis. The data also suggest that independent regulation of TGF-beta1 transcription and translation by glucose and PDGF account for their synergistic effect on TGF-beta1 protein synthesis. We hypothesize that the role of glucose in diabetic nephropathy is to prime the kidney for an injurious response to other stimuli.

Translational regulation of renal proximal tubular epithelial cell transforming growth factor-beta1 generation by insulin

We have previously demonstrated that the proximal tubular cell may contribute to the pathogenesis of renal interstitial fibrosis in diabetes. Transforming growth factor (TGF)-beta1 is one of a group of pro-fibrotic cytokines and growth factors, which have been associated with the development of interstitial fibrosis. The aim of the current study was to examine the effect of insulin on the generation of TGF-beta1 by proximal tubular cells. HK-2 cells were grown to confluence in the absence of insulin, and serum deprived for 48 hours before all experimental manipulations. Addition of insulin (5 microg/ml) to the culture medium led to a time-dependent increase in TGF-beta1 concentration in the cell culture supernatant, and increased incorporation of radiolabeled amino acids into TGF-beta1 suggestive of de novo TGF-beta1 protein synthesis. Addition of insulin did not alter TGF-beta1 mRNA expression as assessed by reverse transcriptase-polymerase chain reaction or Northern analysis. Insulin-induced increase in TGF-beta1 concentration was not abrogated by actinomycin D, however, stimulation by insulin, in the presence of cycloheximide led to a dose-dependent decrease in TGF-beta1 production. Addition of insulin had no effect on TGF-beta1 mRNA stability as assessed by actinomycin D chase, but led to increased binding of a cytoplasmic protein to a putative stem loop structure in the 5'-UTR of TGF-beta1 mRNA, previously implicated in the posttranscriptional control of TGF-beta1 synthesis. To address the functional significance of insulin-induced alteration in TGF-beta1 synthesis, we examined its effect on matrix turnover. Insulin stimulated type IV collagen gene expression and an increase in the concentrations of the type IV collagen laid down in the extracellular matrix. This increase in type IV collagen was abrogated when cells were stimulated by insulin in the presence of an anti-TGF-beta1-blocking antibody. In conclusion the data demonstrate that insulin may directly alter the production of TGF-beta1 by renal proximal tubular cells by a posttranscriptional mechanism, and that this may have implications for the increase in extracellular matrix that accompanies diabetic nephropathy.

Isolation and characterization of As60A, a transforming growth factor-beta gene, from the malaria vector Anopheles stephensi

We have isolated the first mosquito member of the TGF-beta superfamily, As60A. As60A is a single copy gene, approximately 5 kb in length and encodes eight exons. Here we report the isolation and characterization of two of four transcripts produced from this gene. The transcripts As60A(1)and As60A(2)encode related 5'UTR/exon 1 sequences. As60A is most similar to the 60A genes from Drosophila and is thus a member of the Dpp/BMP subfamily of the TGF-beta superfamily. The splice junction of intron 2 is conserved among As60A, BMP2, BMP4, Tc-Dpp, Bm-tgh-1, TGF-beta1 and Dpp. Intron 2 also contains three putative binding sites for a Dorsal/Gambif1 transcription factor. The large number of introns and the conservation of intron 2 indicate that As60A is relatively ancient compared to the other arthropod TGF-beta genes. We also propose that As60A plays a role in the mosquito immune response to Plasmodium infection.

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.

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.