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PMID |
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11696451
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Translational regulation of renal proximal tubular epithelial cell transforming growth factor-beta1 generation by insulin.
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11696451
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The aim of the current study was to examine the effect of insulin on the generation of TGF-beta1 by proximal tubular cells.
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11696451
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HK-2 cells were grown to confluence in the absence of insulin, and serum deprived for 48 hours before all experimental manipulations.
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11696451
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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.
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11696451
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Addition of insulin did not alter TGF-beta1 mRNA expression as assessed by reverse transcriptase-polymerase chain reaction or Northern analysis.
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11696451
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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.
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11696451
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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.
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11696451
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To address the functional significance of insulin-induced alteration in TGF-beta1 synthesis, we examined its effect on matrix turnover.
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11696451
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Insulin stimulated type IV collagen gene expression and an increase in the concentrations of the type IV collagen laid down in the extracellular matrix.
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11696451
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This increase in type IV collagen was abrogated when cells were stimulated by insulin in the presence of an anti-TGF-beta1-blocking antibody.
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11696451
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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.
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17675577
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High glucose-induced thioredoxin-interacting protein in renal proximal tubule cells is independent of transforming growth factor-beta1.
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17675577
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Txnip, heat shock proteins 70 and 90, chemokine (C-C motif) ligand 20, and matrix metalloproteinase-7 were chosen for verification of gene expression.
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17675577
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The increased protein expression of Txnip, CCL20, and MMP7 were also verified by Western blotting and enzyme-linked immunosorbent assay.
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17675577
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Subsequent studies focused on the dependence of Txnip expression on up-regulation of transforming growth factor (TGF)-beta1 under high-glucose conditions.
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17675577
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Overexpression of Txnip and up-regulation of Txnip promoter activity were observed in cells in which the TGF-beta1 gene was silenced in HK-2 cells using short interfering RNA technology.
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17675577
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High glucose further increased both Txnip expression and its promoter activity in TGF-beta1 silenced cells compared with wild-type cells exposed to high glucose, suggesting that high glucose induced Txnip through a TGF-beta1-indepen-dent pathway.
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