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Regulation of plasminogen activator inhibitor-1 mRNA accumulation by basic fibroblast growth factor and transforming
J A Treichel1, M Reddington, G W Kreutzberg
1Department of Neuromorphology, Max Planck Institute of Neurobiology, Martinsried, Germany.
Abstract:
The effects of transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) were examined on the accumulation of plasminogen activator inhibitor-1 (PAI-1) mRNA in astrocytes in vitro. Both cytokines stimulated PAI-1 mRNA expression transiently with a maximal fivefold (bFGF) and 30-fold (TGF-beta1) at 4 h, decreasing to basal levels within 32 h. EC50 values were 1.4 nM for bFGF and 6.7 pM for TGF-beta1 on PAI-1 mRNA accumulation. A twofold increase in content of tPA mRNA was observed with bFGF but not with TGF-beta1. The action of TGF-beta1 on PAI-1 mRNA was inhibited by cycloheximide, indicating a requirement for de novo protein synthesis. In contrast, cycloheximide potentiated the action of bFGF. Nuclear run-on assays showed that bFGF, but not TGF-beta1, stimulated astrocytic PAI-1 gene transcription. Thus, TGF-beta1 predominantly uses posttranscriptional mechanisms to raise the level of PAI-1 mRNA in astrocytes, whereas bFGF acts at both the transcriptional and posttranscriptional levels. The data reveal differences in the mechanisms underlying the regulation of PAI-1 mRNA levels by TGF-beta1 in astrocytes compared with other cells. The action of TGF-beta1 and bFGF on the plasminogen activator system in astrocytes might be involved in the cellular events accompanying glial activation following injury of the CNS.
Insights
Transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) differentially regulate plasminogen activator inhibitor-1 (PAI-1) mRNA in astrocytes. TGF-beta1 acts post-transcriptionally, while bFGF affects both transcription and post-transcription.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Biology
Background:
- Astrocytes play crucial roles in central nervous system (CNS) injury and glial activation.
- The plasminogen activator system, including PAI-1, is implicated in cellular events following CNS injury.
- Understanding cytokine-mediated regulation of PAI-1 in astrocytes is vital for neurobiology research.
Purpose of the Study:
- To investigate the distinct mechanisms by which TGF-beta1 and bFGF influence PAI-1 mRNA accumulation in cultured astrocytes.
- To compare the regulatory pathways of TGF-beta1 and bFGF on PAI-1 expression in astrocytes.
Main Methods:
- In vitro cell culture of astrocytes.
- Quantification of PAI-1 mRNA levels using quantitative assays.
- Assessment of gene transcription using nuclear run-on assays.
- Investigation of protein synthesis requirement using cycloheximide treatment.
Main Results:
- Both TGF-beta1 and bFGF transiently increased PAI-1 mRNA levels in astrocytes.
- TGF-beta1 primarily utilized post-transcriptional mechanisms, whereas bFGF acted on both transcriptional and post-transcriptional levels.
- bFGF, but not TGF-beta1, significantly increased PAI-1 gene transcription.
- Cycloheximide inhibited TGF-beta1's effect but potentiated bFGF's effect on PAI-1 mRNA.
Conclusions:
- TGF-beta1 and bFGF exhibit distinct regulatory mechanisms for PAI-1 mRNA in astrocytes.
- These findings highlight cell-specific differences in TGF-beta1's regulation of PAI-1.
- The modulation of the plasminogen activator system by these cytokines in astrocytes may be relevant to glial responses after CNS injury.