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Regulation by cAMP of STAT1 activation in hepatic stellate cells
1Department of Internal Medicine, Osaka City University Medical School, Abeno, Osaka, Japan.
Abstract:
Previously we reported that dibutyryl cAMP and phosphodiesterase inhibitor methylxanthines block rat stellate cell proliferation. To analyze the underlying mechanism, modulation by these agents of platelet-derived growth factor (PDGF)/BB-stimulating signal pathway was studied. Without reducing STAT1 protein level, these agents were found to attenuate STAT1 activation in stellate cells stimulated with PDGF/BB as revealed by an electrophoretic mobility shift assay. Inhibitory effect started 12 h after exposure of the cells to these agents at concentrations of more than 100 microM. These agents had no effects on DNA binding activity of STAT1 that had already been activated. Treatment with these agents failed to affect the function of PDGF receptors except for partial attenuation of phospholipase C activation under PDGF/BB stimulation. The present results indicate that inhibition of STAT1 activation may be one of factors involved in the cAMP-dependent stellate cell growth arrest.
Insights
Dibutyryl cyclic AMP (cAMP) and methylxanthines inhibit rat stellate cell proliferation by blocking signal transducer and activator of transcription 1 (STAT1) activation. This mechanism contributes to cAMP-dependent stellate cell growth arrest.
Area of Science:
- Cell biology
- Biochemistry
- Molecular signaling
Background:
- Rat stellate cells play a role in liver fibrosis.
- Previous studies indicated that dibutyryl cAMP and methylxanthines inhibit stellate cell proliferation.
Purpose of the Study:
- To investigate the mechanism by which cAMP and methylxanthines inhibit stellate cell proliferation.
- To analyze the modulation of the platelet-derived growth factor (PDGF)/BB signaling pathway by these agents.
Main Methods:
- Electrophoretic mobility shift assay (EMSA) to assess STAT1 activation.
- Stimulation of stellate cells with PDGF/BB.
- Treatment with dibutyryl cAMP and methylxanthines.
- Analysis of PDGF receptor function and phospholipase C activation.
Main Results:
- Dibutyryl cAMP and methylxanthines attenuated STAT1 activation in PDGF/BB-stimulated stellate cells without reducing STAT1 protein levels.
- The inhibitory effect on STAT1 activation was observed after 12 hours of exposure to concentrations above 100 microM.
- These agents did not affect already activated STAT1 DNA binding activity.
- PDGF receptor function was largely unaffected, with only partial attenuation of phospholipase C activation.
Conclusions:
- Inhibition of STAT1 activation is a key mechanism underlying cAMP-dependent stellate cell growth arrest.
- These findings provide insights into the molecular regulation of stellate cell proliferation and potential therapeutic targets for liver fibrosis.