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Cytochalisin D exerts stimulatory and inhibitory effects on insulin-induced glucokinase mRNA expression in
1Department of Medicine, University of Newcastle upon Tyne Medical School, UK.
Abstract:
The microfilament cytoskeleton is postulated to have a role in the localization, transport and anchorage of certain specific mRNAs. We investigated the effects of cytochalasin D, a fungal metabolite that binds to actin and disrupts the microfilament structure, on insulin-induced expression of glucokinase mRNA in rat hepatocyte cultures. Cytochalasin-D significantly potentiates insulin-induced glucokinase mRNA expression at 100 nM concentration but counteracts glucokinase expression at 2-20 microM. The latter effect is at least in part due to an increase in glucokinase mRNA degradation. This effect of cytochalasin D cannot be accounted for by an increase in cAMP and is also not due to a non-specific effect on mRNA degradation since albumin mRNA levels were not affected by cytochalasin-D and actin mRNA and tubulin mRNA levels were increased. Measurement of glucokinase mRNA release from digitonin-permeabilized hepatocytes suggests that cytochalasin D does not cause acute dissociation of glucokinase mRNA from its binding site. The increased degradation of glucokinase mRNA suggests involvement of the cytoskeleton in glucokinase mRNA stability. However, an additional effect of cytochalasin D on the insulin signalling mechanism cannot be excluded.
Insights
Cytochalasin D affects insulin-induced glucokinase mRNA expression in rat liver cells. Low concentrations enhance expression, while higher concentrations increase mRNA degradation, suggesting cytoskeletal involvement in mRNA stability.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The cytoskeleton, particularly microfilaments, is implicated in mRNA localization, transport, and anchorage.
- Understanding the role of the cytoskeleton in gene expression regulation is crucial for cellular processes.
Purpose of the Study:
- To investigate the impact of cytochalasin D, a microfilament disruptor, on insulin-induced glucokinase mRNA expression in rat hepatocytes.
- To elucidate the mechanisms underlying cytochalasin D's effects on glucokinase mRNA levels and stability.
Main Methods:
- Primary rat hepatocyte cultures were treated with varying concentrations of cytochalasin D.
- Insulin-induced glucokinase mRNA expression was quantified.
- mRNA degradation rates and release from permeabilized cells were assessed.
- Levels of other mRNAs (albumin, actin, tubulin) and cAMP were measured.
Main Results:
- Cytochalasin D (100 nM) potentiated insulin-induced glucokinase mRNA expression.
- Higher concentrations (2-20 microM) counteracted this expression, primarily by increasing glucokinase mRNA degradation.
- Albumin mRNA levels remained unaffected, indicating specificity.
- Actin and tubulin mRNA levels increased.
- Cytochalasin D did not acutely dissociate glucokinase mRNA from its binding site.
Conclusions:
- The microfilament cytoskeleton plays a role in regulating glucokinase mRNA stability.
- Cytochalasin D's effects on glucokinase mRNA expression are concentration-dependent and involve altered mRNA degradation.
- While cytoskeletal involvement is suggested, effects on insulin signaling cannot be ruled out.