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Microcystin-LR induced an inhibition of protein synthesis in isolated rat hepatocytes
S Claeyssens1, A Francois, A Chedeville
1Groupe de Biochimie et Physiopathologie Digestive et Nutritionnelle, U.F.R. Médecine-Pharmacie, Saint-Etienne du Rouvray, France.
Abstract:
The effect of microcystin-LR, an inhibitor of protein phosphatases PP1 and PP2A, was studied on protein synthesis by measuring the incorporation of labelled amino acid into protein in isolated rat hepatocytes. Microcystin-LR inhibited protein synthesis in the first minutes of the incubation period, and half-maximum effect was obtained at about 60 nM. Such an inhibition was also observed in the presence of different protein phosphatase inhibitors, i.e. okadaic acid, calyculin A and microcystin-RR. This effect was observed in whole hepatocytes, in the supernatant of the post-mitochondrial fraction and in the microsomal fraction. It was independent of a substrate supply and of the labelled amino acid used. Furthermore, this inhibition preceded the previously reported glucose-6-phosphatase activation induced by microcystin-LR [Claeyssens, Chédeville and Lavoinne (1993) FEBS Lett. 315, 7-10].
Insights
Microcystin-LR, a protein phosphatase inhibitor, significantly disrupts protein synthesis in rat hepatocytes within minutes. This effect, observed with various inhibitors, highlights a critical cellular process impacted by these toxins.
Area of Science:
- Biochemistry
- Toxicology
- Cell Biology
Background:
- Protein phosphatases PP1 and PP2A are crucial regulators of cellular processes.
- Microcystins are potent toxins produced by cyanobacteria, known to inhibit protein phosphatases.
- Understanding the cellular targets and effects of microcystins is vital for assessing their toxicity.
Purpose of the Study:
- To investigate the impact of microcystin-LR on protein synthesis in isolated rat hepatocytes.
- To determine the concentration-dependent effect of microcystin-LR on protein synthesis.
- To compare the effects of microcystin-LR with other protein phosphatase inhibitors on protein synthesis.
Main Methods:
- Isolated rat hepatocytes were incubated with labelled amino acids to measure protein synthesis.
- Microcystin-LR and other protein phosphatase inhibitors (okadaic acid, calyculin A, microcystin-RR) were used.
- Protein synthesis was assessed in whole cells, post-mitochondrial supernatant, and microsomal fractions.
Main Results:
- Microcystin-LR inhibited protein synthesis in isolated rat hepatocytes within minutes of incubation.
- The half-maximum inhibitory concentration (IC50) for microcystin-LR was approximately 60 nM.
- Similar inhibition of protein synthesis was observed with okadaic acid, calyculin A, and microcystin-RR.
- The inhibitory effect was consistent across different cellular fractions and independent of substrate or amino acid type.
- This inhibition preceded the previously reported microcystin-LR-induced activation of glucose-6-phosphatase.
Conclusions:
- Microcystin-LR directly inhibits protein synthesis in rat hepatocytes by targeting protein phosphatases PP1 and PP2A.
- The observed inhibition is a rapid cellular response to microcystin exposure.
- These findings contribute to understanding the molecular mechanisms of microcystin toxicity and its impact on cellular function.