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Published on: December 14, 2017
Microcystin-LR induces protein phosphatase 2A alteration in a human liver cell line
Yu Sun1, Qun Zheng, Yu-Tao Sun
1Department of Biochemistry and Molecular Biology, School of Medicine, Zhejiang University, 310058 Hangzhou, China.
Abstract:
Microcystin-LR (MC-LR) is a potent inhibitor of protein phosphatases 1 and 2A, and has potent hepatotoxicity and tumor promotion activity. Numerous studies on MC-LR toxicity have been conducted in rat hepatocytes, but few studies of the effects of microcystins on human hepatocytes have been done. In this study, HL7702 cells (a human normal liver cell line) were incubated in MC-LR for 24 h. The existence of MC-LR in HL7702 cells was confirmed. Furthermore, PP2A activity and the alteration of PP2A subunits were assessed. The results show that PP2A activity decreased from the concentration of 1 μM MC-LR, showing a concentration-dependent decline, to about 34% at 10 μM MC-LR. This activity undergone opposite change with alternations of phosphorylated Y307-PP2A/C and PP2A/C subunit but showed same change with the alteration of the ratio of methylated L309-PP2A/C to PP2A/C. B55α, a regulatory subunit of PP2A, was slightly increases in cells treated with the highest concentration of MC-LR (10 μM), and colocalized increasedly with rearranged-microtubules after 1 μM MC-LR exposure. However, the proportion of early apoptotic cells did not show any change at various concentration of MC-LR for 24 h. To our knowledge, this is the first report showing MC-LR-induced alteration of PP2A phosphatase in human cultured hepatocytes, and the mechanism of action seems to be similar as described before in vitro. The alteration of PP2A and microtubule seems to be the early event induced by MC-LR exposure.
Insights
Microcystin-LR (MC-LR) exposure in human liver cells inhibits protein phosphatase 2A (PP2A) activity and alters its subunits, affecting microtubules. This occurs without inducing early apoptosis, suggesting early cellular events in MC-LR toxicity.
Area of Science:
- Hepatotoxicity
- Cellular Biology
- Toxicology
Background:
- Microcystin-LR (MC-LR) is a hepatotoxic cyanotoxin inhibiting protein phosphatases 1 and 2A (PP2A).
- Research on MC-LR effects in human hepatocytes is limited compared to rat models.
- Understanding MC-LR's impact on human liver cells is crucial for risk assessment.
Purpose of the Study:
- To investigate the effects of MC-LR on human normal liver cells (HL7702).
- To assess MC-LR's impact on PP2A activity and its subunits in human hepatocytes.
- To explore potential early cellular events induced by MC-LR exposure.
Main Methods:
- Human HL7702 cells were incubated with varying concentrations of MC-LR for 24 hours.
- MC-LR presence in cells was confirmed.
- PP2A activity, subunit alterations (phosphorylation, methylation), and microtubule organization were analyzed.
Main Results:
- MC-LR was detected in HL7702 cells.
- PP2A activity decreased in a dose-dependent manner with MC-LR exposure.
- Alterations in PP2A subunits and increased colocalization with rearranged microtubules were observed, but early apoptosis remained unchanged.
Conclusions:
- This is the first report on MC-LR-induced PP2A alteration in human cultured hepatocytes.
- MC-LR exposure alters PP2A activity and subunits, impacting microtubules in human liver cells.
- PP2A and microtubule alterations appear to be early events in MC-LR toxicity, potentially preceding apoptosis.
