Microcystin‐LR induces a wide variety of biochemical changes in the A549 human non‐small cell lung cancer cell line: Roles for protein phosphatase 2A and its substrates

Our previous studies have described the toxic effects of microcystin‐LR (MC‐LR) in various normal cell lines and human hepatoma SMMC‐7721 cells, but the specific effects of MC‐LR in other types of cancer cells with respect to protein phosphatase 2A (PP2A) have not been fully elaborated. A549 human lung adenocarcinoma cells have been identified to express organic anion‐transporting polypeptides (OATP) involved in cellular uptake of MC‐LR, and thus probably make an appropriate in vitro model to assess MC‐LR's cytotoxicity. Hence, in our present study, A549 cells were treated with various concentrations of MC‐LR for 24 h. The presence of MC‐LR in A549 cells was confirmed, and PP2A activity, PP2A substrates, cytoskeleton, apoptosis, and proliferation were subsequently explored. The results showed that 5–10 μM MC‐LR inhibited PP2A activity significantly but 0.5–1 μM MC‐LR did not change PP2A activity dramatically. The inhibition could result from the hyperphosphorylation of PP2A/C at Tyr307, an elevation in the total PP2A/C expression and the dissociation of α4/PP2A/C complexes. Moreover, MC‐LR led to rearrangements of filamentous actin and microtubules, which might be correlated with the hyperphosphorylation of Ezrin, VASP and HSP27 due to PP2A inhibition and mitogen‐activated protein kinase (MAPK) activation. However, exposure to MC‐LR for 24 h failed to trigger either apoptosis or proliferation, which might be related to PP2A‐inhibition‐induced hyperphosphorylation of Bcl‐2 and Bad and the activation status of Akt. In conclusion, our data indicated that MC‐LR induced extensive molecular and cellular alterations in A549 cells through a PP2A‐centered pathway, which differed in some respects from our previous study in SMMC‐7721 cells. To our knowledge, this is the first report comprehensively demonstrating the effects of MC‐LR in A549 cells, and our findings provide insights into the mechanism of MC‐LR toxicity in cancer cells. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1065–1078, 2017.

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