Protein phosphatase 2A inhibition and subsequent cytoskeleton reorganization contributes to cell migration caused by microcystin-LR in human laryngeal epithelial cells (Hep-2)

Abstract

The major toxic mechanism of Microcystin-LR is inhibition of the activity of protein phosphatase 2A (PP2A), resulting in a series of cytotoxic effects. Our previous studies have demonstrated that microcystin-LR (MCLR) induced very different molecular effects in normal cells and the tumor cell line SMMC7721. To further explore the MCLR toxicity mechanism in tumor cells, human laryngeal epithelial cells (Hep-2) was examined in this study. Western blot, immunofluorescence, immunoprecipitation, and transwell migration assay were used to detect the effects of MCLR on PP2A activity, PP2A substrates, cytoskeleton, and cell migration. The results showed that the protein level of PP2A subunits and the posttranslational modification of the catalytic subunit were altered and that the binding of the AC core enzyme as well as the binding of PP2A/C and α4, was also affected. As PP2A substrates, the phosphorylation of MAPK pathway members, p38, ERK1/2, and the cytoskeleton-associated proteins, Hsp27, VASP, Tau, and Ezrin were increased. Furthermore, MCLR induced reorganization of the cytoskeleton and promoted cell migration. Taken together, direct covalent binding to PP2A/C, alteration of the protein levels and posttranslational modification, as well as the binding of subunits, are the main pattern for the effects of MCLR on PP2A in Hep-2. A dose-dependent change in p-Tau and p-Ezrin due to PP2A inhibition may contribute to the changes in the cytoskeleton and be related to the cell migration in Hep-2. Our data provide a comprehensive exposition of the MCLR mechanism on tumor cells. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 890-903, 2017.

Alpha4‐overexpressing HL7702 cells can counteract microcystin‐LR effects on cytoskeletal structure

“…It is well‐known that MC‐LR can seriously inhibit PP2A activity and cause cell toxicity in numerous cell lines . In our previous work, we observed similar results in different cell lines, and the response profile of PP2A to an MC‐LR insult in different cells presents its own distinguishing feature . In addition, we found that α4, a PP2A regulator, is closely related to the toxic effect of MC‐LR on HEK293 cells.…”

“…A variety of reports have shown that MC‐LR can disrupt the cytoskeletal architecture and lead to the reassembly or reorganization of cytosolic fibers, presumably due to inhibition of PP1 and PP2A, and the phosphorylation balance of the cytoskeleton‐related proteins plays a vital role in the regulation of cytoskeletal mobility and stability . A rearrangement of cell cytoskeleton induced by MC‐LR was observed in our previous study in different cell lines, including HL7702 . In addition, a protective role of α4 on cytoskeletal structure was observed when α4‐overexpressing HEK 293 cells were treated with MC‐LR.…”

“…The activation of the MAPK kinases is reported to contribute to the hyperphosphorylation of cytoskeleton‐associated proteins including tau, VASP, HSP27, and ezrin23 . Our previous study detected the activation of the MAPK kinases in different cell lines exposed to MC‐LR probably due to the inhibition of PP2A because MAPKs are substrates of PP2A . In addition, we observed that P38 is involved in tau phosphorylation and both P38 and JNK are involved in HSP27 phosphorylation .…”

“…The MAPKs mainly consist of 3 super families of serine/threonine kinases that can be activated by a wide variety of extracellular stimulus related to cell proliferation, cell differentiation, cell apoptosis and the cell cycle: ERK1/2, JNK, and P38 . The activation of the MAPK kinases is reported to contribute to the hyperphosphorylation of cytoskeleton‐associated proteins including tau, VASP, HSP27, and ezrin23 . Our previous study detected the activation of the MAPK kinases in different cell lines exposed to MC‐LR probably due to the inhibition of PP2A because MAPKs are substrates of PP2A .…”

Mechanical Changes and Microfilament Reorganization Involved in Microcystin-LR-Promoted Cell Invasion in DU145 and WPMY Cells

“…For example, Liu et al reported that MC-LR promoted proliferation and inhibited apoptosis in normal human liver cells (HL7702) (Liu et al, 2016). The study of Wang et al showed that MC-LR induced cytoskeleton reorganization, resulting in increased cell migration in human laryngeal epithelial cells (Hep-2) (Wang et al, 2017). However, the effect of MC-LR on prostate cancer (PCa) cells and normal prostate cells has yet been studied.…”