A phosphoproteomic study uncovers the importance of PP2A-B56α in liver injury precipitated by NLRP3 activation during MC-LR exposure

Microcystin-LR (MC-LR) is one of the most typical cyanobacterial toxins threating the public health. Protein hyperphosphorylation by PP2A inhibition is a vital way of MC-LR to exert multiple toxic effects, yet the molecular and cellular mechanisms by which its inhibition precipitates injury remain incompletely understood. In this study, we developed an in vivo model for NLRP3 activation using MC-LR treatment in C57BL/6 mice, administering a daily oral gavage at a dosage of 0.4 mg/kg for 21 days. Phosphoproteomic profiling has revealed that perturbation in biological processes, such as cytoskeleton, junction integrity, translation and transcription, and metabolism, play a contributory role in NLRP3 inflammasome-mediated liver injury. In vitro studies have elucidated the roles of phosphorylated proteins in various biological processes: phosphorylated IQGAP2 is associated with the formation of F-actin stress fibers, phosphorylated ZO-1 is implicated in junctional discontinuity, and phosphorylated eIF4B is involved in the enhancement of cap-dependent translation induced by MC-LR. In particular, we demonstrate dysregulation of PP2A B56α-containing holoenzymes based on B56α phosphorylation contributes to MC-LR hepatotoxicity via B56α dissociation with key proteins involved in cytoskeleton, cell junction and translation initiation. Moreover, PKCδ is responsible for B56α phosphorylation and targetable by FDA-approved compounds tamoxifen which shows an antagonistic effect on the hepatotoxicity of MC-LR. This study expanded our knowledge of biological processes during MC-LR exposure and opened new opportunities for identifying additional potential targets of other environmental toxicants.