Proteomics approach on microcystin binding proteins in mouse liver for investigation of microcystin toxicity

Microcystins (MC) produced by freshwater cyanobacteria are potent hepatotoxins. MC inhibit protein phosphatases (PP) I and 2A. MC and okadaic acid (OA), which is a similar PP inhibitor whereas it has a less affinity to PPI than MA, behave similarly to primary culture hepatocytes, with inducements of phosphorylations of cytoskeleton, morphological changes and apoptosis. Although the distribution of OA in mouse liver was observed immunohistochemically, no OA injury was found. The purpose of this study was therefore to determine why only MC has specific toxicities on the liver. A systematic process of MC affinity chromatography and proteomics, using two-dimensional gel electrophoresis and MALDI-TOFMS, indicated the existence of some MC-binding proteins including the complexes of PPI, MA, and PP4 with their own regulatory Subunits ill mouse liver extracts. The competitive inhibition experiments Using affinity chromatography with OA showed that two of the three protein complexes strongly interacted with OA, whereas only the complex of PPI with the inhibitory subunit NIPPI did not strongly interacted with OA. These results Suggest that the PP I complex is not related to the common behavior of MC and OA of primary Culture hepatocytes, and is related to the specific hepatotoxicities of MC. (C) 2004 Elsevier Ltd. All rights reserved.