Inhibition of nuclear protein phosphatase activity in @entity19 hepatocytes by the cyanobacterial toxin XXXX .

@entity8283 @entity16588 @entity108 @entity19 @entity899 @entity107 @entity563 @entity8956
@entity16588 (MCLR) is a cyanobacterial hepatotoxin and protein phosphatase inhibitor that contaminates water reservoirs worldwide. MCLR localizes to the cytosol of hepatocytes, however, immunohistochemical studies indicate that it accumulates in the nucleus. MCLR @entity8956 is associated with decreased hepatic protein phosphatase activity, but effects in nuclear protein phosphatase activity have not been investigated. Balb/c @entity19 were given lethal (100 microg/kg) or sublethal (12, 23 and 45 microg/kg) i.p. doses of MCLR and hepatic nuclear extracts were analyzed for protein phosphatase 1 and 2A activity. There was profound inhibition of nuclear protein phosphatase activity within 50 min of lethal dosing, however an inhibition was not detected with sublethal doses. MCLR immunohistochemistry revealed widespread lobular staining in the lethal group and centrilobular staining in the sublethal groups. At the cellular level there was nuclear and cytoplasmic staining of equal intensity. As an indicator of nuclear protein phosphatase activity, the phosphorylation of @entity899 , a nuclear phosphoprotein and known substrate for protein phosphatases 1 and 2A, was evaluated. Balb/c @entity19 were treated with sublethal doses of MCLR or saline vehicle after induction of hepatic @entity899 by the DNA damaging agent @entity107 ( @entity108 ). @entity899 was immunoprecipitated and probed with @entity8283 specific antibodies by Western blotting. There was greater @entity8283 reactivity of @entity899 protein in animals treated with MCLR relative to saline treated controls, consistent with increased phosphorylation of @entity563 sites. It is concluded that an interaction of this toxin with nuclear protein phosphatases occurs within 50 min of lethal dosing, which leads to a profound inhibition of enzymatic activity. Even sublethal doses of MCLR that do not result in significant inhibition of activity in bulk nuclei, result in detectable changes in phosphorylation of @entity899 .
