MODIFICATION OF HEPATIC IMMUNOGLOBULIN HEAVY-CHAIN BINDING-PROTEIN (BIP GRP78) FOLLOWING EXPOSURE TO STRUCTURALLY DIVERSE PEROXISOME PROLIFERATORS/

This investigation was conducted to determine the comparative effect o f structurally diverse peroxisome proliferators (PP) on the two-dimens ional protein pattern of rat liver whole homogenates. Perfluoro-n-deca noic acid (PFDA), perfluoro-n-octanoic acid (PFOA), clofibrate, and di (2-ethylhexyl)phthalate (DEHP) are all known to cause the proliferatio n of hepatic peroxisomes and the induction of peroxisomal beta-oxidati ve and microsomal omega-oxidative enzymes. To clarify the mechanistic differences between these compounds with regard to the liver, we exami ned the unique patterns of protein alteration produced by in vivo expo sure to them. Following exposure to various doses, whole liver homogen ates were prepared and separated by two-dimensional gel electrophoresi s (2DE) using the ISO-DALT system. Stained gels were digitized and pro tein patterns analyzed using the Kepler 2D gel analysis system. Immuno globulin heavy chain binding protein (BiP), also known as 78-kDa glu- cose-regulated protein (Grp78), was identified immunologically and by comigration of recombinant Grp78. BiP is a luminal endoplasmic reticul ar protein that functions in the assembly and folding of nascent prote ins as they enter the ER. The present results suggest a selective post translational modification of BiP following PFDA exposure. Single-dose exposure to PFDA was associated with a notable charge modification of BiP that persists up to 30 days. PFOA, clofibrate, and DEHP had less effect in this regard. The identity of BiP/Grp78 as the halothane hepa titis-associated trifluoroacetylated protein was also demonstrated, Th e nature of this PFDA-associated protein modification (reactive metabo lite conjugation, abnormal ribosylation, or phosphorylation) is curren tly under investigation. These results document PFDA's unique toxicity as a PP and support the utility of 2D gel analysis in toxicity testin g. (C) 1994 Society of Toxicology.