ASSOCIATION OF TISSUE-SPECIFIC CHANGES IN TRANSLATION ELONGATION AFTER CYCLOSPORINE WITH CHANGES IN ELONGATION-FACTOR-2 PHOSPHORYLATION

In studies of cyclosporin (CsA) toxicity in Sprague-Dawley rats, CsA a dministered in vivo produced tissue-specific, dose-dependent changes i n microsomal translation throughout the bodies of the animals. The mos t pronounced translation inhibition was in microsomes from the kidney, the organ in which dose-limiting CsA toxicity occurs. In contrast, tr anslation was stimulated in microsomes from the liver. CsA produced ch anges at the level of translation elongation, which is regulated by th e reversible phosphorylation of elongation factor 2 (EF2). Changes in translation elongation after CsA were found to be associated with, and most likely caused by, changes in EF2 phosphorylation. Reduced renal translation elongation was associated with increased EF2 phosphorylati on, and increased hepatic elongation with decreased EF2 phosphorylatio n. EF2 is phosphorylated by Ca2+ calmodulin-dependent protein kinase I II (PKIII). Phosphorylated EF2 is a substrate for protein phosphatase 2A (PP2A), but not calcineurin (protein phosphatase 2B or PP2B), the e nzyme inhibited by CsA-cyclophilin complexes in T-cells. When CsA or i nhibitors of PKIII (EGTA, trifluoperazine) were added in vitro to assa ys of EF2 phosphorylation in renal or hepatic cytoplasm, or to assays of renal or hepatic microsomal translation elongation, they were witho ut significant effects. Addition in vitro of the PP2A inhibitor okadai c acid increased EF2 phosphorylation in renal and hepatic cytoplasms, but inconsistently produced an inhibition of microsomal translation. H owever, in less complex rabbit reticulocyte lysates, addition of okada ic acid inhibited PP2A, increased EF2 phosphorylation, and inhibited t ranslation elongation. Furthermore, addition of EGTA and trifluoperazi ne to rabbit reticulocyte lysates inhibited Ca2+ calmodulin-dependent PKIII activity, decreased EF2 phosphorylation, and stimulated translat ion elongation. CsA acting alone or as a complex with cyclophilin coul d alter EF2 phosphorylation by affecting transcriptional regulation or the enzymatic activity of PKIII, PP2A or EF2. Changes in EF2 phosphor ylation and translation in body tissues suggest that CsA causes widesp read disturbances in phosphorylation and dephosphorylation pathways re gulating cellular processes including transcription and translation fa ctor activity. These disturbances may underlie the broad spectrum of t oxicities observed during CsA therapy.