Wc. Buss et al., ASSOCIATION OF TISSUE-SPECIFIC CHANGES IN TRANSLATION ELONGATION AFTER CYCLOSPORINE WITH CHANGES IN ELONGATION-FACTOR-2 PHOSPHORYLATION, Biochemical pharmacology, 48(7), 1994, pp. 1459-1469
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.