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HORMONES AND SIGNALING
1Departments of Molecular and Integrative Physiology and 2Internal Medicine, The University of Michigan Medical School, Ann Arbor, Michigan 48109-0622
Submitted 23 December 2002 ; accepted in final form 19 May 2003
Acute pancreatitis (AP) has been shown in some studies to inhibit total
protein synthesis in the pancreas, whereas in other studies, protein synthesis
was not affected. Previous in vitro work has shown that high concentrations of
cholecystokinin both inhibit protein synthesis and inhibit the activity of the
guanine nucleotide exchange factor eukaryotic initiation factor (eIF)2B by
increasing the phosphorylation of eIF2
. We therefore evaluated in
C57BL/6 mice the effects of caerulein-induced AP on pancreatic protein
synthesis, eIF2B activity and other protein translation regulatory mechanisms.
Repetitive hourly injections of caerulein were administered at 50 µg/kg ip.
Pancreatic protein synthesis was reduced 10 min after the initial caerulein
administration and was further inhibited after three and five hourly
injections. Caerulein inhibited the two major regulatory points of translation
initiation: the activity of the guanine nucleotide exchange factor eIF2B (with
an increase of eIF2
phosphorylation) and the formation of the eIF4F
complex due, in part, to degradation of eIF4G. This inhibition was not
accounted for by changes in the upstream stimulatory pathway, because
caerulein activated Akt as well as phosphorylating the downstream effectors of
mTOR, 4E-BP1, and ribosomal protein S6. Caerulein also decreased the
phosphorylation of the eukaryotic elongation factor 2, implying that this
translation factor was not inhibited in AP. Thus the inhibition of pancreatic
protein synthesis in this model of AP most likely results from the inhibition
of translation initiation as a result of increased eIF2
phosphorylation, reduction of eIF2B activity, and the inhibition of eIF4F
complex formation.
protein translation; mice
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