Mamady, H. and Storey, K.B. 2006. Up-regulation
of the endoplasmic reticulum molecular chaperone GRP78 during hibernation in
thirteen-lined ground squirrels. Mol. Cell. Biochem. 292, 89-98.
Mamady Hapsatou and Kenneth B. Storey
Up-regulation of the endoplasmic reticulum molecular chaperone GRP78 during
hibernation in thirteen-lined ground squirrels
Abstract
Hibernating mammals
endure conditions of hypothermia, ischemia/hypoxia and oxidative stress that
would be highly injurious to nonhibernators. Stress
conditions frequently trigger the production of molecular chaperones; in the
endoplasmic reticulum the glucose-regulated protein-78 (GRP78) helps to
minimize protein misfolding under stress. The present
study evaluated GRP78 response in seven organs of hibernating thirteen-lined
ground squirrels, Spermophilus
tridecemlineatus. Transcript levels of grp78,
assessed by RT-PCR, were significantly higher (3.5- to 4.1-fold) in brown
adipose tissue and brain of hibernating squirrels compared with euthermic
control animals but remained low or stable in all other tissues. GRP78 protein
content, assessed by Western blotting, was also elevated in brown adipose and
brain during hibernation by 1.4-1.6 fold compared with controls. A 2490 bp cDNA sequence was retrieved that contained the full open
reading frame of ground squirrel grp78
and the translated
protein sequence of 654 amino acids shared 98-99 % identity with GRP78 from
other mammalian sources. Selected specific amino acid substitutions occurred in
the ground squirrel sequence that may aid GRP78 function under the near 0°C
body temperatures of the hibernating state. Electrophoretic
mobility shift and supershift assays showed that the
activating transcription factor, ATF4, binds to the promoter region of the grp78 gene in ground squirrel brain and
may be responsible for grp78
up-regulation during hibernation. Changes in grp78 gene and protein expression appear to aid stress tolerance in
two highly oxygen-dependent organs that are critical to whole animal survival
during hibernation.