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2004
LSU-HHMI Summer Undergraduate Research Program |
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 Remona
L. Peterson (Tuskegee University), Jacqueline M. Stephens, Biological
Sciences
Examination of Components of the Unfolded Protein Response
in Fat Cells and Rodent Models of Obesity/Type II diabetes
UPR is an intracellular signaling pathway that regulates the
protein folding and processing capacity of the endoplasmic reticulum.
UPR is activated upon the accumulation of excessive secretory
proteins that are unable to attain correct three-dimensional
structure. Therefore, an experiment was conducted to investigate
how or if proteins in this pathway are regulated in 3T3-L1 cells,
epididymal fat, skeletal muscle, and liver tissues of lean and
obese mice. Several proteins such as BiP (binding protein),
PDI (protein disulfide isomerase), eIF2 (elongation initiation
factor), and Ire-1 (iron response element) are involved in the
unfolded protein response (UPR). BiP, a molecular chaperone
that binds and stabilizes proteins at intracellular stages of
folding, promotes proper folding of polypeptides into their
correct conformations. In this study, BiP protein expression
was not changed by adipocyte differentiation. In epididymal
fat, skeletal muscle, and liver, a small difference was detected
in expression between ob/ob (obese) and ob/+ (lean). PDI is
very important to the endoplasmic reticulum (ER) and in the
formation of disulfide bonds in the lumen. PDI is known to be
abundant in the ER of secretory cells in such organs as the
pancreas and liver. PDI was expressed higher in ob/ob mice from
tissues of epididymal fat, skeletal muscle, and liver. In addition,
two bands were expressed in the 3T3-L1 cells as well as skeletal,
epididymal fat, and liver. Moreover, PDI was also expressed
at a lower molecular weight than previously demonstrated. elF2
is required for transcriptional initiation. It was not expressed
in 3T3-L1 cells or the liver samples. However, there was expression
of elF2 in skeletal muscle and epididymal fat but at very low
levels in both ob/+ and ob/ob mice. Ire-1, an ER membrane protein
that exists as a monomer and dimer, increased throughout adipocyte
differentiation in 3T3-L1 cells. There was no detectable expression
of the Ire-1 protein in epididymal adipose tissue or skeletal
muscle. Ire-1 was present in the liver samples and more expression
was prevalent in the ob/ob (obese) mice. All of the above mentioned
proteins play a role the unfolded protein response. However,
these data indicated that not all are necessarily needed in
the activation of the unfolded protein response in type II diabetes.
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