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2004
LSU-HHMI Summer Undergraduate Research Program |
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 Adriana
Simionescu (Clemson University), Jacqueline M. Stephens Biological
Sciences
Examination of Components of the Ubiquitin Proteasome System
in Fat Cells and Rodent Models of Obesity/Type II Diabetes
Type II diabetes, also called non-insulin dependent diabetes
mellitus (NIDDM), is possibly due to defects in fat cells, which
are unresponsive to insulin and produce a high level of lipids
in the blood, preventing the uptake of glucose by the cells
and causing obesity and diabetes. Insulin sensitivity can be
induced by adipocyte differentiation, which is highly regulated
by transcription factors. Transcription factors and other proteins
no longer needed by the cell are first degraded by the ubiquitin
proteasome system (UPS) in order to stop the cell cycle, and
are then induced to regulate the obese gene and to promote adipogenesis.
The goal of this study was to understand the role of the UPS
in adipose tissue. For this purpose, we studied several UPS
components: ubiquitin, STAT 5A (signal transducer and activator
of transcription), Ubc 9 (ubiquitin conjugating enzyme 9), PPAR?
(peroxisome proliferators-activator receptor), and SUMO-1 (small
ubiquitin-like modifier) during adipocyte cell culture differentiation
and in rodent models of obesity. Whole cell extracts and extracts
obtained from obese and lean mice tissues were analyzed for
levels of UPS components using western blotting. We found that
ubiquitin, STAT 5A and PPAR ? increase during differentiation,
suggesting that they regulate the expression of the obese gene
and promote adipogenesis. However, the ubiquitin-like modifiers
Ubc 9, SUMO-1 and SUMO-1 Ran GAP1 did not appear to regulate
adipogenesis. In rodent models, regulation of the UPS components
in different tissues was observed. We found an increased expression
of ubiquitin in the epididymal fat, skeletal muscle and liver
tissues of both obese and lean mice. STAT 5A and SUMO-1 Ran
GAP1 were not regulated in the epididymal fat tissue of obese
and lean mice, but their level was higher in the obese skeletal
muscle and liver of the obese mice. The PPAR ? was shown to
be higher in all tissues (epidydimal fat, skeletal muscle and
liver) of the obese mice compared to those of the lean. While
equal expression of Ubc 9 in obese mice tissues compared to
lean mice tissues was seen, SUMO-1 showed a higher expression
in the epididymal fat of the obese mice and an unusually higher
level in the liver of the obese mice compared to the lean mice.
Our results confirm the hypothesis that the components of the
UPS are differentially regulated during adipogenesis and in
rodent models.
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