Peroxisome proliferator-activated receptors (PPARs) are members of a
large group of ligand-regulated transcription factors that includes nuclear
receptors for steroid and thyroid hormones, retinoids and vitamin D���.
Synthetic fibrates and thiazolidinediones that bind to and activate PPARs are
used efficaciously in humans to remedy hypertriglyceridemia and non-insulin
dependent diabetes mellitus, respectively. The objective of the studies
described herein was to elucidate the molecular mechanisms of ligand-dependent
PPAR signaling.
Several PPAR ligands, including WY-14,643, were demonstrated to
directly induce PPAR�� conformational changes as evidenced by a differential
protease sensitivity assay. Conformational changes were induced in a dose-dependent
manner which paralleled that of ligand to induce transcriptional
activation. Direct interaction of ligands with, and the resulting conformational
alterations in, PPAR�� may facilitate interaction of the receptor with
transcriptional intermediary factors and thus may underlie the molecular basis
of ligand-dependent transcriptional activation mediated by PPAR��.
The yeast two hybrid screen was utilized to identify downstream
components of the PPAR�� signaling pathway. Using this technique, the
coactivator proteins, p300 and steroid receptor coactivator-1 (SRC-1), were
identified as PPAR��-interacting proteins and WY-14,643 potentiated these
interactions. p300 also enhanced the transcriptional activation properties of
PPAR�� and, therefore, can be considered a bona fide coactivator for this
nuclear receptor. Nuclear receptor corepressor (NCoR) was also isolated as
a PPAR��-interacting protein from a yeast two hybrid screen. In contrast to the
ligand enhanced PPAR��-coactivator interactions, WY-14,643 inhibited NCoR
interaction with PPAR��. NCoR and the coactivators, p300 and SRC-1, were
also demonstrated to require distinct receptor regions for efficient interaction
with PPAR��.
Results described herein demonstrate that ligand induces PPAR��
conformational changes, promotes PPAR��-coactivator (p300 and SRC-1)
interactions, and inhibits PPAR��-NCoR interactions. We hypothesize that
such molecular events are critical for ligand-dependent transcriptional
activation by PPAR��. These results contribute additional knowledge as to the
molecular mechanisms of PPAR-dependent signaling and may act as a
starting part for the improvement and/or development of therapeutic strategies
aimed at manipulating this signaling pathway. / Graduation date: 1999
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33553 |
| Date | 09 June 1998 |
| Creators | Dowell, Paul T. |
| Contributors | Leid, Mark |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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