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onded PPAR is their heterodimenzation with retinoic acid RXR receptors. The PPAR-
RXR dimmer then binds to the specific PPAR response elements (PPARE) on the
promoter region of the transcribed gene. PPARE are charactenzed by the existence of
specific nucleotide sequence AGGTCANAGGTCA. The binding of PPAR-RXR
heterodimer to its response elements results in the regulation of the expression of number
of genes. This regulation will be achieved by the recruitment of co-activator elements
which will cause the acetylation of histone molecules and activation of gene transcription
(Desvergne and Wahli 1999) . The lack of ligand will cause the recruitment of corepressors
and will result in suppression gene expression. This process is almost identical
to the process of retinoic acid signaling and it shares the same co-repressors and coactivators
that are involved in the retinoic acid-induced control of gene transcription. It is
also important to mention that some PPAR receptors may regulate the action of other
members of their family. Thus, it is reported that PPAR ô overexpression will result in
the inactivation of PPAR a and thyroid hormone receptor mediated transcription and this
is achieved by the higher affinity of PPAR ô for the RXR receptors binding sights (Jow
and Mukherjee 1995).
V.c.PPAR and Apoptosis
A number of recent studies have followed the role of PPARs in the regulation of
apoptosis. As obligate heterodimeric partners of RXR receptors, PPARs may be involved
in the regulation of apoptosis and this is confirmed in a number of studies using different
cell lines. Simbula et al (2004) has reported that the usage of PPAR pan-agonists, 8R931
was able to induce apoptosis in FaO cells (Simbula et al. 2004). The same study
conciuded that BR93l-induced apoptosis may be mediated by the number of processes
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