The Pregnane X receptor (PXR) , is a nuclear receptor (NR) which heterodimerizes with RXRa (Retinoid X Receptor alpha) to regulate xenobiotic metabolism. The NR1I2 gene produces three isoforms, PXR1, PXR2 and PXR3. However, only the function of the major isoform PXRl is known. Moreover, PXR has been shown to have an anti-inflammatory function. This is interesting, since the processes of xenobiotic metabolism and inflammation antagonize each other. The mechanism by which PXR performs this anti-inflammatory function remains unclear. However, other nuclear receptors such as PPARa and PPARy repress pro-inflammatory gene induction via transrepression. This is a mechanism that facilitates transcriptional repression by the atypical association of NRs with co-regulatory and co-repressor complexes at foreign response elements. It is thought that SUMOylation allows these NRs to attain transrepressive functions. PXR is conjugated with SUM03 chains so it is believed that it too utilizes transrepression to mediate its anti-inflammatory actions. To study this, the five PXRIIPXR3 lysines were mutated. Additionally, five other so-called 'functional sites' which are critical to the transactivation role of PXR were also mutated. This was important to determine if the transactivation and repressive roles utilized similar mechanism of action. Luciferase reporter assay experiments were performed in RAW264.7 cells to investigate both the transactivation and repressive activities of the aforementioned mutants. Firstly, it was observed that both the putative SUMO sites and functional sites decreased PXREM induction and that PXR3 was transcriptionally inactive. Secondly, PXRl and PXR3 reduced the induction of the IL-8, iNOS and AP-l reporters used. However, the putative PXRl SUMO sites were less able to repress induction of the IL-8 reporter, while the functional mutants repressed induction just as well as wild type PXRl. Interestingly also, both the putative SUMO and functional PXR3 mutants repressed the IL-8 reporter as potently as the wild type.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662201 |
| Date | January 2013 |
| Creators | Alleyne, Jerusalem |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0037 seconds