Pregnane X Receptor Expression in Human Pancreatic Adenocarcinoma: Associations With Clinicopathologic Parameters, Tumor Proliferative Capacity, Patients' Survival, and Retinoid X Receptor Expression.

OBJECTIVES: Pregnane X receptor (PXR) has been involved in human malignancy, either by directly affecting carcinogenesis or by inducing drug-drug interactions and chemotherapy resistance. The present study aimed to assess the clinical significance of PXR in pancreatic adenocarcinoma. METHODS: Pregnane X receptor and its heterodimers' PXR/retinoid X receptor α (RXR-α), RXR-ß, and RXR-γ expression were assessed immunohistochemically on tumoral samples from 55 pancreatic adenocarcinoma patients and were associated with clinicopathologic parameters, tumor proliferative capacity, and patients' survival. RESULTS: Enhanced PXR expression was noted in 24 (43.6%) of 55 pancreatic adenocarcinoma cases. Pancreatic adenocarcinoma patients presenting increased histological grade of tumor differentiation showed a significant increased incidence of elevated PXR expression (P = 0.023). Enhanced PXR/RXR-ß expression was significantly associated with smaller tumor size and earlier clinical stage (P = 0.005 and P = 0.003, respectively). Elevated PXR/RXR-γ expression was significantly associated with smaller tumor size and earlier clinical stage (P = 0.012 and P = 0.014, respectively) and borderline with the absence of lymph node metastases (P = 0.056). In addition, pancreatic adenocarcinoma patients presenting enhanced PXR/RXR-γ expression showed marginally longer survival times compared with those with decreased expression (log-rank test, P = 0.053). CONCLUSIONS: This study supported evidence that PXR and its copartners' overexpression may be associated with favorable clinicopathologic parameters and better outcome in pancreatic adenocarcinoma.

Expression of retinoid X receptor ß is induced in astrocytes during corpus callosum demyelination.

The experimental activation of retinoid receptors reduces pathological symptoms in animal models of multiple sclerosis. In order to assess the involvement of endogenous retinoid signaling during the process of demyelination we investigated retinoic acid synthesizing enzymes and nuclear receptors using the mouse model of cuprizone toxicity. The initiation of myelin degradation in the corpus callosum was accompanied with a local increase of retinaldehyde dehydrogenase (RALDH) immunoreactivity. On the level of receptors we observed a striking increase in protein expression of the retinoid X receptor (RXR)-ß in the affected corpus callosum. The RXRß immunoreactivity appeared exclusively in astrocytes, where it reached a maximum at five weeks of treatment, following the RALDH response. In the cerebral cortex and basal ganglia of affected mice RXRß was also observed in neurons. Among nuclear receptor antigens RARα showed a cuprizone associated increase in the corpus callosum. Quantitative RT-PCR revealed strong basal expression of RXRß and a significant, over 20-fold upregulation of the peroxisome proliferator-activated receptor-γ during demyelination. The results indicate that compensatory mechanisms during central demyelination may engage nuclear receptor dimers with an RXRß partner.