The Toxicologist - Society of Toxicology
The Toxicologist - Society of Toxicology
The Toxicologist - Society of Toxicology
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
showed an enhanced endoplasmic reticulum (ER) stress 5 days post v-Hras1 infection,<br />
characterized by enhanced vacuolation and higher levels <strong>of</strong> several ER stress<br />
markers. Surprisingly, this increased level <strong>of</strong> ER stress did not lead to an increase in<br />
oncogene-induced senescence in Pparβ/δ-null keratinocyte, but rather, Pparβ/δnull<br />
keratinocytes exhibited a lower level <strong>of</strong> cellular senescence compared to wildtype<br />
keratinocytes. Further, ligand activation <strong>of</strong> PPARβ/δ induced terminal differentiation<br />
in v-Hras1- infected wild-type keratinocytes and this effect was not<br />
observed in v-Hras1- infected Pparβ/δ-null keratinocytes. <strong>The</strong>se results suggest that<br />
PPARβ/δ attenuates oncogenic-dependent neoplastic transformation by inhibiting<br />
Hras1 signaling in keratinocytes. (Supported by CA124533, CA126826)<br />
2143 PPARβ/δ -DEPENDENT AND INDEPENDENT<br />
FUNCTIONS OF THE PPARβ/δ ANTAGONIST GSK3787.<br />
P. S. Palkar 1 , M. G. Borland 1 , C. Lee 1 , C. H. Ferry 1 , A. K. Sharma 2 , S. Amin 2 ,<br />
A. N. Billin 3 , T. M. Wilson 3 , F. J. Gonzalez 4 and J. M. Peters 1 . 1 Department <strong>of</strong><br />
Vet. and Biomed Sci, Penn State University, State College, PA, 2 Department <strong>of</strong><br />
Pharmacology, Penn State Cancer Institute, Hershey, PA, 3 Nuclear Receptor Discovery<br />
Research, GlaxoSmithKline, Research Triangle Park, NC and 4 Laboratory <strong>of</strong><br />
Metabolism, NCI, Bethesda, MD.<br />
<strong>The</strong> availability <strong>of</strong> high affinity agonists for peroxisome proliferator-activated receptor-β/δ<br />
(PPARβ/δ) has led to significant advances in our understanding <strong>of</strong> the<br />
functional role <strong>of</strong> PPARβ/δ. <strong>The</strong> first PPARβ/δ antagonist (GSK0660) was recently<br />
described but this compound is not bioavailable precluding its application<br />
for in vivo analysis. In this study, the effect <strong>of</strong> a new PPARβ/δ antagonist,<br />
GSK3787, was examined using in vivo and in vitro models. Oral administration <strong>of</strong><br />
GSK3787 effectively anatagonized GW0742-induced up-regulation <strong>of</strong> Angptl4<br />
mRNA expression in wild-type mouse colon. This antagonism was due to reduced<br />
promoter occupancy based on chromatin immunoprecipitation (ChIP) analysis.<br />
GSK3787 effectively antagonized GW0742-induced expression <strong>of</strong> Angptl4 mRNA<br />
in wild-type mouse fibroblasts and keratinocytes, and this effect was not found in<br />
similarly treated PPARβ/δ-null cells. GW0742 did not significantly influence cell<br />
proliferation at concentrations up to 10 μM in wild-type or PPARβ/δ-null fibroblasts.<br />
Similar results were found in fibroblasts treated with GSK3787 as no changes<br />
in cell proliferation were observed at concentration up to 10 μM. GSK3787 did<br />
not inhibit proliferation <strong>of</strong> A549, MCF7, H1838 cells at concentrations that<br />
specifically antagonized gene expression. Results from these studies demonstrate<br />
that GSK3787 can antagonize PPARβ/δ in vivo and be highly specific in vitro at<br />
concentrations lower than 1 μM. However, results from these studies also show that<br />
inhibition <strong>of</strong> cell proliferation observed with higher concentrations (≥ 10 μM) affecting<br />
non-tumor cells and tumor cell lines are likely due to <strong>of</strong>f-target mechanisms.<br />
(Supported by CA124533, CA126826)<br />
2144 FUNCTIONAL EXAMINATION OF THE ROLE OF<br />
PEROXISOME PROLIFERATOR-ACTIVATED<br />
RECEPTOR-β/δ (PPARβ/δ) IN HUMAN COLON<br />
CANCER.<br />
J. E. Foreman 1 , J. L. Williams 2 , B. Rigas 2 , F. J. Gonzalez 3 and J. M. Peters 1 . 1 <strong>The</strong><br />
Center for Mol. <strong>Toxicology</strong> & Carcinogenesis, Penn. State University, University Park,<br />
PA, 2 Division <strong>of</strong> Cancer Prevention, Stony Brook University, Stony Brook, NY and<br />
3<br />
Laboratory <strong>of</strong> Metabolism, NCI, Bethesda, MD.<br />
<strong>The</strong> role <strong>of</strong> peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) remains<br />
controversial. While some evidence suggests that activating PPARβ/δ promotes tumorigenesis,<br />
other reports suggest that activating PPARβ/δ has no effect or attenuates<br />
tumorigenesis. <strong>The</strong> latter observations are also supported by the well-established<br />
roles <strong>of</strong> PPARβ/δ in regulating glucose and lipid homeostasis and promoting<br />
cellular differentiation. Previous work has suggested that PPARβ/δ is up-regulated<br />
by the APC/β-catenin pathway in colon cancer and that the chemopreventive effects<br />
<strong>of</strong> non-steroidal anti-inflammatory drugs (NSAIDs) are mediated by repression<br />
<strong>of</strong> PPARβ/δ expression and function. However, more comprehensive analysis<br />
<strong>of</strong> human colon cancer cell lines with mutations in the APC/β-catenin pathway indicates<br />
that PPARβ/δ expression is not up-regulated by increased β-catenin-dependent<br />
activity. Further, increased expression <strong>of</strong> PPARβ/δ and function was also<br />
noted in human colon cancer cell lines treated with NSAIDs. Thus, there is a clear<br />
need for more quantitative analysis <strong>of</strong> PPARβ/δ function in colon cancer models.<br />
<strong>The</strong> present study examined expression <strong>of</strong> PPARβ/δ mRNA and protein in normal<br />
and cancerous human colon tissue. Colony formation assays using human colon<br />
cancer cell lines showed that activating PPARβ/δ either inhibited clonogenicity or<br />
had no effect on clonogencity in HT29, HCT116, DLD and RKO cells. Induction<br />
<strong>of</strong> apoptosis in human colon cancer cell lines with NSAIDs was associated with increased<br />
expression <strong>of</strong> PPARβ/δ and activating PPARβ/δ in the presence <strong>of</strong> NSAIDs<br />
either enhanced or had no effect on cleaved poly (ADP-ribose) polymerase (PARP).<br />
Collectively, results from these studies provide additional evidence demonstrating<br />
the ligand activation <strong>of</strong> PPARβ/δ either inhibits cell proliferation or has little effect<br />
in human colon cancer models. (Supported by CA124533, CA128826)<br />
2145 DIELDRIN INDUCES THE RAT PARAOXONASE (PON1)<br />
PROMOTER VIA PXR, RXR.<br />
M. Dail, R. R. Pickin, J. A. Crow and J. E. Chambers. Center for Environmental<br />
Health, Mississippi State, Mississippi State, MS.<br />
Measurable levels <strong>of</strong> the legacy organochlorine insecticide, dieldrin, are still in soil<br />
and accumulation in exposed individuals is a possibility. Paraoxonase (PON1) is<br />
named for its ability to hydrolyze paraoxon, the active metabolite <strong>of</strong> the insecticide<br />
parathion, and is associated with HDL particles. In addition, PON1 has been inversely<br />
related to the prevalence <strong>of</strong> atherosclerotic cardiovascular disease. In vivo rat<br />
studies have shown that dieldrin can increase paraoxonase activity but the mechanism<br />
is unclear. Nuclear receptors can increase pesticide metabolism, and putative<br />
binding sites for PXR exist in the PON1 promoter. <strong>The</strong> present work examined<br />
the effect <strong>of</strong> dieldrin and nuclear receptors on PON1 promoter activity via the<br />
Dual-Glo TM Luciferase Assay System. Expression constructs were created containing<br />
rat liver PXR only, RXR only, and PXR-RXR combined on the same vector. A<br />
construct with the human PXR gene (SXR) was also obtained. <strong>The</strong> rat liver PON1<br />
promoter was subcloned in front <strong>of</strong> the Renilla gene. Plasmids were transiently<br />
transfected, either alone or in combination, into the rat hepatoma cell line, McA-<br />
RH7777. Controls included the empty expression vector and a transfection control<br />
plasmid. Transfected cells were exposed to dieldrin concentrations from 100nM to<br />
0.1mM for a 24 hour period. PON1 promoter activity was measured as a function<br />
<strong>of</strong> luminescence and compared to the level caused by vehicle (DMSO). Dieldrin<br />
concentrations from 10μM to 100μM significantly increased (P