Inhibition of Peroxisome Proliferator-Activated Receptor Increases Estrogen Receptor-Dependent Tumor Specification

Department of Oncology and Lombardi Comprehensive Cancer Center, Georgetown University, Washington, District of Columbia 20007, USA.
Cancer Research (Impact Factor: 9.33). 02/2009; 69(2):687-94. DOI: 10.1158/0008-5472.CAN-08-2446
Source: PubMed


Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor that regulates gene transcription associated with intermediary metabolism, adipocyte differentiation, and tumor suppression and proliferation. To understand the role of PPARgamma in tumorigenesis, transgenic mice were generated with mammary gland-directed expression of the dominant-negative transgene Pax8PPARgamma. Transgenic mice were phenotypically indistinguishable from wild-type (WT) mice, but mammary epithelial cells expressed a greater percentage of CD29(hi)/CD24(neg), CK5(+), and double-positive CK14/CK18 cells. These changes correlated with reduced PTEN and increased Ras and extracellular signal-regulated kinase (ERK) and AKT activation. Although spontaneous tumorigenesis did not occur, transgenic animals were highly susceptible to progestin/7,12-dimethylbenz(a)anthracene-induced mammary carcinogenesis, which in contrast to WT mice resulted in a high tumor multiplicity and, most importantly, in the appearance of predominantly estrogen receptor alpha-positive (ER(+)) ductal adenocarcinomas. Tumors expressed a similar PTEN(lo)/pERK(hi)/pAKT(hi) phenotype as mammary epithelium and exhibited high activation of estrogen response element-dependent reporter gene activity. Tumorigenesis in MMTV-Pax8PPARgamma mice was insensitive to the chemopreventive effect of a PPARgamma agonist but was profoundly inhibited by the ER antagonist fulvestrant. These results reveal important new insights into the previously unrecognized role of PPARgamma in the specification of mammary lineage and the development of ER(+) tumors.

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    • "Stomach and tumors were excised, and formalin-fixed, paraffin-embedded sections were prepared for H&E staining and IHC. Antigen retrieval was carried out by incubation of tissue sections in 10 mM sodium citrate buffer (pH 6.0) for 20 min at a subboiling temperature in an electric steamer as previously described [19, 39]. Endogenous peroxidase activity was quenched with 3% hydrogen peroxide for 10 min and incubated for 30 min with blocking solution (10% goat serum in Tris-buffered saline), followed by incubation overnight at 4°C with the appropriate primary antibody diluted in blocking solution. "
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    • "In summary, PPFP can act as a dominant negative inhibitor of wild-type PPAR␥ action both in vitro (Au et al., 2006; Espadinha et al., 2007; Gregory Powell et al., 2004; Kroll et al., 2000) and in vivo (Yin et al., 2009). PPFP is also capable of both stimulating and inhibiting selected PAX8-responsive genes (Espadinha et al., 2007). "
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