Besides its established functions in intermediary metabolism and developmental processes, the nuclear receptor peroxisome proliferator-activated receptor β/δ (PPARβ/δ) has a less defined role in tumorigenesis. In the present study, we have identified a function for PPARβ/δ in cancer cell invasion. We show that two structurally divergent inhibitory ligands for PPARβ/δ, the inverse agonists ST247 and DG172, strongly inhibit the serum- and transforming growth factor β (TGFβ)-induced invasion of MDA-MB-231 human breast cancer cells into a three-dimensional matrigel matrix. To elucidate the molecular basis of this finding, we performed chromatin immunoprecipitation sequencing (ChIP-Seq) and microarray analyses, which identified the gene encoding angiopoietin-like 4 (ANGPTL4) as the major transcriptional PPARβ/δ target in MDA-MB-231 cells, previously implicated in TGFβ-mediated tumor progression and metastatic dissemination. We show that the induction of ANGPTL4 by TGFβ and other oncogenic signals is strongly repressed by ST247 and DG172 in a PPARβ/δ-dependent fashion, resulting in the inhibition of ANGPTL4 secretion. This effect is attributable to these ligands' ability to induce a dominant transcriptional repressor complex at the site of transcription initiation that blocks preinitiation complex formation through an histone deacetylase-independent, non-canonical mechanism. Repression of ANGPTL4 transcription by inverse PPARβ/δ agonists is functionally linked to the inhibition of cancer cell invasion into a three-dimensional matrix, as (i) invasion of MDA-MB-231 cells is critically dependent on ANGPTL4 expression, (ii) recombinant ANGPTL4 stimulates invasion, and (iii) reverses the inhibitory effect of ST247 and DG172. These findings indicate that a PPARβ/δ-ANGPTL4 pathway is involved in the regulation of tumor cell invasion and that its pharmacological manipulation by inverse PPARβ/δ agonists is feasible.
Source: Inverse PPARβ/δ agonists suppress oncogenic signaling to the ANGPTL4 gene and inhibit cancer cell invasion. Adhikary T, Brandt DT, Kaddatz K, Stockert J, Naruhn S, Meissner W, Finkernagel F, Obert J, Lieber S, Scharfe M, Jarek M, Toth PM, Scheer F, Diederich WE, Reinartz S, Grosse R, Müller-Brüsselbach S, Müller R (email@example.com). Oncogene. 2012 Dec 3.
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