Peroxisome proliferator-activated receptors modulate proliferation and angiogenesis in human endometrial carcinoma

Peroxisome proliferator-activated receptors (PPAR) and retinoid X receptors (RXR) are implicated in the development of several obesity-related cancers. Little is known of either the expression or function of PPARs and RXRs in endometrial cancer although this increasingly common disease is highly associated with both obesity and insulin resistance. We investigated the expression of PPAR and RXR subtypes in human endometrial cancers and normal endometrium with immunoblotting and immunohistochemistry and subsequently showed PPAR/RXR binding preferences by coimmunoprecipitation. To determine the functions of PPARs within the endometrium, we investigated proliferation, apoptosis, PTEN expression, and secretion of vascular endothelial growth factor (VEGF) in endometrial cell lines after reducing the expression of PPARα and PPARγ with antisense RNA. The functional effects of PPAR ligands were also investigated in vitro. We identified differential expression of PPAR and RXR subtypes in endometrial cancers and discovered that PPARγ expression correlated with expression of PTEN. PPARα activation influences endometrial cell growth and VEGF secretion. PPARγ activation reduces proliferation of endometrial cells via regulation of PTEN and appears to reduce VEGF secretion. We conclude that the PPAR/RXR pathway contribute to endometrial carcinogenesis by control of PTEN expression and modulation of VEGF secretion. We propose that PPAR ligands should be considered for clinical investigation in early phase studies of women with endometrial cancer.