Activation of Peroxisome Proliferator-Activated Receptor-γ Reverses Squamous Metaplasia and Induces Transitional Differentiation in Normal Human Urothelial Cells

Abstract

We observed that in urothelium, both cornifying and noncornifying forms of squamous metaplasia are accompanied by changes in the localization of the nuclear hormone receptors, peroxisome proliferator activated receptor gamma (PPAR-gamma) and retinoid X receptor (RXR-alpha). To obtain objective evidence for a role for PPAR-gamma-mediated signaling in urothelial differentiation, we examined expression of the cytokeratin isotypes CK13, CK20, and CK14 as indicators of transitional, terminal transitional, and squamous differentiation, respectively, in cultures of normal human urothelial cells. In control culture conditions, normal human urothelial cells showed evidence of squamous differentiation (CK14+, CK13-, CK20-). Treatment with the high-affinity PPAR-gamma agonist, troglitazone (TZ), resulted in gain of CK13 and loss of CK14 protein expression. The effect of TZ was significantly augmented when the autocrine-stimulated epidermal growth factor receptor pathway was inhibited and this resulted in induction of CK20 expression. The RXR-specific inhibitors PA452, HX531, and HX603 inhibited the TZ-induced CK13 expression, supporting a role for RXR in the induction of CK13 expression. Thus, signaling through PPAR-gamma can mediate transitional differentiation of urothelial cells and this is modulated by growth regulatory programs.

PPARγ‐regulated tight junction development during human urothelial cytodifferentiation

“…As a positive control, cytokeratin markers of transitional and terminal urothelial differentiation (CK13 and CK20, respectively) were included and confirmed our previous report (Varley et al, 2004b) that co-treatment with TZ and PD153035 resulted in upregulation of CK13 (data not shown) and de novo expression of CK20 (Fig. 4).…”

“…Increasing exogenous [Ca 2+ ] to 2 mM results in desmosome formation, but the cells do not undergo cytodifferentiation (Southgate et al, 1994;Varley et al, 2004a) and, as demonstrated above, there was no induction of claudin protein expression or claudin relocalisation to TJs. By contrast, when EGFR-mediated proliferation is blocked, activation of PPARγ initiates a sequence of events culminating in expression of the uroplakins (Varley et al, 2004a) and cytokeratin markers of terminal urothelial cytodifferentiation (Varley et al, 2004b Our study indicates that the changes in claudin expression are regulated through both transcriptional and post-translational mechanisms. It appears that claudin 3 gene expression may be transcriptionally regulated directly by PPARγ, as analysis of the claudin 3 gene promoter revealed consensus PPARγ-binding response elements (PPRE) and claudin 3 mRNA was detected within 3 days of PPARγ activation and was specifically knocked-down by PPARγ siRNA.…”

“…Increasing exogenous [Ca 2+ ] to 2 mM results in desmosome formation, but the cells do not undergo cytodifferentiation (Southgate et al, 1994;Varley et al, 2004a) and, as demonstrated above, there was no induction of claudin protein expression or claudin relocalisation to TJs. By contrast, when EGFR-mediated proliferation is blocked, activation of PPARγ initiates a sequence of events culminating in expression of the uroplakins (Varley et al, 2004a) and cytokeratin markers of terminal urothelial cytodifferentiation (Varley et al, 2004b). Crucially, such differentiating NHU cells show a pattern of TJ-associated changes that mirrors the normal tissue counterpart in situ.…”

“…Immunohistochemistry was performed on paraffin wax-embedded tissue sections using the StreptABComplex/Horseradish Peroxidase system from Dako Cytomation (Ely, UK), as previously described (Varley et al, 2004b). Blocking steps were included to neutralise endogeneous peroxidase and avidin-binding activities and sections were boiled for 10 min in 10 mM citric acid buffer, pH 6.0 to retrieve antigens lost during tissue processing.…”

Increased expression of type 2 3α-hydroxysteroid dehydrogenase/type 5 17β-hydroxysteroid dehydrogenase (AKR1C3) and its relationship with androgen receptor in prostate carcinoma

“…Lipid metabolism including arachidonic acid and PG has been implicated in these disorders (Heller et al 1998). Furthermore, involvement of PPARg has been reported in regulating lipid homeostasis, immune response, cell differentiation and cell proliferation (Heller et al 1998, Bishop-Bailey & Wray 2003, Varley et al 2004. We conclude that upregulation of AKR1C3 as reflected by an increase in immunoreactivity is associated with both neoplastic and nonneoplastic pathological changes in the prostate.…”