gw0742 and ciglitazone

ATP-binding cassette (ABC) transporter, family 12 (ABCA12), a member of the ABC superfamily, facilitates the delivery of lipids to lamellar bodies (LB) in keratinocytes, which is critical for permeability barrier function. Recently, gene mutations of ABCA12 were found to underlie Harlequin ichthyosis and lamellar ichthyosis, two devastating skin disorders. Previously we and others have demonstrated that peroxisome proliferators-activated receptors (PPARs) and liver X receptor (LXR) activation improved epidermal permeability barrier homeostasis by stimulating keratinocyte differentiation, lipid synthesis, and increasing LB formation/secretion. Here we report that both PPAR-gamma and -beta/delta activators markedly stimulate ABCA12 mRNA expression in cultured human keratinocyte (CHK) in a dose- and time-dependent manner. Increased ABCA12 mRNA levels are accompanied by an increase in ABCA12 protein, suggesting biological importance of this upregulation. LXR activators also increase ABCA12 mRNA levels in CHK, but to a lesser extent. In contrast, activators of PPAR-alpha, RAR, RXR, or vitamin D receptor did not alter ABCA12 expression. Two major ABCA12 alternative transcripts and their corresponding proteins are also expressed and upregulated by PPAR or LXR activator in both undifferentiated and differentiated CHK. Together, our data demonstrate that PPAR and LXR activators increase ABCA12 expression, providing an additional mechanism by which PPAR and LXR activators promote epidermal permeability barrier homeostasis.

Topics: ATP-Binding Cassette Transporters; Cells, Cultured; DNA-Binding Proteins; Dose-Response Relationship, Drug; Epidermis; Gene Expression Regulation; Humans; Keratinocytes; Liver X Receptors; Orphan Nuclear Receptors; Permeability; Peroxisome Proliferator-Activated Receptors; Receptors, Calcitriol; Receptors, Cytoplasmic and Nuclear; RNA, Messenger; Thiazoles; Thiazolidinediones

The phthalates di(2-ethylhexyl)phthalate (DEHP) and di-n-butyl phthalate (DBP) are environmental contaminants with significant human exposures. Both compounds are known reproductive toxins in rodents and DEHP also induces rodent hepatocarcinogenesis in a process believed to be mediated via the peroxisome proliferator-activated receptor alpha (PPARalpha). DEHP and DBP are metabolised to their respective monoesters, mono-(2-ethylhexyl)phthalate (MEHP) and mono-n-butyl phthalate (MBP), which are the active metabolites. MEHP also activates another member of the PPAR subfamily, PPARgamma. The effects of PPARalpha and PPARgamma activation in human breast cells appears to be opposing; PPARalpha activators in breast cells cause an increase in proliferation, while PPARgamma activation in breast cells is associated with differentiation and an inhibition of cell proliferation. Further to this the activation of the PPARs is cell and ligand specific, suggesting the importance of examining the effect of MEHP and MBP on the activation of PPARalpha, PPARbeta and PPARgamma in human breast. We used the common model of human breast cancer MCF-7 and examined the ability of MEHP and MBP to activate human PPARs in this system. The ability of MBP and MEHP to block PPAR responses was also assessed. We found that both human PPARalpha and PPARgamma were activated by MEHP whereas MEHP could not activate PPARbeta. MBP was unable to activate any PPAR isoforms in this breast model, despite being a weak peroxisome proliferator in liver, although MBP was an antagonist for both PPARgamma and PPARbeta. Our results suggest that the toxicological consequences of MEHP in the breast could be complex given the opposing effects of PPARalpha and PPARgamma in human breast cells.

Topics: Breast Neoplasms; Butyrates; Cell Differentiation; Cell Line, Tumor; Cell Proliferation; Diethylhexyl Phthalate; Dose-Response Relationship, Drug; Female; Humans; Phenylurea Compounds; Phthalic Acids; Plasticizers; PPAR alpha; PPAR gamma; PPAR-beta; Statistics, Nonparametric; Thiazoles; Thiazolidinediones; Transfection