PPARα and PPARβ Are Differentially Affected by Ethanol and the Ethanol Metabolite Acetaldehyde in the MCF-7 Breast Cancer Cell Line
The activity and/or the level of the peroxisome proliferator–activated receptors (PPARs) in liver and oligodendrocytes are regulated by ethanol. Despite the association between ethanol consumption and breast cancer risk, and the increasing evidence for an involvement of PPARs in some cancers, there have been no studies on the effect of ethanol or its metabolite acetaldehyde on PPARs in breast cancer. Using the MCF-7 breast cancer cell line, we examined the relationship between ethanol and its metabolite acetaldehyde on PPARα and PPARβ transactivation. Ethanol (20mM) reduced the potency of the PPARβ ligand GW0742, evident by a rightward shift in the GW0742 dose-response curve, whereas for PPARα activation by GW7647, ethanol mediated its effects primarily through reducing efficacy as evidenced by a reduction in maximal response. Using the enzyme inhibitors 4-methylpyrazole and cyanamide and the metabolite acetaldehyde, we showed that PPARα and PPARβ are differentially modulated by ethanol and acetaldehyde. While acetaldehyde is responsible for the inhibition of PPARα ligand inhibition with a concentration that inhibits 50% of activity (IC50) of 111 nM, acetaldehyde has no effect on PPARβ or its ligand activation. Instead, inhibition of PPARβ transactivation is mediated directly by ethanol. The differential effect of ethanol and acetaldehyde on PPARα and PPARβ further underscores the differences between these receptors and may indicate the relevance of PPARs in the effects of ethanol in the human breast.