Nitroalkene fatty acids mediate activation of Nrf2/ARE-dependent and PPARγ-dependent transcription by distinct signaling pathways and with significantly different potencies.

Naturally occurring nitroalkene fatty acids (NAs) derived from oleic (NO(2)-OA) and linoleic (NO(2)-LA) acids mediate a variety of cellular responses. We examined the signaling pathways involved in NA activation of Nrf2/ARE-dependent versus PPARγ/PPRE-dependent transcription in human MCF7 breast cancer cells. Additionally, we compared the relative potencies of NO(2)-OA and NO(2)-LA in activating these two transcriptional programs. Here it is demonstrated that, in addition to the direct adduct formation of NA with the Nrf2 inhibitory protein, Keap1, shown by others, NA activation of Nrf2/ARE-mediated transcription results from increased nuclear Nrf2 levels and depends upon activation of the PI3K/AKT and PKC, but not ERK and JNK MAPK, signaling pathways. Examination of the relationship between NA stimulation of the Nrf2/ARE versus PPARγ/PPRE transcriptional programs revealed concentration-dependent activation of distinct signaling pathways that were readily distinguished by selective attenuation of Nrf2/ARE-dependent, but not PPARγ-dependent, transcription by inhibitors of PI3K and PKC. Moreover, measurable, statistically significant activation of PPARγ/PPRE-dependent transcription occurred at nanomolar concentrations of NAs-the 12-NO(2) isomer of NO(2)-LA showing the most potent activity-whereas significant activation of Nrf2/ARE-dependent transcription occurred at much higher NA concentrations (≥3 μM) with the NO(2)-OA isomers the most potent. These findings have implications for the physiological roles of NAs, suggesting that, at concentrations likely to be encountered in vivo, their direct activation of PPARγ transcription will dominate over their electrophilic activation of Nrf2 antioxidant/protective responses.