Guiding Ligands to Nuclear Receptors

Retinoic acid—the active metabolite of vitamin A—influences biological processes by activating the retinoic acid receptor (RAR). In this issue, demonstrate that retinoic acid also activates the peroxisome proliferator-activated receptor β/δ (PPARβ/δ). Remarkably, retinoic acid signaling through RAR or PPARβ/δ—which depends on cytoplasmic retinoic acid transporters—commits the cell to opposite fates, apoptosis or survival, respectively.