Retinoic acid as cause of cell proliferation or cell growth inhibition depending on activation of one of two different nuclear receptors

Retinoic acid can combine with the nuclear retinoic acid receptor (RAR), leading to cell growth inhibition, as in certain tumors. Retinoic acid can also bind to the orphan nuclear receptor peroxisome proliferator-activated receptor β/δ (PPARβ/δ), resulting in stimulation of cell growth and inhibition of apoptosis. To bind to RAR, retinoic acid is carried into the nucleus by the cytosolic cellular retinoic acid-binding protein-II; to bind to PPARβ/δ, it is transported into the nucleus by the cytosolic fatty acid-binding protein 5.