Methods for assessing the interaction of apocarotenoids with vertebrate nuclear receptors.

Apocarotenoids occur in the diets of human and other vertebrates and form from the metabolism of intact carotenoids. The metabolism of the provitamin A carotenoid, β-carotene, produces β-apo-15-carotenoic acid or retinoic acid. Retinoic acid functions as a hormone by binding to and activating nuclear retinoic acid receptors to modulate gene transcription. It is likely that other apocarotenoids may similarly modulate other ligand-activated nuclear receptors. This chapter describes in vitro biochemical and biophysical methods to characterize the direct binding of apocarotenoids to nuclear receptors and to assess their effect on binding of transcriptional coactivators to the receptor. It also provides a few widely used methods to study the consequences of nuclear receptor activation in intact cells. The effects of β-apocarotenoids on retinoid receptors provide examples.