Steroid hormone receptors and related receptors are generally soluble proteins that function through gene activation. Lipid-soluble hormones target specific sequences of DNA by diffusing into the cell. When they have diffused into the cell, they bind to receptors (intracellular), and migrate into the nucleus.  heir response elements are DNA sequences (promoters) that are bound by the complex of the steroid bound to its receptor. The receptors themselves are zinc-finger proteins.  These receptors include those for glucocorticoids ( glucocorticoid receptors ), estrogens ( estrogen receptors ), androgens ( androgen receptors ), thyroid hormone (T3) ( thyroid hormone receptors ), calcitriol (the active form of vitamin D ) ( calcitriol receptors ), and the retinoids ( vitamin A ) ( retinoid receptors ). Receptor-protein interactions induce the uptake and destruction of their respective hormones in order to regulate their concentration in the body. This is especially important for steroid hormones because many body systems are entirely steroid dependent. 
Bile acids, in particular chenodeoxycholic acid (CDCA) and cholic acid (CA), can regulate the expression of genes involved in their synthesis, thereby, creating a feed-back loop. The elucidation of this regulatory pathway came about as a consequence of the isolation of a class of receptors called the farnesoid X receptors, FXRs . The FXRs belong to the superfamily of nuclear receptors that includes the steroid/thyroid hormone receptor family as well as the liver X receptors (LXRs) , retinoid X receptors (RXRs), and the peroxisome proliferator-activated receptors (PPARs) .