nuclear receptor

A nuclear receptor works deep inside the cell, like a manager who, once activated, walks straight to the control room and rewrites which genes are switched on. Instead of relaying a message through other proteins, the activated receptor itself binds DNA and turns gene transcription up or down — so its effects appear slowly but can last a long time.

These receptors sit inside the cytoplasm or nucleus rather than on the surface, so their ligands must be small and fat-soluble enough to cross the cell membrane. Steroid hormones, thyroid hormone, vitamin D and vitamin A derivatives all act this way. Once the ligand binds, the receptor changes shape, often partners with a second receptor, and docks onto specific DNA sequences to recruit the machinery that reads genes.

Because the end result is a change in protein production, nuclear-receptor drugs typically take hours to show full effect and may persist after the drug is gone. This delay is clinically important: the anti-inflammatory benefits of a glucocorticoid are not immediate, and abruptly stopping long-term steroids is dangerous because the body's own hormone production has been suppressed.