TABLE 2

Terms for nuclear receptors For nuclear receptors, the concept of agonist and antagonist is response- and gene-specific.

Terms Definition/Description/Examples
Isoforms Products of the same gene produced by alternative splicing, alternative promoter usage, alternative translational initiation; does not consider post-translational modifications; examples: RARα1 and RARα2
Subtypes Products of related (paralogous) genes; subtype should be preferred to isotype; examples: RARα /RARβ/ RARγ
Coregulators Macromolecules that associate with NRs to modulate their transcriptional activity; divisible into coregulators that promote positive activity (coactivators) and those that promote negative activity (corepressors)
Ligands for NRs Compounds that bind reversibly to NRs into the C-terminal LBP
Unliganded receptor Considered preferable compared with apo-receptor
Selective agonist and antagonist Ligands with an affinity difference (preferably greater than 100-fold) between their primary target and other receptors
Agonists Ligands that induce an active conformation of the receptor
Antagonists Ligands that produce a conformation and an action of the receptor distinct from that produced by an agonist
SNuRM Selective ligand with partial function-, cell-, and/or promoter-specific action
Partial agonists Agonists that in a given tissue, under specific conditions, cannot elicit as optimal an effect (even when applied at high concentration, so that all the receptors should be occupied) as can another agonist acting through the same receptors in the same tissue
Inverse agonists Ligands that can promote corepressor recruitment
Potency An expression of the activity of a drug, in terms of the concentration or amount needed to produce a defined effect—an imprecise term that should always be further defined (e.g., EC50, IC50, etc.); drug potency depends on both receptor (affinity, efficacy) and tissue (receptor numbers, drug accessibility) parameters; term is sometimes incorrectly used to refer to the maximum effect attainable
Transactivation Activation of transcription by the binding of a transcription factor (and coregulators?) to a DNA regulatory sequence