Plasma Membrane Receptors for Steroid Hormones in Cell Signaling and Nuclear Function

Steroid hormones play an important role in coordinating rapid, as well as sustained, responses of target cells in complex organisms to changes in the internal and external environment. The broad physiologic effects of steroid hormones in the regulation of growth, development, and homeostasis have been known for decades. Often, these hormone actions culminate in altered gene expression, which is preceded many hours earlier by enhanced nutrient uptake, increased flux of critical ions, and other preparatory changes in the synthetic machinery of the cell. Because of certain homologies of molecular structure, specific receptors for steroid hormones, vitamin D, retinoids, and thyroid hormone are often considered a receptor superfamily. The actions of ligands in this superfamily are postulated to be regulated by receptors in the cell nucleus. On binding ligand, nuclear receptors associate with target genes and permit selective transcription. This genomic mechanism is generally slow, often requiring hours or days before the consequences of hormone exposure are evident.