The Identities of Membrane Steroid Receptors

The nature of rapid (nongenomic) steroid signaling has been re-probed with experimental tools. Cellular responses to steroids start with membrane-initiated signals, eventually culminating in major transcriptional commitment and overhaul of cellular components. While much is known about the execution of the ultimate decision, little is known about how reception and processing of the first steroid signal notifies the cell of impending change. Therefore, it is very important to establish the identity of the proteins initiating these cellular responses. This text juxtaposes identifications from different laboratories and presents several possibilities: nuclear steroid receptor-like forms in non-nuclear locations, other known membrane receptors or channels with additional steroid binding sites, enzymes, transporters, receptors for serum steroid-binding proteins, and unique, previously undescribed proteins.