Nuclear Receptors

Nuclear receptors are transcription factors that regulate the expression of target genes in response to steroid hormones and other ligands. Many hormones (including glucocorticoids, gonadal steroids, and thyroid hormones) are able to rapidly penetrate into the lipid bilayer membrane, because of their lipophilic composition, and thereby directly interact with these cytoplasmic receptors inside the cell (see Figure 1-1). Upon activation by a hormone, the nuclear receptor-ligand complex translocates to the nucleus, where it binds to specific DNA sequences referred to as hormone-responsive elements (HREs), and subsequently regulates gene transcription (Mangelsdorf et al. 1995; Truss and Beato 1993). Nuclear receptors often interact with a variety of coregulators that promote transcriptional activation when recruited (coactivators) and those that attenuate promoter activity (corepressors).

With this overview of neurotransmitters and receptor subtypes, we now turn to a discussion of selected individual neurotransmitters and neuropeptides before discussing the intricacies of cellular signal transduction systems.

0 0

Post a comment