Jennifer Stewart
Many studies have shown that there is significant cross-talk between signal transduction pathways and steroid receptors, in addition to the conventional hormone-dependent regulation of the activity of steroid/ thyroid receptor family members. In some cases, modulation of kinase/ phosphatase activity in cells leads to steroid receptor activation in the absence of hormone. The glucocorticoid receptor appears to be resistant to activation, so this novel mechanism may not be universal without the presence of hormone Estrogen receptors, on the other hand, are Retinoic acid receptors, progesterone receptors, androgen receptors Retinoic acid receptors, retinoid X receptors, and vitamin D receptors are examples of such receptors. Under the right conditions, all of them exhibit ligandindependent activation. For many years, the prevailing view of how steroid hormone receptors exert their effects on gene transcription was that these intracellular receptor proteins transform a state capable of interacting with chromatin and regulating the transcription of specific genes upon association with their specific cognate ligands. In the field of biochemical endocrinology, it has become unspoken dogma that receptor activation is entirely dependent on this ligand-binding event.
Recent research by Bert O'Malley and colleagues, described here, has shown that a cell membrane receptor agonist, the neurotransmitter dopamine, can activate certain members of the steroid hormone receptor superfamily in a completely ligand-independent manner.