Further evidence for a membrane receptor that binds glucocorticoids in the rodent hypothalamus

Abstract

In parallel with their well-characterized delayed genomic effects, steroid hormones exhibit rapid, non-genomic effects at molecular, cellular and behavioral levels. We have proposed a model of rapid, non-genomic glucocorticoid inhibition of hypothalamic neuroendocrine cells through a putative membrane-associated glucocorticoid receptor (GR). Here we tested for plasma membrane GR immunoreactivity and binding in the hypothalamic supraoptic and paraventricular nuclei. Selective cross-linking of membrane proteins with membrane-impermeant BS3 and subsequent Western blot analysis with a monoclonal GR antibody revealed a reduction in the intensities of a ~98 kDa immunoreactive band and a ~64 kDa band in the rat paraventricular and supraoptic nuclei, and of a 64 kDa band in hippocampal tissue, which suggested that these proteins are associated with the membrane. Saturation binding of [3H]-corticosterone and [3H]-dexamethasone in rat and mouse hypothalamic tissue revealed a Kd 4–24-fold lower and a Bmax 4–7-fold lower for the membrane-associated GR compared to the intracellular GR, suggesting a lower affinity and abundance of the glucocorticoid binding sites in the membrane than in the cytosol. Together, these findings suggest the presence of a low-affinity, low-abundance membrane-associated GR in the hypothalamus that shares homology with the intracellular GR, and are consistent with physiological evidence of rapid, non-genomic glucocorticoid actions in hypothalamic neuroendocrine cells that are GR dependent.

Actions of Steroids: New Neurotransmitters

“…rodents (for review, see Micevych and Mermelstein, 2008). Importantly, this work identified an interesting dichotomy in the regulation of male sexual behavior by membrane-and nuclearinitiated signaling of estrogens.…”

“…Steroids, such as progesterone, have been shown to have rapid neurotransmitter-like effects that rapidly change the activity of neuronal systems through multiple types of receptors (for review, see Micevych and Mermelstein, 2008;Mani and Oyola, 2012;Sinchak and Wagner, 2012;Micevych et al, 2015;ValadezCosmes et al, 2016). Some of these steroid receptors that initiate rapid signaling are, as expected, classified as extranuclear or membrane receptors, which signal through G-proteins or other second messenger systems (Zhou et al, 1996;Razandi et al, 1999;Boulware et al, 2005;Zuloaga et al, 2012;Valadez-Cosmes et al, 2016).…”

“…Some of these steroid receptors that initiate rapid signaling are, as expected, classified as extranuclear or membrane receptors, which signal through G-proteins or other second messenger systems (Zhou et al, 1996;Razandi et al, 1999;Boulware et al, 2005;Zuloaga et al, 2012;Valadez-Cosmes et al, 2016). However, a relatively recent finding shows that classical steroid receptors that are classified as transcription factors and bind to response elements on the DNA to regulate gene expression also contain palmitoylation sequences that allow them to be trafficked to the plasma membrane to rapidly alter cellular activity Pedram et al, 2007;Meitzen et al, 2013; for review, see Micevych and Mermelstein, 2008;Grove-Strawser et al, 2010;Mani et al, 2012;Schwartz et al, 2016). These nuclear transcription factors are trafficked to the plasma membrane and require direct interactions with other proteins to initiate their signaling at the level of the plasma membrane (Boonyaratanakornkit et al, 2001(Boonyaratanakornkit et al, , 2007Micevych and Mermelstein, 2008;Boulware and Mermelstein, 2009).…”

“…However, a relatively recent finding shows that classical steroid receptors that are classified as transcription factors and bind to response elements on the DNA to regulate gene expression also contain palmitoylation sequences that allow them to be trafficked to the plasma membrane to rapidly alter cellular activity Pedram et al, 2007;Meitzen et al, 2013; for review, see Micevych and Mermelstein, 2008;Grove-Strawser et al, 2010;Mani et al, 2012;Schwartz et al, 2016). These nuclear transcription factors are trafficked to the plasma membrane and require direct interactions with other proteins to initiate their signaling at the level of the plasma membrane (Boonyaratanakornkit et al, 2001(Boonyaratanakornkit et al, , 2007Micevych and Mermelstein, 2008;Boulware and Mermelstein, 2009). From here, intracellular signaling cascades involving effectors (e.g., MAPK) are initiated via the transactivation of cell surface-bound receptors, most notably metabotropic glutamate receptors (mGluRs).…”

“…It has been known for decades that steroid hormones can have acute actions (within minutes) on physiology (Szego and Davis, 1967), the activity of neurons (Kelly et al, 1976), and the expression of behavior (Hayden-Hixson and Ferris, 1991). More recently, data demonstrate that steroids can and do function in ways that are "neurotransmitter-like," as they are synthesized at precise spatial locations within neural circuits and can act within minutes as local neuromodulators to rapidly regulate cognitive functions and behaviors (Balthazart and Ball, 2006;Dewing et al, 2007;Saldanha et al, 2011;Remage-Healey, 2014). Here we discuss the ever-growing body of evidence detailing nonclassical, neurotransmitter-like steroid hormone action across neural systems, species, and classes of steroids, and suggest that these compounds should also be considered neurotransmitters, as they regularly function independently of classical hormone signaling in an increasing number of systems and species.…”