Rasd1, a small G protein with a big role in the hypothalamic response to neuronal activation

Abstract

BackgroundRasd1 is a member of the Ras family of monomeric G proteins that was first identified as a dexamethasone inducible gene in the pituitary corticotroph cell line AtT20. Using microarrays we previously identified increased Rasd1 mRNA expression in the rat supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus in response to increased plasma osmolality provoked by fluid deprivation and salt loading. RASD1 has been shown to inhibit adenylyl cyclase activity in vitro resulting in the inhibition of the cAMP-PKA-CREB signaling pathway. Therefore, we tested the hypothesis that RASD1 may inhibit cAMP stimulated gene expression in the brain.ResultsWe show that Rasd1 is expressed in vasopressin neurons of the PVN and SON, within which mRNA levels are induced by hyperosmotic cues. Dexamethasone treatment of AtT20 cells decreased forskolin stimulation of c-Fos, Nr4a1 and phosphorylated CREB expression, effects that were mimicked by overexpression of Rasd1, and inhibited by knockdown of Rasd1. These effects were dependent upon isoprenylation, as both farnesyltransferase inhibitor FTI-277 and CAAX box deletion prevented Rasd1 inhibition of cAMP-induced gene expression. Injection of lentiviral vector into rat SON expressing Rasd1 diminished, whereas CAAX mutant increased, cAMP inducible genes in response to osmotic stress.ConclusionsWe have identified two mechanisms of Rasd1 induction in the hypothalamus, one by elevated glucocorticoids in response to stress, and one in response to increased plasma osmolality resulting from osmotic stress. We propose that the abundance of RASD1 in vasopressin expressing neurons, based on its inhibitory actions on CREB phosphorylation, is an important mechanism for controlling the transcriptional responses to stressors in both the PVN and SON. These effects likely occur through modulation of cAMP-PKA-CREB signaling pathway in the brain.

Transcription factor Creb3l1 regulates the synthesis of prohormone convertase enzyme PC1/3 in endocrine cells

“…We reasoned that because Creb3l1 is increased in the SON by dehydration, target genes would also be increased in this model, and so we made comparisons with transcriptome catalogues from the dehydrated rat and mouse SON. A number of common genes were identified and validated, including Nr4a1 , which was previously identified by us as a transcription factor regulating Creb3l1 expression, 16 Scg2 , a potential sorting receptor that targets proteins to secretory granules, and Rasd1 , a small G protein that we recently identified in AVP neurones of the hypothalamus 39 . These genes are highly expressed in neuroendocrine cells of the hypothalamus, including the SON and paraventricular nucleus (PVN), although they were not subjected to further investigation at this time.…”

Array-based molecular karyotyping in fetuses with isolated brain malformations identifies disease-causing CNVs

“…RASD1 was shown to be a protein with enriched expression in brain, specifically coupled to neuronal nitric oxide synthase [ 34 ]. No embryonic expression data have been published; however, RASD1 has yet been localized to the suprachiasmatic nucleus, thalamus, piriform cortex, and the hippocampus in adult mice and in rat vasopressin neurons of the supraoptic nucleus and paraventricular nucleus [ 35 , 36 ]. As most recently outlined by Chen and colleagues [ 37 ], RASD1 plays a central role in neuronal iron trafficking and the regulation of adenylyl cyclase and G-protein-linked neurotransmitter, making it an attractive candidate for DVM.…”

The α-Tubulin gene TUBA1A in Brain Development: A Key Ingredient in the Neuronal Isotype Blend

“…This reduced folding efficiency does not completely cause tubulin heterodimers containing the p.R264C mutant to drop out of the polymerization-competent tubulin pool, as they have been seen to form microtubules in HeLa, COS-7, and P19 cells [ 16 , 151 ]. p.R264C has also been modeled using iPSCs derived from patient cells, revealing that neurospheres generated from the patient iPSCs are capable of normal neurite extension [ 138 ]. Taken together, these data reveal that the p.R264C TUBA1A mutation probably follows the mutant scenario outlined by Figure 3 A, and more importantly that partial haploinsufficiency to TUBA1A is sufficient to disrupt cortical migration enough to cause pachygyria.…”

“…Three other lissencephaly-causing mutations have been investigated for their effects on cellular function, p.N329S, p.C25F, and p.R64W. Mutation p.N329S causes lissencephaly with cerebellar hypoplasia [ 16 , 138 ], and when neurospheres were generated from patient iPSCs, the mutation caused abnormal neurite extension [ 138 ]. While these cellular data suggest that defective neurite extension leads to lissencephaly with cerebellar hypoplasia, how the microtubules are altered by the p.N329S mutation to cause this diminished neurite growth is unknown.…”