Regulation of cAMP Responsive Element Binding Protein 3-Like 1 (Creb3l1) Expression by Orphan Nuclear Receptor Nr4a1

Abstract

Cyclic AMP (cAMP) inducible transcription factor cAMP responsive element binding protein 3 like 1 (Creb3l1) is strongly activated in the hypothalamus in response to hyperosmotic cues such as dehydration (DH). We have recently shown that Creb3l1 expression is upregulated by cAMP pathways in vitro, however the exact mechanisms are not known. Here we show that increasing Creb3l1 transcription by raising cAMP levels in mouse pituitary AtT20 cells automatically initiates cleavage of Creb3l1, leading to a greater abundance of the transcriptionally active N-terminal portion. Inhibiting protein synthesis indicated that de novo protein synthesis of an intermediary transcription factor was required for Creb3l1 induction. Strategic mining of our microarray data from dehydrated rodent hypothalamus revealed four candidates, reduced to two by analysis of acute hyperosmotic-induced transcriptional activation profiles in the hypothalamus, and one, orphan nuclear receptor Nr4a1, by direct shRNA mediated silencing in AtT20 cells. We show that activation of Creb3l1 transcription by Nr4a1 involves interaction with a single NBRE site in the promoter region. The ability to activate Creb3l1 transcription by this pathway in vitro is dictated by the level of methylation of a CpG island within the proximal promoter/5′UTR of this gene. We thus identify a novel cAMP-Nr4a1-Creb3l1 transcriptional pathway in AtT20 cells and also, our evidence would suggest, in the hypothalamus.

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.…”

“…To direct our candidate search towards secretory cells, we compared the AtT20 cell gene list with previously published transcriptomic data from the dehydrated rat and mouse SON 11 . Creb3l1 is increased in the SON by dehydration 8,12,15,16 . Thus, we considered genes that increased in the SON in response to dehydration and decreased in AtT20 cells following stable knockdown of Creb3l1 .…”

CREB3 Transcription Factors: ER-Golgi Stress Transducers as Hubs for Cellular Homeostasis

“…Interestingly, in dendritic cells, expression of constitutively active form of CREB3 increases its own transcript levels (Sanecka et al, 2012). In chondrocytes, CREB3L2 is a direct target gene of the master regulator for chondrogenesis, Sox9 (Hino et al, 2014) and orphan nuclear receptor Nr4a1 controls the expression of CREB3L1 in Arginine vasopressin neurons (Greenwood et al, 2017). Ceramide also acts as a CREB3L1 upstream regulator by promoting its proteolytical activation (Denard et al, 2012).…”

“…In the mouse pituitary cell line AtT20, CREB3L1 expression is up-regulated by cAMP in vitro , and orphan nuclear receptor Nr4a1 is the transcription factor controlling the expression of CREB3L1. Furthermore, the ability to activate CREB3L1 by Nr4a1 is related to the level of methylation of the CpG island within the CREB3L1 proximal promoter (Greenwood et al, 2017).…”

CREB3L2 Modulates Nerve Growth Factor-Induced Cell Differentiation

“…Furthermore, CREB3, CREB3L1, and CREB3L2 are expressed in different cell types of the central nervous system (CNS), where they perform important functions. For instance, CREB3 and CREB3L1 contribute to neuroendocrine regulation of the hypothalamic/pituitary/adrenal axis by modulating the glucocorticoid receptor activity and the arginine vasopressin gene transcription ( Greenwood et al, 2017 ; Penney et al, 2018 ). Also, in hippocampal cells, CREB3 regulates gene expression of several components of Golgi outposts and, therefore, their formation ( Chung et al, 2017 ).…”