Interplay between EGR1 and SP1 is critical for 13-cis retinoic acid-mediated transcriptional repression of angiotensin type 1A receptor

Abstract

Recently, we have demonstrated that 13-cis retinoic acid (13cRA) down-regulates rat angiotensin type 1A receptor (AT1AR) gene transcription through a MAP Kinase (ERK1/2) dependent mechanism in rat liver epithelial and aortic smooth muscle cells. However, the exact mechanism remained unknown. In this study, we determined the signaling intermediates activated by ERK1/2 involved in 13cRA mediated AT1AR down-regulation. Serially deleted rat AT1AR promoter CAT constructs indicate fragments containing a region −2541 and −1836 bp upstream of the 5 prime possess an Sp1 consensus sequence (5′-TGGGGCGGGGCGGGG-3′) have reduced CAT activity. Mobility shift analysis using untreated nuclear extracts in the presence of mithramycin A suggest the trans-acting factor binding to this cis-acting element is Sp1. 13cRA significantly reduced specific binding without any change in Sp1 protein expression. Studies showed 13cRA maximally phosphorylates and tranlocates to the nucleus ERK1/2 within 5–10 minutes, activating Egr-1 mRNA expression at 20 minutes followed by de novo protein synthesis, leading to an Egr-1/Sp1 interaction. siRNA silencing of Egr-1 restored AT1AR mRNA and protein expression in 13cRA treated cells, and Sp1 silencing results in complete loss of AT1AR expression. Our study suggests that 13cRA mediated activation of ERK1/2, through Egr-1, is capable of disrupting Sp1, the requisite transactivator for AT1AR expression, providing a novel paradigm in AT1AR gene transcription.

The Role of the Transcription Factor EGR1 in Cancer

“…Several of the EGR1 downstream target genes have multiple overlapping SP1 and EGR1 binding sites in their proximal promoter regions. The regulatory relationship in this overlapping area is complex, in some genes the two factors are synergistic, and antagonistic in others ( 70 , 92 , 93 ). The duality of EGR1 is related to the regulatory relationship between the two factors.…”

Egr-1 regulates the transcription of NGX6 gene through a Sp1/Egr-1 overlapping site in the promoter

“…Similar Sp1/Egr-1 overlapping binding sites have been shown to play a critical role in the expression of some genes, such as TF , NDRG1 and PDGF-A [ 14 - 16 ]. The regulation of transcription by these two transcription factors has been shown to be complex: in some genes the two factors are synergistic, whereas in other systems the factors appear to compete [ 17 , 18 ]. Egr-1 encodes a nuclear phosphoprotein that binds to the GC-rich sequence 5'-GCGGGGGCG-3' and regulates transcription of target gene through the GC-rich consensus sequence [ 19 ].…”

All-Trans Retinoic Acid Modulates ORMDL3 Expression via Transcriptional Regulation

“…This process leads to activation of ATRA-responsive genes via alteration of chromatin structure and enables cellular differentiation of normal myelomonocytic progenitor cells [33]. Compared with the endogenously formed isoforms ATRA and 9-cis RA, 13-cis RA has relatively weak transactivation activity for RAR/RXR, and it may possess a novel signaling pathway of its own [34]. It has reported that ATRA could be, at least partially, converted into 9-cis RA and 13-cis RA in vitro, but 9-cis RA and 13-cis RA may produce biological effects distinct from those produced by ATRA [35].…”

“…Studies have shown that 13-cis RA can act as a potent inhibitor of many of the retinoid and hydroxysteroid mediated pathways [36]. A recent research showed that 13-cis RA mediated activation of ERK1/2, is capable of disrupting transcription factor Sp1, the requisite transactivator for angiotensin type 1A receptor (AT1AR) gene transcription, leading to an inhibition on AT1AR expression [34]. Besides, in our study, we only focused on transcription factor CREB, we could not rule out whether RA or RAR may in conjunction with other transcription factors such as SP1/3 and modulate ORMDL3 expression.…”