Prostaglandin F2.ALPHA. Inhibits SERCA2 Gene Transcription Through an Induction of Egr-1 in Cultured Neonatal Rat Cardiac Myocytes

Abstract

SUMMARYProstaglandin F 2α (PGF 2α ) stimulates hypertrophic growth of neonatal rat cardiac myocytes, a feature of which includes downregulation of the Ca 2+ -ATPase (SERCA2), a major Ca 2+ transport protein in SR. The molecular mechanisms by which PGF 2α inhibits SERCA2 gene expression remain unknown. We determined the cis-regulatory elements responsible for the regulation of the SERCA2 gene expression in cultured neonatal rat cardiac myocytes exposed to PGF 2α . The role of Egr-1 was evaluated by transient transfection of its expression vector and antisense oligonucleotide. Signaling pathways were determined by using the pharmacological inhibitors or cDNA expression plasmids coding for dominant negative forms of Ras and Rac. PGF 2α reduced the SERCA2 mRNA levels in a time-and dose-dependent manner in cultured rat cardiac myocytes. Transient transfection analyses showed that PGF 2α -responsive elements are located between -284 and -72 of the SERCA2 promoter, which contains G+C-rich sequences homologous to Sp1, Egr-1 and AP2-binding sites. PGF 2α significantly increased Egr-1 expression, and overexpression of Egr-1 largely reduced the transcription of the SERCA2 gene. Egr-1 antisense oligonucleotides blocked the PGF 2α -mediated decrease in SERCA2 mRNA expression. Furthermore, inhibitors for either genistein-sensitive tyrosine kinase or p38 MAPK, and dominant negative forms of either Ras or Rac, prevented PGF 2α -induced repression of SERCA2 mRNA levels. These results suggest that Egr-1, as well as Ras, Rac, and p38 MAPK, plays a crucial role in the repression of SERCA2 gene expression during PGF 2α -induced cardiac hypertrophy. (Int Heart J 2008; 49: 329-342)

PG F2α Receptor: A Promising Therapeutic Target for Cardiovascular Disease

“…Through FP receptor, PGF 2α promotes expression of c-fos, atrial natriuretic factor (ANF), and alpha-skeletal actin in cardiomyocytes and induces cardiac myocyte hypertrophy in vitro and cardiac growth in rat (Lai et al, 1996), but does not affect myocyte proliferation in culture (Adams et al, 1996). Mechanistic studies showed PGF 2α inhibits expression Ca 2+ -ATPase (SERCA2) via induction of Early Growth Response Protein 1 (Egr-1) in cultured neonatal cardiac myocytes (Hara et al, 2008). We have recently found that selective deletion of cardiomyocyte COX-2 releases a restraint on expression of fibroblast COX-2, thereby augmenting PGF 2α formation.…”

Trichloroethylene Induces Methylation of the Serca2 Promoter in H9c2 Cells and Embryonic Heart

“…In particular, Kitazawa et al [27] reported that in rat leukemia cell lines, methylation that was not within but adjacent to the two SP1 sites in the promoter significantly reduced cyclin D expression. Finally, although Serca2 promoter region is approximately 2 kb, the region analyzed in this study is the one containing the highest CG percentage, and essential for transcriptional activity, as documented by previous studies using luciferase reporter assays [5,21]. Therefore, even if we cannot exclude the possibility of TCE affecting methylation of more upstream regions in the promoter, the region we analyzed is central for determining Serca2 transcriptional activity and even subtle changes in methylation patterns likely influence promoter activity.…”

“…In the heart, Serca is mainly represented by the isoform Serca2a where it is responsible for proper cardiac diastolic function [21]. Reduced expression of Serca2a protein leads to decreased calcium uptake and is associated with heart malformations and impaired function [31,36], whereas over-expression of the Serca2a gene in transgenic mouse hearts produces altered contractility by increasing sarcoplasmic reticulum calcium transport [20].…”

Transcriptional mechanisms regulating Ca2+ homeostasis

“…Interestingly, while a relationship between EGR1 and SERCA2 expression has been demonstrated [66,67], the precise nature of this relationship remains somewhat unclear [68]. The first indication that EGR1 might be involved in control of SERCA2 expression was based on examination of doxorubicin-induced cardiomyopathy [67].…”