Prostaglandin F_2α Inhibits SERCA2 Gene Transcription Through an Induction of Egr-1 in Cultured Neonatal Rat Cardiac Myocytes

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Prostaglandin F_2α (PGF_2α) stimulates hypertrophic growth of neonatal rat cardiac myocytes, a feature of which includes downregulation of the Ca²⁺-ATPase (SERCA2), a major Ca²⁺ 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.