Gata4 Regulates Expression of the Erythropoietin Receptor in Cardiomyocytes.

Abstract 3610

Poster Board III-546

Experimental studies indicate significant cardioprotective effects of recombinant erythropoietin (Epo) by binding to the Epo receptor (EpoR) and by inducing various molecular mechanisms, including activation of Gata4, a transcription factor that induces anti-apoptotic genes. However, specific molecular mechanisms of EpoR regulation in cardiomyocytes are unknown. Using reporter gene assays, we identified in murine HL-1 cardiomyocytes a 774 bp regulatory domain in the 5′-flanking region of the EpoR gene. Fragments that include an E-box, CACCC motifs, GC-rich elements, and binding sites for members of the Gata and Sp transcription factor families contribute to EpoR promoter activity. EMSA experiments indicated the specific binding of Gata4 and Sp1 (a known interaction factor of Gata4) to the minimal EpoR promoter. Forced expression of Gata4 resulted in a significant induction of EpoR mRNA expression, while Sp1 overexpression did not affect EpoR expression. Depletion of Gata4 by treating mice with high-dose doxorubicin led to the downregulation of EpoR expression, followed by the upregulation of EpoR when Gata4 levels recovered after 5 days. Transgenic mice with an inducible short hairpin RNA against Gata4 confirmed the suppression of EpoR expression if Gata4 levels were reduced. Under hypoxia, however, a 2-fold induction of EpoR mRNA expression in cardiomyocytes was independent from Gata4, since Gata4 levels decreased. Our data indicate that Gata4 activates EpoR mRNA expression in cardiomyocytes. This is a novel mechanism that differs from EpoR regulation in neurons and hematopoietic cells.