Differential effects of overexpression of two forms of ephrin-A5 on neonatal rat cardiomyocytes

Eph receptors constitute the largest family of receptor tyrosine kinases. M ultiple transcripts of ephrin-A5, the cognate ligand of the EphA3 receptor, were found in neonatal rat cardiomyocytes. Two cDNA clones encoding the fu ll-length ephrin-A5 (ephrin-A5 alpha) and a 27-amino acid deletion form (ep hrin-A5 beta) were isolated. To examine the role of ephrin-A5 in cardiomyoc ytes, the cDNAs were inserted into adenoviral vectors, termed Ad.ephrin-A5 alpha and Ad.ephrin-A5 beta, respectively, and overexpressed in cardiomyocy tes. The effect of ephrin-A5 on cardiomyocyte gene expression was investiga ted using a cDNA expression array and Western blot analysis. The results sh owed that both ephrin-A5 alpha and ephrin-A5 beta downregulated cyclin D2, cyclin-dependent kinase-4 proteins, and their cognate receptor EphA3, which were associated with reduced bromodeoxyuridine incorporation in cardiomyoc ytes. Whereas ephrin-A5 alpha and ephrin-A5 beta also induced differential gene expression, only ephrin-A5 beta significantly upregulated the transcri ption of brain natriuretic peptide and downregulated ras-related protein RA B2, protein kinase C inhibitor protein-1, clusterin, and insulin-like growt h factor-binding protein. The results suggest that the two forms of ephrin- A5 share similar function while differ in regulating different sets of gene s in cardiomyocytes.