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

Eph receptors constitute the largest family of receptor tyrosine kinases. Multiple transcripts of ephrin-A5, the cognate ligand of the EphA3 receptor, were found in neonatal rat cardiomyocytes. Two cDNA clones encoding the full-length ephrin-A5 (ephrin-A5α) and a 27-amino acid deletion form (ephrin-A5β) were isolated. To examine the role of ephrin-A5 in cardiomyocytes, the cDNAs were inserted into adenoviral vectors, termed Ad.ephrin-A5α and Ad.ephrin-A5Β, respectively, and overexpressed in cardiomyocytes. The effect of ephrin-A5 on cardiomyocyte gene expression was investigated using a cDNA expression array and Western blot analysis. The results showed that both ephrin-A5α and ephrin-A5β downregulated cyclin D2, cyclin-dependent kinase-4 proteins, and their cognate receptor EphA3, which were associated with reduced bromodeoxyuridine incorporation in cardiomyocytes. Whereas ephrin-A5α and ephrin-A5β also induced differential gene expression, only ephrin-A5β significantly upregulated the transcription of brain natriuretic peptide and downregulated ras-related protein RAB2, protein kinase C inhibitor protein-1, clusterin, and insulin-like growth factor-binding protein. The results suggest that the two forms of ephrin-A5 share similar function while differ in regulating different sets of genes in cardiomyocytes.