ENH, Containing PDZ and LIM Domains, Heart/Skeletal Muscle-Specific Protein, Associates with Cytoskeletal Proteins through the PDZ Domain

Abstract

The Enigma homologue protein (ENH), containing an N-terminal PDZ domain and three C-terminal LIM domains, is a heart and skeletal muscle-specific protein that has been shown to preferentially interact with protein kinase C β (PKCβ) through the LIM domains (Kuroda et al., J. Biol. Chem. 271, 31029–31032, 1996). We here demonstrate that ENH is colocalized with a cytoskeletal protein α-actinin in the Z-disk region of rat neonatal cardiomyocytes. Pull-down assays using the glutathione-S-transferase-fusion system also showed the interaction of the PDZ domain of ENH with actin and α-actinin. Furthermore, by combined use of the in silico and conventional cDNA cloning methods, we have isolated three ENH-related clones from a mouse heart-derived cDNA library: mENH1 (591 amino acid residues) corresponding to rat ENH, mENH2 (337 residues), and mENH3 (239 residues); the latter two containing only a single PDZ domain. Deciphering their cDNA sequences, these mENH1–3 mRNAs appear to be generated from a single mENH gene by alternative splicing. Northern blot analyses using human cancer cells and mouse embryos have shown expression of each mENH mRNA to vary considerably among the cell types and during the developmental stage. Together with a recent finding that PKCβ is markedly activated in the cardiac hypertrophic signaling, these results suggest that ENH1 plays an important role in the heart development by scaffolding PKCβ to the Z-disk region and that ENH2 and ENH3 negatively modulate the scaffolding activity of ENH1.