Metalloprotease-disintegrin ADAM 12 interacts with alpha-actinin-1

ADAM 12, a member of the ADAM family of proteins (containing A Disintegrin And Metalloprotease domain), has been implicated in differentiation and fusion of myoblasts. While the extracellular domain of ADAM 12 contains an active metalloprotease and a region involved in cell adhesion, the function of the cytoplasmic tail of ADAM 12 has been less clear. Here we show that the cytoplasmic domain of ADAM 12 interacts in vitro and in vivo with alpha-actinin-1, an actin-binding and cross-linking protein. Green fluorescent protein fused to ADAM 12 cytoplasmic domain co-localizes with alpha-actinin-1-containing actin stress fibres in C2C12 cells. The interaction between ADAM 12 and alpha-actinin-1 is direct and involves the 58-amino acid C-terminal fragment of ADAM 12 and the 27 kDa N-terminal domain of alpha-actinin-1. Consistently, expression of the 27 kDa fragment of alpha-actinin-1 in C2C12 cells using a mitochondrial targeting system results in recruitment of the co-expressed ADAM 12 cytoplasmic domain to the mitochondrial surface. Moreover, alpha-actinin-1 co-purifies with a transmembrane, His6-tagged form of ADAM 12 expressed in C2C12 myoblasts, indicating that the transmembrane ADAM 12 forms a complex with alpha-actinin-1 in vivo. These results indicate that the actin cytoskeleton may play a critical role in ADAM 12-mediated cell-cell adhesion or cell signalling during myoblast differentiation and fusion.