An intracellular fragment of osteoactivin formed by ectodomain shedding translocated to the nucleoplasm and bound to RNA binding proteins.

Osteoactivin is a type I transmembrane protein upregulated by unloading stresses, including denervation, prolonged bed rest, and space flight, but the regulatory mechanisms of its expression and activation under these conditions remain undefined. Here we report that osteoactivin protein exists in two forms: an intact transmembrane form and a secreted form. The secreted form, the extracellular fragment of osteoactivin, was produced by ectodomain shedding and was released into a culture medium.