Human Skeletal Muscle-Specific α-Actinin-2 and -3 Isoforms Form Homodimers and Heterodimersin Vitroandin Vivo

Abstract

α-actinins belong to a family of actin-binding and crosslinking proteins and are expressed in many different cell types. Multiple isoforms of α-actinin are found in humans and are encoded by at least four distinct genes. Human skeletal muscle contains two sarcomeric isoforms, α-actinin-2 and -3. Previous studies have shown that the α-actinins function as anti-parallel homodimers but the question of heterodimer formation between two different isoforms expressed in the same cell type has not been explored. To address this issue, we expressed both α-actinin-2 and -3in vitroand were able to detect their interaction by both blot overlay and co-immunoprecipitation methods. We were also able to demonstrate the presence of heterodimersin vivoin human skeletal muscle and in COS-1 cells transiently transfected with both isoforms. Our results clearly demonstrate the potential for α-actinin isoforms to form heterodimers which might have unique functional characteristics.