Tripartite motif family proteins mediate vesicular trafficking during membrane repair in striated muscle

Abstract

Tripartite motif (TRIM) proteins constitute a family of proteins that all contain a canonical RING finger, B-box and coiled-coil domains which participate in several cellular processes. TRIM72, also known as mitsugumin 53 (MG53), is an essential component of the membrane repair machinery in striated muscles. The TRIM72/MG53 knockout mouse displays compromised muscle membrane repair and trim72-/- mice develop skeletal myopathy and defects following cardiovascular stress. Previous studies indicate that both endocytosis and exocytosis are important in the membrane repair process, and also that TRIM72/MG53 expression can appear in vesicles that are released from myocytes. In this study we examined the role of TRIM72/MG53 in vesicular endocytosis and exocytosis in C2C12 myoblasts overexpressing TRIM72/MG53, where overexpression of TRIM72/MG53 increased both endocytosis measured by labeled dextran entry and exocytosis as assayed by transferrin internalization and recycling. Our recent findings show that TRIM72/MG53 overexpression is sufficient to activate the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) signaling pathway. Therefore, we hypothesized that this TRIM72/MG53 mediated vesicular translocation may be regulated by a PI3K-dependent pathway. To test this hypothesis, dextran uptake and transferrin internalization/recycling were measured in the presence of chemical and genetic inhibition of PI3K signaling. We conclude that TRIM72/MG53 is an important regulator of the PI3K signaling pathway and positively regulates translocation of vesicles to the site of membrane injury.