Novel Membrane Repair Proteins
Original project description:
Following the identification of dysferlin, genetic heterogeneity was recognized in Miyoshi Myopathy. With Jain Foundation funding, Dr. Bashir recently identified Anoctamin 5 as the gene involved in non-dysferlin Miyoshi Myopathy (designated MMD3). Like dysferlinopathy, MMD3 has been associated with defective membrane repair and mutations in ANO5 are associated with both a limb-girdle muscular dystrophy (LGMD2L) and a Miyoshi Myopathy (MMD3) phenotype. ANO5 is a member of the anoctamin protein family and several ANO proteins have been shown to function as calcium activated chloride channels (CaCC). Currently, we are investigating whether dysferlin and ANO5 function in a common pathway to mediate muscle membrane repair.
The first non-dysferlin MM gene, MMD3 is anoctamin 5, which is also responsible for a LGMD phenotype, LGMD2L. We have suggested that ANO5 functions in the dysferlin membrane trafficking pathway because of the clinical similarities shared by dysferlin MM and non-dysferlin MM patients and because muscle from MMD3/LGMD2L is characterized by membrane breaks. We have previously reported that MMD3 patient fibroblasts exhibit defective membrane repair. ANO5 belongs to the anoctamin protein family, several members of which have been shown to function as calcium activated chloride channels. We and others have not detected calcium activated chloride currents following heterologous expression of ANO5 plasmids in non-muscle cells. Recently other functions have also been attributed to anoctamin proteins; ANO6 which is most similar to ANO5 at the molecular level, functions as a phospholipid scramblase. We have generated monoclonal antibodies using specific N- and C-terminal ANO5 peptides to analyze ANO5 expression in muscle cells and tissue. Our results so far suggest that several isoforms of ANO5 are expressed in muscle tissue and cultured cells. There is evidence of ANO5 oligomerization. ANO5 shows predominant Z-line localization and minimal co-localization with dysferlin.