| First Author | Charton K | Year | 2015 |
| Journal | Hum Mol Genet | Volume | 24 |
| Issue | 13 | Pages | 3718-31 |
| PubMed ID | 25877298 | Mgi Jnum | J:223343 |
| Mgi Id | MGI:5648692 | Doi | 10.1093/hmg/ddv116 |
| Citation | Charton K, et al. (2015) CAPN3-mediated processing of C-terminal titin replaced by pathological cleavage in titinopathy. Hum Mol Genet 24(13):3718-31 |
| abstractText | Mutations in the extreme C-terminus of titin (TTN), situated in the sarcomeric M-band, cause tibial muscular dystrophy (TMD) and limb-girdle muscular dystrophy 2J (LGMD2J). The mutations ultimately cause a loss of C-terminal titin, including a binding site for the protease calpain 3 (CAPN3), and lead to a secondary CAPN3 deficiency in LGMD2J muscle. CAPN3 has been previously shown to bind C-terminal titin and to use it as a substrate in vitro. Interestingly, mutations in CAPN3 underlie limb-girdle muscular dystrophy 2A (LGMD2A). Here, we aimed to clarify the relationship of CAPN3 and M-band titin in normal and pathological muscle. In vitro analyses identified several CAPN3 cleavage sites in C-terminal titin that were defined by protein sequencing. Furthermore, cleavage products were detected in normal muscle extracts by western blotting and in situ by immunofluorescence microscopy. The TMD/LGMD2J mutation FINmaj proved to alter this processing in vitro, while binding of CAPN3 to mutant titin was preserved. Unexpectedly, the pathological loss of M-band titin due to TMD/LGMD2J mutations was found to be independent of CAPN3, whereas the involvement of ubiquitous calpains is likely. We conclude that proteolytic processing of C-terminal titin by CAPN3 may have an important role in normal muscle, and that this process is disrupted in LGMD2A and in TMD/LGMD2J due to CAPN3 deficiency and to the loss of C-terminal titin, respectively. |
