FLNC, Filamin-c, Filamin-2 (FLN2), Actin binding-like protein (APBL) (290.8 kDa) is an isoform of the Filamin proteins family. Filamins are broadly expressed and function as actin-binding and actin-crosslinking proteins. Structurally, Filamins consist of three main domains; N-terminal actin-binding domain, multiple central immunoglobulin (Ig) domains, and a C-terminal domain which supports homodimerization (1, 2). Functionally, Filamins play a role in cytoskeleton structure through interactions with actin, but they are implicated in a wide range of processes through their interactions with diverse molecular partners such as signaling molecules (MKK4, JNK1), ion channels (Kv4.2, Kir2.1), receptors (Insulin, Calcitonin), and transcription factors (Smad1-6, Foxc1) (3).
Three isoforms of Filamin are expressed in mammals, identified as FLNA, FLNB and FLNC. FLNC is considered a muscle specific Filamin isoform for its high expression in cardiac and skeletal muscles. In muscle tissue, FLNC localizes to the Z-line, sarcolemma, myotendinous and intercalated disks (2). FLNC interacts with various muscle proteins via a non-conserved sequence within its Ig domain 20. Some muscle binding partners for FLNC include gamma and delta-sarcoglycans in the sarcolemma, and FATZ, myozenins, myotilin and myopodin in the Z-discs (2, 4). FLNC variants are associated with various inherited pathological conditions including myofibrillar myopathy 5, distal myopathy 4, dilated cardiomyopathy, hypertrophic cardiomyopathy, and restrictive cardiomyopathy (2, 5).
References
1. Chiang, W., Greaser, M. L., & Lyons, G. E. (2000). Filamin isogene expression during mouse myogenesis. Developmental Dynamics. https://doi.org/10.1002/(sici)1097-0177(200001)217:1<99::aid-dvdy9>3.3.co;2-x
2. Leber, Y., Ruparelia, A. A., Kirfel, G., van der Ven, P. F. M., Hoffmann, B., Merkel, R., ... Furst, D. O. (2016). Filamin C is a highly dynamic protein associated with fast repair of myofibrillar microdamage. Human Molecular Genetics. https://doi.org/10.1093/hmg/ddw135
3. Nakamura, F., Stossel, T. P., & Hartwig, J. H. (2011). The filamins: Organizers of cell structure and function. Cell Adhesion and Migration. https://doi.org/10.4161/cam.5.2.14401
4. Thompson, T. G., Chan, Y. M., Hack, A. A., Brosius, M., Rajala, M., Lidov, H. G. W., ... Kunkel, L. M. (2000). Filamin 2 (FLN2): A muscle-specific sarcoglycan interacting protein. Journal of Cell Biology. https://doi.org/10.1083/jcb.148.1.115
5. Brodehl, A., Ferrier, R. A., Hamilton, S. J., Greenway, S. C., Brundler, M. A., Yu, W., ... Scherer, S. (2016). Mutations in FLNC are Associated with Familial Restrictive Cardiomyopathy. Human Mutation. https://doi.org/10.1002/humu.22942