Ferlins Show Tissue‐Specific Expression and Segregate as Plasma Membrane/Late Endosomal or Trans‐Golgi/Recycling Ferlins

• Published in: Traffic (Copenhagen, Denmark) Vol. 17; no. 3; pp. 245 - 266
• Main Authors: Redpath, Gregory M. I., Sophocleous, Reece A., Turnbull, Lynne, Whitchurch, Cynthia B., Cooper, Sandra T.
• Format: Journal Article
• Language: English
• Published: Former Munksgaard John Wiley & Sons A/S 01.03.2016; Wiley Subscription Services, Inc
• Subjects: Amino Acid Sequence; Animals; Brain - metabolism; Calcium-Binding Proteins - chemistry; Calcium-Binding Proteins - genetics; Calcium-Binding Proteins - metabolism; Cell Membrane - metabolism; Cercopithecus aethiops; COS Cells; dysferlin; Endosomes - metabolism; Fer1L4; Fer1L5; Fer1L6; HEK293 Cells; Humans; late endosome; Localization; Membrane Proteins - chemistry; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mice; Molecular Sequence Data; Muscle Proteins - chemistry; Muscle Proteins - genetics; Muscle Proteins - metabolism; Muscular dystrophy; Mutation; myoferlin; Organ Specificity; otoferlin; Pancreas - metabolism; Plasma; Protein Transport; rab GTP-Binding Proteins - metabolism; Rab7; recycling endosome; trans-Golgi Network - metabolism; trans‐Golgi; Fer1L5; Fer1L4; Rab7; otoferlin; recycling endosome; dysferlin; myoferlin; trans-Golgi; late endosome; Fer1L6
• ISSN: 1398-9219; 1600-0854
• DOI: 10.1111/tra.12370

Ferlins are an ancient family of Ca2+‐binding, multi‐C2 domain vesicle fusion proteins. Of the six human ferlins, mutations in dysferlin cause muscular dystrophy and otoferlin cause deafness. We detail the tissue‐distribution, subcellular localization and endocytic trafficking of the human ferlins. Dysferlin and myoferlin, type‐I ferlins, localize to the plasma membrane and late endosomes, which display potential for occasional recycling. Otoferlin and Fer1L6, type‐II ferlins, localize to dedicated recycling subcompartments of the trans‐Golgi network. We establish that type‐I and type‐II ferlins segregate into late‐endosomal and recycling trans‐Golgi compartments. Ferlins are a family of transmembrane‐anchored vesicle fusion proteins uniquely characterized by 5–7 tandem cytoplasmic C2 domains, Ca2+‐regulated phospholipid‐binding domains that regulate vesicle fusion in the synaptotagmin family. In humans, dysferlin mutations cause limb‐girdle muscular dystrophy type 2B (LGMD2B) due to defective Ca2+‐dependent, vesicle‐mediated membrane repair and otoferlin mutations cause non‐syndromic deafness due to defective Ca2+‐triggered auditory neurotransmission. In this study, we describe the tissue‐specific expression, subcellular localization and endocytic trafficking of the ferlin family. Studies of endosomal transit together with 3D‐structured illumination microscopy reveals dysferlin and myoferlin are abundantly expressed at the PM and cycle to Rab7‐positive late endosomes, supporting potential roles in the late‐endosomal pathway. In contrast, Fer1L6 shows concentrated localization to a specific compartment of the trans‐Golgi/recycling endosome, cycling rapidly between this compartment and the PM via Rab11 recycling endosomes. Otoferlin also shows trans‐Golgi to PM cycling, with very low levels of PM otoferlin suggesting either brief PM residence, or rare incorporation of otoferlin molecules into the PM. Thus, type‐I and type‐II ferlins segregate as PM/late‐endosomal or trans‐Golgi/recycling ferlins, consistent with different ferlins mediating vesicle fusion events in specific subcellular locations.