Autoantibodies to the Amino-Terminal Fragment of β-Fodrin Expressed in Glandular Epithelial Cells in Patients with Sjögren’s Syndrome

Abstract

Sjögrens’s syndrome (SS) is an autoimmune disease characterized by destruction of lacrimal and salivary glands, but the mechanisms underlying the disease process are unclear. By immunoscreening a HepG2 cDNA library with serum from an SS patient we isolated a cDNA encoding amino-terminal 616 aa of β-fodrin, a membrane skeleton protein associated with ion channels and pumps. Serum Ab to the amino-terminal fragment of β-fodrin was frequently detected in SS patients compared with rheumatic disease patients without SS or healthy controls (70 vs 12 or 4%; p < 0.00001). All the anti-β-fodrin-positive sera recognized the amino-terminal fragment with no homology to α-fodrin. Anti-β-fodrin Abs in patients’ sera as well as mouse polyclonal sera raised against the amino-terminal β-fodrin fragment did not react with intact β-fodrin, but recognized the 65-kDa amino-terminal fragment generated through cleavage by caspase-3 or granzyme B. When expression of intact and fragmented β-fodrin in lacrimal glands was assessed by immunohistochemistry, the antigenic amino-terminal fragment was distributed diffusely in acinar epithelial cell cytoplasm, whereas the carboxyl-terminal fragment and/or intact β-fodrin were localized in peripheral cytoplasm, especially at the basal membrane, in SS patients. In contrast, intact β-fodrin was detected primarily at the apical membrane of epithelia, and the amino-terminal fragment was scarcely detected in control patients with chronic graft-vs-host disease. These findings suggest that cleavage and altered distribution of β-fodrin in glandular epithelial cells may induce impaired secretory function and perpetuate an autoimmune response to β-fodrin, leading to autoantibody production and glandular destruction in SS.

The genetics of primary Sjögren’s syndrome

“…CXL13 and CXCR5 attract B cells to target organs and are expressed in SS [44]. Other possible candidate genes include alpha-fodrin [45], beta-fodrin [46], Sjögren's 56 [47], ABCA1 [48], P230 trans Golgi network protein [49], 97 kD protein associated with Golgi complex [50], alpha-amylase [51], and the muscarinic-3 receptor [52]. In addition, there are protein expression changes that have been found in SS, including the cysteinerich secretory protein-3 [53], aquaporin-5 [54], aquaporin-1 [55], cyclooxygenase-1 [56], prolactin, and cathepsin B and D [57].…”

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

“…215 During epithelial cell apoptosis, GrB may cleave several autoantigens in SS, namely the SS-B (La) autoantigen, a-fodrin, b-fodrin, and type 3 muscarinic acetylcholine receptor. [216][217][218] GrB-mediated cleavage of the La protein resulted in its translocation from the nucleus into the cytoplasm, where the autoantigen is easily accessible to antigenpresenting cells and can initiate an immune response. 219 As such, GrB may not only synthesize autoantigens in SS but may also render them more readily accessible for immunorecognition.…”

Analysis of parotid glands of primary Sjögren's syndrome patients using proteomic technology reveals altered autoantigen composition and novel antigenic targets

“…This response is an antigen-driven process and results in the formation of autoantibodies against several epitopes of each protein component (intramolecular spreading), as well as to the other protein-members of the complex (intermolecular spreading) [2]. Several reports have described various novel targets of autoantibodies in SS, such as the nuclear mitotic apparatus (NuMA) [14], members of the golgin family [15], a-and b-fodrin [16,17], the 90 kDa nucleolar organizer region (NOR-90), p80 coilin [18] and centromere protein-C (CENP-C) [19].…”