Septin-3 autoimmunity in patients with paraneoplastic cerebellar ataxia

Abstract

Background Septins are cytoskeletal proteins with filament forming capabilities, which have multiple roles during cell division, cellular polarization, morphogenesis, and membrane trafficking. Autoantibodies against septin-5 are associated with non-paraneoplastic cerebellar ataxia, and autoantibodies against septin-7 with encephalopathy with prominent neuropsychiatric features. Here, we report on newly identified autoantibodies against septin-3 in patients with paraneoplastic cerebellar ataxia. We also propose a strategy for anti-septin autoantibody determination. Methods Sera from three patients producing similar immunofluorescence staining patterns on cerebellar and hippocampal sections were subjected to immunoprecipitation followed by mass spectrometry. The identified candidate antigens, all of which were septins, were expressed recombinantly in HEK293 cells either individually, as complexes, or combinations missing individual septins, for use in recombinant cell-based indirect immunofluorescence assays (RC-IIFA). Specificity for septin-3 was further confirmed by tissue IIFA neutralization experiments. Finally, tumor tissue sections were analyzed immunohistochemically for septin-3 expression. Results Immunoprecipitation with rat cerebellum lysate revealed septin-3, -5, -6, -7, and -11 as candidate target antigens. Sera of all three patients reacted with recombinant cells co-expressing septin-3/5/6/7/11, while none of 149 healthy control sera was similarly reactive. In RC-IIFAs the patient sera recognized only cells expressing septin-3, individually and in complexes. Incubation of patient sera with five different septin combinations, each missing one of the five septins, confirmed the autoantibodies’ specificity for septin-3. The tissue IIFA reactivity of patient serum was abolished by pre-incubation with HEK293 cell lysates overexpressing the septin-3/5/6/7/11 complex or septin-3 alone, but not with HEK293 cell lysates overexpressing septin-5 as control. All three patients had cancers (2 × melanoma, 1 × small cell lung cancer), presented with progressive cerebellar syndromes, and responded poorly to immunotherapy. Expression of septin-3 was demonstrated in resected tumor tissue available from one patient. Conclusions Septin-3 is a novel autoantibody target in patients with paraneoplastic cerebellar syndromes. Based on our findings, RC-IIFA with HEK293 cells expressing the septin-3/5/6/7/11 complex may serve as a screening tool to investigate anti-septin autoantibodies in serological samples with a characteristic staining pattern on neuronal tissue sections. Autoantibodies against individual septins can then be confirmed by RC-IIFA expressing single septins.

Case report: Anti septin-5-encephalitis as a treatable cause of cerebellar ataxia and psychiatric symptoms

“…Although detailed pathophysiology of anti septin-5 IgG is unclear, septines play a crucial role in the CNS, organizing neuronal cytoskeletal development and regulating endo-and exocytosis at synaptic terminals, so it is feasible that disrupting their function may lead to neurological deficits (6)(7)(8). Apart from septin-5, septin-3 and septin-7 are also associated with autoimmune CNS diseases (3,9). Whether there is direct pathogenic effect of anti-septin-5 IgG or other components such as T-cell mediated cytotoxicity also play a role is unclear.…”

Detection of High‐Risk Paraneoplastic Antibodies against TRIM9 and TRIM67 Proteins

“…Melanoma-associated paraneoplastic cerebellar syndromes are exceedingly rare, many of which have been reported without an identified autoantibody. [24][25][26][27][28][29] Seropositive melanoma-associated paraneoplastic cerebellar cases include SEPTIN3 30 (n = 2), Yo 31 (n = 1), GABABR 32 (n = 1), CARP-VIII 33 (n = 1), ARHGAP26 34 (n = 1), and an anti-TRIM9/67-IgG case (n = 1). 3 This study highlights some additional benefits of complementing traditional autoantibody discovery and validation methods with PhIP-Seq.…”

Neuronal antibodies in nonparaneoplastic autoimmune cerebellar ataxias

“…Septin-5 is a member of a large family of guanosine triphosphate-binding proteins, which play a crucial role in several cellular processes regulating endocytosis and exocytosis at synaptic terminals [40]. Apart from septin-5 antibodies, autoimmunity against septins include septin-7 antibodies described in 11 patients with diffuse encephalitis (seven patients), myelitis (three), and episodic ataxia (one) [36 && ] and septin-3 antibodies identified in three patients with paraneoplastic cerebellar degeneration associated with melanoma and small cell lung cancer [41].…”