Objective: Patients with ovarian cancer (OC) may develop anti‐Yo‐associated paraneoplastic cerebellar degeneration (PCD)—a cerebellar ataxia associated with tumor‐induced autoimmunity against CDR2 and CDR2L proteins. Dysregulation of circulating exosomal microRNAs (miRNAs) occur in OC. Here, we investigated whether PCD is associated with changes in the exosomal miRNA profiles of OC patients.Methods: Serum exosomes were isolated from patients with OC (n = 15), patients with OC and anti‐Yo‐associated PCD (n = 14) and healthy controls (HC, n = 15). Small RNA sequencing was used to identify differentially expressed miRNAs. Receiver operating characteristic curves were used to evaluate biomarker sensitivity and specificity, and miRNA target prediction analysis was employed to elucidate gene targets.Results: OC patients with PCD exhibited a distinct exosomal miRNA expression profile. We detected 103 differentially expressed exosomal miRNAs in PCD patients compared to OC patients without PCD and 139 differentially expressed exosomal miRNAs compared to controls. Particularly miR‐486‐5p, miR‐4732‐5p, miR‐98‐5p and miR‐21‐5p exhibited notable sensitivity and specificity for discriminating PCD patients from both OC patients without PCD and healthy controls. miRNA target prediction showed that several of the differentially expressed miRNAs in PCD patients targeted the CDR2 and CDR2L genes.Interpretation: Our results demonstrate that OC patients with anti‐Yo‐associated PCD exhibit a distinct exosomal miRNA profile compared to OC patients without PCD. Several of the differentially expressed exosomal miRNAs in PCD patients showed diagnostic potential and may hold relevance for understanding the pathogenesis of PCD.

Background: Cerebellar degeneration-related (CDR) proteins are associated with paraneoplastic cerebellar degeneration (PCD) – a rare, neurodegenerative disease caused by tumour-induced autoimmunity against neural antigens resulting in degeneration of Purkinje neurons in the cerebellum. The pathogenesis of PCD is unknown, in large part due to our limited understanding of the functions of CDR proteins. To this end, we performed an extensive, multi-omics analysis of CDR-knockout cells focusing on the CDR2L protein, to gain a deeper understanding of the properties of the CDR proteins in ovarian cancer. Methods: Ovarian cancer cell lines lacking either CDR1, CDR2, or CDR2L were analysed using RNA sequencing and mass spectrometry-based proteomics to assess changes to the transcriptome, proteome and secretome in the absence of these proteins. Results: For each knockout cell line, we identified sets of differentially expressed genes and proteins. CDR2L-knockout cells displayed a distinct expression profile compared to CDR1- and CDR2-knockout cells. Knockout of CDR2L caused dysregulation of genes involved in ribosome biogenesis, protein translation, and cell cycle progression, ultimately causing impaired cell proliferation in vitro. Several of these genes showed a concurrent upregulation at the transcript level and downregulation at the protein level. Conclusions: Our study provides the first integrative multi-omics analysis of the impact of knockout of the CDR genes, providing both new insights into the biological properties of the CDR proteins in ovarian cancer, and a valuable resource for future investigations into the CDR proteins.

Background: Cerebellar degeneration-related protein 1 (CDR1) is associated with paraneoplastic cerebellar degeneration – an autoimmunedisease characterized by neurodegeneration in the cerebellum. Paraneoplastic syndromes are believed to be triggered by ectopic tumour expression of neuronal proteins. The CDR1 protein is expressed by neurons in the cerebellar cortex and in certain cancers. In this study, we characterized the subcellular localization of CDR1 to help delineate potential functions in cancer cells and neurons. Methods: Ovarian cancer cells, cerebellar sections, and Purkinje cells in culture were immunostained and imaged by super-resolution stimulated emission depletion microscopy and potential interaction partners were investigated using a proximity ligation assay. Results: CDR1 was localized to the mitochondria in cancer cells and was colocalized with proteins of the outer mitochondrial membrane. Using a proximity ligation assay, we discovered that CDR1 interacts with mitofusin 1 – a transmembrane GTPase involved in mitochondrial fusion – in both cancer cells and rat cerebellum. CDR1 also colocalized with intermediate filaments, including vimentin, in cancer cells and with neurofilaments in human cerebellum. Conclusion: The dual localization to mitochondria and intermediate filaments as well as colocalization with key proteins involved in mitochondrial dynamics suggest that CDR1 is involved in the subcellular distribution of mitochondria in cells.