LAUSR

Previously, we identified missense mutations in CCNF that are causative of familial and sporadic amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Hallmark features of these diseases include the build-up of insoluble protein aggregates as well as the mislocalisation of proteins such as TDP-43. In recent years, the dysregulation of SFPQ has also emerged as a pathological hallmark of ALS/FTD. CCNF encodes for the protein cyclin F, a substrate recognition component of an E3-ubiquitin ligase. We have previously shown that ALS/FTD-linked mutations in CCNF cause disruptions to overall protein homeostasis that leads to a build-up of K48-linked ubiquitylated proteins as well as defects in autophagic machinery. To investigate further processes that may be affected by cyclin F, we used a protein-proximity ligation method, known as BioID, standard immunoprecipitations and mass spectrometry (MS) to identify novel interaction partners of cyclin F and infer further process that may be affected by the ALS/FTD-causing mutation. Results demonstrate that cyclin F closely associates with proteins involved with RNA metabolism as well as a number of RNA binding proteins previously linked to ALS/FTD, including splicing factor proline and glutamine rich (SFPQ). Notably, the overexpression of cyclin F(S621G) led to the aggregation and altered subcellular distribution of SFPQ in HEK293 cells, whilst leading to altered degradation in primary neurons. Overall, our data links ALS/FTD-causing mutations in CCNF to converging pathological features of ALS/FTD and provides a link between defective protein degradation systems and the pathological accumulation of a protein involved in RNA processing and metabolism.