Characterising mutant Cyclin F in the development of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a relentless neurodegenerative disease typically leading to death of patients within 5 years from onset. Recently, several ALS-causing gene mutations in CCNF, the gene encoding Cyclin F have been identified. We have focused on the substitution from serine to glycine at amino acid 621 and show that mutation affects the functionality of the ubiquitin ligase, SCF Cyclin F. Specifically, the mutation impacts proteostasis of a known substrate, RRM2 (ribonucleotide reductase family member 2). Although the abundance of RRM2 is not affected, there is increasing abundance of ubiquitinated RRM2 in transfected Neuro-2A cells after 24 hours post-transfection. Using a label-free proteomic workflow, a total of 60 differentially expressed proteins were associated with mutant Cyclin F-mCherry expressing cells after 8 and 24 hours post-transfection. Many changes are functionally involved in protein translation and RNA processing, which is consistent with ALS pathogenesis. Using a workflow consisting of SDS-PAGE and LC-MS/MS we also obtained protein aggregate profiles that are linked to the mutation in Neuro-2A cells under heat-stress.Notably, Septin 2 was increasingly insoluble in association with mutant Cyclin F. This is a strong candidate for validation studies, as it is known to form insoluble aggregates within Parkinsonism models.