Casein kinase II phosphorylation of cyclin F at serine 621 regulates the Lys48-ubiquitylation E3 ligase activity of the SCF ^{(cyclin F)} complex

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that is characterized by progressive weakness, paralysis and muscle loss often resulting in patient death within 3–5 years of diagnosis. Recently, we identified disease-linked mutations in the CCNF gene, which encodes the cyclin F protein, in cohorts of patients with familial and sporadic ALS and frontotemporal dementia (FTD) (Williams KL et al. 2016 Nat. Commun. 7, 11253. (doi:10.1038/ncomms1125310.1038/ncomms11253)). Cyclin F is a part of a Skp1-Cul-F-box (SCF) E3 ubiquitin-protein ligase complex and is responsible for ubiquitylating proteins for degradation by the proteasome. In this study, we investigated the phosphorylation status of cyclin F and the effect of the serine to glycine substitution at site 621 (S621G) on E3 ligase activity. This specific mutation (S621G) was found in a multi-generational Australian family with ALS/FTD. We identified seven phosphorylation sites on cyclin F, of which five are newly reported including Ser621. These phosphorylation sites were mostly identified within the PEST (proline, glutamic acid, serine and threonine) sequence located at the C-terminus of cyclin F. Additionally, we determined that casein kinase II (CK2) can phosphorylate Ser621 and thereby regulate the E3 ligase activity of the SCF(cyclin F) complex. Furthermore, the S621G mutation in cyclin F prevents phosphorylation by CK2 and confers elevated Lys48-ubiquitylation activity, a hallmark of ALS/FTD pathology. These findings highlight the importance of phosphorylation in regulating the activity of the SCF(cyclin F) E3 ligase complex that can affect downstream processes and may lead to defective motor neuron development, neuron degeneration and ultimately ALS and FTD.

Defect of SIRT1-FoxO3a axis is associated with the production of reactive oxygen species during protein kinase CK2 downregulation-mediated cellular senescence and nematode aging

“…How does CK2 activity modulate the ubiquitination of SIRT1? Because it has been determined that CK2 phosphorylates E3 ubiquitin ligases such as MDM2 and SCF (cyclin F) complex (28, 29), we speculate that CK2 regulates SIRT1 ubiquitination via CK2-mediated phosphorylation of SIRT1 and/or E3 ubiquitin ligases. Although further studies are required to identify more regulators for SIRT1 ubiquitination, the discovery of CK2 regulation of SIRT1 ubiquitination provides a new avenue of research in the fields of SIRT1 regulation and senescence.…”

β-TrCP- and Casein Kinase II-Mediated Degradation of Cyclin F Controls Timely Mitotic Progression

“…It has been suggested that cyclin F is phosphorylated by CKIIα at S621 and S709 to control its activity ( Lee et al., 2017 ). However, the biochemical mechanism of this regulation is unclear, because the S621 residue is far from the F-box motif required for the ubiquitylation activity of cyclin F. We observe that CKIIα interacts with the C-terminal region of cyclin F, which includes the S621 residue.…”

Molecular crosstalk between cancer and neurodegenerative diseases

“…These findings drive the need to investigate whether TDP-43 is a substrate of the SCF-cyclin F E3 ubiquitin ligase complex. An ALS/FTD-causing pathogenic mutation in cyclin F at amino acid position 621 from serine to glycine (Cyclin F-S621G) was shown to increase the specific ubiquitination at lysine-48 of proteins, which led to the accumulation of lysine-48-ubiquitinated proteins and the impairment of autophagic degradation [199], indicating autophagy to be a degradative mechanism underlying the pathogenesis of ALS/FTD. The roles of cyclin F, which acts as a cyclin as well as an F-box protein, have not been explored in this context, and thus can be further investigated to understand their relevance in mediating neurodegenerative diseases.…”