Acebron, S. P. | Search bioRxiv

bioRxiv2021

DEAD-box RNA Helicases Act as Nucleotide Exchange Factors for Casein Kinase 2

DDX RNA helicases promote RNA processing but DDX3X is also known to activate casein kinase 1 {varepsilon} (CK1{varepsilon}). Here we show that not only is protein kinase stimulation a latent property of other DDX proteins towards CK1{varepsilon}, but that this extends to casein kinase 2 (CK22) as well. CK22 enzymatic activity is stimulated by a variety of DDX proteins and we identify DDX1/24/41/54 as physiological activators required for full kinase activity in vitro and in Xenopus embryos. Mutational analysis of DDX3X reveals that CK1 and CK2 kinase stimulation engages its RNA binding-but not catalytic motifs. Mathematical modelling of enzyme kinetics and stopped-flow spectroscopy converge that DDX proteins function as nucleotide exchange factor towards CK22 that reduce unproductive reaction intermediates and substrate inhibition. Our study reveals protein kinase stimulation by nucleotide exchange as a new principle in kinase regulation and an evolved function of DDX proteins.

biochemistry↗

bioRxiv2020

Wnt signaling recruits KIF2A to the spindle to ensure chromosome congression and alignment during mitosis

Canonical Wnt signaling plays critical roles in development and tissue renewal by regulating {beta}-catenin target genes. Recent evidence showed that {beta}-catenin-independent Wnt signaling is also required for faithful execution of mitosis. This mitotic Wnt signaling functions through Wnt-dependent stabilization of proteins (Wnt/STOP), as well as through components of the LRP6 signalosome. However, the targets and specific functions of mitotic Wnt signaling still remain uncharacterized. Using phosphoproteomics, we identified that Wnt signaling regulates the microtubule depolymerase KIF2A during mitosis. We found that Dishevelled recruits KIF2A via its N-terminal and motor domains, which is further promoted upon LRP6 signalosome formation during mitosis. We show that Wnt signaling modulates KIF2A interaction with PLK1, which is critical for KIF2A localization at the spindle. Accordingly, Wnt signaling promotes chromosome congression and alignment by monitoring KIF2A protein levels at the spindle poles both in somatic cells and in pluripotent stem cells. Our findings highlight a novel function of Wnt signaling during cell division, which could have important implications for genome maintenance, notably in stem cells. SIGNIFICANCEWnt signaling plays essential roles in embryonic patterning, stem cell renewal, and cell cycle progression from G1 to S phase via the regulation of {beta}-catenin target genes. Here, we show that Wnt signaling also promotes faithful execution of mitosis by ensuring chromosome congression and alignment before cell division, including in pluripotent stem cells. We demonstrate that the Wnt signaling transducer Dishevelled recruits the mitotic kinesin KIF2A, and mediates its binding to the spindle. KIF2A is a microtubule depolymerase that controls chromosome alignment and congression during mitosis. Consequently, we found that inhibition of Wnt signaling leads to KIF2A-dependent chromosome congression and alignment defects.

cell biology↗