Biology subjects

Ohkuni, K.

Publications and source records attributed to Ohkuni, K..

3 recordsLinked to original sources

bioRxiv2026

Yra2 regulates proteolysis of Cse4 to prevent its mislocalization to non-centromeric regions for chromosomal stability in budding yeast

Restricting the localization of centromere-specific histone H3 variant Cse4 (CENP-A in humans) to centromeric chromatin is essential for chromosome segregation. Mislocalization of overexpressed Cse4/CENP-A to non-centromeric regions contributes to chromosomal instability (CIN) in model organisms and human cells. CIN is an important hallmark of many cancers and hence defining mechanisms that prevent mislocalization of Cse4 is clinically significant. Here we report a role for YRA2 (Yeast RNA Annealing Protein 2) in ubiquitin mediated proteolysis of Cse4 to prevent its mislocalization for chromosomal stability. YRA2 was identified in a genome-wide screen for gene deletions that exhibit synthetic dosage lethality (SDL) upon overexpression of CSE4 (GALCSE4). We determined that yra2{Delta} strains exhibit increased Cse4 stability, enriched Cse4 chromatin association, reduced Cse4 ubiquitination, Cse4 mislocalization, and CIN. Defects in interaction of E3 ubiquitin ligase Psh1 with Cse4 contributes to stability of Cse4 in yra2{Delta} strains. Consistent with these results, overexpression of PSH1 suppresses GALCSE4 SDL in yra2{Delta} strain. We determined that Yra2 mediated proteolysis of Cse4 is independent of its RNA related functions as strain deleted for the C-terminal ChTOP domain of Yra2 with an intact N-terminal RNA binding domain exhibits GALCSE4 SDL and defects in Cse4 proteolysis. Furthermore, poly(A)+ RNA export mutants in YRA1 (yra1-2) and MEX67 (mex67-5), that interact with Yra2, do not exhibit GALCSE4 SDL and defects in RNA export are not observed in yra2{Delta} cells. In summary, we have defined a key role for Yra2 in preventing mislocalization of Cse4 by facilitating its proteolysis to preserve chromosomal stability. Article summaryAccurate segregation of chromosomes during cell division is essential because segregation errors are linked to cancer and developmental disorders. We investigated how cells prevent mislocalization of centromere-specific histone H3 variant Cse4, which is essential for faithful chromosome segregation. We found that the yeast RNA annealing protein Yra2 prevents Cse4 mislocalization by promoting Psh1 mediated ubiquitination and degradation of Cse4. Cells lacking Yra2 showed increased stability of Cse4, enhanced chromatin enrichment with mislocalization to non-centromeric regions and CIN. These defects were suppressed by induction of Psh1. Our findings reveal a novel role for Yra2 in regulating Cse4 levels for chromosomal stability.

genetics↗

bioRxiv2020

Reduced Gene Dosage of Histone H4 Prevents CENP-A Mislocalization in Budding Yeast

Mislocalization of the centromeric histone H3 variant (Cse4 in budding yeast, CID in flies, CENP-A in humans) to non-centromeric regions contributes to chromosomal instability (CIN) in yeast, fly, and human cells. Overexpression and mislocalization of CENP-A has been observed in cancers, however, the mechanisms that facilitate the mislocalization of overexpressed CENP-A have not been fully explored. Defects in ubiquitin-mediated proteolysis of overexpressed Cse4 (GALCSE4) leads to its mislocalization and synthetic dosage lethality (SDL) in mutants for E3 ubiquitin ligases (Psh1, Slx5, SCFMet30, SCFCdc4), Doa1, Hir2, and Cdc7. In contrast, defects in sumoylation of GALcse4K215/216/A/R prevent its mislocalization and do not cause SDL in a psh1{Delta} strain. Here, we used a genome-wide screen to identify factors that facilitate the mislocalization of overexpressed Cse4 by characterizing suppressors of the psh1{Delta} GALCSE4 SDL. Deletions of histone H4 alleles (HHF1 or HHF2), which were among the most prominent suppressors, also suppress slx5{Delta}, cdc4-1, doa1{Delta}, hir2{Delta}, and cdc7-4 GALCSE4 SDL. Reduced dosage of H4 contributes to defects in sumoylation and reduced mislocalization of overexpressed Cse4. We determined that the hhf1-20, cse4-102, and cse4-111 mutants, which are defective in the Cse4-H4 interaction, also exhibit reduced sumoylation of Cse4 and do not display psh1{Delta} GALCSE4 SDL. In summary, we have identified genes that contribute to the mislocalization of overexpressed Cse4 and defined a role for the gene dosage of H4 in facilitating Cse4 sumoylation and mislocalization to non-centromeric regions, contributing to SDL when Cse4 is overexpressed in mutant strains.

genetics↗

bioRxiv2017

N-terminal sumoylation of centromeric histone H3 variant Cse4 regulates its proteolysis to prevent mislocalization to non-centromeric chromatin

Stringent regulation of cellular levels of evolutionarily conserved centromeric histone H3 variant (CENP-A in humans, CID in flies, Cse4 in yeast) prevents its mislocalization to non-centromeric chromatin. Overexpression and mislocalization of CENP-A has been observed in cancers and leads to aneuploidy in yeast, flies, and human cells. Ubiquitin-mediated proteolysis of Cse4 by E3 ligases such as Psh1 and Sumo-Targeted Ubiquitin Ligase (STUbL) Slx5 prevent mislocalization of Cse4. Previously, we identified Siz1 and Siz2 as the major E3 ligases for sumoylation of Cse4. In this study, we identify lysine 65 (K65) in Cse4 as a SUMO site and show that sumoylation of Cse4 K65 regulates its ubiquitin-mediated proteolysis by Slx5. Strains expressing cse4 K65R exhibit reduced levels of sumoylated and ubiquitinated Cse4 in vivo. Furthermore, co-immunoprecipitation experiments reveal reduced interaction of cse4 K65R with Slx5. Defects in sumoylation of cse4 K65R contribute to increased stability and mislocalization of cse4 K65R under normal physiological conditions. Based on the increased stability of cse4 K65R in psh1{triangleup} strains but not in slx5{triangleup} strains, we conclude that Slx5 targets sumoylated Cse4 K65 for ubiquitination-mediated proteolysis independent of Psh1. In summary, we have identified and characterized the physiological role of Cse4 sumoylation and determined that sumoylation of Cse4 K65 regulates ubiquitin-mediated proteolysis and prevents mislocalization of Cse4 which is required for genome stability.

molecular biology↗