Skp, Cullin, F-box (SCF)-Met30 and SCF-Cdc4-Mediated Proteolysis of CENP-A Prevents Mislocalization of CENP-A for Chromosomal Stability in Budding Yeast

Restricting the localization of the histone H3 variant CENP-A (Cse4 in yeast, CID in flies) to centromeres is essential for faithful chromosome segregation. Mislocalization of CENP-A leads to chromosomal instability (CIN) in yeast, fly and human cells. Overexpression and mislocalization of CENP-A has been observed in many cancers and this correlates with increased invasiveness and poor prognosis. Yet genes that regulate CENP-A levels and localization under physiological conditions have not been defined. In this study we used a genome-wide genetic screen to identify essential genes required for Cse4 homeostasis to prevent its mislocalization for chromosomal stability. We show that two Skp, Cullin, F-box (SCF) ubiquitin ligases with the evolutionarily conserved F-box proteins Met30 and Cdc4 interact and cooperatively regulate proteolysis of endogenous Cse4 and prevent its mislocalization for faithful chromosome segregation under physiological conditions. The interaction of Met30 with Cdc4 is independent of the D domain, which is essential for their homodimerization and ubiquitination of other substrates. The requirement for both Cdc4 and Met30 for ubiquitination is specifc for Cse4; and a common substrate for Cdc4 and Met30 has not previously been described. Met30 is necessary for the interaction between Cdc4 and Cse4, and defects in this interaction lead to stabilization and mislocalization of Cse4, which in turn contributes to CIN. We provide the first direct link between Cse4 mislocalization to defects in kinetochore structure and show that SCF-mediated proteolysis of Cse4 is a major mechanism that prevents stable maintenance of Cse4 at non-centromeric regions, thus ensuring faithful chromosome segregation. In summary, we have identified essential pathways that regulate cellular levels of endogenous Cse4 and shown that proteolysis of Cse4 by SCF-Met30/Cdc4 prevents mislocalization and CIN in unperturbed cells

Yeast hEST1A/B (SMG5/6)- Like proteins contribute to environment-sensing adaptive gene expression responses

During its natural life cycle, budding yeast (Saccharomyces cerevisiae) has to adapt to drastically changing environments, but how environmental-sensing pathways are linked to adaptive gene expression changes remains incompletely understood. Here, we des

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 have identified lysine 65 (K65) in Cse4 as a site that regulates sumoylation and ubiquitin-mediated proteolysis of Cse4 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, leading to increased stability and mislocalization of cse4 K65R under normal physiological conditions. Based on the increased stability of cse4 K65R in psh1 strains but not in slx5 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 K65 in sumoylation, ubiquitin-mediated proteolysis, and localization of Cse4 for genome stability

SUMO-targeted ubiquitin ligase (STUbL) Slx5 regulates proteolysis of centromeric histone H3 variant Cse4 and prevents its mislocalization to euchromatin

Centromeric histone H3, CENP-ACse4, is essential for faithful chromosome segregation. Stringent regulation of cellular levels of CENP-ACse4 restricts its localization to centromeres. Mislocalization of CENP-ACse4 is associated with aneuploidy in yeast and flies and tumorigenesis in human cells; thus defining pathways that regulate CENP-A levels is critical for understanding how mislocalization of CENP-A contributes to aneuploidy in human cancers. Previous work in budding yeast shows that ubiquitination of overexpressed Cse4 by Psh1, an E3 ligase, partially contributes to proteolysis of Cse4. Here we provide the first evidence that Cse4 is sumoylated by E3 ligases Siz1 and Siz2 in vivo and in vitro. Ubiquitination of Cse4 by the small ubiquitin-related modifier (SUMO)-targeted ubiquitin ligase (STUbL) Slx5 plays a critical role in proteolysis of Cse4 and prevents mislocalization of Cse4 to euchromatin under normal physiological conditions. Accumulation of sumoylated Cse4 species and increased stability of Cse4 in slx5∆ strains suggest that sumoylation precedes ubiquitin-mediated proteolysis of Cse4. Slx5-mediated Cse4 proteolysis is independent of Psh1, since slx5∆ psh1∆ strains exhibit higher levels of Cse4 stability and mislocalization than either slx5∆ or psh1∆ strains. Our results demonstrate a role for Slx5 in ubiquitin-mediated proteolysis of Cse4 to prevent its mislocalization and maintain genome stability

Polo kinase Cdc5 associates with centromeres to facilitate the removal of centromeric cohesin during mitosis

Sister chromatid cohesion is essential for tension-sensing mechanisms that monitor bipolar attachment of replicated chromatids in metaphase. Cohesion is mediated by the association of cohesins along the length of sister chromatid arms. In contrast, centromeric cohesin generates intrastrand cohesion and sister centromeres, while highly cohesin enriched, are separated by >800 nm at metaphase in yeast. Removal of cohesin is necessary for sister chromatid separation during anaphase, and this is regulated by evolutionarily conserved polo-like kinase (Cdc5 in yeast, Plk1 in humans). Here we address how high levels of cohesins at centromeric chromatin are removed. Cdc5 associates with centromeric chromatin and cohesin-associated regions. Maximum enrichment of Cdc5 in centromeric chromatin occurs during the metaphase-to-anaphase transition and coincides with the removal of chromosome-associated cohesin. Cdc5 interacts with cohesin in vivo, and cohesin is required for association of Cdc5 at centromeric chromatin. Cohesin removal from centromeric chromatin requires Cdc5 but removal at distal chromosomal arm sites does not. Our results define a novel role for Cdc5 in regulating removal of centromeric cohesins and faithful chromosome segregation

Dbf4-dependent kinase (DDK)-mediated proteolysis of CENP-A prevents mislocalization of CENP-A in Saccharomyces cerevisiae

The evolutionarily conserved centromeric histone H3 variant (Cse4 in budding yeast, CENP-A in humans) is essential for faithful chromosome segregation. Mislocalization of CENP-A to non-centromeric chromatin contributes to chromosomal instability (CIN) in yeast, fly, and human cells and CENP-A is highly expressed and mislocalized in cancers. Defining mechanisms that prevent mislocalization of CENP-A is an area of active investigation. Ubiquitin-mediated proteolysis of overexpressed Cse4 (GALCSE4)byE3 ubiquitin ligases such as Psh1 prevents mislocalization of Cse4, and psh1D strains display synthetic dosage lethality (SDL) with GALCSE4. We previously performed a genome-wide screen and identified five alleles of CDC7 and DBF4 that encode the Dbf4-dependent kinase (DDK) complex, which regulates DNA replication initiation, among the top twelve hits that displayed SDL with GALCSE4. We determined that cdc7-7 strains exhibit defects in ubiquitin-mediated proteolysis of Cse4 and show mislocalization of Cse4. Mutation of MCM5 (mcm5-bob1) bypasses the requirement of Cdc7 for replication initiation and rescues replication defects in a cdc7-7 strain. We determined that mcm5-bob1 does not rescue the SDL and defects in proteolysis of GALCSE4 in a cdc7-7 strain, suggesting a DNA replication-independent role for Cdc7 in Cse4 proteolysis. The SDL phenotype, defects in ubiquitin-mediated proteolysis, and the mislocalization pattern of Cse4 in a cdc7-7 psh1D strain were similar to that of cdc7-7 and psh1D strains, suggesting that Cdc7 regulates Cse4 in a pathway that overlaps with Psh1. Our results define a DNA replication initiation-independent role of DDK as a regulator of Psh1-mediated proteolysis of Cse4 to prevent mislocalization of Cse4.Fil: Eisenstatt, Jessica R.. National Institutes of Health; Estados UnidosFil: Boeckmann, Lars. National Institutes of Health; Estados UnidosFil: Au, Wei Chun. National Institutes of Health; Estados UnidosFil: Garcia, Valerie. National Institutes of Health; Estados UnidosFil: Bursch, Levi. National Institutes of Health; Estados UnidosFil: Ocampo, Josefina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentina. National Instituto of Child Health & Human Development; Estados UnidosFil: Costanzo, Michael. National Institutes of Health; Estados Unidos. University of Toronto; CanadáFil: Weinreich, Michael. Van Andel Research Institute; Estados UnidosFil: Sclafani, Robert A.. University of Colorado; Estados UnidosFil: Baryshnikova, Anastasia. University of Princeton; Estados UnidosFil: Myers, Chad L.. University of Minnesota; Estados UnidosFil: Boone, Charles. University of Toronto; Canadá. National Institutes of Health; Estados UnidosFil: Clark, David J.. National Institutes of Health; Estados UnidosFil: Baker, Richard. University of Massachusetts; Estados UnidosFil: Basrai, Munira A.. National Institutes of Health; Estados Unido

Phosphorylation of centromeric histone H3 variant regulates chromosome segregation in S. cerevisiae

The centromeric histone H3 variant (CenH3) is essential for chromosome segregation in eukaryotes. We have identified posttranslational modifications of S. cerevisiae CenH3, Cse4. Functional characterization of cse4 phosphorylation mutants showed growth and chromosome segregation defects when combined with kinetochore mutants okp1 and ame1. Using a phosphoserine-specific antibody we showed that the association of phosphorylated Cse4 with centromeres is increased in response to defective microtubule attachment or reduced cohesion. We determined that evolutionarily conserved Ipl1/Aurora B contributes to phosphorylation of Cse4, as levels of phosphorylated Cse4 were reduced at centromeres in ipl1 strains in vivo and in vitro assays showed phosphorylation of Cse4 by Ipl1. Consistent with these results we observed that a phosphomimetic cse4-4SD mutant suppressed the temperature sensitive growth of ipl1-2 and Ipl1 substrate mutants dam1 spc34 and ndc80 that are defective for chromosome biorientation. Furthermore, cell biology approaches using a GFP labeled chromosome showed that cse4-4SD suppressed chromosome segregation defects in dam1 spc34 strains. Based these results we propose that phosphorylation of Cse4 destabilizes defective kinetochores to promote biorientation and ensure faithful chromosome segregation. Taken together, our study provides a detailed analysis, in vivo and in vitro, of Cse4 phosphorylation and its role in promoting faithful chromosome segregation

Skp, Cullin, F-box (SCF)-Met30 and SCF-Cdc4-Mediated Proteolysis of CENP-A Prevents Mislocalization of CENP-A for Chromosomal Stability in Budding Yeast

Restricting the localization of the histone H3 variant CENP-A (Cse4 in yeast, CID in flies) tocentromeres is essential for faithful chromosome segregation. Mislocalization of CENP-Aleads to chromosomal instability (CIN) in yeast, fly and human cells. Overexpression andmislocalization of CENP-A has been observed in many cancers and this correlates withincreased invasiveness and poor prognosis. Yet genes that regulate CENP-A levels andlocalization under physiological conditions have not been defined. In this study we used agenome-wide genetic screen to identify essential genes required for Cse4 homeostasis toprevent its mislocalization for chromosomal stability. We show that two Skp, Cullin, Fbox(SCF) ubiquitin ligases with the evolutionarily conserved F-box proteins Met30 andCdc4 interact and cooperatively regulate proteolysis of endogenous Cse4 and prevent itsmislocalization for faithful chromosome segregation under physiological conditions. Theinteraction of Met30 with Cdc4 is independent of the D domain, which is essential for theirhomodimerization and ubiquitination of other substrates. The requirement for both Cdc4and Met30 for ubiquitination is specifc for Cse4; and a common substrate for Cdc4 andMet30 has not previously been described. Met30 is necessary for the interaction betweenCdc4 and Cse4, and defects in this interaction lead to stabilization and mislocalization ofCse4, which in turn contributes to CIN. We provide the first direct link between Cse4 mislocalizationto defects in kinetochore structure and show that SCF-mediated proteolysis ofPLOS Genetics Cse4 is a major mechanism that prevents stable maintenance of Cse4 at non-centromericregions, thus ensuring faithful chromosome segregation. In summary, we have identifiedessential pathways that regulate cellular levels of endogenous Cse4 and shown that proteolysisof Cse4 by SCF-Met30/Cdc4 prevents mislocalization and CIN in unperturbed cells.Fil: Au, Wei-Chun. National Institutes of Health; Estados UnidosFil: Zhang, Tianyi. National Institutes of Health; Estados UnidosFil: Mishra, Prashant K.. National Institutes of Health; Estados UnidosFil: Eisenstatt, Jessica R.. National Institutes of Health; Estados UnidosFil: Walker, Robert L.. National Institutes of Health; Estados UnidosFil: Ocampo, Josefina. National Institutes of Health; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Dawson, Anthony. National Institutes of Health; Estados UnidosFil: Warren, Jack. National Institutes of Health; Estados UnidosFil: Costanzo, Michael. University of Toronto; CanadáFil: Baryshnikova, Anastasia. California Life Company; Estados UnidosFil: Flick, Karin. University of California; Estados UnidosFil: Clark, David J.. National Institutes of Health; Estados UnidosFil: Meltzer, Paul S.. National Institutes of Health; Estados UnidosFil: Baker, Richard E.. University of Massachussets; Estados UnidosFil: Myers, Chad. University of Minnesota; Estados UnidosFil: Boone, Charles. University of Toronto; CanadáFil: Kaiser, Peter. University of California; Estados UnidosFil: Basrai, Munira A.. National Institutes of Health; Estados Unido

Bone-targeting agents in major solid tumour metastases: a multinational cohort study

OBJECTIVE: To describe the epidemiology, clinical characteristics and utilisation patterns of bone-targeting agents (BTAs) in patients with bone metastases from breast, prostate and lung cancer. METHODS: This is a multinational retrospective cohort study including patients with three major solid tumours (breast, prostate and lung cancer) and newly initiated on BTAs (ie, denosumab, zoledronic acid and pamidronate). Records were retrieved from nationwide health databases from Hong Kong and Taiwan (HK and TW: 2013–2017) and Korea (KR: 2012–2016). Descriptive analyses included the annual incidence rates of bone metastases and the cumulative incidence curves of BTA initiation. We used Sankey diagrams to visualise the dynamic BTA utilisation patterns. RESULTS: The annual incidence rate of bone metastases ranged from 3.5% to 4.5% in TW, from 9.6% to 10.3% in HK and from 2.9% to 3.8% in KR. We identified 14.1% (5127), 9.3% (883) and 9.4% (4800) of patients with bone metastases newly initiated on BTAs in TW, HK and KR, respectively. The most frequently used BTA in TW (67.1%) and HK (51.9%) was denosumab, while in KR (84.8%) it was zoledronic acid. Sankey diagrams indicated the proportion of patients remaining on denosumab was highest in TW and HK, while it was zoledronic acid in KR. Specifically, in TW, patients who were on bisphosphonates or had discontinued treatment frequently switched to or reinitiated denosumab. CONCLUSIONS: We found the rate of BTA utilisation remained low across all sites and tumour types in recent years. The dynamic utilisation patterns of BTAs provide better understanding of the treatment landscape for future evaluation of associated outcomes of patients

Misregulation of Scm3p/HJURP Causes Chromosome Instability in Saccharomyces cerevisiae and Human Cells

The kinetochore (centromeric DNA and associated proteins) is a key determinant for high fidelity chromosome transmission. Evolutionarily conserved Scm3p is an essential component of centromeric chromatin and is required for assembly and function of kinetochores in humans, fission yeast, and budding yeast. Overexpression of HJURP, the mammalian homolog of budding yeast Scm3p, has been observed in lung and breast cancers and is associated with poor prognosis; however, the physiological relevance of these observations is not well understood. We overexpressed SCM3 and HJURP in Saccharomyces cerevisiae and HJURP in human cells and defined domains within Scm3p that mediate its chromosome loss phenotype. Our results showed that the overexpression of SCM3 (GALSCM3) or HJURP (GALHJURP) caused chromosome loss in a wild-type yeast strain, and overexpression of HJURP led to mitotic defects in human cells. GALSCM3 resulted in reduced viability in kinetochore mutants, premature separation of sister chromatids, and reduction in Cse4p and histone H4 at centromeres. Overexpression of CSE4 or histone H4 suppressed chromosome loss and restored levels of Cse4p at centromeres in GALSCM3 strains. Using mutant alleles of scm3, we identified a domain in the N-terminus of Scm3p that mediates its interaction with CEN DNA and determined that the chromosome loss phenotype of GALSCM3 is due to centromeric association of Scm3p devoid of Cse4p/H4. Furthermore, we determined that similar to other systems the centromeric association of Scm3p is cell cycle regulated. Our results show that altered stoichiometry of Scm3p/HJURP, Cse4p, and histone H4 lead to defects in chromosome segregation. We conclude that stringent regulation of HJURP and SCM3 expression are critical for genome stability