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) by E3 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.
Bibliographical noteFunding Information:
We gratefully acknowledge Sue Biggins for reagents, Kathy McKin-non of the National Cancer Institute Vaccine Branch FACS Core for assistance with FACS analysis, Inbal Gazy for plasmid construction, Sara Azeem for experimental assistance, and the members of the Basrai laboratory for helpful discussions and comments on the manuscript. MAB is supported by the NIH Intramural Research Program at the National Cancer Institute and DJC by the NIH Intramural Research Program at the National Institute of Child Health and Human Development. MW is funded by The Van Andel Institute. This research was also supported by grants from the National Institutes of Health to CLM (R01HG005084), to CB and CLM (R01HG005853), to CB and MC (R01HG005853), to RAS (R01GM35078) and from the Canadian Institute of Health Research to CB and MC (FDN-143264), and the Lewis-Sigler Fellowship to AB. CLM and CB are fellows in the Canadian Institute for Advanced Research (CIFAR, https://www.cifar.ca/) Genetic Networks Program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Copyright © 2020 Eisenstatt et al.