Chronic Mcm10 deficiency causes defects in telomere maintenance in human cells

Minichromosome maintenance protein 10 (Mcm10) is essential for eukaryotic DNA replication initiation and fork stability. Recently, a compound heterozygous MCM10 mutation was identified in a patient who presented with natural killer (NK) cell deficiency. To understand the mechanism of disease, we modeled this mutation in human cell lines. We demonstrate that Mcm10 deficiency causes chronic replication stress that reduces cell viability due to increased genomic instability and telomere maintenance defects. Our data suggests that Mcm10 deficiency constrains telomerase-dependent telomere extension. This limitation can be overcome by increasing telomerase activity, although defects in telomere replication persist. We propose that stalled replication forks in Mcm10-deficient cells arrest terminally, especially within hard-to-replicate regions, and require nuclease processing involving Mus81, as MCM10:MUS81 double mutants displayed decreased viability and accelerated telomere erosion. Our results reveal that Mcm10 is critical for telomere replication and provide insights into how MCM10 mutations cause NK cell deficiency.