The mammalian meiosis-specific KASH protein KASH5 connects the telomere-associated SUN1 protein to the cytoplasmic force–generating mechanism involved in meiotic chromosome movement.

The DNA damage response (DDR) and DNA repair are critical for maintaining genomic stability and evading many human diseases. Recent findings indicate that accumulation of SUN1, a nuclear envelope (NE) protein, is a significant pathogenic event in Emery-Dreifuss muscular dystrophy and Hutchinson-Gilford progeria syndrome, both caused by mutations in LMNA. However, roles of mammalian SUN proteins in mitotic cell division and genomic stability are unknown. Here we report that the inner NE proteins SUN1 and SUN2 may play a redundant role in DDR. Mouse embryonic fibroblasts from Sun1(-/-)Sun2(-/-) mice displayed premature proliferation arrest in S phase of cell cycle, increased apoptosis and DNA damage, and decreased perinuclear heterochromatin, indicating genome instability. Furthermore, activation of ATM and H2A.X, early events in DDR, were impaired in Sun1(-/-)Sun2(-/-) fibroblasts. A biochemical screen identified interactions between SUN1 and SUN2 and DNA-dependent protein kinase (DNAPK) complex that functions in DNA nonhomologous end joining repair and possibly in DDR. Knockdown of DNAPK reduced ATM activation in NIH 3T3 cells, consistent with a potential role of SUN1- and SUN2-DNAPK interaction during DDR. SUN1 and SUN2 could affect DDR by localizing certain nuclear factors to the NE or by mediating communication between nuclear and cytoplasmic events.

Highlights d A genome-wide CRISPR screen identifies regulators and components of the NMD pathway d ABCE1 is required for NMD and other forms of 3ʹ UTRmediated regulation d Upon ABCE1 loss, ribosomes move into 3ʹ UTRs and displace bound regulators d Iron deficiency and oxidative stress impair ABCE1 and posttranscriptional control

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