NSMCE2 is an E3 SUMO-protein ligase component of the SMC5-SMC6 complex, which mediates DNA double-strand break repair by homologous recombination and regulates telomere maintenance. The complex promotes sister chr8 recombination by recruiting cohesin to double-strand breaks and is required for telomere maintenance via recombination in ALT cell lines through sumoylation of shelterin complex components. NSMCE2 facilitates recovery from replication fork stalling and is essential for sister chr8 cohesion during mitosis. Patho logically, hypomorphic NSMCE2 mutations cause primordial dwarfism with extreme insulin resistance and gonadal failure; cellular defects include increased micronucleus formation, delayed DNA synthesis recovery, and impaired BLM focus formation 1. The SUMO ligase activity is critical for this phenotype, as SUMO-ligase-deficient mutants fail to rescue dwarfism in zebrafish 1. Conversely, cancer-associated upregulation of NSMCE2—often driven by super-enhancer dysregulation—correlates with poor prognosis and chemotherapy resistance in breast cancer, particularly in triple-negative and HER2-positive tumors 2. In hepatocellular carcinoma, elevated NSMCE2 promotes tumor development by SUMOylating PPARα and activating the PPARα-CYP7A1 axis 3. Notably, a murine model shows that NSMCE2 deletion—but not SUMO-ligase mutation—leads to Bloom syndrome–like pathology and increased cancer/aging phenotypes, suggesting SUMO-independent functions 4. Recent evidence indicates TAK-981, a SUMO E1 inhibitor, suppresses SMC5/6-mediated HIV-1 latency establishment in CD4+ T cells 5, pointing to potential therapeutic targeting of NSMCE2's SUMOylation activity.