Telomere occupancy by TRF2 is altered by KIT mutations and correlates with mastocytosis regression.

Mastocytosis, a clonal disorder characterized by the accumulation of mast cells in various tissues, affects both adults and children. Adults frequently exhibit KIT activating mutations, usually in the phospho-transferase domain (PTD KIT mutations). Our previous findings revealed that children also harbor oncogenic KIT activating mutations, but more commonly within the extra-cellular domain (non-PTD KIT mutations). While the disease persists chronically in adults, it often regresses spontaneously in children through an unknown mechanism. Here, we report that tumor senescence in childhood mastocytosis may be triggered by significantly shortened telomeres in mast cells harboring non-PTD KIT mutations compared to those with PTD KIT mutations. In vitro models further demonstrated a senescent phenotype associated with shorter telomeres for the non-PTD KIT mutant compared to the PTD KIT mutant. Mechanistically, we found that telomere shortening in mast cells from children with non-PTD KIT mutations is linked with increased p38 MAP-kinase activation, resulting in lower TRF2 occupancy on telomeres. Thus, non-PTD KIT mutations trigger distinct signaling pathways leading to telomere shortening and cellular senescence, providing mechanistic insights into the differing outcomes between childhood- and adult-onset mastocytosis.