About 10% of cancer cells employ the "alternative lengthening of telomeres" (ALT) pathway instead of reactivating the hTERT subunit of human telomerase. The hTR RNA subunit is also abnormally silenced in some ALT + cells not expressing hTERT, suggesting a possible negative non-canonical impact of hTR on ALT. Indeed, we show that ectopically expressed hTR reduces phosphorylation of ssDNA-binding protein RPA (p-RPA S33) at ALT telomeres by promoting the hnRNPA1-and DNA-PK-dependent depletion of RPA. The resulting defective ATR checkpoint signaling at telomeres impairs recruitment of the homologous recombination protein, RAD51. This induces ALT telomere fragility, increases POLD3-dependent C-circle production, and promotes the recruitment of the DNA damage marker 53BP1. In ALT + cells that naturally retain hTR expression, NHP2 H/ACA ribonucleoprotein levels are downregulated, likely in order to restrain DNA damage response (DDR) activation at telomeres through reduced 53BP1 recruitment. This unexpected role of NHP2 is independent from hTR's non-canonical function in modulating telomeric p-RPA S33. Collectively, our study shines new light on the interference between telomerase-and ALT-dependent pathways and unravels a crucial role for hTR and NHP2 in DDR regulation at ALT telomeres.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.