Histone Variant H3.3 Mediates DNA Repair and cGAS-STING Pathway Activation in Telomere Dysfunction

Abstract

The telomere damage response is a critical mechanism that regulates cellular senescence. Deprotected telomeres activate the cytosolic DNA sensing cGAS-STING pathway, leading to cellular senescence. Our previous studies revealed that extrachromosomal telomere repeats (ECTRs) activate the cGAS-STING pathway, and this process is attenuated by histone H3.3 depletion. However, the role of histone H3.3 in telomere deprotection-dependent cGAS-STING pathway activation remains unclear. Here, we discover that histone H3.3 is required for cGAS-STING pathway activation in cells with deprotected telomeres. Expression of the TRF2 dominant-negative mutant, TRF2{Delta}B{Delta}M, induces telomere dysfunction in fibroblast cells, triggering cGAS-STING pathway activation and growth inhibition. Histone H3.3 depletion significantly reduces this activation, highlighting its critical role in linking telomere deprotection to the cGAS-STING-mediated innate immune signaling. Furthermore, we assess the role of histone H3.3 in telomere fusion. Our findings reveal that histone H3.3 regulates cGAS-STING signaling by controlling telomere fusion. Additionally, depletion of histone H3.3 chaperones, including ATRX, DAXX, and HIRA, inhibits telomere fusion and cGAS-STING pathway activation, underscoring the role of histone H3.3 in telomere maintenance and the DNA damage response. Collectively, our study establishes histone H3.3 as a key regulator of telomere fusion and telomere dysfunction-induced cGAS-STING pathway activation, emphasizing the importance of this pathway in cellular senescence.