Deposition of onco-histone H3.3-G34W leads to DNA repair deficiency and activates cGAS/STING-mediated immune responses

Mutations in histone H3.3-encoding genes causing mutant histone tails are associated with specific cancers such as pediatric glioblastomas (H3.3-G34R/V) and giant cell tumor of the bone (H3.3-G34W). The mechanisms by which these mutations promote malignancy are not completely understood. Here we show that cells expressing H3.3-G34W exhibit DNA double-strand breaks (DSBs) repair defects and increased cellular sensitivity to ionizing radiation. Mechanistically, H3.3-G34W can be deposited to damaged chromatin, but in contrast to wild-type H3.3, does not interact with non-homologous end-joining (NHEJ) key effectors KU70/80 and XRCC4 leading to NHEJ deficiency. As a consequence H3.3-G34W cells displayed an accumulation of micronuclei and cytosolic DNA, which led to activation of the cyclic GMP–AMP synthase/stimulator of interferon genes (cGAS/STING) pathway, thereby inducing release of immunestimulatory cytokines. These findings suggest a potential for radiotherapy for tumors expressing H3.3- G34W, which can be further improved by combination with STING agonists to induce immune-mediated therapeutic efficacy.