DNA damage repair kinase DNA‐PK and cGAS synergize to induce cancer‐related inflammation in glioblastoma

Abstract

Cytosolic DNA promotes inflammatory responses upon detection by the cyclic GMP-AMP (cGAMP) synthase (cGAS). It has been suggested that cGAS downregulation is an immune escape strategy harnessed by tumor cells. Here, we used glioblastoma cells that show undetectable cGAS levels to address if alternative DNA detection pathways can promote pro-inflammatory signaling. We show that the DNA-PK DNA repair complex (i) drives cGAS-independent IRF3-mediated type I Interferon responses and (ii) that its catalytic activity is required for cGAS-dependent cGAMP production and optimal downstream signaling. We further show that the cooperation between DNA-PK and cGAS favors the expression of chemokines that promote macrophage recruitment in the tumor microenvironment in a glioblastoma model, a process that impairs early tumorigenesis but correlates with poor outcome in glioblastoma patients. Thus, our study supports that cGAS-dependent signaling is acquired during tumorigenesis and that cGAS and DNA-PK activities should be analyzed concertedly to predict the impact of strategies aiming to boost tumor immunogenicity.

Harnessing the cooperation between DNA‐PK and cGAS in cancer therapies

“…Knowing the non-canonical functions of cGAS and cGAMP, such compounds may have interesting properties and have distinct target and off-target profiles as compared to STING agonists. cGAS inhibitors may be beneficial in contexts where cGAS signalling drives tumour progression [11,86] (Figure 2). Several small molecules have been reported as potential human cGAS inhibitors.…”

“…This is notably the case of DEAD-Box Helicase 41 (DDX41), [8] interferon gamma inducible protein (IFI16) [9] and the DNA-dependent protein kinase (DNA-PK). [10,11] DNA-PK is a holoenzyme comprised of the KU70 and KU80 proteins, essential for the recruitment of the DNA-PK catalytic subunit (DNA-PKcs) to free ends of dsDNAs. [12,13] The major function of DNA-PK is in the repair of double stand breaks (DSBs), genomic DNA lesions, by facilitating non-homologous end joining (NHEJ).…”

“…[11,18] Mechanistically, dsDNA transfection or genotoxic stress-associated accumulation of dsDNA in the cytosol lead to cytosolic re-localisation and DNA binding of the DNA-PK complex, followed by DNA-PKcs activation as attested by S2056autophosphorylation. [11] In conditions in which both cGAS and DNA-PK are expressed, DNA-PKcs-dependent phosphorylation of cGAS at residue S435 strongly enhances cGAS-mediated production of cGAMP and downstream signalling in response to dsDNA transfection and genotoxic stress [11] (Figure 3). DNA-PKcs-dependent cGAS phosphorylation may be counteracted by the protein phosphatase 6C (PPP6C) that has been shown to regulate the S435 site.…”

“…DNA-PK-cGAS cooperation may be particularly important for cGAS-STING-mediated sensing of endogenous DNA in absence of infection and at early time points. [11] In contrast, several reports indicate that DNA-PK can counteract cGAS-mediated dsDNA sensing in response to Herpes simplex virus 1 (HSV-1) DNA virus infection and at late time points after stimulation. [80,81] In that context, DNA-PKcs has been proposed to phosphorylate cGAS at residues T68 and S213 and to thereby inhibit cGAS-STING signalling [80] (Figure 3).…”

“…This is the case for instance of esophageal adenocarcinoma, [100] renal cell carcinoma, [101] nasopharyngeal carcinoma [102] and non-small cell lung cancer. [103] Moreover, PRKDC/DNA-PKcs expression positively correlates with tumour grade in glioma, [11] colorectal carcinoma and nasopharyngeal carcinoma. [102] It is believed that under normal growth conditions DNA-PKcs acts as a tumour suppressor, for instance by modulating p53 functions, or by maintaining genome integrity.…”