Ubiquitin-mediated DNA damage response is synthetic lethal with G-quadruplex stabilizer CX-5461.

CX-5461 is a G-quadruplex (G4) ligand currently in trials with initial indications of clinical activity in cancers with defects in homologous recombination repair. To identify more genetic defects that could sensitize tumors to CX-5461, we tested synthetic lethality for 480 DNA repair and genome maintenance genes to CX-5461, pyridostatin (PDS), a structurally unrelated G4-specific stabilizer, and BMH-21, which binds GC-rich DNA but not G4 structures. We identified multiple members of HRD, Fanconi Anemia pathways, and POLQ, a polymerase with a helicase domain important for G4 structure resolution. Significant synthetic lethality was observed with UBE2N and RNF168, key members of the DNA damage response associated ubiquitin signaling pathway. Loss-of-function of RNF168 and UBE2N resulted in significantly lower cell survival in the presence of CX-5461 and PDS but not BMH-21. RNF168 recruitment and histone ubiquitination increased with CX-5461 treatment, and nuclear ubiquitination response frequently co-localized with G4 structures. Pharmacological inhibition of UBE2N acted synergistically with CX-5461. In conclusion, we have uncovered novel genetic vulnerabilities to CX-5461 with potential significance for patient selection in future clinical trials.

Malt1 blocks IL-1ß production by macrophages in vitro and limits dextran sodium sulfate-induced intestinal inflammation in vivo.

This study tested the hypothesis that Malt1 deficiency in macrophages contributes to dextran sodium sulfate (DSS)-induced intestinal inflammation in Malt1-deficient mice. In people, combined immunodeficiency caused by a homozygous mutation in the MALT1 gene is associated with increased susceptibility to bacterial infections and chronic inflammation, including severe inflammation along the gastrointestinal tract. The consequences of Malt1 deficiency have largely been attributed to its role in lymphocytes, but Malt1 is also expressed in macrophages, where it is activated downstream of TLR4 and dectin-1. The effect of Malt1 deficiency in murine macrophages and its contribution to DSS-induced colitis have not been investigated. Our objectives were to compare the susceptibility of Malt1+/+ and Malt1-/- mice to DSS-induced colitis, to determine the contribution of macrophages to DSS-induced colitis in Malt1-/- mice, and to assess the effect of innate immune stimuli on Malt1-/- macrophage inflammatory responses. We found that Malt1 deficiency exacerbates DSS-induced colitis in mice, accompanied by higher levels of IL-1ß, and that macrophages and IL-1 signaling contribute to pathology in Malt1-/- mice. Malt1-/- macrophages produce more IL-1ß in response to either TLR4 or dectin-1 ligation, whereas inhibition of Malt1 proteolytic (paracaspase) activity blocked IL-1ß production. TLR4 or dectin-1 stimulation induced Malt1 protein levels but decreased its paracaspase activity. Taken together, these data support the hypothesis that Malt1-/- macrophages contribute to increased susceptibility of Malt1-/- mice to DSS-induced colitis, which is dependent on IL-1 signaling. Increased IL-1ß production by MALT1-deficient macrophages may also contribute to chronic inflammation in people deficient in MALT1.