Compromised nuclear envelope integrity drives TREX1-dependent DNA damage and tumor cell invasion

Although mutations leading to a compromised nuclear envelope cause diseases such as muscular dystrophies or accelerated aging, the consequences of mechanically induced nuclear envelope ruptures are less known. Here, we show that nuclear envelope ruptures induce DNA damage that promotes senescence in non-transformed cells and induces an invasive phenotype in human breast cancer cells. We find that the endoplasmic reticulum (ER)-associated exonuclease TREX1 translocates into the nucleus after nuclear envelope rupture and is required to induce DNA damage. Inside the mammary duct, cellular crowding leads to nuclear envelope ruptures that generate TREX1-dependent DNA damage, thereby driving the progression of in situ carcinoma to the invasive stage. DNA damage and nuclear envelope rupture markers were also enriched at the invasive edge of human tumors. We propose that DNA damage in mechanically challenged nuclei could affect the pathophysiology of crowded tissues by modulating proliferation and extracellular matrix degradation of normal and transformed cells.

Bloom syndrome protein restrains innate immune sensing of micronuclei by cGAS

Cellular innate immune sensors of DNA are essential for host defense against invading pathogens. However, the presence of self-DNA inside cells poses a risk of triggering unchecked immune responses. The mechanisms limiting induction of inflammation by self-DNA are poorly understood. BLM RecQ-like helicase is essential for genome integrity and is deficient in Bloom syndrome (BS), a rare genetic disease characterized by genome instability, accumulation of micronuclei, susceptibility to cancer, and immunodeficiency. Here, we show that BLM-deficient fibroblasts show constitutive up-regulation of inflammatory interferon-stimulated gene (ISG) expression, which is mediated by the cGAS-STING-IRF3 cytosolic DNA-sensing pathway. Increased DNA damage or down-regulation of the cytoplasmic exonuclease TREX1 enhances ISG expression in BLM-deficient fibroblasts. cGAS-containing cytoplasmic micronuclei are increased in BS cells. Finally, BS patients demonstrate elevated ISG expression in peripheral blood. These results reveal that BLM limits ISG induction, thus connecting DNA damage to cellular innate immune response, which may contribute to human pathogenesis.

Challenging the Roles of NSP3 and Untranslated Regions in Rotavirus mRNA Translation

Rotavirus NSP3 is a translational surrogate of the PABP-poly(A) complex for rotavirus mRNAs. To further explore the effects of NSP3 and untranslated regions (UTRs) on rotavirus mRNAs translation, we used a quantitative in vivo assay with simultaneous cytoplasmic NSP3 expression (wild-type or deletion mutant) and electroporated rotavirus-like and standard synthetic mRNAs. This assay shows that the last four GACC nucleotides of viral mRNA are essential for efficient translation and that both the NSP3 eIF4G- and RNA-binding domains are required. We also show efficient translation of rotavirus-like mRNAs even with a 5’UTR as short as 5 nucleotides, while more than eleven nucleotides are required for the 3’UTR. Despite the weak requirement for a long 5’UTR, a good AUG environment remains a requirement for rotavirus mRNAs translation.

Identification of mutations in the genome of rotavirus SA11 temperature-sensitive mutants D, H, I and J by whole genome sequences analysis and assignment of tsI to gene 7 encoding NSP3

The complete coding sequences of the four unassigned temperature-sensitive (ts) Baylor prototype rotavirus mutants (SA11ts D, H, I and J) were sequenced by deep sequencing double-stranded RNA using RNA-seq. Non-silent mutations were assigned to a specific mutant by Sanger sequencing RT-PCR products from each mutant. Mutations that led to amino acid changes were found in all genes except for genes 1 (VP1), 10 (NSP4) and 11 (NSP5/6). Based on these sequence analyses and earlier genetic analyses, the ts mutations in gene 7, which encodes the protein NSP3, were assigned to ts mutant groups I and H, and confirmed by an in vitro RNA-binding assay with recombinant proteins. In addition, ts mutations in gene 6 were assigned to tsJ. The presence of non-conservative mutations in two genes of two mutants (genes 4 and 2 in tsD and genes 3 and 7 in tsH) underscores the necessity of sequencing the whole genome of each rotavirus ts mutant prototype.