TDRD3 is an antiviral restriction factor that promotes IFN signaling with G3BP1.

Stress granules (SGs) are highly dynamic cytoplasmic foci that form in response to activation of the integrated stress response (ISR) that results in eIF2α phosphorylation and global translation shutdown. Stress granules, which are largely nucleated by G3BP1, serve as hubs for mRNA triage, but there is mounting evidence that they also perform cell signaling functions that are vital to cell survival, particularly during viral infection. We previously showed that SG formation leads to NFκB activation and JNK signaling and that this association may be due in part to G3BP1-dependent recruitment of PKR to SGs. Others have reported close associations between G3BP1 and various innate immune PRRs of the type 1 interferon signaling system, including RIG-I. We also reported SG assembly dynamics is dependent on the arginine-methylation status of G3BP1. Another protein that rapidly localizes to SGs, TDRD3, is a methyl reader protein that performs transcriptional activation and adaptor functions within the nucleus, but neither the mechanism nor its function in SGs is clear. Here, we present evidence that TDRD3 localizes to SGs partly based upon methylation potential of G3BP1. We also characterize granules that TDRD3 forms during overexpression and show that these granules can form in the absence of G3BP but also contain translation components found in canonical SGs. We also show for the first time that SGs recruit additional interferon effectors IRF3, IRF7, TBK1, and Sting, and provide evidence that TDRD3 may play a role in recruitment of these factors. We also present evidence that TDRD3 is a novel antiviral protein that is cleaved by enteroviral 2A proteinase. G3BP1 and TDRD3 knockdown in cells results in altered transcriptional regulation of numerous IFN effectors in complex modulatory patterns that are distinctive for G3BP1 and TDRD3. Overall, we describe a novel role of TDRD3 in innate immunity in which G3BP1 and TDRD3 may coordinate to play important roles in regulation of innate antiviral defenses.

Combination therapy with atorvastatin and celecoxib delays tumor formation in a Fanconi anemia mouse model.

BACKGROUND: Fanconi anemia is an inherited bone marrow failure disorder associated with a high incidence of leukemia and solid tumors. Currently, no interventions to prevent or delay the formation of solid tumors are available. PROCEDURE: Two of the most important hallmarks of Fanconi anemia are inflammation and oxidative stress. In this study, we administrated the antioxidant atorvastatin and the anti-inflammatory drug celecoxib to cohorts of Fancd2-/- /Trp53+/- mice, a model of Fanconi anemia. Treatment started at weaning and continued until the mice developed a palpable mass or suffered from >20% weight loss. Tumor samples and selected tissues were subjected to histopathological examination. χ2 test was performed to analyze tumor incidence, and Kaplan-Meier survival curves were evaluated with log-rank test. In addition, a small cohort of mice was monitored for the safety of the drugs. RESULTS: The combined oral administration of both drugs significantly delayed tumor onset in Fancd2-/- /Trp53+/- mice. Specifically, the treatment delayed the onset of ovarian tumors in Fancd2-/- /Trp53+/- mice and increased the mean ovarian tumor-free survival time by 17%, whereas this combinatorial drug regimen did not have a significant effect on other tumor types. In addition, no detrimental effects on hematopoiesis from the drug treatment were observed during a 12-month safety monitoring. CONCLUSIONS: The data presented here suggest that a combination of atorvastatin and celecoxib may be a good candidate for chemoprevention in Fanconi anemia.

Metformin improves defective hematopoiesis and delays tumor formation in Fanconi anemia mice.

Fanconi anemia (FA) is an inherited bone marrow failure disorder associated with a high incidence of leukemia and solid tumors. Bone marrow transplantation is currently the only curative therapy for the hematopoietic complications of this disorder. However, long-term morbidity and mortality remain very high, and new therapeutics are badly needed. Here we show that the widely used diabetes drug metformin improves hematopoiesis and delays tumor formation in Fancd2-/- mice. Metformin is the first compound reported to improve both of these FA phenotypes. Importantly, the beneficial effects are specific to FA mice and are not seen in the wild-type controls. In this preclinical model of FA, metformin outperformed the current standard of care, oxymetholone, by improving peripheral blood counts in Fancd2-/- mice significantly faster. Metformin increased the size of the hematopoietic stem cell compartment and enhanced quiescence in hematopoietic stem and progenitor cells. In tumor-prone Fancd2-/-Trp53+/- mice, metformin delayed the onset of tumors and significantly extended the tumor-free survival time. In addition, we found that metformin and the structurally related compound aminoguanidine reduced DNA damage and ameliorated spontaneous chromosome breakage and radials in human FA patient-derived cells. Our results also indicate that aldehyde detoxification might be one of the mechanisms by which metformin reduces DNA damage in FA cells.

The Sirt1 activator SRT3025 expands hematopoietic stem and progenitor cells and improves hematopoiesis in Fanconi anemia mice.

Fanconi anemia is a genetic bone marrow failure syndrome. The current treatment options are suboptimal and do not prevent the eventual onset of aplastic anemia requiring bone marrow transplantation. We previously showed that resveratrol, an antioxidant and an activator of the protein deacetylase Sirt1, enhanced hematopoiesis in Fancd2 mutant mice and improved the impaired stem cell quiescence observed in this disease. Given that Sirt1 is important for the function of hematopoietic stem cells, we hypothesized that Sirt1 activation may improve hematopoiesis. Indeed, Fancd2(-/-) mice and wild-type mice treated with the selective Sirt1 activator SRT3025 had increased numbers of hematopoietic stem and progenitor cells, platelets and white blood cells. SRT3025 was also protective against acetaldehyde-induced hematopoietic damage. Unlike resveratrol, however, SRT3025 did not affect stem cell quiescence, suggesting distinct mechanisms of action. Conditional deletion of Sirt1 in hematopoietic cells did not abrogate the beneficial effects of SRT3025, indicating that the drug did not act by directly stimulating Sirt1 in stem cells, but must be acting indirectly via extra-hematopoietic effects. RNA-Seq transcriptome analysis revealed the down-regulation of Egr1-p21 expression, providing a potential mechanism for improved hematopoiesis. Overall, our data indicate that SRT3025 or related compounds may be beneficial in Fanconi anemia and other bone marrow failure syndromes.

Oxymetholone therapy of fanconi anemia suppresses osteopontin transcription and induces hematopoietic stem cell cycling.

Androgens are widely used for treating Fanconi anemia (FA) and other human bone marrow failure syndromes, but their mode of action remains incompletely understood. Aged Fancd2(-/-) mice were used to assess the therapeutic efficacy of oxymetholone (OXM) and its mechanism of action. Eighteen-month-old Fancd2(-/-) mice recapitulated key human FA phenotypes, including reduced bone marrow cellularity, red cell macrocytosis, and peripheral pancytopenia. As in humans, chronic OXM treatment significantly improved these hematological parameters and stimulated the proliferation of hematopoietic stem and progenitor cells. RNA-Seq analysis implicated downregulation of osteopontin as an important potential mechanism for the drug's action. Consistent with the increased stem cell proliferation, competitive repopulation assays demonstrated that chronic OXM therapy eventually resulted in stem cell exhaustion. These results expand our knowledge of the regulation of hematopoietic stem cell proliferation and have direct clinical implications for the treatment of bone marrow failure.

Evaluation of resveratrol and N-acetylcysteine for cancer chemoprevention in a Fanconi anemia murine model.

Fanconi anemia (FA) patients suffer from progressive bone marrow failure and often develop cancers. Previous studies showed that antioxidants tempol and resveratrol (RV) delayed tumor onset and reduced hematologic defects in FA murine models, respectively. Here we tested whether antioxidants N-acetylcysteine (NAC) or RV could delay cancer in tumor prone Fancd2(-/-) /Trp53(+/-) mice. Unlike tempol, neither compound had any significant chemopreventive effect in this model. We conclude that not all anti-oxidants are chemopreventive in FA. In addition, when given to Fancd2(-/-) mice, NAC helped maintain Fancd2(-/-) KSL cells in quiescence while tempol did not. The mechanisms behind the different actions of these antioxidants await further investigation.