Drug-induced cleavage of DNA by topoisomerase II mediates the formation of chromosomal translocation breakpoints in mitoxantrone-related APL and in APL that occurs after therapy with other topoisomerase II poisons.

c Toxoplasma gondii transmission between intermediate hosts is dependent on the ingestion of walled cysts formed during the chronic phase of infection. Immediately following consumption, the parasite must ensure survival of the host by preventing adverse inflammatory responses and/or by limiting its own replication. Since the Toxoplasma secreted effectors rhoptry 16 kinase (ROP16) and dense granule 15 (GRA15) activate the JAK-STAT3/6 and NF-B signaling pathways, respectively, we explored whether a particular combination of these effectors impacted intestinal inflammation and parasite survival in vivo. Here we report that expression of the STAT-activating version of ROP16 in the type II strain (strain II؉ROP16 I ) promotes host resistance to oral infection only in the context of endogenous GRA15 expression. Protection was characterized by a lower intestinal parasite burden and dampened inflammation. Host resistance to the II؉ROP16 I strain occurred independently of STAT6 and the T cell coinhibitory receptors B7-DC and B7-H1, two receptors that are upregulated by ROP16. In addition, coexpression of ROP16 and GRA15 enhanced parasite susceptibility within tumor necrosis factor alpha/gamma interferon-stimulated macrophages in a STAT3/6-independent manner. Transcriptional profiling of infected STAT3-and STAT6-deficient macrophages and parasitized Peyer's patches from mice orally challenged with strain II؉ROP16 I suggested that ROP16 activated STAT5 to modulate host gene expression. Consistent with this supposition, the ROP16 kinase induced the sustained phosphorylation and nuclear localization of STAT5 in Toxoplasma-infected cells. In summary, only the combined expression of both GRA15 and ROP16 promoted host resistance to acute oral infection, and Toxoplasma may possibly target the STAT5 signaling pathway to generate protective immunity in the gut.

Few t(9;11) translocations in DNA topoisomerase II inhibitor-related leukemias have been studied in detail and the DNA damage mechanism remains controversial. We characterized the der(11) and der(9) genomic breakpoint junctions in a case of AML following etoposide and doxorubicin. Etoposide-, etoposide metabolite- and doxorubicin-induced DNA topoisomerase II cleavage was examined in normal homologues of the MLL and AF-9 breakpoint sequences using an in vitro assay. Induction of DNA topoisomerase II cleavage complexes in CEM and K562 cell lines was investigated using an in vivo complex of enzyme assay. The translocation occurred between identical 5'-TATTA-3' sequences in MLL intron 8 and AF-9 intron 5 without the gain or loss of bases. The 5'-TATTA-3' sequences were reciprocally cleaved by DNA topoisomerase II in the presence of etoposide, etoposide catechol or etoposide quinone, creating homologous 4-base 5' overhangs that would anneal to form both breakpoint junctions without any processing. der(11) and der(4) translocation breakpoints in a treatment-related ALL at the same site in MLL are consistent with a damage hotspot. Etoposide and both etoposide metabolites induced DNA topoisomerase II cleavage complexes in the hematopoietic cell lines. These results favor the model in which the chromosomal breakage leading to MLL translocations in DNA topoisomerase II inhibitor-related leukemias is a consequence of DNA topoisomerase II cleavage.

Summary The innate and adaptive immune responses that confer resistance to the intracellular pathogen Toxoplasma gondii critically depend on IL-12 production, which drives interferon-γ (IFN-γ) expression. Certain cytokines can activate STAT3 and limit IL-12 production to prevent infection-associated immune pathology but T.gondii also directly activates STAT3 to evade host immunity. We show that Suppressor of Cytokine Signaling molecule 3 (SOCS3), a target of STAT3 which limits signaling by the pleiotropic cytokine IL-6, is upregulated in response to infection but is dispensable for the immune-inhibitory effects of T. gondii. Unexpectedly, mice with targeted deletion of SOCS3 in macrophages and neutrophils have reduced IL-12 responses and succumb to toxoplasmosis. Anti–IL-6 administration or IL-12 treatment blocked disease susceptibility suggesting that in the absence of SOCS3, macrophages are hypersensitive to the anti-inflammatory properties of IL-6. Thus, SOCS3 has a critical role in suppressing IL-6 signals and promoting immune responses to control T. gondii infection.