H2A.Z histone variants facilitate HDACi-dependent removal of H3.3K27M mutant protein in pediatric high-grade glioma cells

Diffuse intrinsic pontine gliomas (DIPGs) are deadly pediatric brain tumors, non-resectable due to brainstem localization and diffusive growth. Over 80% of DIPGs harbor a mutation in histone 3 (H3.3 or H3.1) resulting in a lysine-to-methionine substitution (H3K27M). Patients with DIPG have a dismal prognosis with no effective therapy. We show that histone deacetylase (HDAC) inhibitors lead to a significant reduction in the H3.3K27M protein (up to 80%) in multiple glioma cell lines. We discover that the SB939-mediated H3.3K27M loss is partially blocked by a lysosomal inhibitor, chloroquine. The H3.3K27M loss is facilitated by co-occurrence of H2A.Z, as evidenced by the knockdown of H2A.Z isoforms. Chromatin immunoprecipitation sequencing (ChIP-seq) analysis confirms the occupancy of H3.3K27M and H2A.Z at the same SB939-inducible genes. We discover a mechanism showing that HDAC inhibition in DIPG leads to pharmacological modulation of the oncogenic H3.3K27M protein levels. These findings show the possibility of directly targeting the H3.3K27M oncohistone.

Trypanosoma cruzi infection changes the chromatin proteome profile of infected human cells

Chagas disease is endemic in 22 Latin American countries, with approximately 8 million individuals infected worldwide and 10,000 deaths yearly. Trypanosoma cruzi presents an intracellular life cycle in mammalian hosts to sustain infection. Parasite infection activates host cell responses, promoting an unbalance in reactive oxygen species (ROS) in the intracellular environment inducing genomic DNA lesions in the host cell during infection. To further understand changes in host cell chromatin induced by parasite infection, we investigated alterations in chromatin caused by infection by performing quantitative proteomic analysis. DNA Damage Repair proteins, such as Poly-ADP-ribose Polymerase 1 (PARP-1) and X-Ray Repair Cross Complementing 6 (XRRC6), were recruited to the chromatin during infection. Also, changes in chromatin remodeling enzymes suggest that parasite infection may shape the epigenome of the host cells. Interestingly, the abundance of oxidative phosphorylation mitochondrial and vesicle-mediated transport proteins increased in the host chromatin at the final stages of infection. In addition, Apoptosis-inducing Factor (AIF) is translocated to the host cell nucleus upon infection, suggesting that cells enter parthanatos type of death. Altogether, this study reveals how parasites interfere with the host cells' responses at the chromatin level leading to significant crosstalk that support and disseminate infection. SIGNIFICANCE: The present study provides novel insights into the effects of Trypanosoma cruzi on the chromatin from the host cell. This manuscript investigated proteomic alterations in chromatin caused by parasite infection at early and late infection phases by performing a quantitative proteomic analysis. In this study, we revealed that parasites interfere with DNA metabolism in the early and late stages of infection. We identified that proteins related to DNA damage repair, oxidative phosphorylation, and vesicle-mediated transport have increased abundance at the host chromatin. Additionally, we have observed that Apoptosis-inducing Factor is translocated to the host cell nucleus upon infection, suggesting that the parasites could lead the cells to enter Parthanatos as a form of programmed cell death. The findings improve our understanding on how the parasites modulate the host cell chromatin to disseminate infection. In this study, we suggest a mechanistic parasite action towards host nucleus that could be used to indicate targets for future treatments.

A Carbohydrate Moiety of Secreted Stage-Specific Glycoprotein 4 Participates in Host Cell Invasion by Trypanosoma cruzi Extracellular Amastigotes

Trypanosoma cruzi is the etiologic agent of Chagas' disease. It is known that amastigotes derived from trypomastigotes in the extracellular milieu are infective in vitro and in vivo. Extracellular amastigotes (EAs) have a stage-specific surface antigen called Ssp-4, a GPI-anchored glycoprotein that is secreted by the parasites. By immunoprecipitation with the Ssp-4-specific monoclonal antibodies (mAb) 2C2 and 1D9, we isolated the glycoprotein from EAs. By mass spectrometry, we identified the core protein of Ssp-4 and evaluated mRNA expression and the presence of Ssp-4 carbohydrate epitopes recognized by mAb1D9. We demonstrated that the carbohydrate epitope recognized by mAb1D9 could promote host cell invasion by EAs. Although infectious EAs express lower amounts of Ssp-4 compared with less-infectious EAs (at the mRNA and protein levels), it is the glycosylation of Ssp-4 (identified by mAb1D9 staining only in infectious strains and recognized by galectin-3 on host cells) that is the determinant of EA invasion of host cells. Furthermore, Ssp-4 is secreted by EAs, either free or associated with parasite vesicles, and can participate in host-cell interactions. The results presented here describe the possible role of a carbohydrate moiety of T. cruzi surface glycoproteins in host cell invasion by EA forms, highlighting the potential of these moieties as therapeutic and vaccine targets for the treatment of Chagas' disease.