Project description:TET-family dioxygenases oxidize 5-methylcytosine (5mC) in DNA, and exert tumour suppressor activity in many types of cancers. Even in the absence of TET coding region mutations, TET loss-of-function is strongly associated with cancer. Here we show that acute elimination of TET function induces the rapid development of an aggressive, fully-penetrant and cell-autonomous myeloid leukaemia in mice, pointing to a causative role for TET loss-of-function in this myeloid malignancy. Phenotypic and transcriptional profiling shows aberrant differentiation of haematopoietic stem/progenitor cells, impaired erythroid and lymphoid differentiation and strong skewing to the myeloid lineage, with only a mild relation to changes in DNA modification. We also observe progressive accumulation of phospho-H2AX and strong impairment of DNA damage repair pathways, suggesting a key role for TET proteins in maintaining genome integrity.
Project description:To evaluate the DNA methylation in LSK cells from the bone marrow of wildtype or Tet2/3 DKO mice. In order to address the impact of the loss of Tet2/3 proteins in DNA methylation in LSK cells, we compared by WGBS the methylome of wild and, Tet2/3 DKO LSK cells in bone marrow.
Project description:TET-family dioxygenases oxidize 5-methylcytosine (5mC) in DNA, and exert tumor suppressor activity in many types of cancers. Even in the absence of TET coding region mutations, TET loss-of-function is strongly associated with cancer. We show that acute elimination of TET function induces the rapid development of an aggressive, fully-penetrant and cell-autonomous myeloid leukemia in mice, pointing to a causative role for TET-loss-of-function in this myeloid malignancy. Phenotypic and transcriptional profiling showed aberrant differentiation of hematopoietic stem/ progenitor cells, impaired erythroid and lymphoid differentiation and strong skewing to the myeloid lineage, with only a mild relation to changes in DNA modification. We also observed progressive accumulation of DNA damage and strong impairment of DNA break repair, suggesting a key role for TET proteins in maintaining genomic integrity.
Project description:TET family members (TETs) encode proteins that represent crucial factors in the active DNA demethylation pathway. Evidence has proved that TET2 mutation is associated with leukemogenesis, drug response, and prognosis in acute myeloid leukemia (AML). However, few studies revealed the TETs expression and its clinical significance in AML. We conducted a detailed expression and prognosis analysis of TETs expression in human AML cell lines and patients by using public databases. We observed that TETs expression especially TET2 and TET3 was closely associated with AML among various human cancers. TET1 expression was significantly reduced in AML patients, whereas TET2 and TET3 expression was significantly increased. Kaplan-Meier analysis showed that only TET3 expression was associated with overall survival (OS) and disease-free survival (DFS) among both total AML as well as non-M3 AML, and was confirmed by another independent cohort. Moreover, Cox regression analysis revealed that TET3 expression may act as an independent prognostic factor for OS and DFS in total AML. Interestingly, patients that received hematopoietic stem cell transplantation (HSCT) did not show significantly longer OS and DFS than those who did not receive HSCT in TET3 high-expressed groups; whereas, in TET3 low-expressed groups, patients that accepted HSCT showed significantly longer OS and DFS than those who did not accept HSCT. By bioinformatics analysis, TET3 expression was found positively correlated with tumor suppressor gene including CDKN2B, ZIC2, miR-196a, and negatively correlated with oncogenes such as PAX2 and IL2RA. Our study demonstrated that TETs showed significant expression differences in AML, and TET3 expression acted as a potential prognostic biomarker in AML, which may guide treatment choice between chemotherapy and HSCT.
Project description:Rab27 small GTPases regulate secretion and movement of lysosome-related organelles such as T cell cytolytic granules and platelet-dense granules. Previous studies indicated that Rab27a and Rab27b are expressed in the murine lung suggesting that they regulate secretory processes in the lung. Consistent with those studies, we found that Rab27a and Rab27b are expressed in cell types that contain secretory granules: alveolar epithelial type II (AEII) and Clara cells. We then used Rab27a/Rab27b double knockout (DKO) mice to examine the functional consequence of loss of Rab27 proteins in the murine lung. Light and electron microscopy revealed a number of morphological changes in lungs from DKO mice when compared with those in control animals. In aged DKO mice we observed atrophy of the bronchiolar and alveolar epithelium with reduction of cells numbers, thinning of the bronchiolar epithelium and alveolar walls, and enlargement of alveolar airspaces. In these samples we also observed increased numbers of activated foamy alveolar macrophages and granulocyte containing infiltrates together with reduction in the numbers of Clara cells and AEII cells compared with control. At the ultrastructural level we observed accumulation of cytoplasmic membranes and vesicles in Clara cells. Meanwhile, AEII cells in DKO accumulated large mature lamellar bodies and lacked immature/precursor lamellar bodies. We hypothesize that the morphological changes observed at the ultrastructural level in DKO samples result from secretory defects in AEII and Clara cells and that over time these defects lead to atrophy of the epithelium.
Project description:Cancer genomes are characterized by focal increases in DNA methylation, co-occurring with widespread hypomethylation. Here, we show that TET loss of function results in a similar genomic footprint. Both 5hmC in wild-type (WT) genomes and DNA hypermethylation in TET-deficient genomes are largely confined to the active euchromatic compartment, consistent with the known functions of TET proteins in DNA demethylation and the known distribution of 5hmC at transcribed genes and active enhancers. In contrast, an unexpected DNA hypomethylation noted in multiple TET-deficient genomes is primarily observed in the heterochromatin compartment. In a mouse model of T cell lymphoma driven by TET deficiency (Tet2/3 DKO T cells), genomic analysis of malignant T cells revealed DNA hypomethylation in the heterochromatic genomic compartment, as well as reactivation of repeat elements and enrichment for single-nucleotide alterations, primarily in heterochromatic regions of the genome. Moreover, hematopoietic stem/precursor cells (HSPCs) doubly deficient for Tet2 and Dnmt3a displayed greater losses of DNA methylation than HSPCs singly deficient for Tet2 or Dnmt3a alone, potentially explaining the unexpected synergy between DNMT3A and TET2 mutations in myeloid and lymphoid malignancies. Tet1-deficient cells showed decreased localization of DNMT3A in the heterochromatin compartment compared with WT cells, pointing to a functional interaction between TET and DNMT proteins and providing a potential explanation for the hypomethylation observed in TET-deficient genomes. Our data suggest that TET loss of function may at least partially underlie the characteristic pattern of global hypomethylation coupled to regional hypermethylation observed in diverse cancer genomes, and highlight the potential contribution of heterochromatin hypomethylation to oncogenesis.