Suv39h-Mediated Histone H3 Lysine 9 Methylation Directs DNA Methylation to Major Satellite Repeats at Pericentric Heterochromatin

AbstractBackground: Histone H3 lysine 9 (H3-K9) methylation and DNA methylation are characteristic hallmarks of mammalian heterochromatin. H3-K9 methylation was recently shown to be a prerequisite for DNA methylation in Neurospora crassa and Arabidopsis thaliana. Currently, it is unknown whether a similar dependence exists in mammalian organisms.Results: Here, we demonstrate a physical and functional link between the Suv39h-HP1 histone methylation system and DNA methyltransferase 3b (Dnmt3b) in mammals. Whereas in wild-type cells Dnmt3b interacts with HP1α and is concentrated at heterochromatic foci, it fails to localize to these regions in Suv39h double null (dn) mouse embryonic stem (ES) cells. Consistently, the Suv39h dn ES cells display an altered DNA methylation profile at pericentric satellite repeats, but not at other repeat sequences. In contrast, H3-K9 trimethylation at pericentric heterochromatin is not impaired in Dnmt1 single- or Dnmt3a/Dnmt3b double-deficient ES cells. We also show that pericentric heterochromatin is not transcriptionally inert and can give rise to transcripts spanning the major satellite repeats.Conclusions: These data demonstrate an evolutionarily conserved pathway between histone H3-K9 methylation and DNA methylation in mammals. While the Suv39h HMTases are required to direct H3-K9 trimethylation and Dnmt3b-dependent DNA methylation at pericentric repeats, DNA methylation at centromeric repeats occurs independent of Suv39h function. Thus, our data also indicate a more complex interrelatedness between histone and DNA methylation systems in mammals. Both methylation systems are likely to be important in reinforcing the stability of heterochromatic subdomains and thereby in protecting genome integrity

In vivo characterization of the lysine-methyltransferases Set7/9 and G9a by conditional mutagenesis in the mouse

Increasing evidence suggests that site-specific lysine methylation of histone and non-histone proteins is fundamentally involved in epigenetic regulation of gene expression during cellular differentiation and tumorigenesis. To study the in vivo relevance of the lysine methyltransferases Set7/9 and G9a, I have generated and characterized two conditional knockout mouse strains. Despite its widely proposed role in transcriptional activation through the methylation of histone H3 lysine 4 (H3K4) and a number of transcription factors, I found that Set7/9 knockout mice develop normally and do not display any overt phenotypic alteration. Since Set7/9 was shown to methylate the tumor suppressor protein p53 and was suggested to be important for its activity, I mainly focused my characterization of the Set7/9 knockout strain towards the proposed impairment of p53 function in these mice. Contrary to all reports, I found that in the absence of Set7/9, the p53 target genes p21WAF¹/CIP¹, Mdm2, Puma and Bax are normally expressed under basal and stressed conditions in different cell types. As a consequence, no functional p53 impairment was detectable upon DNA damage or in response to ectopic oncogene expression in Set7/9⁻/⁻ cells. Hence, my data demonstrates that Set7/9-mediated methylation of p53 represents, if at all, only a minor event in its regulation and does not appreciably control p53 activity in vivo. In the generated conditional G9a knockout strain, I primarily focused my efforts towards describing its role in the hematopoietic system. Mice that conditionally lack G9a expression in the blood, develop normally and can sustain the development of all hematopoietic cell types under homeostatic conditions. Interestingly however, when performing competitive bone marrow transplantation assays, I detected a marked impairment in G9a knockout bone marrow cells in the reconstitution of the hematopoietic system. Consistently, G9a-deficient myeloid and erythroid progenitors are dramatically reduced in their proliferation capacity. My experiments indicate for the first time, that G9a is specifically important for the biology of hematopoietic stem and progenitor cells under stress conditions and its inactivation might represent a promising way to interfere with blood development in pathological and regenerative settings.Medicine, Faculty ofMedicine, Department ofExperimental Medicine, Division ofGraduat

EPCR expression marks UM171-expanded CD34 cord blood stem cells.

A small subset of human cord blood CD34 cells express endothelial protein C receptor (EPCR/CD201/PROCR) when exposed to the hematopoietic stem cell (HSC) self-renewal agonist UM171. In this article, we show that EPCR-positive UM171-treated cells, as opposed to EPCR-negative cells, exhibit robust multilineage repopulation and serial reconstitution ability in immunocompromised mice. In contrast to other stem cell markers, such as CD38, EPCR expression is maintained when cells are introduced in culture, irrespective of UM171 treatment. Although engineered overexpression of EPCR fails to reproduce the effects of UM171 on HSC activity, its expression is required for the repopulating activity of human HSCs. Altogether, our results indicate that EPCR is a reliable and cell culture-compatible marker of UM171-expanded human cord blood HSCs

UBAP2L is amplified in a large subset of human lung adenocarcinoma and is critical for epithelial lung cell identity and tumor metastasis

International audienceThe ubiquitin-associated protein 2-like (UBAP2L) gene remains poorly studied in human and mouse development. UBAP2L interacts with the Polycomb group protein B lymphoma Mo-MLV insertion region 1 homolog (BMI1) and determines the activity of mouse hematopoietic stem cells in vivo Here we show that loss of Ubap2l leads to disorganized respiratory epithelium of mutant neonates, which die of respiratory failure. We also show that UBAP2L overexpression leads to epithelial-mesenchymal transition-like phenotype in a non-small cell lung carcinoma (NSCLC) cell line. UBAP2L is amplified in 15% of human primary lung adenocarcinoma specimens. Such patients express higher levels of UBAP2L and show a reduction in survival when compared with those who do not have this gene amplification. Supporting a possible role for UBAP2L in lung tumor progression, NSCLC cells engineered to express low levels of this gene produce much smaller tumors in vivo than wild-type control cells. Together, these results suggest that UBAP2L contributes to epithelial lung cell identity in mice and that it plays an important role in human lung adenocarcinoma.-Aucagne, R., Girard, S., Mayotte, N., Lehnertz, B., Lopes-Paciencia, S., Gendron, P., Boucher, G., Chagraoui, J., Sauvageau, G. UBAP2L is amplified in a large subset of human lung adenocarcinoma and is critical for epithelial lung cell identity and tumor metastasis

UM171 induces a homeostatic inflammatory-detoxification response supporting human HSC self-renewal.

Elucidation of the molecular cues required to balance adult stem cell self-renewal and differentiation is critical for advancing cellular therapies. Herein, we report that the hematopoietic stem cell (HSC) self-renewal agonist UM171 triggers a balanced pro- and anti-inflammatory/detoxification network that relies on NFKB activation and protein C receptor-dependent ROS detoxification, respectively. We demonstrate that within this network, EPCR serves as a critical protective component as its deletion hypersensitizes primitive hematopoietic cells to pro-inflammatory signals and ROS accumulation resulting in compromised stem cell function. Conversely, abrogation of the pro-inflammatory activity of UM171 through treatment with dexamethasone, cAMP elevating agents or NFkB inhibitors abolishes EPCR upregulation and HSC expansion. Together, these results show that UM171 stimulates ex vivo HSC expansion by establishing a critical balance between key pro- and anti-inflammatory mediators of self-renewal

Hyaluronic acid-GPRC5C signalling promotes dormancy in haematopoietic stem cells

Altres ajuts: The Behrens-Weise-Foundation, the German Research Foundation (DFG) under the German Excellence Strategy (CIBSS-EXC-2189, project ID 390939984), SFB1425 (Project #422681845), SFB992 (Project #192904750; B07), SFB1479 (P05); Wellcome-MRC Cambridge Stem Cell Institute (203151/Z/16/Z)Bone marrow haematopoietic stem cells (HSCs) are vital for lifelong maintenance of healthy haematopoiesis. In inbred mice housed in gnotobiotic facilities, the top of the haematopoietic hierarchy is occupied by dormant HSCs, which reversibly exit quiescence during stress. Whether HSC dormancy exists in humans remains debatable. Here, using single-cell RNA sequencing, we show a continuous landscape of highly purified human bone marrow HSCs displaying varying degrees of dormancy. We identify the orphan receptor GPRC5C, which enriches for dormant human HSCs. GPRC5C is also essential for HSC function, as demonstrated by genetic loss- and gain-of-function analyses. Through structural modelling and biochemical assays, we show that hyaluronic acid, a bone marrow extracellular matrix component, preserves dormancy through GPRC5C. We identify the hyaluronic acid-GPRC5C signalling axis controlling the state of dormancy in mouse and human HSCs

GPRC5C drives branched-chain amino acid metabolism in leukemogenesis

Altres ajuts: Jose Carreras Leukämie-StiftungLeukemia stem cells (LSCs) share numerous features with healthy hematopoietic stem cells (HSCs). G-protein coupled receptor family C group 5 member C (GPRC5C) is a regulator of HSC dormancy. However, GPRC5C functionality in acute myeloid leukemia (AML) is yet to be determined. Within patient AML cohorts, high GPRC5C levels correlated with poorer survival. Ectopic Gprc5c expression increased AML aggression through the activation of NF-κB, which resulted in an altered metabolic state with increased levels of intracellular branched-chain amino acids (BCAAs). This onco-metabolic profile was reversed upon loss of Gprc5c, which also abrogated the leukemia-initiating potential. Targeting the BCAA transporter SLC7A5 with JPH203 inhibited oxidative phosphorylation and elicited strong antileukemia effects, specifically in mouse and patient AML samples while sparing healthy bone marrow cells. This antileukemia effect was strengthened in the presence of venetoclax and azacitidine. Our results indicate that the GPRC5C-NF-κB-SLC7A5-BCAAs axis is a therapeutic target that can compromise leukemia stem cell function in AML