JunB Protects against Myeloid Malignancies by Limiting Hematopoietic Stem Cell Proliferation and Differentiation without Affecting Self-Renewal

Abstract

SUMMARY Loss of the JunB/AP-1 transcription factor induces a myeloproliferative disease (MPD) arising from the hematopoietic stem cell (HSC) compartment. Now we show that JunB inactivation deregulates the cell cycle machinery and increases the proliferation of long-term repopulating HSCs (LT-HSCs) without impairing their self-renewal or regenerative potential in vivo. We found that JunB loss destabilizes a complex network of genes and pathways that normally limit myeloid differentiation, leading to impaired responsiveness to both Notch and TGF-β signaling due, in part, to transcriptional deregulation of the Hes1 gene. These results demonstrate that LT-HSC proliferation and differentiation are uncoupled from self-renewal, and establish some of the mechanisms by which JunB normally limits the production of myeloid progenitors hence preventing initiation of myeloid malignancies.

Mixed-lineage-leukemia (MLL) fusion protein collaborates with Ras to induce acute leukemia through aberrant Hox expression and Raf activation

“…Meanwhile, the BM progenitors transduced with Hoxa9 and NRAS G12V seemed to result in engraftment failure under sublethal conditioning, but these rapidly developed myeloid malignancy under lethal conditioning. A recent study using BM transplantation showed the possibility of drastic fluctuation in the engraftment of donor cells receiving pathological modification under sublethal conditioning; 41 hence, our unsuccessful results under sublethal conditioning might be associated with some instability of the transplantation.…”

Invasive breast cancer reprograms early myeloid differentiation in the bone marrow to generate immunosuppressive neutrophils

“…Cells were passed through a 70-μm filter, RBCs were lysed, and then cells were resuspended at 1:1 with a total of 3 × 10 6 cells/100 μL in SM. Congenic recipient mice (CD45.1 WT C57BL/6) were irradiated using a cesium source irradiator with a lethal dose (9 Gy) delivered in two doses (4.5 Gy) 3 h apart and were given antibiotic-containing water (1.l g/L neomycin sulfate and 10 U/L of polymyxin B sulfate) for 4 wk after irradiation as described previously (64).…”

“…Cells were blocked with rat IgG (10 μg/mL; Sigma) for at least 20 min on ice, washed with staining media [2% (vol/vol) HI, FBS in HBSS (BSS) without Ca 2+ or Mg 2+ , denoted SM], and then stained with fluorescently conjugated antibodies in SM for 30 min on ice, unless stated otherwise. For evaluation of MPs and HSPCs in BM and spleen, cells were stained as previously described (64). In brief, a six-step staining procedure was used that included the following combinations of antibodies: (i) mixture of unconjugated rat antibodies to lineage specific markers (B220, CD3, CD4, CD5, CD8, CD11b, Ter119, Gr1); (ii) fluorescentlytagged (PE-Cy5 or PE-Cy5.5) anti-rat secondary antibody; (iii) rat IgG (as described above) to block nonspecific binding; (iv) mixture of biotin-or fluorophore-conjugated antibodies to c-Kit, Sca-1, FcγR, and CD34 (for staining MPs) or c-Kit, Sca-1, Flk2, CD48, and CD150 (for staining HSPCs); (v) streptavidin conjugated to a fluorophore; and (vi) propidium iodide to identify live and dead cells.…”

Cell cycle regulation in hematopoietic stem cells

“…These data may also help explain why SCF and TPO are associated with HSC quiescence and not proliferation in vivo, as factors such as TGF- that are present in the BM niche may prevent activation of Akt by these cytokines. Furthermore, TGF- also collaborates with Notch ligands to induce expression of p21 Cip via a mechanism involving the transcription factors junB and Hes1 (Yu et al, 2006;Santaguida et al, 2009). Mice deficient in the transcription factor Smad4, which interacts with TGF-R-activated Smad2/3, express lower levels of Notch1 but the effect of Smad4 deficiency on HSC cell cycle activity has not yet been directly studied (Karlsson et al, 2007).…”