Analysis of mechanisms involved in the prevention of gamma irradiation-induced apoptosis by hGM-CSF

Chemically inducible split protein regulators for mammalian cells

Chemically inducible systems represent valuable synthetic biology tools that enable the external control of biological processes. However, their translation to therapeutic applications has been limited because of unfavorable ligand characteristics or the immunogenicity of xenogeneic protein domains. To address these issues, we present a strategy for engineering inducible split protein regulators (INSPIRE) in which ligand-binding proteins of human origin are split into two fragments that reassemble in the presence of a cognate physiological ligand or clinically approved drug. We show that the INSPIRE platform can be used for dynamic, orthogonal and multiplex control of gene expression in mammalian cells. Furthermore, we demonstrate the functionality of a glucocorticoid-responsive INSPIRE platform in vivo and apply it for perturbing an endogenous regulatory network. INSPIRE presents a generalizable approach toward designing small-molecule responsive systems that can be implemented for the construction of new sensors, regulatory networks and therapeutic applications.

Chemical development of intracellular protein heterodimerizers

Cell activation initiated by receptor ligands or oncogenes triggers complex and convoluted intracellular signaling. Techniques initiating signals at defined starting points and cellular locations are attractive to elucidate the output of selected pathways. Here, we present the development and validation of a protein heterodimerization system based on small molecules cross-linking fusion proteins derived from HaloTags and SNAP-tags. Chemical dimerizers of HaloTag and SNAP-tag (HaXS) show excellent selectivity and have been optimized for intracellular reactivity. HaXS force protein-protein interactions and can translocate proteins to various cellular compartments. Due to the covalent nature of the HaloTag-HaXS-SNAP-tag complex, intracellular dimerization can be easily monitored. First applications include protein targeting to cytoskeleton, to the plasma membrane, to lysosomes, the initiation of the PI3K/mTOR pathway, and multiplexed protein complex formation in combination with the rapamycin dimerization system.

JAK2(V617F) negatively regulates p53 stabilization by enhancing MDM2 via La expression in myeloproliferative neoplasms

JAK2(V617F) is a gain of function mutation that promotes cytokine-independent growth of myeloid cells and accounts for a majority of myeloproliferative neoplasms (MPN). Mutations in p53 are rarely found in these diseases before acute leukemia transformation, but this does not rule out a role for p53 deregulation in disease progression. Using Ba/F3-EPOR cells and ex vivo cultured CD34(+) cells from MPN patients, we demonstrate that expression of JAK2(V617F) affected the p53 response to DNA damage. We show that E3 ubiquitin ligase MDM2 accumulated in these cells, due to an increased translation of MDM2 mRNA. Accumulation of the La autoantigen, which interacts with MDM2 mRNA and promotes its translation, was responsible for the increase in MDM2 protein level and the subsequent degradation of p53 after DNA damage. Downregulation of La protein or cell treatment with nutlin-3, a MDM2 antagonist, restored the p53 response to DNA damage and the cytokine-dependence of Ba/F3-EPOR-JAK2(V617F) cells. Altogether, these data indicate that the JAK2(V617F) mutation affects p53 response to DNA damage through the upregulation of La antigen and accumulation of MDM2. They also suggest that p53 functional inactivation accounts for the cytokine hypersensitivity of JAK2(V617F) MPN and might have a role in disease progression.

Design and Applications of Bifunctional Small Molecules: Why Two Heads Are Better Than One

Induction of protein--protein interactions is a daunting challenge, but recent studies show promise for small molecules that specifically bring two or more protein molecules together for enhanced or novel biological effect. The first such bifunctional molecules were the rapamycin- and FK506-based "chemical inducers of dimerization", but the field has since expanded with new molecules and new applications in chemical genetics and cell biology. Examples include coumermycin-mediated gyrase B dimerization, proteolysis targeting chimeric molecules (PROTACs), drug hybrids, and strategies for exploiting multivalency in toxin binding and antibody recruitment. This Review discusses these and other advances in the design and use of bifunctional small molecules and potential strategies for future systems.

CpG-oligodeoxynucleotide protects immune cells from gamma-irradiation-induced cell death

Synthetic oligodeoxynucleotides (CpG-ODNs) and bacterial DNA containing unmethylated CpG dinucleotides in the context of particular base sequences (CpG motifs) are known to inhibit anti-IgM-induced growth arrest and apoptosis of WHEI 231 B lymphocytes, and spontaneous apoptosis of mature spleen B cells in a sequence-specific fashion of the CpG-ODN. Here we report that CpG-ODN protects from the cell death induced by gamma-irradiation of primary mouse spleen cells as well as mouse RAW 264.7 macrophage cells and human RPMI 8226 B cells. Experimental results showed that CpG-ODN promotes growth of the cells, and protects the cells from gamma-irradiation-induced cell death accompanying Bcl-xS/L and Bcl-2 upregulation. Furthermore, survival of macrophages was enhanced when splenocytes were pretreated with CpG-ODN. Our results suggest the potential application of CpG-ODNs for more efficient cancer radiotherapy by enhancing survival of normal immune cells after radiation damage.

GATA-1 Converts Lymphoid and Myelomonocytic Progenitors into the Megakaryocyte/Erythrocyte Lineages

GATA-1 is an essential transcription factor for megakaryocyte and erythrocyte (MegE) development. Here we show that hematopoietic progenitors can be reprogrammed by the instructive action of GATA-1. Enforced expression of GATA-1 in hematopoietic stem cells led to loss of self-renewal activity and the exclusive generation of MegE lineages. Strikingly, ectopic GATA-1 reprogrammed common lymphoid progenitors as well as granulocyte/monocyte (GM) progenitors to differentiate into MegE lineages, while inhibiting normal lymphoid or GM differentiation. GATA-1 upregulated critical MegE-related transcription factors such as FOG-1 and GATA-2 in lymphoid and GM progenitors, and their MegE development did not require "permissive" erythropoietin signals. Furthermore, GATA-1 induced apoptosis of proB and myelomonocytic cells, which could not be prevented by enforced permissive Bcl-2 or myeloid cytokine signals. Thus, GATA-1 specifically instructs MegE commitment while excluding other fate outcomes in stem and progenitor cells, suggesting that regulation of GATA-1 is critical in maintaining multilineage homeostasis.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) induces antiapoptotic and proapoptotic signals in acute myeloid leukemia

High levels of cytokines are associated with a poor prognosis in acute myeloid leukemia (AML). However, cytokines may induce, on one hand, survival factor expression and cell proliferation and, on the other hand, expression of inhibitory signals such as up-regulation of suppressors of cytokine signaling (SOCS) and induce apoptotic cell death. Because blasts from patients with AML express high procaspase protein levels, we asked whether granulocyte-macrophage colony-stimulating factor (GM-CSF) enhances procaspase protein production in AML cells. In the GM-CSF-responsive OCIM2 AML cell line, GM-CSF induced signal transducer and activator of transcription 5 (Stat 5) phosphorylation, up-regulated cyclin D2, and stimulated cell cycle progression. Concurrently, GM-CSF stimulated expression of SOCS-2 and -3 and of procaspases 2 and 3 and induced caspase 3 activation, poly(ADP[adenosine 5'-diphosphate]-ribose) polymerase (PARP) cleavage, and apoptotic cell death. The Janus kinase (Jak)-Stat inhibitor AG490 abrogated GM-CSF-induced expression of procaspase 3 and activation of caspase 3. Under the same conditions GM-CSF up-regulated production of BAX as well as Bcl-2, Bcl-XL, survivin, and XIAP. GM-CSF also increased procaspase 3 protein levels in OCI/AML3 and Mo7e cells, suggesting that this phenomenon is not restricted to a single leukemia cell line. Our data suggest that GM-CSF exerts a dual effect: it stimulates cell division but contemporaneously up-regulates Jak-Stat-dependent proapoptotic proteins. Up-regulation of procaspase levels in AML is thus a beacon for an ongoing growth-stimulatory signal.

Enforced granulocyte/macrophage colony-stimulating factor signals do not support lymphopoiesis, but instruct lymphoid to myelomonocytic lineage conversion

We evaluated the effects of ectopic granulocyte/macrophage colony-stimulating factor (GM-CSF) signals on hematopoietic commitment and differentiation. Lineage-restricted progenitors purified from mice with the ubiquitous transgenic human GM-CSF receptor (hGM-CSFR) were used for the analysis. In cultures with hGM-CSF alone, hGM-CSFR-expressing (hGM-CSFR+) granulocyte/monocyte progenitors (GMPs) and megakaryocyte/erythrocyte progenitors (MEPs) exclusively gave rise to granulocyte/monocyte (GM) and megakaryocyte/erythroid (MegE) colonies, respectively, providing formal proof that GM-CSF signals support the GM and MegE lineage differentiation without affecting the physiological myeloid fate. hGM-CSFR transgenic mice were crossed with mice deficient in interleukin (IL)-7, an essential cytokine for T and B cell development. Administration of hGM-CSF in these mice could not restore T or B lymphopoiesis, indicating that enforced GM-CSF signals cannot substitute for IL-7 to promote lymphopoiesis. Strikingly, >50% hGM-CSFR+ common lymphoid progenitors (CLPs) and >20% hGM-CSFR+ pro-T cells gave rise to granulocyte, monocyte, and/or myeloid dendritic cells, but not MegE lineage cells in the presence of hGM-CSF. Injection of hGM-CSF into mice transplanted with hGM-CSFR+ CLPs blocked their lymphoid differentiation, but induced development of GM cells in vivo. Thus, hGM-CSF transduces permissive signals for myeloerythroid differentiation, whereas it transmits potent instructive signals for the GM differentiation to CLPs and early T cell progenitors. These data suggest that a majority of CLPs and a fraction of pro-T cells possess plasticity for myelomonocytic differentiation that can be activated by ectopic GM-CSF signals, supporting the hypothesis that the down-regulation of GM-CSFR is a critical event in producing cells with a lymphoid-restricted lineage potential.

Antiapoptotic effect of interferon-alpha on hepatic stellate cells (HSC): a novel pathway of IFN-alpha signal transduction via Janus kinase 2 (JAK2) and caspase-8

The hepatic stellate cell (HSC), the pericyte of the liver sinusoids belongs to the mesenchymal cells of the liver. Damaging noxae induce a transformation from the quiescent (vitamin A-storing cell) to the activated (connective tissue-producing cell) state. The balance between proapoptotic and surviving factors decides about the fate of the activated HSC. Interferon-alpha (IFN-alpha) has been shown to elicit antiproliferative and/or antifibrogenic effects in various cell types of mesenchymal origin. We therefore investigated the effect of IFN-alpha on primary cultured rat HSC in their quiescent (day 2) and activated state (day 7). IFN-alpha significantly inhibited spontaneous apoptosis in activated HSC in vitro and simultaneously inhibited cell cycle progression by inducing a G1 arrest. The effect of IFN-a is not accompanied by a modulation of CD95, CD95L, p53, p21(WAF1), p27, bcl-2, bcl-xL, bax, NFkappaB, or IkappaB gene expression. Surprisingly, the IFN-alpha effect could be abolished completely by blocking JAK2 activity or JAK2 translation. The downregulating effect of IFN-alpha on the activity of caspase-8 and caspase-3 could also be neutralized using tyrphostin AG490 or JAK-2 antisense. Taken together IFN-alpha inhibits apoptosis of activated HSC by activation of JAK2 which inhibits the caspase-8 apoptosis pathway.

Evidence of a possible epigenetic inactivation mechanism operating on a region of mouse chromosome 19 in γ-radiation-induced thymic lymphomas

Loss of heterozygosity (LOH) analysis, performed in 68 gamma-radiation-induced primary thymic lymphomas of F1 hybrid mice, provided evidence of significant LOH on chromosome 19 in a region defined by the D19Mit106 (22 cM) and D19Mit100 (27 cM) markers (Thymic Lymphoma Suppressor Region 8, TLSR8). Cd95 and Pten, two genes mapped at this region, were inactivated in a vast majority of these tumors (85.3% for Cd95 and 61.8% for Pten). Moreover, altered expression of Cd95 and Pten occurred concomitantly in 34 of 68 (50%) thymic lymphomas suggesting a coordinated mechanism of inactivation of these genes. Surprisingly, we also found that Jak2, a proto-oncogene located between Cd95 and Pten, was simultaneously inactivated in a significant fraction of the tumors analysed (24 of 34, 70.6%). Taken together these findings and the lack of mutations in the coding sequences of the mentioned genes clearly suggest a possible regional epigenetic inactivation mechanism on mouse chromosome 19 operating during the development of these tumors.