Evidence for a role of RUNX1 as recombinase cofactor for TCRß rearrangements and pathological deletions in ETV6-RUNX1 ALL.

T-cell receptor gene beta (TCRß) gene rearrangement represents a complex, tightly regulated molecular mechanism involving excision, deletion and recombination of DNA during T-cell development. RUNX1, a well-known transcription factor for T-cell differentiation, has recently been described to act in addition as a recombinase cofactor for TCRδ gene rearrangements. In this work we employed a RUNX1 knock-out mouse model and demonstrate by deep TCRß sequencing, immunostaining and chromatin immunoprecipitation that RUNX1 binds to the initiation site of TCRß rearrangement and its homozygous inactivation induces severe structural changes of the rearranged TCRß gene, whereas heterozygous inactivation has almost no impact. To compare the mouse model results to the situation in Acute Lymphoblastic Leukemia (ALL) we analyzed TCRß gene rearrangements in T-ALL samples harboring heterozygous Runx1 mutations. Comparable to the Runx1+/- mouse model, heterozygous Runx1 mutations in T-ALL patients displayed no detectable impact on TCRß rearrangements. Furthermore, we reanalyzed published sequence data from recurrent deletion borders of ALL patients carrying an ETV6-RUNX1 translocation. RUNX1 motifs were significantly overrepresented at the deletion ends arguing for a role of RUNX1 in the deletion mechanism. Collectively, our data imply a role of RUNX1 as recombinase cofactor for both physiological and aberrant deletions.

SHIP1, but not an AML-derived SHIP1 mutant, suppresses myeloid leukemia growth in a xenotransplantation mouse model.

Constitutive activation of the PI3K/AKT signaling pathway is found in ~50-70% of AML patients. The SH2-containing inositol 5-phosphatase 1 (SHIP1) is a negative regulator of PI3K/AKT signaling in hematopoietic cells. SHIP1 knockout mice develop a myeloproliferative syndrome and concomitant deletion of SHIP1 and the tumor suppressor PTEN leads to the development of lethal B-cell lymphomas. In the study presented here, we investigated the role of SHIP1 as a tumor suppressor in myeloid leukemia cells in an in vivo xenograft transplantation model. NSG Mice transplanted with UKE-1 cells derived from a secondary AML showed a significantly extended lifespan after lentiviral-mediated overexpression of SHIP1 in comparison to the vector control cohort. In contrast, the AML-derived SHIP1Y643H mutant, which has a strongly reduced enzymatic activity showed a significant reversion of the SHIP1-induced prolongation of the survival time. In addition, the analysis of 290 AML patients revealed a correlation between expression of SHIP1 and overall survival of the AML patients. These results indicate that SHIP1 can act as a tumor suppressor in acute myeloid leukemia cells and that higher SHIP1 expression is associated with prolonged overall survival in AML patients. SHIP1 may be an interesting candidate for gene therapy.

Silencing AML1-ETO gene expression leads to simultaneous activation of both pro-apoptotic and proliferation signaling.

The t(8;21)(q22;q22) rearrangement represents the most common chromosomal translocation in acute myeloid leukemia (AML). It results in a transcript encoding for the fusion protein AML1-ETO (AE) with transcription factor activity. AE is considered to be an attractive target for treating t(8;21) leukemia. However, AE expression alone is insufficient to cause transformation, and thus the potential of such therapy remains unclear. Several genes are deregulated in AML cells, including KIT that encodes a tyrosine kinase receptor. Here, we show that AML cells transduced with short hairpin RNA vector targeting AE mRNAs have a dramatic decrease in growth rate that is caused by induction of apoptosis and deregulation of the cell cycle. A reduction in KIT mRNA levels was also observed in AE-silenced cells, but silencing KIT expression reduced cell growth but did not induce apoptosis. Transcription profiling of cells that escape cell death revealed activation of a number of signaling pathways involved in cell survival and proliferation. In particular, we find that the extracellular signal-regulated kinase 2 (ERK2; also known as mitogen-activated protein kinase 1 (MAPK1)) protein could mediate activation of 23 out of 29 (79%) of these upregulated pathways and thus may be regarded as the key player in establishing the t(8;21)-positive leukemic cells resistant to AE suppression.

[Universal modular system for in vitro screening of potential inhibitors of HIV-1 replication].

Here we describe a system based on recombinant lentiviral vectors for the safe screening of potential anti-HIV drugs. The system allows to evaluate the sensitivity of HIVl-1 reverse transcriptase and integrase (wild-type as well as mutant forms of these enzymes detected in drug-resistant virus isolates) towards different drugs and substances, but also to screen inhibitors of other stages of HIV-1 life cycle.

[Expression of FLT3-ITD oncogene confers mice progenitor B-cells BAF3 sensitivity to the ribonuclease binase cytotoxic action].

Acute myeloid leukemia is the most common acute leukemia affecting adults, and its incidence increases with age. Along with chromosomal translocations in leukemic cells mutations in the genes of receptor tyrosine kinases KIT and FLT3 were found with a high frequency. Here we show that transgenic progenitor of B-cells BAF3/FLT3-ITD are much more sensitive to the ribonuclease binase cytotoxic effects than the original BAF3 cells. The principal difference between BAF3/FLT3-ITD and the original BAF3 cells is the expression of FLT3-ITD oncogene, which leads to a change in the normal cell signaling pathways. Earlier, we described a similar effect for the cytotoxic action of binase on Kasumi-1 and FDC-P1-N822K cells, which express the activated KIT-N822K oncogene. Increased binase cytotoxicity toward the cells, expressing FLT3-ITD oncogene, suggests that, as in the case of FDC-P1 cells, transduced by KIT oncogene, the expression of an activated oncogene determines the sensitivity of cells to binase.

[Replication-competent γ-retrovirus Mo-MuLV expressing green fluorescent protein gene as an efficient tool for screening of inhibitors of retroviruses that use heparan sulfate as the primary cell receptor].

The effect of sulfated polysaccharides on the efficiency of infection of mouse embryonic fibroblast cell lines SC-1 and NIH-3T3 by replication-competent recombinant Moloney murine leukemia virus (Mo-MuLV) carrying the eGFP gene was investigated. It was shown that used polysaccharides have no cytostatic and cytotoxic effects on SC-1 and NIH 3T3 cells inthe concentrations from 0.01 to 100 µg/ml and have virucidal activity against Mo-MuLV. Polysaccharides in the indicated concentrations inhibit cell infection by Mo-MuLV, that prevents further expansion of viral infection. It was detected that sulfated polysaccharides are effective inhibitors of other retroviruses, including lentiviruses, that use heparan sulfate as cell receptors for non-specific binding.

Screening of Potential HIV-1 Inhibitors/Replication Blockers Using Secure Lentiviral in Vitro System.

The development and usage of safe cell systems for testing agents which possess anti-HIV activity is a very important factor in the design of new drugs. We have described in detail a system we designed that is based on lentiviral vectors (Prokofjeva et. al.,Antiviral Therapy,in print) for swift and completely safe screening of potential HIV-1 replication inhibitors. The system enables one to test the efficiency of the inhibitory activity of compounds whose action is directed towards either wild-type HIV-1 reverse transcriptase or integrase, or mutant enzymes corresponding to the drug-resistant virus form. Testing results of a number of already known drugs, which correlate well with published data as well as data on newly synthesized compounds, were obtained. Application of this system substantially broadens the possibilities of preclinical anti-HIV drugs testing.

[Modulation of activated oncogene c-kit expression with RNA-interference].

Hyperexpression of oncogene c-kit is found in 80% patients with acute myeloid leukemia (AML). The transgenic model cell line expressing the oncogene c-kit was obtained by transduction with recombinant retrovirus. We have designed small interfering RNAs (siRNA) efficiently suppressing the expression of activated oncogene c-kit. Further small hairpin RNAs (shRNA) targeting c-kit mRNA were designed and expressed in lentiviral vectors. We report a stable reduction in c-kit expression following the introduction of shRNAs into model cells as well as Kasumi-1 cells from the patient with AML.

[Downregulation of activated leukemic oncogenes AML1-ETO and RUNX1(K83N) expression with RNA-interference].

In the present study we have applied the siRNA approach for substantial reduction of AML1-ETO and RUNX1 (K83N) expression, which are frequently found in the leukemic cells. We have designed small hairpin RNAs (shRNA) for targeting AML1-ETO oncogene and a region close to the 5'-untranslated region of mRNA for the mutant RUNX1 (K83N) oncogene and expressed the shRNAs in lentiviral vectors. We report a stable reduction in expression of the oncogenes following the introduction of shRNAs into cells.

RUNX1 and its fusion oncoprotein derivative, RUNX1-ETO, induce senescence-like growth arrest independently of replicative stress.

A role for the RUNX genes in cancer fail-safe processes has been suggested by their induction of senescence-like growth arrest in primary murine fibroblasts and the failure of RAS-induced senescence in Runx2-deficient cells. We now show that RUNX1 induces senescence in human primary fibroblasts. High-affinity DNA binding is necessary but not sufficient, as shown by the functional attenuation of the truncated RUNX1/AML1a isoform and the TEL-RUNX1 fusion oncoprotein. However, a similar phenotype was potently induced by the RUNX1-ETO (AML1-ETO) oncoprotein, despite its dominant-negative potential. A detailed comparison of H-RAS(V12), RUNX1 and RUNX1-ETO senescent phenotypes showed that the RUNX effectors induce earlier growth stasis with only low levels of DNA damage signaling and a lack of chromatin condensation, a marker of irreversible growth arrest. In human fibroblasts, all effectors induced p53 in the absence of detectable p14(Arf), whereas only RUNX1-ETO induced senescence in p16(Ink4a)-null cells. Correlation was noted between induction of p53, reactive oxygen species and phospho-p38, whereas p38(MAPK) inhibition rescued cell growth markedly. These findings indicate a role for replication-independent pathways in RUNX and RUNX1-ETO senescence, and show that the context-specific oncogenic activity of RUNX1 fusion proteins is mirrored in their distinctive interactions with fail-safe responses.

Reduced proliferation of CD34(+) cells from patients with acute myeloid leukemia after gene transfer of INPP5D.

Acute myeloid leukemia (AML) is a malignant disease characterized by deregulated proliferation of immature myeloid cells. Constitutive activation of the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway is frequently detected in approximately 50-70% of AML patients. The gene INPP5D encodes the SH2-containing inositol 5-phosphatase 1 (SHIP1), which is a negative regulator of PI3K/AKT signaling. After lentiviral-mediated gene transfer of INPP5D into CD34(+) cells derived from AML patients (n=12) the granulocyte macrophage-colony stimulating factor (GM-CSF)-dependent proliferation was reduced in all samples analyzed (average 86%; range 72-93%). An enzymatically inactive form of SHIP1 (D672A) had no effect. In addition, SHIP1 reduced the autonomous proliferation of CD34(+) cells from a patient with a secondary AML who had a very high peripheral blast count (300 x 10(9) l(-1)). These data show that SHIP1 can effectively block GM-CSF-dependent and autonomous proliferation of AML cells.

Murine endogenous retroviruses.

Up to 10% of the mouse genome is comprised of endogenous retrovirus (ERV) sequences, and most represent the remains of ancient germ line infections. Our knowledge of the three distinct classes of ERVs is inversely correlated with their copy number, and their characterization has benefited from the availability of divergent wild mouse species and subspecies, and from ongoing analysis of the Mus genome sequence. In contrast to human ERVs, which are nearly all extinct, active mouse ERVs can still be found in all three ERV classes. The distribution and diversity of ERVs has been shaped by host-virus interactions over the course of evolution, but ERVs have also been pivotal in shaping the mouse genome by altering host genes through insertional mutagenesis, by adding novel regulatory and coding sequences, and by their co-option by host cells as retroviral resistance genes. We review mechanisms by which an adaptive coexistence has evolved. (Part of a multi-author review).

Mutations in the catalytic subunit of class IA PI3K confer leukemogenic potential to hematopoietic cells.

Constitutive activation of the phosphoinositide 3-kinase (PI3K)-AKT pathway is observed in up to 70% of acute myelogenous leukemia. To investigate the relevance of an intrinsic PI3K-AKT pathway activation in hematopoietic malignancies, we analysed the effect of point mutations in the catalytic (p110alpha) and regulatory (p85alpha) subunit of class IA PI3K. We demonstrated that mutations in the helical (E542K, E545A) and kinase domain (H1047R) of p110alpha constitutively activate the PI3K-AKT pathway and lead to factor-independent growth of early hematopoietic cells. Proliferation and survival of the cells were inhibited in a time- and dose-dependent manner using either PI3K or AKT inhibitors. The mammalian target of rapamycin (mTOR) was demonstrated to be important for mitogenic, but not antiapoptotic signaling of mutant p110alpha. In a syngenic mouse model, hematopoietic cells expressing mutated p110alpha induced a leukemia-like disease characterized by anemia, neoplastic infiltration of hematopoietic organs and 90% mortality within 5 weeks, whereas activated mutants of the receptor tyrosine kinase c-KIT led to 100% mortality within 10 days. Our data show that point mutations in the p110alpha subunit of class IA PI3K confer factor independence to hematopoietic cells in vitro and leukemogenic potential in vivo, but have lower transforming activity than a deregulated class III receptor tyrosine kinase.

Acceleration of chronic myeloproliferation by enforced expression of Meis1 or Meis3 in Icsbp-deficient bone marrow cells.

Identifying genetic pathways that cooperate in leukemogenesis facilitates our understanding of the molecular mechanisms at play. Interferon consensus sequence-binding protein (ICSBP) is a tumor suppressor, whose downregulation cooperates with BCR-ABL and NUP98-TOP1 gene products to accelerate leukemia induction in mouse models. Similarly, Meis1 synergizes with HoxA9 or NUP98-HOX (but not NUP98-TOP1) fusion genes to promote the early onset of leukemia. To investigate whether Icsbp deficiency interacts with Meis1 or its family member Meis3, we transplanted Icsbp(-/-) bone marrow (BM) cells after transduction with Meis1 or Meis3 retroviral vectors. Here, we show that enforced expression of Meis1 or Meis3 in Icsbp(-/-) BM cells induces a fatal, invasive myeloproliferative disease. Secondary mutations, such as activation of Mn1, led to the progression to acute myeloid leukemia in a few mice. Interestingly, expression of endogenous Meis1 and Meis3 mRNAs was repressed in the granulocytic progenitor population of Icsbp(-/-) mice. These results reveal a novel collaboration between Icsbp deficiency and Meis1/Meis3 in the acceleration of chronic myeloid leukemia-like disease.

Gadd45 beta is a pro-survival factor associated with stress-resistant tumors.

Tumors that acquire resistance against death stimuli constitute a severe problem in the context of cancer therapy. To determine genetic alterations that favor the development of stress-resistant tumors in vivo, we took advantage of polyclonal tumors generated after retroviral infection of newborn Elambda-MYC mice, in which the retroviral integration acts as a mutagen to enhance tumor progression. Tumor cells were cultivated ex vivo and exposed to gamma-irradiation prior to their transplantation into syngenic recipients, thereby providing a strong selective pressure for pro-survival mutations. Secondary tumors developing from stress-resistant tumor stem cells were analysed for retroviral integration sites to reveal candidate genes whose dysregulation confer survival. In addition to the gene encoding the antiapoptotic Bcl-x(L) protein, we identified the gadd45b locus to be a novel common integration site in these tumors, leading to enhanced expression. In accord with a thus far undocumented role of Gadd45beta in tumorigenesis, we showed that NIH3T3 cells overexpressing Gadd45beta form tumors in NOD/SCID mice. Interestingly and differently to other known 'classical' antiapoptotic factors, high Gadd45beta levels did not protect against MYC-, UV- or gamma-irradiation-induced apoptosis, but conferred a strong and specific survival advantage to serum withdrawal.

Gene transfer of SHIP-1 inhibits proliferation of juvenile myelomonocytic leukemia cells carrying KRAS2 or PTPN11 mutations.

Juvenile myelomonocytic leukemia (JMML) is a malignant disease of early childhood characterized by a hypersensitivity to granulocyte/macrophage colony-stimulating factor (GM-CSF). Mutations in RAS or PTPN11 are frequently detected in JMML patients. The SH2-containing inositol 5-phosphatase 1 (SHIP-1) is a negative regulator of GM-CSF signaling, and inactivation of SHIP-1 in mice results in a myeloproliferative disease. Here, we report the effects of SHIP-1 expression on GM-CSF-dependent proliferation and colony formation of human hematopoietic cells. After retroviral-mediated transduction of SHIP-1 into CD34+ cells from cord blood of healthy newborns or peripheral blood of JMML patients carrying mutations in KRAS2 or PTPN11, we observed a reduction in GM-CSF-dependent proliferation and colony formation. An enzymatically inactive form of SHIP-1 (D672A) had no effect. These data indicate that SHIP-1 can effectively block GM-CSF hypersensitivity in JMML progenitor cells with mutations in KRAS2 or PTPN11 and may be a useful approach for the treatment of JMML patients.

Speaking of research advance directives: planning for future research participation.

OBJECTIVE: To examine one model of research advance directive as a possible way to reduce the mismatch between patient and proxy choices and also to learn more about how patients with mild to moderate dementia may want to keep decision making or cede it to their proxies in the future. METHODS: Separate interviews were conducted with 149 dyads of dementia patients and family proxies about future enrollment in five types of research. Subsequent joint interviews were conducted with 69 of those dyads to discuss their separately articulated decisions and ask whether the patient prefers future enrollment decisions to be made as he or she directs today or as the proxy deems best in the future. RESULTS: Patients chose to cede future decision making to their proxies in 82.9% of the trials. Patients ceded decisions to their proxies in 80.7% of those trials about which the dyad had given opposite answers (n = 74, 49.7%). Patients who had expressed discomfort about the prospect of the proxy making an enrollment decision in a trial (n = 49, 32.9%) ceded decision making to their proxies in 45.7% of those trials. CONCLUSIONS: Both patients and proxies were willing to discuss future research enrollment in the context of an advance directive for research. Such a document may be helpful to proxies and researchers in the future to judge the types of research and associated risks patients are willing to enroll in. Although most patients willingly cede future decisions to their proxies, a sizeable minority do not wish to do so.