Mary Ann Thompson

Murine Leukemias with Retroviral Insertions at Lmo2 Are Predictive of the Leukemias Induced in SCID-X1 Patients Following Retroviral Gene Therapy

Five X-linked severe combined immunodeficiency patients (SCID-X1) successfully treated with autologous bone marrow stem cells infected ex vivo with an IL2RG-containing retrovirus subsequently developed T-cell leukemia and four contained insertional mutations at LMO2. Genetic evidence also suggests a role for IL2RG in tumor formation, although this remains controversial. Here, we show that the genes and signaling pathways deregulated in murine leukemias with retroviral insertions at Lmo2 are similar to those deregulated in human leukemias with high LMO2 expression and are highly predictive of the leukemias induced in SCID-X1 patients. We also provide additional evidence supporting the notion that IL2RG and LMO2 cooperate in leukemia induction but are not sufficient and require additional cooperating mutations. The highly concordant nature of the genetic events giving rise to mouse and human leukemias with mutations at Lmo2 are an encouraging sign to those wanting to use mice to model human cancer and may help in designing safer methods for retroviral gene therapy.

Histone deacetylase inhibitors induce the degradation of the t(8;21) fusion oncoprotein

The t(8;21) chromosomal translocation that generates the fusion oncoprotein RUNX1-ETO predominates in leukemia patients of the French-American-British (FAB) class M2 subtype. The oncoprotein has the capacity to promote expansion of hematopoietic stem/progenitor cells and induces leukemia in association with other genetic alterations. Here, we show that RUNX1-ETO undergoes degradation in response to treatment with histone deacetylase inhibitors, one of which, depsipeptide (DEP), is currently undergoing phase II clinical testing in a variety of malignancies. These compounds induce turnover of RUNX1-ETO without affecting the stability of RUNX1-ETO partner proteins. In addition, RUNX1-ETO physically interacts with heat shock protein 90 (HSP90). DEP treatment interrupts the association of RUNX1-ETO with HSP90 and induces proteasomal degradation of RUNX1-ETO. DEP and the HSP90 antagonist 17-allylamino-geldanamycin (17-AAG) both triggered RUNX1-ETO degradation, but without any additive or cooperative effects. These findings may stimulate the development of more rational and effective approaches for treating t(8;21) patients using histone deacetylase inhibitors or HSP90 inhibitors.

Mtgr1 Is a Transcriptional Corepressor That Is Required for Maintenance of the Secretory Cell Lineage in the Small Intestine

ABSTRACT Two members of the MTG/ETO family of transcriptional corepressors, MTG8 and MTG16, are disrupted by chromosomal translocations in up to 15% of acute myeloid leukemia cases. The third family member, MTGR1, was identified as a factor that associates with the t(8;21) fusion protein RUNX1-MTG8. We demonstrate that Mtgr1 associates with mSin3A, N-CoR, and histone deacetylase 3 and that when tethered to DNA, Mtgr1 represses transcription, suggesting that Mtgr1 also acts as a transcriptional corepressor. To define the biological function of Mtgr1, we created Mtgr1-null mice. These mice are proportionally smaller than their littermates during embryogenesis and throughout their life span but otherwise develop normally. However, these mice display a progressive reduction in the secretory epithelial cell lineage in the small intestine. This is not due to the loss of small intestinal progenitor cells expressing Gfi1, which is required for the formation of goblet and Paneth cells, implying that loss of Mtgr1 impairs the maturation of secretory cells in the small intestine.

Deletion of Mtg16, a Target of t(16;21), Alters Hematopoietic Progenitor Cell Proliferation and Lineage Allocation

ABSTRACT While a number of DNA binding transcription factors have been identified that control hematopoietic cell fate decisions, only a limited number of transcriptional corepressors (e.g., the retinoblastoma protein [pRB] and the nuclear hormone corepressor [N-CoR]) have been linked to these functions. Here, we show that the transcriptional corepressor Mtg16 (myeloid translocation gene on chromosome 16), which is targeted by t(16;21) in acute myeloid leukemia, is required for hematopoietic progenitor cell fate decisions and for early progenitor cell proliferation. Inactivation of Mtg16 skewed early myeloid progenitor cells toward the granulocytic/macrophage lineage while reducing the numbers of megakaryocyte-erythroid progenitor cells. In addition, inactivation of Mtg16 impaired the rapid expansion of short-term stem cells, multipotent progenitor cells, and megakaryocyte-erythroid progenitor cells that is required under hematopoietic stress/emergency. This impairment appears to be a failure to proliferate rather than an induction of cell death, as expression of c-Myc, but not Bcl2, complemented the Mtg16−/− defect.

Rgs2 Mediates Pro-Angiogenic Function of Myeloid Derived Suppressor Cells in the Tumor Microenvironment via Upregulation of MCP-1

Background Tumor growth is intimately linked with stromal interactions. Myeloid derived suppressor cells (MDSCs) are dramatically elevated in cancer patients and tumor bearing mice. MDSCs modulate the tumor microenvironment through attenuating host immune response and increasing vascularization. Methodology/Principal Findings In searching for molecular mediators responsible for pro-tumor functions, we found that regulator of G protein signaling-2 (Rgs2) is highly increased in tumor-derived MDSCs compared to control MDSCs. We further demonstrate that hypoxia, a common feature associated with solid tumors, upregulates the gene expression. Genetic deletion of Rgs2 in mice resulted in a significant retardation of tumor growth, and the tumors exhibit decreased vascular density and increased cell death. Interestingly, deletion of Rgs2 in MDSCs completely abolished their tumor promoting function, suggesting that Rgs2 signaling in MDSCs is responsible for the tumor promoting function. Cytokine array profiling identified that Rgs2−/− tumor MDSCs produce less MCP-1, leading to decreased angiogenesis, which could be restored with addition of recombinant MCP-1. Conclusion Our data reveal Rgs2 as a critical regulator of the pro-angiogenic function of MDSCs in the tumor microenvironment, through regulating MCP-1 production.

HDAC3 is essential for DNA replication in hematopoietic progenitor cells

Histone deacetylase 3 (HDAC3) contributes to the regulation of gene expression, chromatin structure, and genomic stability. Because HDAC3 associates with oncoproteins that drive leukemia and lymphoma, we engineered a conditional deletion allele in mice to explore the physiological roles of Hdac3 in hematopoiesis. We used the Vav-Cre transgenic allele to trigger recombination, which yielded a dramatic loss of lymphoid cells, hypocellular bone marrow, and mild anemia. Phenotypic and functional analysis suggested that Hdac3 was required for the formation of the earliest lymphoid progenitor cells in the marrow, but that the marrow contained 3-5 times more multipotent progenitor cells. Hdac3(-/-) stem cells were severely compromised in competitive bone marrow transplantation. In vitro, Hdac3(-/-) stem and progenitor cells failed to proliferate, and most cells remained undifferentiated. Moreover, one-third of the Hdac3(-/-) stem and progenitor cells were in S phase 2 hours after BrdU labeling in vivo, suggesting that these cells were impaired in transit through the S phase. DNA fiber-labeling experiments indicated that Hdac3 was required for efficient DNA replication in hematopoietic stem and progenitor cells. Thus, Hdac3 is required for the passage of hematopoietic stem/progenitor cells through the S phase, for stem cell functions, and for lymphopoiesis.

Transcriptional repression of the Neurofibromatosis-1 tumor suppressor by the t(8;21) fusion protein

ABSTRACT Von Recklinghausens disease is a relatively common familial genetic disorder characterized by inactivating mutations of the Neurofibromatosis-1 (NF1) gene that predisposes these patients to malignancies, including an increased risk for juvenile myelomonocytic leukemia. However, NF1 mutations are not common in acute myeloid leukemia (AML). Given that the RUNX1 transcription factor is the most common target for chromosomal translocations in acute leukemia, we asked if NF1 might be regulated by RUNX1. In reporter assays, RUNX1 activated the NF1 promoter and cooperated with C/EBPα and ETS2 to activate the NF1 promoter over 80-fold. Moreover, the t(8;21) fusion protein RUNX1-MTG8 (R/M), which represses RUNX1-regulated genes, actively repressed the NF1 promoter. R/M associated with the NF1 promoter in vivo and repressed endogenous NF1 gene expression. In addition, similar to loss of NF1, R/M expression enhanced the sensitivity of primary myeloid progenitor cells to granulocyte-macrophage colony-stimulating factor. Our results indicate that the NF1 tumor suppressor gene is a direct transcriptional target of RUNX1 and the t(8;21) fusion protein, suggesting that suppression of NF1 expression contributes to the molecular pathogenesis of AML.

Antiepileptic drugs during pregnancy in primary care: a UK population based study.

Objective Antiepileptic drugs (AEDs) are commonly prescribed for epilepsy and bipolar disorder but little is known about their use in pregnancy. We examined secular trends in AED prescribing in pregnancy and pregnancy as a determinant for stopping AED prescribing. Methods We identified 174,055 pregnancies from The Health Improvement Network UK primary care database. Secular trends in AED prescribing during pregnancy were examined between 1994 and 2009. We used Coxs regression analyses to compare time to discontinuation of AED prescriptions between pregnant and non-pregnant women and to identify predictors of discontinuation of AEDs in pregnancy. Results Prescribing of carbamazepine and sodium valproate have declined since 1994 despite being the most commonly prescribed AEDs in pregnancy up to 2004. Prescribing of lamotrigine in pregnancy has steadily increased and has been the most popular AED prescribed in pregnancy since 2004. Pregnant women with epilepsy were twice as likely to stop receiving AEDs (Hazard Ratio (HR) 2.00, 95% Confidence Interval (CI) 1.62–2.47) when compared to non-pregnant women and for women with bipolar disorder this was even higher (HR 3.07, 95% CI 2.04–4.62). For pregnant women with epilepsy, those receiving AEDs less regularly before pregnancy were more likely to stop receiving AEDs in pregnancy. Conclusions Lamotrigine has been increasingly prescribed in pregnancy over older AEDs namely carbamazepine and sodium valproate. Pregnancy is a strong determinant for the discontinuation of AED prescribing particularly for women with bipolar disorder.

MYC cytogenetic status correlates with expression and has prognostic significance in patients with MYC/BCL2 protein double-positive diffuse large B-cell lymphoma.

MYC/BCL2 double-hit lymphoma (DHL), defined by conventional cytogenetic or fluorescence in situ hybridization (FISH) analysis, and MYC/BCL2 double-positive lymphoma (DPL), defined by immunohistochemistry, are associated with a poor prognosis. However, DHL and DPL are not concordant, and it is unclear whether MYC and BCL2 aberrations have prognostic impact in DPL patients. In a cohort of 135 patients diagnosed with large B-cell lymphoma between 2010 and 2014 in whom MYC/8q24 and BCL2/t(14;18)(q32;q21) statuses were assessed by FISH at diagnosis, we evaluated MYC and BCL2 expression by immunohistochemistry. A total of 54 (40%) cases were positive for MYC and BCL2 supporting DPL. Among them, 19 (35%) had MYC rearrangement including 11 DHLs, 12 (22%) had multiple copies of MYC, 19 had no MYC abnormalities, and in 4 cases FISH analysis failed. BCL2 abnormalities were present in 28/54 (52%) cases (20 rearranged and 8 multiple copies). MYC rearrangement correlated with a significantly worse overall survival in DPL (P<0.05), whereas BCL2 genetic status did not correlate with survival (P>0.05). MYC and BCL2 expression by immunohistochemistry correlates with gene status by FISH; however, immunohistochemistry is neither specific nor adequately sensitive to be used as a surrogate for MYC and BCL2 gene status using any cutoff level. In conclusion, MYC rearrangement identifies a subset of patients with DPL who have a significantly worse prognosis. Although immunohistochemical assessment for MYC and BCL2 may be a helpful initial screen to identify higher-risk patients, FISH analysis for MYC remains important for further risk stratification in patients with DPL.

Co-occurrence of Langerhans cell histiocytosis and Rosai-Dorfman disease: possible relationship of two histiocytic disorders in rare cases

Rosai–Dorfman disease and Langerhans cell histiocytosis are both disorders of accessory immune cells. Two cases have been previously reported of concurrent Langerhans cell histiocytosis and Rosai–Dorfman disease. In this report, we characterize the findings and selected molecular studies in nine additional cases. Histology was reviewed. Immunohistochemical stains were performed on all cases in which slides or blocks were available. A combination of CD1a, S-100, CD3, CD20, langerin, CD68, CD163, CD21, CD35 and CD123 immunohistochemical stains were performed. High-resolution array comparative genomic hybridization was performed on six samples from five cases. In these cases, seven were female and two male, with an average age of 25 years (15 months−59 years). A majority of the cases were identified in lymph node. Areas of Langerhans cell histiocytosis had a typical appearance with the existence of bland ‘coffee-bean’ nuclei, clear cytoplasm and associated eosinophils. The immunophenotype was typical, including expression of CD1a, S100, CD68 and langerin. In areas of Rosai–Dorfman disease, there was emperipolesis seen in all cases. Cells were intermediate-large in size with large round nuclei and ample clear or pale cytoplasm. The lesional cells were positive for S100, CD68, CD163, without expression of langerin or CD1a. Array comparative genomic hybridization showed gains and/or losses in four of the six samples. One case showed no gains or losses and one additional case showed gains and losses in the Langerhans cell histiocytosis, while no abnormalities were discovered in the Rosai–Dorfman disease component. These findings are comparable to those seen in previous studies of Langerhans cell histiocytosis. We report the clinical and pathologic findings of the combination of Langerhans cell histiocytosis and Rosai–Dorfman disease. Furthermore, we suggest on the basis of evidence from our cases that, when simultaneous, the two entities may be pathophysiologically related.