Mechanism of action for the cytotoxic effects of the nitric oxide prodrug JS-K in murine erythroleukemia cells.

The nitric oxide (NO) prodrug JS-K, a promising anti-cancer agent, consists of a diazeniumdiolate group necessary for the release of NO as well as an arylating ring. In this study, we research the mechanism by which JS-K kills a murine erythroleukemia cell line and determine the roles of NO and arylation in the process. Our studies indicate that JS-K inhibits the PI 3-kinase/Akt and MAP kinase pathways.

The human lung adenocarcinoma cell line EKVX produces an infectious xenotropic murine leukemia virus.

The cell lines of the NCI-60 panel represent different cancer types and have been widely utilized for drug screening and molecular target identification. Screening these cell lines for envelope proteins or gene sequences related to xenotropic murine leukemia viruses (X-MLVs) revealed that one cell line, EKVX, was a candidate for production of an infectious gammaretrovirus. The presence of a retrovirus infectious to human cells was confirmed by the cell-free transmission of infection to the human prostate cancer cell line LNCaP.

Role of N-terminal sequences of the tyrosine kinase sf-Stk in transformation of rodent fibroblasts by variants of Friend spleen focus-forming virus.

Infection of erythroid cells by Friend spleen focus-forming virus (SFFV) leads to acute erythroid hyperplasia in mice, due to expression of its unique envelope glycoprotein, gp55. Erythroid cells expressing SFFV gp55 proliferate in the absence of their normal regulator, erythropoietin, because of the interaction among the viral envelope protein, the erythropoietin receptor, and a short form of the receptor tyrosine kinase Stk (sf-Stk). This leads to constitutive activation of several signal transduction pathways.

Friend Spleen Focus-Forming Virus Activates the Tyrosine Kinase sf-Stk and the Transcription Factor PU.1 to Cause a Multi-Stage Erythroleukemia in Mice.

HEMATOLOGICAL MALIGNANCIES IN HUMANS TYPICALLY INVOLVE TWO TYPES OF GENETIC CHANGES: those that promote hematopoietic cell proliferation and survival (often the result of activation of tyrosine kinases) and those that impair hematopoietic cell differentiation (often the result of changes in transcription factors). The multi-stage erythroleukemia induced in mice by Friend spleen focus-forming virus (SFFV) is an excellent animal model for studying the molecular basis for both of these changes. Significant progress has been made in understanding the molecular basis for the multi-stage erythroleukemia induced by Friend SFFV.

Retrovirus-transformed erythroleukemia cells induce central nervous system failure in a new syngeneic mouse model of meningeal leukemia.

Lack of suitable mouse models for central nervous system (CNS)-associated leukemias has hindered mechanism-guided development of therapeutics. By transplanting retrovirus-transformed mouse erythroleukemia cells into syngeneic mice, we developed a new animal model of meningeal leukemia associated with rapid paralysis. Necropsy revealed massive proliferation of the leukemic cells in the bone marrow (BM) followed by pathological angiogenesis and invasion of the leukemic cells into the meninges of the CNS.

Importance of macrophage inflammatory protein-1α and splenic macrophages in neurodegeneration induced by PVC-211 murine leukemia virus.

We recently reported that infection of rats with the neurodegenerative disease-causing retrovirus PVC-211 MuLV results in elevated levels of the chemokine MIP-1α followed by the accumulation of activated microglia in the brain. To investigate the importance of MIP-1α in recruitment of microglia to the brain, we treated rats with MIP-1α antibodies before and after PVC-211 MuLV infection. This caused a delay in the development of paralysis which was associated with a decrease in activated microglia without affecting virus expression.

Role of phosphatidylinositol 3-kinase in friend spleen focus-forming virus-induced erythroid disease.

Infection of erythroid cells by Friend spleen focus-forming virus (SFFV) leads to acute erythroid hyperplasia in mice due to expression of its unique envelope glycoprotein, gp55. Erythroid cells expressing SFFV gp55 proliferate in the absence of their normal regulator, erythropoietin (Epo), because of interaction of the viral envelope protein with the erythropoietin receptor and a short form of the receptor tyrosine kinase Stk (sf-Stk), leading to constitutive activation of several signal transduction pathways. Our previous in vitro studies showed that phosphatidylinositol 3-kinase (PI3-kinase) is activated in SFFV-infected cells and is important in mediating the biological effects of the virus.

Detection of an infectious retrovirus, XMRV, in blood cells of patients with chronic fatigue syndrome.

Chronic fatigue syndrome (CFS) is a debilitating disease of unknown etiology that is estimated to affect 17 million people worldwide. Studying peripheral blood mononuclear cells (PBMCs) from CFS patients, we identified DNA from a human gammaretrovirus, xenotropic murine leukemia virus-related virus (XMRV), in 68 of 101 patients (67%) as compared to 8 of 218 (3.7%) healthy controls.

Neurodegeneration induced by PVC-211 murine leukemia virus is associated with increased levels of vascular endothelial growth factor and macrophage inflammatory protein 1 alpha and is inhibited by blocking activation of microglia.

PVC-211 murine leukemia virus (MuLV) is a neuropathogenic retrovirus that has undergone genetic changes from its nonneuropathogenic parent, Friend MuLV, that allow it to efficiently infect rat brain capillary endothelial cells (BCEC). To clarify the mechanism by which PVC-211 MuLV expression in BCEC induces neurological disease, we examined virus-infected rats at various times during neurological disease progression for vascular and inflammatory changes. As early as 2 weeks after virus infection and before any marked appearance of spongiform neurodegeneration, we detected vessel leakage and an increase in size and number of vessels in the areas of the brain that eventually become diseased.

DNA hypomethylation caused by Lsh deletion promotes erythroleukemia development.

Hematopoietic malignancies are frequently associated with DNA hypomethylation but the molecular mechanisms involved in tumor formation remain poorly understood. Here we report that mice lacking Lsh develop leukemia associated with DNA hypomethylation and oncogene activation. Lsh is a member of the SNF2 chromatin remodeling family and is required for de novo methylation of genomic DNA.

The tyrosine kinase sf-Stk and its downstream signals are required for maintenance of friend spleen focus-forming virus-induced fibroblast transformation.

Infection of erythroid progenitor cells by Friend spleen focus-forming virus (SFFV) leads to acute erythroid hyperplasia and eventually to erythroleukemia in susceptible strains of mice. The viral envelope protein, SFFV gp55, forms a complex with the erythropoietin receptor (EpoR) and a short form of the receptor tyrosine kinase Stk (sf-Stk), activating both and inducing Epo-independent proliferation. Recently, we discovered that coexpression of SFFV gp55 and sf-Stk is sufficient to transform NIH 3T3 and primary fibroblasts.

Erythroblast transformation by the friend spleen focus-forming virus is associated with a block in erythropoietin-induced STAT1 phosphorylation and DNA binding and correlates with high expression of the hematopoietic phosphatase SHP-1.

Infection of mice with Friend spleen focus-forming virus (SFFV) results in a multistage erythroleukemia. In the first stage, the SFFV envelope glycoprotein interacts with the erythropoietin receptor and a short form of the receptor tyrosine kinase sf-Stk, resulting in constitutive activation of signal transducing molecules and the development of erythropoietin (Epo)-independent erythroid hyperplasia and polycythemia. The second stage results from the outgrowth of a rare virus-infected erythroid cell that expresses nonphysiological levels of the myeloid transcription factor PU.

Friend spleen focus-forming virus transforms rodent fibroblasts in cooperation with a short form of the receptor tyrosine kinase Stk.

Friend spleen focus-forming virus (SFFV) causes rapid erythroleukemia in mice due to expression of its unique envelope glycoprotein, gp55. Erythroid cells expressing SFFV gp55 proliferate in the absence of their normal regulator erythropoietin (Epo) because of constitutive activation of Epo signal transduction pathways. Although SFFV infects many cell types, deregulation of cell growth occurs only when SFFV infects erythroid cells, suggesting that these cells express unique proteins that the virus requires to mediate its biological effects.

Activation of the Jun N-terminal kinase pathway by friend spleen focus-forming virus and its role in the growth and survival of friend virus-induced erythroleukemia cells.

Members of the mitogen-activated protein kinase (MAPK) family, including Jun amino-terminal kinase (JNK) and extracellular signal-related kinase (ERK), play an important role in the proliferation of erythroid cells in response to erythropoietin (Epo). Erythroid cells infected with the Friend spleen focus-forming virus (SFFV) proliferate in the absence of Epo and show constitutive activation of Epo signal transduction pathways. We previously demonstrated that the ERK pathway was constitutively activated in Friend SFFV-infected erythroid cells, and in this study JNK is also shown to be constitutively activated.

Ex vivo and in vivo biological effects of a truncated form of the receptor tyrosine kinase stk when activated by interaction with the friend spleen focus-forming virus envelope glycoprotein or by point mutation.

The erythroleukemia-inducing Friend spleen focus-forming virus (SFFV) encodes a unique envelope protein, gp55, which interacts with the erythropoietin (Epo) receptor complex, causing proliferation and differentiation of erythroid cells in the absence of Epo. Susceptibility to SFFV-induced erythroleukemia is conferred by the Fv-2 gene, which encodes a short form of the receptor tyrosine kinase Stk/Ron (sf-Stk) only in susceptible strains of mice. We recently demonstrated that sf-Stk becomes activated by forming a strong interaction with SFFV gp55.

Expression of inducible nitric oxide synthase and elevation of tyrosine nitration of a 32-kilodalton cellular protein in brain capillary endothelial cells from rats infected with a neuropathogenic murine leukemia virus.

PVC-211 murine leukemia virus (MuLV) is a neuropathogenic variant of Friend MuLV (F-MuLV) which causes a rapidly progressive spongiform neurodegenerative disease in rodents. The primary target of PVC-211 MuLV infection in the brain is the brain capillary endothelial cell (BCEC), which is resistant to F-MuLV infection. Previous studies have shown that changes in the envelope gene of PVC-211 MuLV confer BCEC tropism to the virus.

Identification and characterization of a novel Ste20/germinal center kinase-related kinase, polyploidy-associated protein kinase.

A novel protein kinase, polyploidy-associated protein kinase (PAPK), was isolated using a subtraction cDNA library approach from a mouse erythroleukemia cell line that had been induced to polyploidy after serum withdrawal. PAPK shares homology with members of the Ste20/germinal center kinase family of protein kinases and is ubiquitously expressed as two spliced forms, PAPK-A and PAPK-B, that encode for proteins of 418 and 189 amino acids, respectively. The expression of endogenous PAPK-A protein increased after growth factor withdrawal in murine hematopoietic and fibroblast cells.

Analysis of the disease potential of a recombinant retrovirus containing Friend murine leukemia virus sequences and a unique long terminal repeat from feline leukemia virus.

We have molecularly cloned a feline leukemia virus (FeLV) (clone 33) from a domestic cat with acute myeloid leukemia (AML). The long terminal repeat (LTR) of this virus, like the LTRs present in FeLV proviruses from other cats with AML, contains an unusual structure in its U3 region upstream of the enhancer (URE) consisting of three tandem direct repeats of 47 bp. To test the disease potential and specificity of this unique FeLV LTR, we replaced the U3 region of the LTR of the erythroleukemia-inducing Friend murine leukemia virus (F-MuLV) with that of FeLV clone 33.