1438

CSF2RA

CD116|CDw116|CSF2R|CSF2RAX|CSF2RAY|CSF2RX|CSF2RY|GM-CSF-R-alpha|GMCSFR|GMR|SMDP4;colony stimulating factor 2 receptor, alpha, low-affinity (granulocyte-macrophage);CSF2RA;colony stimulating factor 2 receptor, alpha, low-affinity (granulocyte-macrophage)

CD116 antigen|GM-CSF receptor alpha subunit|GMCSFR-alpha|GMR-alpha|colony stimulating factor 2 receptor alpha subunit|granulocyte-macrophage colony-stimulating factor receptor alpha chain|granulocyte-macrophage colony-stimulating factor receptor subunit a

Xp22.32 and Yp11.3

protein-coding

Juvenile myelomonocytic leukemia (JMML) is an aggressive childhood disorder withfew therapeutic options. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor-alpha (TNF-alpha) promote JMML cell growth. Ahyperactive function of the ras oncogene is a hallmark of JMML. We therefore targeted the protein kinase Raf-1 downstream of Ras using a DNA enzyme that degrades mRNA-Raf-1. Western blots of JMML cell lysates revealed phosphorylated Raf-1 protein, indicating constitutive activation. Addition of GM-CSF, but not TNF-alpha, increased phosphorylation of both Raf-1 and the mitogen-activated protein kinases (MAPKs) JNK-1 and ERK-1. Depletion of Raf-1 protein markedly impaired activation of MAPKs, induced substantial inhibition of JMML cell colonyformation, and virtually abolished GM-CSF hypersensitivity in JMML cells. Exogenous TNF-alpha, but not GM-CSF, restored colony formation of JMML cells pretreated with the enzyme. We could not detect any effect of the enzyme on the proliferation of normal bone marrow cells, indicating its specificity and potential safety. When immunodeficient mice engrafted with JMML cells were treated continuously with the enzyme via a peritoneal osmotic mini-pump for 4 weeks, a profound reduction in the JMML cell numbers in the recipient murine bone marrows was found. We conclude that GM-CSF is a chief regulator of JMML growth and exerts its proleukemic effects primarily via the Ras/Raf-1 signaling cascade. TNF-alpha plays a permissive role, being dependent upon GM-CSF to induce JMML cell proliferation. The DNA enzyme efficiently catabolized mRNA-Raf-1 with subsequent inhibition of JMML cell growth, suggesting its potential as a mechanism-based therapy in this fatal leukemia.

Proliferation and differentiation of hematopoietic progenitor cells are regulated by a network of stimulatory and inhibitory cytokines. An understanding of the molecular mechanisms of growth control may provide a physiologic basis for the innovative therapy of bone marrow disorders. Among various accessory cells, bonemarrow T lymphocytes are capable of stimulating, as well as inhibiting, hematopoietic progenitor cells. We have now elucidated molecular mechanisms regulating the differential expression of T cell genes encoding for the stimulatory and inhibitory hematopoietic programs. Stimulation of hematopoiesis requires granulocyte-macrophage colony stimulating factor (GM-CSF), whereas inhibition requires interferon-gamma (IF gamma). Both cytokines can be induced by interleukin-2 (IL2). The T cell IL2 receptor consists of a 75 kD chain (p75) mainly expressed on a subset of resting T cells and a 55 kD chain (p55) which isstrongly expressed upon T cell activation. P55 and p75 associate on activated T cells to form a dimeric receptor molecule exhibiting high affinity for IL2. The p75 monomer has an intermediate affinity for IL2. expression of p55 in the context of the high affinity IL2 receptor constitutes a requirement for T cell IFg release. In contrast, p75 alone is capable of mediating the production of GM-CSF. Thus, T cells may be capable of selective production of cytokines with specific effects in hematopoietic growth control. Utilizing a human peripheral blood leukocyte genomic library, we identified various clones containing the entire GM-CSF gene, including coding and regulatory regions. Cloning of the GM-CSF gene allowed clinical studies utilizing recombinant DNA-derived GM-CSF. Chemotherapy-induced neutropenia contributes to both complications of cytotoxic therapy as well as increased relapse incidence of underlying disease. In a prospective randomized study, we have demonstrated that GM-CSF abrogates neutropenia following aplasiogenic chemotherapy in children and adolescents withsolid tumors, and that GM-CSF may reduce the duration of infectious episodes after cytotoxic therapy. Next, we escalated the cumulative doses of cytotoxic therapy in an ablative regimen followed by hematopoietic stem cell transplantation to treat patients with poor prognosis pediatric tumors. Morbidity of this highly toxic ablative regimen depends on the duration of myeloid aplasia. Median duration of aplasia following hyper-VAMP was 13 days with CM-CSF and 29 days without GM-CSF. In addition, we have employed p55 blocking monoclonal antibody for prevention of graft vs. host disease in bone marrow transplantation. The understanding of specific molecular mechanisms of hematopoietic immuno-regulation can thus be utilized to provide novel approaches to the treatment of bone marrow failure and cancer.

Multidrug resistance is a severe clinical problem in the chemotherapy of malignant disease. Acute megakaryoblastic leukemia (AMKL) is a rare form of childhood leukemia, and is often resistant to many anti-cancer chemotherapeutic drugs. Here we report the expression of the mdr-1/P-glycoprotein in a cell line,CMK, established from a patient with AMKL. expression of mdr-1 mRNA in CMK11-5 cells, a well differentiated subline, was higher than in CMK6 cells, a poorly differentiated subline. The level of P-glycoprotein was also higher in CMK11-5 cells. The cytokines interferon-gamma (IFN-gamma), GM-CSF and IL-3, which were shown to induce megakaryocytic differentiation of CMK cells, enhanced the expression of the mdr-1 mRNA and levels of P-glycoprotein. These results imply that differentiated megakaryocytic cells may have higher levels of the P-glycoprotein expression, suggesting a possible normal physiological function of P-glycoprotein in mature megakaryocytes.