Biologically active Fas antigen and its cognate ligand are expressed on plasma membrane-derived extracellular vesicles.

Exfoliation of plasma membrane components is a directed process that consumes energy and requires active cell metabolism. Proteins involved in regulating the survival and proliferation of eukaryotic cells are released on exfoliated vesicles. We examine here whether the Fas receptor and its cognate ligand (FasL) are present on vesicles shed from high metastatic potential CX-1 cells and low metastatic potential MIP-101 cells and from HuT 78 cells, respectively.

The Raf-1 protein mediates insulin-like growth factor-induced proliferation of erythroid progenitor cells.

Previous studies from this and other laboratories have shown that insulin-like growth factor-1 (IGF-I) and insulin-like growth factor-2 (IGF-II) support erythroid colony formation in cultures supplemented with serum substitute and recombinant erythropoietin. Subpopulations of IGF-I- and IGF-II-dependent, erythropoietin-independent colony-forming unit-erythroid (CFU-E)-derived colonies and BFU-E-derived colonies were identified under serum-substituted conditions for adult bone-marrow-derived erythroid progenitors which proliferate in the absence and presence of exogenous anti-erythropoietin receptor monoclonal antibody and in serum-substituted medium that was preadsorbed with anti-erythropoietin IgG. To assess whether Raf-1 is required for the formation of IGF-dependent, erythropoietin-independent human erythroid colonies, 5-15 microM sense or antisense oligomer to raf-1 were added to serum-substituted cultures containing either 2 U/ml recombinant human erythropoietin (rHuEpo) alone or 0-1,000 ng/ml IGF-I or IGF-II with/without 2 U/ml rHuEpo.

Early identification of radiation accident victims for therapy of bone marrow failure.

Ionizing radiation damages the lymphohematopoietic system via direct effects on viability and/or function of hematopoietic stem/progenitor cells and via abnormal production of cytokines (i.e., growth factors).

Human macrophage colony-stimulating factor is expressed at and shed from the cell surface.

Surface membrane-associated growth factors are being recognized as important for developmental processes, including cell assembly, differentiation, and growth. To investigate the role of membrane-bound macrophage colony-stimulating factor (M-CSF) in myelopoiesis, and whether this factor is released from the cell surface in association with shed membrane-derived vesicles, COS-1 cells were transfected with cDNAs for M-CSF-tau (containing the transmembrane domain) or a soluble mutant form of the molecule lacking the transmembrane domain ([s]M-CSF-alpha). COS-1 cells transfected with either cDNA released activity into the spent culture medium.

Expression of membrane-bound burst-promoting activity is mediated by allogeneic effector cells.

To investigate whether "self" and "non-self" recognition processes are involved in murine erythropoiesis, the expression of membrane-bound burst-promoting activity (mBPA) was determined for B lymphocytes purified from spleens of CF-1, C57 BL/6J, B6021-7115, and CAF-1J mice using syngeneic and allogeneic bone marrow cultures. Addition of B lymphocyte conditioned medium (LCM), shed membrane-derived vesicles, or intact plasma membranes prepared from syngeneic murine cells stimulated erythroid burst-forming unit (BFU-E) proliferation by two- to three-fold above control levels. BFU-E proliferation was increased by six- to eight-fold, however, when LCM, shed membrane vesicles, or plasma membranes purified from allogenic B lymphocytes were used as sources of growth-stimulatory activity.