The survival and proliferation of the UT-7 human leukemic cell line is strictly dependent on the presence of either interleukin 3, granulocyte-macrophage colony-stimulating factor or erythropoietin. In these cells, erythropoietin stimulation led to the rapid phosphorylation of several proteins including the erythropoietin receptor and proteins with molecular masses around 45 kDa which could be mitogenactivated protein (MAP) kinases. Separation of cytosol from resting or erythropoietin-stimulated UT-7 cells by anion-exchange chromatography revealed two peaks of myelin basic protein kinase activity. The kinase activity of the first peak was independent of erythropoietin treatment of the cells and corresponded to an unidentified 50-kDa kinase, whereas the second peak was only present in erythropoietin-stimulated cells and corresponded to three forms of MAP kinases with molecular masses of 45, 44 and 42 kDa. The three forms were separated by hydrophobic chromatography and were shown to be activated in erythropoietin-stimulated cells. The 44-kDa and 42-kDa forms corresponded to extracellular signal-regulated kinase (ERK)-1 and ERK-2, respectively. Evidence was obtained showing that the 45-kDa form i s not a shifted form of ERK-I but corresponded to a less well defined form of MAP kinase which may be the previously described ERK-4. MAP kinase activation was detected after 1 min erythropoietin stimulation and remained detectable after more than 1 hour. A role for MAP kinase activation in erythropoietinstimulated cell proliferation was suggested by the simultaneous inhibition of erythropoietin-induced MAP kinase stimulation and cell proliferation. The potential activator of MAP kinase, RAF-1, was hyperphosphorylated in erythropoietin-stimulated cells and its autophosphorylation activity was strongly increased. The protein adaptor Shc was heavily phosphorylated in UT-7 erythropoietin-stimulated cells and associated strongly with a unidentified 145-kDa protein. However, Shc bound poorly to the activated erythropoietin receptor and most Shc proteins were cytosolic in both unstimulated and erythropoietin-stimulated cells. In contrast, Grb2 associated efficiently with the activated erythropoietin receptor and a significant part of Grb2 was associated to a particulate subcellular fraction upon erythropoietin stimulation.Keywords: erythropoietin receptor; mitogen-activated kinases; RAF-1; Grb2 ; Shc.The survival, proliferation and differentiation of the 'late' erythroid progenitors (the so-called colony forming units-erythroid) are mainly controlled by the hormone erythropoietin (see [l] for review). The erythropoietin receptor belongs to the family of cytokine receptors 12, 31 which includes receptors for other heniatopoietic growth factors such as the interleukins and colony-stimulating factors, together with receptors for nonhematopoietic stimulators such as prolactin, growth hormone and ciliary neurotrophic factor 141. Considerable progress has been made in understanding the mode of action of erythropoietin since the clon...

Laboratoire d'lmmunologie et de Virologie des Tumeurs, INSERM U 152, Hgpital Cochin, ParisThe nature of the target antigen, expressed on murine sarcoma virus (MSV) and related murine tumors which reacts with T killer lymphocytes, remains ill-defined. The experiments reported here show that: (a) the previously described H-2 restriction phenomenon is found under all experimental conditions including 3-4 and 16-20-h chromium release tests. With 16-20 h tests and highly efficient T lymphocytes however, quantitative methods are necessary to demonstrate the H-2 restriction. These results support the hypothesis that H-2 molecules may be determinant in the structure and/or in the function of the cytolytic T lymphocyte (CTL) reactive antigen. (b) Under syngeneic conditions (ie. using H-2-identical immune lymphocytes, stimulators and target cells), the pattern of specificities recognized by anti-MSV or antiFriend T killer cells on 20 different lymphomas suggests that the main reactive antigen is an "FMR-like" substance. Identical conclusions were drawn from competition experiments. (c) Blockings were obtained by pre-incubation of the target cells with a goat anti-gp70, suggesting a possible role of the viral gp70 in the antigen recognized. However, this could be due to nonspecific reactions as two other anti-gp70 sera as well as with antisera directed against the viral componentsgp45, pr60, p30, p15, p12 and p10 did not block. The CTL/tumor cell interaction was not inhibited by virion-associated antigens added to the medium. Lysostrip and co-capping experiments have failed to reveal an association between H-2 and gp70. The nature of the viral protein bearing the "FMR-like" substance therefore remains to be established.

The ability of tumor cells to produce and to respond to their own growth factor (autocrine secretion) may be of importance for their growth. We describe a human tumor cell line regulated by an autocrine secretion of the growth factor interleukin 2 (IL-2). This T-lymphocyte cell line, IARC 301, was established from a patient with a T-cell lymphoma in the absence of any added specific growth factor. It constitutively expresses biologically functional high-affinity cell-surface receptors for IL-2 as shown by the binding of both radiolabeled purified IL-2 and monoclonal antibodies to IL-2 receptors. In addition, it synthesizes IL-2, which is bound to cell surface receptors. Monoclonal antibodies directed against either IL-2 or the IL-2 receptor block IARC 301 cell growth. These findings demonstrate that the proliferation of this tumor cell line is mediated by an autocrine pathway involving endogenous IL-2 production and its binding to cell surface receptors.