A myelomonocytic leukaemia cell line, WEHI-3, releases into its growth medium factors which stimulate the development of pluripotential cells, granulocyte/macrophage progenitor cells, megakaryocytic and erythroid progenitor cells. Also present is a factor which is essential for the continued proliferation in vitro of a variety of haemopoietic precursor cell lines of a granulocytic nature (FDC-P cells). Characterization of this growth factor has demonstrated that it is a glycoprotein of apparent Mr 25 800, in which the carbohydrate component appears to be important for activity. After several purification steps, there is an increase in specific activity of approx. 4000-fold over the starting material. At each stage of purification, the factor necessary for the proliferation of FDC-P cells 'co-purifies' with activity which stimulates the proliferation and development of normal multipotential haemopoietic cells as well as megakaryocytic, erythroid and granulocytic committed progenitor cells. This 'co-purification' occurs to the extent that the multilineage stimulating factor and the FDC-P growth factor can be eluted from the same region of sodium dodecyl sulphate/polyacrylamide gels. Thus, evidence so far, using different starting methods and purification regimes, suggests that one molecule may have multiple activities on diverse cell types.

A number of haematopoietic precursor cell lines have been established which exhibit an absolute dependence on haematopoietic cell growth factor (HCGF) which is secreted by WEHI‐3 myelomonocytic leukaemia cells. In the presence of HCGF, ATP levels are maintained in these factor‐dependent cells (FDC‐P cells); in the absence of HCGF, intracellular ATP levels undergo a steady depletion. The cell death that follows this ATP depletion can be prevented by supplying exogenous ATP suggesting that HCGF maintains these cells via its effects on energy metabolism. We have investigated the effect of HCGF on FDC‐P cells further and found that: (i) HCGF markedly and rapidly increases lactate production; (ii) high extracellular glucose or glycolytic intermediate concentrations can maintain FDC‐P cell viability to some extent whilst stimulating lactate production; (iii) the uptake of 2‐deoxyglucose by FDC‐P2 cells is stimulated by HCGF in a dose‐dependent fashion. This uptake is inhibited by cytochalasin B; (iv) HCGF does not stimulate L‐glucose uptake by FDC‐P cells. These results suggest that HCGF acts to maintain FDC‐P cells via its action on glucose transport. The significance of these results to haemopoiesis and leukaemogenesis is discussed.

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