Phorbol esters activate protein kinase c and glucose transport and can replace the requirement for growth factor in interleukin-3-dependent multipotent stem cells

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Abstract
Interleukin 3 (IL-3) promotes the survival, proliferation and development of progenitor cells from several distinct haemopoietic lineages and can also stimulate the self-renewal of stem cells. We have explored the mode of action of this growth factor in promoting survival and proliferation, using a multipotent haemopoietic stem cell line FDC-Mix 1. In the absence of IL-3 these cells died within 16–48 h. However, this requirement for IL-3 could be replaced by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) plus Ca2+ ionophore, which promoted not only survival but also DNA synthesis with no concomitant loss of the multipotential nature of these cells. TPA and Ca2+ ionophore, respectively, could also interact synergistically with IL-3 to promote DNA synthesis. Both IL-3 and TPA stimulated the translocation of protein kinase C (PK-C) from the cytosol to a membrane-bound form in FDC-Mix 1 cells. Previously we suggested that IL-3 can activate the primary metabolism of IL-3-dependent cells so that increased glucose transport and glycolysis lead to maintenance of ATP levels and cellular survival. To investigate whether TPA and, or, Ca2+ ionophore could also influence cellular survival via an activation of glucose uptake we assessed the effects of these agents on hexose transport. TPA ± Ca2+ ionophore activated hexose transport to the same degree as does IL-3 but these agents cannot superstimulate FDC-Mix 1 hexose transport in cells that already exhibit an activated transport system from preincubation with IL-3. We conclude that IL-3 maintains FDC-Mix 1 cells via its ability to activate PK-C and increase cytosolic levels of Ca2+, and that an IL-3-mediated activation of PK-C may promote cellular survival via its ability to enhance hexose uptake by phosphorylating the glucose transport protein.