Hematopoietic stem cells need two signals to prevent apoptosis; BCL-2 can provide one of these, Kitl/c-Kit signaling the other.
Growth factors can cause cells to proliferate, differentiate, survive, or die. Distinguishing between these responses is difficult in multicellular, multiparameter systems. Yet this is essential to understand the impact on cells like hematopoietic stem cells (HSCs), which have strict and still poorly understood growth factor requirements. Single cell plating in serum-free medium allows direct assessment of growth factor responses. The range of tested factors can be expanded if the cells are protected from growth factor deprivation-induced apoptosis. BCL-2 is overexpressed in HSCs of H2K-BCL-2 transgenic mice, protecting them from many apoptotic stimuli. The response of single wild-type and transgenic HSCs to stimulations with individual factors was tested. Surprisingly, we find that high level BCL-2 expression does not prevent rapid death under serum-free conditions, even though it does in the presence of serum. We also find that transgenic, but not wild-type cells, survive and proliferate rapidly in response to steel factor (Kit ligand). These studies show that two separate signals are necessary to prevent apoptosis in HSCs, and that Kit ligand by itself provides a strong proliferative stimulus to HSCs. However, the proliferative response does not result in self-renewal, but in differentiation to all known hematopoietic oligolineage progenitors.
Domen
J
J
Department of Pathology and Developmental Biology, Stanford University School of Medicine, Stanford, California 94305, USA.
Weissman
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IL
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002452:Cell Count; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D005786:Gene Expression Regulation / Q000187:drug effects; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D006651:Histocytochemistry; D007377:Interleukin-3 / Q000494:pharmacology; D008407:Mast Cells / Q000166:cytology / Q000187:drug effects; D051379:Mice; D008822:Mice, Transgenic; D010529:Peritoneal Cavity / Q000166:cytology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D019089:Stem Cell Factor / Q000494:pharmacology*; D013234:Stem Cells / Q000166:cytology / Q000187:drug effects; D013926:Thrombopoietin / Q000494:pharmacology
D016895:Culture Media, Serum-Free; D007377:Interleukin-3; D019253:Proto-Oncogene Proteins c-bcl-2; D019089:Stem Cell Factor; D013926:Thrombopoietin; D019009:Proto-Oncogene Proteins c-kit