Phosphatidylinositol 3-kinase is essential for kit ligand-mediated survival, whereas interleukin-3 and flt3 ligand induce expression of antiapoptotic Bcl-2 family genes.
Cytokines such as interleukin 3 (IL-3), kit ligand (KL), and flt3 ligand (FL) promote survival of hematopoietic stem cells and myeloid progenitor cells. In many cell types, members of the Bcl-2 gene family are major regulators of survival, but the mediating mechanisms are not fully understood. Using two myeloid progenitor cell lines, FDCP-mix and FDC-P1, as well as primary mouse bone marrow progenitors, we demonstrate that KL-mediated survival is dependent on the activation of phosphatidylinositol-3 (PI-3) kinase. The inhibitor LY294002 was able to completely abolish survival mediated by KL, whereas IL-3 and FL were only partially affected. Although all three cytokines induced phosphorylation of protein kinase B (PKB), only KL required PI-3 kinase activity to elicit survival in hematopoietic progenitors. In contrast, pretreatment of cells with inhibitors to the MAP kinase pathway did not affect the survival. We next established if IL-3 and FL activated antiapoptotic Bcl-2 and the related genes Bcl-XL and Mcl-1. By RNA protection assay and Western blot analysis, we show that all three genes are induced by IL-3, whereas FL induces Bcl-2 and to some extent Bcl-XL. Importantly, KL could not sustain their expression. Moreover, use of inhibitors implied that IL-3 was mainly exerting its effect on Bcl-2 at the level of transcription. The addition of LY294002 did not affect the expression of Bcl-2 and Bcl-XL, and thus, we conclude that expression of antiapoptotic Bcl-2 family member genes is not dependent on PI-3 kinase activity. Our results indicate that cytokines exert distinct survival effects and that FL and IL-3 are capable of sustaining progenitor survival by up-regulating the expression of Bcl-2 and related genes.
Karlsson
Richard
R
Department of Laboratory Medicine, Lund University, University Hospital MAS, Malmö, Sweden.
Engström
Maria
M
Jönsson
Maria
M
Karlberg
Peter
P
Pronk
Cornelis J H
CJ
Richter
Johan
J
Jönsson
Jan-Ingvar
JI
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000502:physiology*; D019254:Genes, bcl-2; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000502:physiology; D007377:Interleukin-3 / Q000494:pharmacology*; D007700:Kinetics; D008024:Ligands; D008565:Membrane Proteins / Q000494:pharmacology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D005810:Multigene Family; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019089:Stem Cell Factor / Q000502:physiology*
D007377:Interleukin-3; D008024:Ligands; D008565:Membrane Proteins; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019089:Stem Cell Factor; C084881:flt3 ligand protein