Loss of SIMPL compromises TNF-alpha-dependent survival of hematopoietic progenitors.
OBJECTIVE
Emerging work has revealed an integral role of the tumor necrosis factor-alpha (TNF-alpha) nuclear factor (NF)-kappaB pathway in the regulation of hematopoiesis. TNF-alpha inhibition of hematopoietic stem/progenitor cell growth involves type I TNF-alpha receptor (TNF-RI) and type II TNF-alpha receptor (TNF-RII). However, the role of TNF-RI vs TNF-RII in mediating this response is less clear. Full induction of NF-kappaB-dependent gene expression through TNF-RI requires the transcriptional coactivator SIMPL (substrate that interacts with mouse pelle-like kinase). To address the role of SIMPL in TNF-alpha-dependent signaling in hematopoiesis, endothelial cells and hematopoietic progenitors expressing SIMPL short hairpin RNA were characterized.


METHODS
In vitro gene expression and progenitor assays employing SIMPL short hairpin RNA were used to examine the requirement for SIMPL in TNF-alpha-dependent effects upon cytokine gene expression and hematopoietic progenitor cell growth. Competitive repopulation studies were used to extend these studies in vivo.


RESULTS
SIMPL is required for full TNF-RI-dependent expression of NF-kappaB-controlled cytokines in endothelial cells. Hematopoietic progenitor cell expansion is not affected if progenitors lacked SIMPL or if progenitors are treated with human TNF-alpha, which signals through TNF-RI. In the absence of SIMPL, human TNF-alpha leads to a dramatic decrease in progenitor cell expansion that is not due to apoptosis. Loss of SIMPL does not affect the activity of transforming growth factor-beta1 and interferon-gamma, other known suppressors of hematopoiesis.


CONCLUSIONS
Suppression of myeloid progenitor cell expansion requires signaling through TNF-RI and TNF-RII. Signals transduced through the TNF-alpha-TNF-RI-SIMPL pathway support hematopoietic progenitor cell survival, growth and differentiation.
Benson
Eric A
EA
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202-5122, USA.
Goebl
Mark G
MG
Yang
Feng-Chun
FC
Kapur
Reuben
R
McClintick
Jeanette
J
Sanghani
Sonal
S
Clapp
D Wade
DW
Harrington
Maureen A
MA
D000818:Animals; D017209:Apoptosis; D001854:Bone Marrow Cells / Q000737:chemistry / Q000378:metabolism; D002352:Carrier Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002470:Cell Survival; D004622:Embryo, Mammalian; D042783:Endothelial Cells / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000737:chemistry / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D055014:Granulocyte-Macrophage Progenitor Cells / Q000166:cytology / Q000502:physiology; D006410:Hematopoiesis / Q000187:drug effects / Q000502:physiology; D006412:Hematopoietic Stem Cells / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D055029:Inverted Repeat Sequences; D007668:Kidney; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000502:physiology; D012313:RNA / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D018124:Receptors, Tumor Necrosis Factor / Q000502:physiology; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B; D012333:RNA, Messenger; D018124:Receptors, Tumor Necrosis Factor; D011994:Recombinant Proteins; C493527:SIMPL protein, mouse; D014409:Tumor Necrosis Factor-alpha; D012313:RNA