title: Convergence of hypoxia and TGFβ pathways on cell cycle regulation in human hematopoietic stem/progenitor cells.
abstract: Although it has been shown that HIF1 and 2 fulfill essential roles within the hematopoietic system and in the regulation of HSC fate, little is currently known about the specific mechanisms that are involved. We identified transcriptome changes induced by hypoxia, constitutively active HIF1(P402/564) and HIF2(P405/531) in human cord blood CD34+ cells. Thus, we were able to identify common hypoxia-HIF1-HIF2 gene signatures, but we also identified specific target genes that were exclusively regulated by HIF1, HIF2 or hypoxia. Geneset enrichment analysis (GSEA) revealed that, besides known pathways associated with "hypoxia-induced signaling", also significant enrichment for the Transforming Growth Factor beta (TGFβ) pathway was observed within the hypoxia/HIF1/HIF2 transcriptomes. One of the most significantly upregulated genes in both gene sets was the cyclin dependent kinase inhibitor CDKN1C (p57kip2). Combined hypoxia treatment or HIF overexpression together with TGFβ stimulation resulted in enhanced expression of CDKN1C and enhanced cell cycle arrest within the CD34+/CD38- stem cell compartment. Interestingly, we observed that CD34+ cells cultured under hypoxic conditions secreted high levels of latent TGFβ, suggesting an auto- or paracrine role of TGFβ in the regulation of quiescence of these cells. However, knockdown of SMAD4 could not rescue the hypoxia induced cell cycle arrest, arguing against direct effects of hypoxia-induced secreted TGFβ. Finally, the Gα-coupled receptor GTPase RGS1 was identified as a HIF-dependent hypoxia target that dampens SDF1-induced migration and signal transduction in human CD34+ stem/progenitor cells.
authors.affiliation: Department of Experimental Hematology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands; Department of Laboratory Medicine, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: Albertus T J
authors.initials: AT
authors.lastname: Wierenga
authors.affiliation: Department of Experimental Hematology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: Edo
authors.initials: E
authors.lastname: Vellenga
authors.affiliation: Department of Experimental Hematology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: Jan Jacob
authors.initials: JJ
authors.lastname: Schuringa
mesh_terms: D051997:ADP-ribosyl Cyclase 1 / Q000235:genetics; D018952:Antigens, CD34 / Q000235:genetics; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D002453:Cell Cycle / Q000235:genetics*; D059447:Cell Cycle Checkpoints / Q000235:genetics; D002478:Cells, Cultured; D050761:Cyclin-Dependent Kinase Inhibitor p57 / Q000235:genetics; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000235:genetics*; D051793:Hypoxia-Inducible Factor 1 / Q000235:genetics; D020710:RGS Proteins / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics*; D051901:Smad4 Protein / Q000235:genetics; D013234:Stem Cells / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000235:genetics*; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051997:ADP-ribosyl Cyclase 1; D018952:Antigens, CD34; D051792:Basic Helix-Loop-Helix Proteins; D050761:Cyclin-Dependent Kinase Inhibitor p57; D051793:Hypoxia-Inducible Factor 1; D020710:RGS Proteins; D051901:Smad4 Protein; D016212:Transforming Growth Factor beta; D000099162:Endothelial PAS Domain-Containing Protein 1; C493964:CDKN1C protein, human; C080831:RGS1 protein, human; C497796:SMAD4 protein, human