Constitutive Expression of Inducible Cyclic Adenosine Monophosphate Early Repressor (ICER) in Cycling Quiescent Hematopoietic Cells: Implications for Aging Hematopoietic Stem Cells.
Despite extensive insights on the interaction between hematopoietic stem cells (HSCs) and the supporting bone marrow (BM) stroma in hematopoietic homeostasis there remains unanswered questions on HSC regulation. We report on the mechanism by which HSCs attain cycling quiescence by addressing a role for inducible cyclic AMP early repressor (ICER). ICER negatively transcriptional regulators of cAMP activators such as CREM and CREB. These activators can be induced by hematopoietic stimulators such as cytokines. We isolated subsets of hematopoietic cells from ten healthy donors: CD34+CD38-/c-kit+(primitive progenitor), CD34+CD38+/c-kitlow(mature progenitor) and CD34-CD38+/-/c-kitlow/-(differentiated lineage-). The relative maturity of the progenitors were verified in long-term culture initiating assay. Immunoprecipitation indicated the highest level of ICER in the nuclear extracts of CD34+/CD38-cells. Phospho (p)-CREM was also present suggesting a balance between ICER and p-CREM in HSC. ICER seems to be responsible for decrease in G1 transition, based on reduced Cdk4 protein, decreased proliferation and functional studies with propidium iodide. There were no marked changes in the cycling inhibitors, p15 and p-Rb, suggesting that ICER may act independently of other cycling inhibitors. The major effects of ICER were validated with BM mononuclear cells (BMNCs) in which ICER was ectopically expressed, and with BMNCs resistant to 5-fluorouracil- or cyclophosphamide. In total, this study ascribes a novel role for ICER in G1 checkpoint regulation in HSCs. These findings are relevant to gene therapy that require engineering of HSCs, age-related disorders that are associated with hematopoietic dysfunction and other hematological disorders.
Department of Medicine, Division of Hematology-Oncology, New Jersey Medical School, Rutgers School of Biomedical Health Science, Newark, NJ, 07103, USA.
Steven J
SJ
Greco
Office of Research Advancement, Rutgers University, New Brunswick, USA.
Ghassan
G
Yehia
Department of Medicine, Division of Hematology-Oncology, New Jersey Medical School, Rutgers School of Biomedical Health Science, Newark, NJ, 07103, USA.
Julius A
JA
Potian
Department of Biology and Molecular Biology, Montclair University, Montclair, NJ, USA.
Carlos A
CA
Molina
Department of Medicine, Division of Hematology-Oncology, New Jersey Medical School, Rutgers School of Biomedical Health Science, Newark, NJ, 07103, USA. rameshwa@njms.rutgers.edu.
Pranela
P
Rameshwar
D051997:ADP-ribosyl Cyclase 1 / Q000378:metabolism; D000375:Aging / Q000235:genetics / Q000378:metabolism; D018952:Antigens, CD34 / Q000378:metabolism; D015153:Blotting, Western; D002453:Cell Cycle / Q000235:genetics*; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D051786:Cyclic AMP Response Element Modulator / Q000235:genetics* / Q000378:metabolism; D003520:Cyclophosphamide / Q000494:pharmacology; D005472:Fluorouracil / Q000494:pharmacology; D015870:Gene Expression; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
D018952:Antigens, CD34; C497410:CREM protein, human; D007166:Immunosuppressive Agents; D051786:Cyclic AMP Response Element Modulator; D003520:Cyclophosphamide; D019009:Proto-Oncogene Proteins c-kit; D051997:ADP-ribosyl Cyclase 1; D005472:Fluorouracil
Bone marrow; Cell cycle; Cytokines; Hematopoietic stem cell; Inducible cAMP early repressor; Transcription factors