title: REX-1 expression and p38 MAPK activation status can determine proliferation/differentiation fates in human mesenchymal stem cells.
abstract: BACKGROUND
  REX1/ZFP42 is a well-known embryonic stem cell (ESC) marker. However, the role of REX1, itself, is relatively unknown because the function of REX1 has only been reported in the differentiation of ESCs via STAT signaling pathways. Human mesenchymal stem cells (hMSCs) isolated from young tissues and cancer cells express REX1.
  
  
  RESULTS
  Human umbilical cord blood-derived MSCs (hUCB-MSCs) and adipose tissue-derived MSCs (hAD-MSCs) strongly express REX1 and have a lower activation status of p38 MAPK, but bone marrow-derived MSCs (hBM-MSCs) have weak REX1 expression and higher activation of p38 MAPK. These results indicated that REX1 expression in hMSCs was positively correlated with proliferation rates but inversely correlated with the phosphorylation of p38 MAPK. In hUCB-MSCs, the roles of REX1 and p38 MAPK were investigated, and a knockdown study was performed using a lentiviral vector-based small hairpin RNA (shRNA). After REX1 knockdown, decreased cell proliferation was observed. In REX1 knocked-down hUCB-MSCs, the osteogenic differentiation ability deteriorated, but the adipogenic potential increased or was similar to that observed in the controls. The phosphorylation of p38 MAPK in hUCB-MSCs significantly increased after REX1 knockdown. After p38 MAPK inhibitor treatment, the cell growth in REX1 knocked-down hUCB-MSCs almost recovered, and the suppressed expression levels of CDK2 and CCND1 were also restored. The expression of MKK3, an upstream regulator of p38 MAPK, significantly increased in REX1 knocked-down hUCB-MSCs. The direct binding of REX1 to the MKK3 gene was confirmed by a chromatin immunoprecipitation (ChIP) assay.
  
  
  CONCLUSIONS
  These findings showed that REX1 regulates the proliferation/differentiation of hMSCs through the suppression of p38 MAPK signaling via the direct suppression of MKK3. Therefore, p38 MAPK and REX-1 status can determine the cell fate of adult stem cells (ASCs). These results were the first to show the role of REX1 in the proliferation/differentiation of ASCs.
authors.affiliation: Adult Stem Cell Research, College of Veterinary Medicine, Seoul National University, Seoul, Republic of Korea.
authors.forename: Dilli Ram
authors.initials: DR
authors.lastname: Bhandari
authors.forename: Kwang-Won
authors.initials: KW
authors.lastname: Seo
authors.forename: Kyoung-Hwan
authors.initials: KH
authors.lastname: Roh
authors.forename: Ji-Won
authors.initials: JW
authors.lastname: Jung
authors.forename: Soo-Kyung
authors.initials: SK
authors.lastname: Kang
authors.forename: Kyung-Sun
authors.initials: KS
authors.lastname: Kang
mesh_terms: D000328:Adult; D017209:Apoptosis; D002454:Cell Differentiation; D019070:Cell Lineage; D049109:Cell Proliferation; D016213:Cyclins / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D055785:Gene Knockdown Techniques; D006801:Humans; D051741:Kruppel-Like Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048371:MAP Kinase Kinase 3 / Q000378:metabolism; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000201:enzymology*; D010766:Phosphorylation; D051880:Receptors, Notch / Q000378:metabolism; D015398:Signal Transduction; D051153:Wnt Proteins / Q000378:metabolism; D055815:Young Adult; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D016213:Cyclins; D051741:Kruppel-Like Transcription Factors; D051880:Receptors, Notch; D051153:Wnt Proteins; C507976:ZFP42 protein, human; D048051:p38 Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; C482530:MAP2K3 protein, human
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