title: Regulation of the cell cycle inhibitor p27 and its ubiquitin ligase Skp2 in differentiation of human embryonic stem cells.
abstract: Embryonic stem cells combine the features of robust proliferation with precise differentiation capacity. p27 is a cell cycle inhibitor that is involved in the regulation of proliferation and differentiation in many developing tissues. Recent studies in murine embryonic stem cells have suggested that p27 is involved in the progression of normal differentiation programs in these cells. However, the expression and regulation of p27 and its role in the differentiation of human embryonic stem cells (hESc) has not been previously explored. Herein we show that p27 expression was low in undifferentiated hESc, but increased markedly in differentiated cells. The expression of Skp2, the ubiquitin ligase that targets p27 for degradation, was inversely related to p27 expression. Moreover, embryoid bodies (EBs) with low p27 expression and high Skp2/p27 ratio showed poorer differentiation than those with high p27 expression. Modulation of Skp2 expression is mainly regulated by its rate of degradation. In contrast to somatic cells, which have high levels of Skp2 mainly in S and G2/M, in undifferentiated hESc Skp2 levels were also high in G1. These results point to a potentially important role for p27 regulation in hESc.
authors.affiliation: Department of Plastic Surgery, Rambam Medical Center and the Ruth and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.
authors.forename: Dana
authors.initials: D
authors.lastname: Egozi
authors.forename: Maanit
authors.initials: M
authors.lastname: Shapira
authors.forename: Galit
authors.initials: G
authors.lastname: Paor
authors.forename: Ofer
authors.initials: O
authors.lastname: Ben-Izhak
authors.forename: Karl
authors.initials: K
authors.lastname: Skorecki
authors.forename: Dan D
authors.initials: DD
authors.lastname: Hershko
mesh_terms: D002453:Cell Cycle / Q000502:physiology*; D002454:Cell Differentiation; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases; D003513:Cycloheximide / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D053595:Embryonic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005434:Flow Cytometry; D016193:G1 Phase / Q000502:physiology; D016195:G2 Phase / Q000502:physiology; D006801:Humans; D015151:Immunoblotting; D007976:Leupeptins / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016196:S Phase / Q000502:physiology; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D011500:Protein Synthesis Inhibitors; D044786:S-Phase Kinase-Associated Proteins; D025801:Ubiquitin; D050760:Cyclin-Dependent Kinase Inhibitor p27; D003513:Cycloheximide; D018844:Cyclin-Dependent Kinases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde