C/EBPdelta regulates cell cycle and self-renewal of human limbal stem cells.
Human limbal stem cells produce transit amplifying progenitors that migrate centripetally to regenerate the corneal epithelium. Coexpression of CCAAT enhancer binding protein delta (C/EBPdelta), Bmi1, and DeltaNp63alpha identifies mitotically quiescent limbal stem cells, which generate holoclones in culture. Upon corneal injury, a fraction of these cells switches off C/EBPdelta and Bmi1, proliferates, and differentiates into mature corneal cells. Forced expression of C/EBPdelta inhibits the growth of limbal colonies and increases the cell cycle length of primary limbal cells through the activity of p27(Kip1) and p57(Kip2). These effects are reversible; do not alter the limbal cell proliferative capacity; and are not due to apoptosis, senescence, or differentiation. C/EBPdelta, but not DeltaNp63alpha, indefinitely promotes holoclone self-renewal and prevents clonal evolution, suggesting that self-renewal and proliferation are distinct, albeit related, processes in limbal stem cells. C/EBPdelta is recruited to the chromatin of positively (p27(Kip1) and p57(Kip2)) and negatively (p16(INK4A) and involucrin) regulated gene loci, suggesting a direct role of this transcription factor in determining limbal stem cell identity.
Barbaro
Vanessa
V
Epithelial Stem Cell Research Center, The Veneto Eye Bank Foundation, H. SS Giovanni and Paolo, 30100 Venice, Italy.
Testa
Anna
A
Di Iorio
Enzo
E
Mavilio
Fulvio
F
Pellegrini
Graziella
G
De Luca
Michele
M
D051743:CCAAT-Enhancer-Binding Protein-delta / Q000032:analysis / Q000502:physiology*; D002453:Cell Cycle; D049109:Cell Proliferation; D002478:Cells, Cultured; D002843:Chromatin; D004268:DNA-Binding Proteins / Q000032:analysis; D006801:Humans; D016850:Limbus Corneae / Q000166:cytology*; D009687:Nuclear Proteins / Q000032:analysis; D063150:Polycomb Repressive Complex 1; D011518:Proto-Oncogene Proteins / Q000032:analysis; D012097:Repressor Proteins / Q000032:analysis; D013234:Stem Cells / Q000166:cytology*; D015534:Trans-Activators / Q000032:analysis; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins / Q000032:analysis
C069077:BMI1 protein, human; D002843:Chromatin; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; C115051:TP63 protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D051743:CCAAT-Enhancer-Binding Protein-delta; D063150:Polycomb Repressive Complex 1