title: C/EBPα regulates CRL4(Cdt2)-mediated degradation of p21 in response to UVB-induced DNA damage to control the G1/S checkpoint.
abstract: The bZIP transcription factor, C/EBPα is highly inducible by UVB and other DNA damaging agents in keratinocytes. C/EBPα-deficient keratinocytes fail to undergo cell cycle arrest in G1 in response to UVB-induced DNA damage and mice lacking epidermal C/EBPα are highly susceptible to UVB-induced skin cancer. The mechanism through which C/EBPα regulates the cell cycle checkpoint in response to DNA damage is unknown. Here we report untreated C/EBPα-deficient keratinocytes have normal levels of the cyclin-dependent kinase inhibitor, p21, however, UVB-treated C/EBPα-deficient keratinocytes fail to up-regulate nuclear p21 protein levels despite normal up-regulation of Cdkn1a mRNA levels. UVB-treated C/EBPα-deficient keratinocytes displayed a 4-fold decrease in nuclear p21 protein half-life due to the increased proteasomal degradation of p21 via the E3 ubiquitin ligase CRL4(Cdt2). Cdt2 is the substrate recognition subunit of CRL4(Cdt2) and Cdt2 mRNA and protein levels were up-regulated in UVB-treated C/EBPα-deficient keratinocytes. Knockdown of Cdt2 restored p21 protein levels in UVB-treated C/EBPα-deficient keratinocytes. Lastly, the failure to accumulate p21 in response to UVB in C/EBPα-deficient keratinocytes resulted in decreased p21 interactions with critical cell cycle regulatory proteins, increased CDK2 activity, and inappropriate entry into S-phase. These findings reveal C/EBPα regulates G1/S cell cycle arrest in response to DNA damage via the control of CRL4(Cdt2) mediated degradation of p21.
authors.affiliation: a Department of Biological Sciences ; North Carolina State University ; Raleigh , NC USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Hall
authors.forename: Michael S
authors.initials: MS
authors.lastname: Bereman
authors.forename: Angelito I
authors.initials: AI
authors.lastname: Nepomuceno
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Thompson
authors.forename: David C
authors.initials: DC
authors.lastname: Muddiman
authors.forename: Robert C
authors.initials: RC
authors.lastname: Smart
mesh_terms: D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics / Q000378:metabolism*; D059447:Cell Cycle Checkpoints / Q000235:genetics / Q000528:radiation effects; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D004249:DNA Damage / Q000235:genetics* / Q000528:radiation effects; D059585:G1 Phase Cell Cycle Checkpoints / Q000235:genetics; D015603:Keratinocytes / Q000378:metabolism / Q000528:radiation effects; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D014466:Ultraviolet Rays; D054462:p21-Activated Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D022763:CCAAT-Enhancer-Binding Protein-alpha; D050759:Cyclin-Dependent Kinase Inhibitor p21; C429530:DTL protein, human; D009687:Nuclear Proteins; D044767:Ubiquitin-Protein Ligases; C515905:Pak1 protein, mouse; D054462:p21-Activated Kinases
keywords: C/EBPα; C/EBPα, CCAAT/enhancer binding protein α; CRL, Cullin-RING ubiquitin ligases; CRL4Cdt2; DCAF, DDB1/CUL4-associated factor; Cdt2, Cdc10 dependent transcript 2; G1/S DNA damage checkpoint; SCF, Skp, Cullin, F-box containing complex; UVB, ultraviolet B; keratinocytes, p21