Extracellular Signal-Regulated Kinase 2 and CHOP Restrict the Expression of the Growth Arrest-Specific p20K Lipocalin Gene to G0.
The activation of the growth arrest-specific (gas) p20K gene depends on the interaction of C/EBPβ with two elements of a 48-bp promoter region termed the quiescence-responsive unit (QRU). Here we identify extracellular signal-related kinase 2 (ERK2) as a transcriptional repressor of the p20K QRU in cycling chicken embryo fibroblasts (CEF). ERK2 binds to repeated GAAAG sequences overlapping the C/EBPβ sites of the QRU. The recruitment of ERK2 and C/EBPβ is mutually exclusive and dictates the expression of p20K. C/EBP homologous protein (CHOP) was associated with C/EBPβ under conditions promoting endoplasmic reticulum (ER) stress and, to a lesser extent, in cycling CEF but was not detectable when C/EBPβ was immunoprecipitated from contact-inhibited cells. During ER stress, overexpression of CHOP inhibited p20K, while its downregulation promoted p20K, indicating that CHOP is also a potent inhibitor of p20K. Transcriptome analyses revealed that hypoxia-responsive genes are strongly induced in contact-inhibited but not serum-starved CEF, and elevated levels of nitroreductase activity, a marker of hypoxia, were detected at confluence. Conditions of hypoxia (2% O2) induced growth arrest in subconfluent CEF and markedly stimulated p20K expression, suggesting that the control of proliferation and gas gene expression is closely linked to limiting oxygen concentrations associated with high cell densities.
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
M J
MJ
Erb
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
D
D
Camacho
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
W
W
Xie
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
B M
BM
Maslikowski
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
B
B
Fielding
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
R
R
Ghosh
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
F-A
FA
Poujade
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
M
M
Athar
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
S
S
Assee
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
L-E
LE
Mantella
Department of Biology, McMaster University, Hamilton, Ontario, Canada abedard@mcmaster.ca.
P-A
PA
Bédard
D000818:Animals; D030161:Avian Proteins / Q000235:genetics / Q000378:metabolism; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism*; D002453:Cell Cycle; D015687:Cell Hypoxia; D049109:Cell Proliferation; D002478:Cells, Cultured; D002642:Chick Embryo; D059865:Endoplasmic Reticulum Stress; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism; D020869:Gene Expression Profiling / Q000379:methods; D005786:Gene Expression Regulation; D054834:Lipocalins / Q000235:genetics*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D051742:Transcription Factor CHOP / Q000378:metabolism*
D030161:Avian Proteins; D022782:CCAAT-Enhancer-Binding Protein-beta; D054834:Lipocalins; D051742:Transcription Factor CHOP; D019950:Mitogen-Activated Protein Kinase 1