CCAAT/enhancer binding protein alpha uses distinct domains to prolong pituitary cells in the growth 1 and DNA synthesis phases of the cell cycle.
BACKGROUND
A number of transcription factors coordinate differentiation by simultaneously regulating gene expression and cell proliferation. CCAAT/enhancer binding protein alpha (C/EBPalpha) is a basic/leucine zipper transcription factor that integrates transcription with proliferation to regulate the differentiation of tissues involved in energy balance. In the pituitary, C/EBPalpha regulates the transcription of a key metabolic regulator, growth hormone.


RESULTS
We examined the consequences of C/EBPalpha expression on proliferation of the transformed, mouse GHFT1-5 pituitary progenitor cell line. In contrast to mature pituitary cells, GHFT1-5 cells do not contain C/EBPalpha. Ectopic expression of C/EBPalpha in the progenitor cells resulted in prolongation of both growth 1 (G1) and the DNA synthesis (S) phases of the cell cycle. Transcription activation domain 1 and 2 of C/EBPalpha were required for prolongation of G1, but not of S. Some transcriptionally inactive derivatives of C/EBPalpha remained competent for G1 and S phase prolongation. C/EBPalpha deleted of its leucine zipper dimerization functions was as effective as full-length C/EBPalpha in prolonging G1 and S.


CONCLUSIONS
We found that C/EBPalpha utilizes mechanistically distinct activities to prolong the cell cycle in G1 and S in pituitary progenitor cells. G1 and S phase prolongation did not require that C/EBPalpha remained transcriptionally active or retained the ability to dimerize via the leucine zipper. G1, but not S, arrest required a domain overlapping with C/EBPalpha transcription activation functions 1 and 2. Separation of mechanisms governing proliferation and transcription permits C/EBPalpha to regulate gene expression independently of its effects on proliferation.
Liu
Weiqun
W
Metabolic Research Unit, Diabetes Research Center and Department of Medicine, University of California, San Francisco, CA 94143-0540, USA. liu_weiqun@hotmail.com
Enwright
John F
JF
Hyun
William
W
Day
Richard N
RN
Schaufele
Fred
F
D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002461:Cell Line, Transformed; D002503:Centromere / Q000235:genetics; D004247:DNA / Q000096:biosynthesis*; D016193:G1 Phase / Q000235:genetics / Q000502:physiology*; D018390:Gene Targeting; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism* / Q000502:physiology*; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016196:S Phase / Q000235:genetics / Q000502:physiology; D013234:Stem Cells / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D015533:Transcriptional Activation / Q000235:genetics / Q000502:physiology
D022763:CCAAT-Enhancer-Binding Protein-alpha; D018797:Cell Cycle Proteins; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D004247:DNA