C/EBPalpha is required to maintain postmitotic growth arrest in adipocytes.
Terminal differentiation is often coupled with irreversible loss of proliferative potential. The CCAAT enhancer binding protein alpha (C/EBPalpha) preferentially accumulates in postmitotic, differentiated 3T3-L1 adipocytes but declines during tumor necrosis factor alpha (TNFalpha)-induced dedifferentiation. We have discovered that this decline in C/EBPalpha correlates with an increased mitotic growth potential. In order to further investigate the antimitotic activity of C/EBPalpha, we introduced antisense C/EBPalpha RNA into 3T3-L1 cells to block endogenous C/EBPalpha expression. When treated according to the standard differentiation protocol, stable cells lines harboring antisense C/EBPalpha RNA did not differentiate into fat-laden adipocytes, consistent with previous findings (Lin F, Lane MD, Genes Dev 1992;6:533-544). We found that these undifferentiated cells expressing antisense-C/EBPalpha can reenter the cell cycle after mitogenic stimulation at a time in development when parental 3T3-L1 cells cannot. Moreover, the expression profiles of the growth-arrest-associated genes gas1 and gas2 revealed that the antisense C/EBPalpha-expressing cells withdrew from the cell cycle after the period of clonal expansion but failed to progress to the state of least proliferative potential characteristic of terminally differentiated adipocytes.
Tao
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Department of Biology, University of Virginia, Charlottesville 22903, USA. taoheng@leland.stanford.edu
Umek
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D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D022762:CCAAT-Enhancer-Binding Proteins; D018797:Cell Cycle Proteins; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005434:Flow Cytometry; D058851:GPI-Linked Proteins; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism; D008938:Mitosis / Q000235:genetics* / Q000502:physiology; D009687:Nuclear Proteins / Q000378:metabolism*; D016372:RNA, Antisense / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C066709:GAS1 protein, S cerevisiae; C096192:GAS1 protein, human; D058851:GPI-Linked Proteins; C501180:Gas1 protein, mouse; C099165:Gas2 protein, mouse; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D008840:Microfilament Proteins; D009687:Nuclear Proteins; D016372:RNA, Antisense; D029701:Saccharomyces cerevisiae Proteins; D014409:Tumor Necrosis Factor-alpha