Tao H, Umek R M
Department of Biology, University of Virginia, Charlottesville 22903, USA.
DNA Cell Biol. 2000 Jan;19(1):9-18. doi: 10.1089/104454900314663.
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.
终末分化通常伴随着增殖潜能的不可逆丧失。CCAAT增强子结合蛋白α（C/EBPα）优先积累在有丝分裂后、已分化的3T3-L1脂肪细胞中，但在肿瘤坏死因子α（TNFα）诱导的去分化过程中会减少。我们发现C/EBPα的这种减少与有丝分裂生长潜能的增加相关。为了进一步研究C/EBPα的抗有丝分裂活性，我们将反义C/EBPα RNA导入3T3-L1细胞以阻断内源性C/EBPα的表达。按照标准分化方案处理时，携带反义C/EBPα RNA的稳定细胞系不会分化为充满脂肪的脂肪细胞，这与先前的研究结果一致（Lin F，Lane MD，Genes Dev 1992；6：533 - 544）。我们发现这些表达反义C/EBPα的未分化细胞在发育过程中，在有丝分裂原刺激后能够重新进入细胞周期，而此时亲代3T3-L1细胞则不能。此外，生长停滞相关基因gas1和gas2的表达谱显示，表达反义C/EBPα的细胞在克隆扩增期后退出细胞周期，但未能进展到终末分化脂肪细胞所特有的增殖潜能最低的状态。
