Leff M A, Buckley D J, Krumenacker J S, Reed J C, Miyashita T, Buckley A R
Department of Pharmacology and Toxicology, University of North Dakota School of Medicine, Grand Forks 58202-9037, USA.
Endocrinology. 1996 Dec;137(12):5456-62. doi: 10.1210/endo.137.12.8940371.
The Nb2 rat lymphoma represents a useful model for investigation of molecular events coupled to PRL-induced proliferation. Moreover, recent evidence has also demonstrated the utility of this system to study mechanisms linked to programmed cell death (apoptosis). Thus, glucocorticosteroids activate apoptosis in lactogen-dependent Nb2 cells, whereas the addition of PRL abrogates this effect. The present study was conducted to determine whether PRL stimulation in lactogen-dependent Nb2-11 or autonomous Nb2-SFJCD1 cultures alters expression of bcl-2 or bax, genes that suppress or facilitate apoptosis, respectively. We demonstrate that PRL stimulation in stationary Nb2-11 cultures significantly increased the level of bcl-2 messenger RNA (mRNA) within 3 h (15-fold) and its protein product by 6 h, time points previously shown to correspond with G1 cell cycle progression. In Nb2-SFJCD1 cells, bcl-2 mRNA was found to be constitutively present. Addition of PRL to these lactogen-independent cultures further enhanced its expression at the mRNA and protein levels with a kinetic pattern similar to that observed in the PRL-dependent line. Results from stability studies indicated that increased bcl-2 mRNA evoked by PRL in Nb2 cell lines was most likely not attributable to increased stability of its transcripts. Furthermore, the rapid increase in its expression in PRL-stimulated Nb2-11 cells was not altered by inhibition of protein synthesis suggesting a direct action of the hormone. PRL also increased bax mRNA by 8 h in Nb2-11 cultures. However, hormone stimulation markedly attenuated the level of the Bax protein from 2-6 h. In contrast, bax expression in Nb2-SFJCD1 cultures remained unaltered by the addition of the hormone. These results demonstrate that altered expression of bcl-2 and bax are each associated with PRL-stimulated cell cycle progression in Nb2 cells. Moreover, bcl-2 appears to be an immediate-early gene induced by PRL in the hormone-dependent line and may represent an important regulator of early G1 cell cycle progression most likely by suppressing cell death mechanisms.
Nb2大鼠淋巴瘤是研究与催乳素诱导的增殖相关分子事件的有用模型。此外，最近的证据还证明了该系统在研究与程序性细胞死亡（凋亡）相关机制方面的实用性。因此，糖皮质激素可激活依赖催乳素的Nb2细胞中的凋亡，而添加催乳素可消除这种作用。本研究旨在确定在依赖催乳素的Nb2-11或自主的Nb2-SFJCD1培养物中催乳素刺激是否会改变bcl-2或bax的表达，这两个基因分别抑制或促进凋亡。我们证明，在静止的Nb2-11培养物中催乳素刺激在3小时内显著增加了bcl-2信使核糖核酸（mRNA）水平（15倍），并在6小时内增加了其蛋白质产物，这些时间点先前已显示与G1细胞周期进程相对应。在Nb2-SFJCD1细胞中，发现bcl-2 mRNA是组成性存在的。向这些不依赖催乳素的培养物中添加催乳素进一步增强了其在mRNA和蛋白质水平的表达，其动力学模式与在依赖催乳素的细胞系中观察到的相似。稳定性研究结果表明，催乳素在Nb2细胞系中引起的bcl-2 mRNA增加很可能不是由于其转录本稳定性增加所致。此外，在催乳素刺激的Nb2-11细胞中其表达的快速增加不受蛋白质合成抑制的影响，这表明该激素具有直接作用。催乳素在Nb2-11培养物中8小时后也增加了bax mRNA。然而，激素刺激在2至6小时内显著降低了Bax蛋白水平。相比之下，在Nb2-SFJCD1培养物中添加激素后bax表达未改变。这些结果表明，bcl-2和bax表达的改变均与催乳素刺激的Nb2细胞中的细胞周期进程相关。此外，bcl-2似乎是催乳素在激素依赖细胞系中诱导的即刻早期基因，并且很可能通过抑制细胞死亡机制代表早期G1细胞周期进程的重要调节因子。
