Ko Y, Banerji S S, Liu Y, Li W, Liang J, Soule H D, Pauley R J, Willson J K, Zborowska E, Brattain M G
Department of Biochemistry and Molecular Biology, Medical College of Ohio, Toledo, USA.
J Cell Physiol. 1998 Aug;176(2):424-34. doi: 10.1002/(SICI)1097-4652(199808)176:2<424::AID-JCP21>3.0.CO;2-1.
To analyze transforming growth factor-beta (TGF-beta) response during MCF-7 cell progression, early passage (MCF-7E, < 200 passage) and late passage (MCF-7L, > 500 passage) cells were compared. MCF-7E cells showed an IC50 of approximately 10 ng/ml of TGF-beta1, whereas MCF-7L cells were insensitive. MCF-7E cells contained approximately threefold higher levels of TGF-beta receptor type II (TbetaRII) mRNA than MCF-7L, but their TbetaRI levels were similar. MCF-7E parental cells showed higher TbetaRII promoter activity than MCF-7L cells, which could be attributed to changes in Sp1 nuclear protein levels. Receptor cross-linking studies indicated that the cell surface receptor levels parallel mRNA levels in both cell lines. Limiting dilution clones of MCF-7E cells were established to determine the heterogeneity of TbetaRII expression in this cell line, and they showed varying degrees of TbetaRII expression. Fibronectin was induced at higher levels in cells expressing higher TbetaRII levels. All three TGF-beta isoforms were detected in limiting dilution clones and parental cells, but TGF-beta1 was more abundant relative to TGF-beta2 or 3, and no correlation between TGF-beta isoform profile with TGF-beta sensitivity was found. MCF-7L cells were tumorigenic and formed xenografts rapidly and progressively, whereas MCF-7E parental and limiting dilution clonal cells showed transient tumor formation followed by regression. These results indicate that decreased TbetaRII transcription in breast cancer cells leads to a loss of TbetaRII expression, resulting in cellular resistance to TGF-beta which contributes to escape from negative growth regulation and tumor progression.
为分析MCF-7细胞进程中转化生长因子-β（TGF-β）的反应，对早期传代（MCF-7E，传代次数<200）和晚期传代（MCF-7L，传代次数>500）细胞进行了比较。MCF-7E细胞对TGF-β1的半数抑制浓度（IC50）约为10 ng/ml，而MCF-7L细胞不敏感。MCF-7E细胞中转化生长因子-β II型受体（TβRII）mRNA水平比MCF-7L细胞高约三倍，但其TβRI水平相似。MCF-7E亲本细胞的TβRII启动子活性高于MCF-7L细胞，这可能归因于Sp1核蛋白水平的变化。受体交联研究表明，两种细胞系中细胞表面受体水平与mRNA水平平行。建立了MCF-7E细胞的有限稀释克隆，以确定该细胞系中TβRII表达的异质性，结果显示它们的TβRII表达程度不同。在TβRII水平较高的细胞中，纤连蛋白的诱导水平更高。在有限稀释克隆和亲本细胞中均检测到所有三种TGF-β亚型，但相对于TGF-β2或3，TGF-β1更为丰富，且未发现TGF-β亚型谱与TGF-β敏感性之间存在相关性。MCF-7L细胞具有致瘤性，能迅速且持续地形成异种移植瘤，而MCF-7E亲本细胞和有限稀释克隆细胞则表现为短暂的肿瘤形成，随后消退。这些结果表明，乳腺癌细胞中TβRII转录的降低导致TβRII表达缺失，从而使细胞对TGF-β产生抗性，这有助于细胞逃避负生长调节并促进肿瘤进展。
