Isolation and characterization of rat urinary bladder cancer cell lines with different invasive activities

我们在体外分离了具有独特形态的大鼠膀胱肿瘤NBT-II细胞系的自发变体。在获得的5个亚系中，有3个(NBT-L1、L2a和L2b)在体外表现出细长的形状和中等到高的侵袭活性。另外两个亚系(NBT-T1和T2)形成紧密的菌落，侵袭活性很低或可以忽略不计。编码细胞黏附分子(E-钙粘蛋白、a-连环蛋白和b-连环蛋白)的mRNAs含量与细胞的侵袭活性无关。然而，在侵袭性细胞(NBT-L1、L2a和L2b)中，E-钙粘蛋白的表达水平低于非侵袭性细胞(NBT-T1和T2)，而在连接素的表达水平则不是。对几种生长因子及其受体编码的mRNAs分析表明，侵袭性细胞的转化生长因子-α(TGF-α)mRNA含量高于非侵袭性细胞，而NBT-T2细胞的表皮生长因子受体mRNA含量较低。尽管已知NBT-II能在多种生长因子的作用下获得成纤维细胞的外观和细胞运动能力，但侵袭性细胞亚系的条件培养液几乎不影响非侵袭性细胞的形态和运动能力。这些结果表明，E-钙粘蛋白表达降低是膀胱肿瘤细胞由非侵袭性表型向侵袭性表型转变的主要原因，转录后过程在细胞中E-钙粘附素的表达调控中起重要作用。这些亚系可能成为研究膀胱肿瘤恶变的有用模型。

We isolated, in vitro, spontaneous variants of the rat bladder tumor NBT-II cell line with a distinctive morphology. Of five sublines obtained, three (NBT-L1, L2a, and L2b) exhibited an elongated shape and moderate to high invasive activity in vitro. The other two sublines (NBT-T1 and T2) formed tight colonies and exhibited very low or negligible invasive activity. The contents of mRNAs coding for cell adhesion molecules (E-cadherin, a-catenin and b-catenin) were not correlated with the invasive activity of the cells. However, the expression level of the E-cadherin protein, but not those of catenins, was lower in invasive cells (NBT-L1, L2a and L2b) than in noninvasive cells (NBT-T1 and T2) . Analysis of mRNAs coding for several growth factors and their receptors showed that the transforming growth factor-alpha (TGF-alpha) mRNA content in invasive cells was higher than that in noninvasive cells, and that the content of epidermal growth factor receptor mRNA was low in NBT-T2. Although NBT-II is known to acquire a fibroblastic appearance and cell motility in response to several growth factors, the conditioned media of the invasive sublines hardly affected the morphology or motility of noninvasive cells. These results indicate that the decreased E-cadherin expression is a major cause of the transition from the noninvasive to the invasive phenotype of the bladder tumor cells, and that post-transcriptional process is important in the control of E-cadherin expression in the cells. These sublines may constitute useful models for studies on the malignant transformation of bladder tumors.