Sun H, Santoro S A, Zutter M M
Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Cancer Res. 1998 May 15;58(10):2224-33.
Our previous studies demonstrated that reexpression of the alpha2beta1 integrin by a poorly differentiated breast carcinoma cell line, Mm5MT, resulted in dramatic reversion of a malignant phenotype to a differentiated epithelial phenotype. We hypothesized that reexpression of the alpha2beta1 integrin may regulate expression of other genes, the expression of which contributed to the dramatic phenotypic change. We now show that reexpression of the alpha2beta1 integrin results in up-regulation of both the alpha6 and beta4 integrin subunits but no change in the alpha1, alpha3, alpha5, or beta1 integrin subunits or E-cadherin. To further investigate the role of the alpha6 and beta4 integrin subunits in mediating the phenotypic changes elicited by reexpression of the alpha2beta1 integrin, the alpha6 or beta4 integrin subunit was expressed in our Mm5MT model. Expression of either subunit increased adhesion to laminin-1. Although adhesion to collagen was unaltered, contraction of three-dimensional collagen gels was reduced. Expression of either the alpha6 or beta4 integrin subunit also restored some aspects of a less malignant phenotype, including the acquisition of contact inhibition and diminution of anchorage-dependent and anchorage-independent growth rates. The alpha6 and beta4 transfectants formed three-dimensional organized structures when grown in gels of reconstituted basement membrane but did not form the highly branched, duct-like structures formed by the alpha2 transfectants. In contrast to the reduced invasiveness of the alpha2 transfectants, the alpha6 and beta4 transfectants retained an invasive phenotype. These results suggest that expression of the alpha6beta4 integrin contributes to some but not all of the phenotypic changes elicited by reexpression of the alpha2 integrin subunit and modulates the function of other integrins on these cells. Using our Mm5MT model, we are defining the cascade of integrin expression required for maintenance of the differentiated mammary epithelial cell phenotype.
我们之前的研究表明，低分化乳腺癌细胞系Mm5MT重新表达α2β1整合素后，恶性表型显著逆转，转变为分化的上皮表型。我们推测，α2β1整合素的重新表达可能会调节其他基因的表达，而这些基因的表达促成了显著的表型变化。我们现在发现，α2β1整合素的重新表达导致α6和β4整合素亚基上调，但α1、α3、α5或β1整合素亚基以及E-钙黏蛋白没有变化。为了进一步研究α6和β4整合素亚基在介导α2β1整合素重新表达引发的表型变化中的作用，我们在Mm5MT模型中表达了α6或β4整合素亚基。任一亚基的表达均增加了对层粘连蛋白-1的黏附。虽然对胶原蛋白的黏附未改变，但三维胶原凝胶的收缩减少。α6或β4整合素亚基的表达还恢复了一些恶性程度较低的表型特征，包括获得接触抑制以及降低锚定依赖性和非锚定依赖性生长速率。α6和β4转染细胞在重组基底膜凝胶中生长时形成三维有序结构，但未形成α2转染细胞形成的高度分支的导管样结构。与α2转染细胞侵袭性降低相反，α6和β4转染细胞保留了侵袭性表型。这些结果表明，α6β4整合素的表达促成了α2整合素亚基重新表达引发的部分而非全部表型变化，并调节了这些细胞上其他整合素的功能。利用我们的Mm5MT模型，我们正在确定维持分化乳腺上皮细胞表型所需的整合素表达级联。
