Department of Biochemistry and Molecular Biology, Stanley Scott Cancer Center, LSU Health Sciences Center, New Orleans, LA 70112, USA.
Mol Cancer. 2011 Jul 13;10:84. doi: 10.1186/1476-4598-10-84.
Although integrins have been implicated in the progression of breast cancer, the exact mechanism whereby they exert this regulation is clearly not understood. To understand the role of integrins in breast cancer, we examined the expression levels of several integrins in mouse breast cancer cell lines by flow cytometry and the data were validated by Western and RT-PCR analysis. The importance of integrins in cell migration and cell invasion was examined by in vitro assays. Further the effect of integrins on metastasis was investigated by in vivo experimental metastasis assays using mouse models.
Integrin α5 subunit is highly expressed in the nonmetastatic cell line 67NR and is significantly low in the highly invasive cell line 4T1. In contrast, expression levels of integrin α6 subunit are high in 4T1 cells and low in 67NR cells. In vitro data indicated that overexpression of α5 subunit and knockdown of α6 integrin subunit inhibited cell proliferation, migration, and invasion. Our in vivo findings indicated that overexpression of integrin α5 subunit and knockdown of α6 subunit decreased the pulmonary metastasis property of 4T1 cells. Our data also indicated that overexpression of alpha 5 integrin subunit and suppression of alpha6 integrin subunit inhibited cells entering into S phase by up-regulating p27, which results in downregulation of cyclinE/CDK2 complexes, This suggests that these integrins regulate cell growth through their effects on cell-cycle-regulated proteins. We also found that modulation of these integrins upregulates E2F, which may induce the expression of chk1 to regulate cdc25A/cyclin E/CDK2/Rb in a feedback loop mechanism.
This study indicates that Integrin α5 subunit functions as a potential metastasis suppressor, while α6 subunit functions as a metastasis promoter. The modulation of integrins reduces cdc25 A, another possible mechanism for downregulation of CDK2. Taken together we demonstrate a link between integrins and the chk1-cdc25-cyclin E/CDK2-Rb pathway.
尽管整合素已被牵涉到乳腺癌的进展中,但它们发挥这种调节作用的确切机制显然尚未被理解。为了了解整合素在乳腺癌中的作用,我们通过流式细胞术检查了几种整合素在小鼠乳腺癌细胞系中的表达水平,并通过 Western 和 RT-PCR 分析验证了数据。通过体外测定法检查了整合素在细胞迁移和细胞侵袭中的重要性。进一步通过使用小鼠模型的体内实验转移测定法研究了整合素对转移的影响。
整合素 α5 亚基在非转移性细胞系 67NR 中高度表达,而在高度侵袭性细胞系 4T1 中则明显降低。相反,整合素 α6 亚基的表达水平在 4T1 细胞中较高,而在 67NR 细胞中较低。体外数据表明,α5 亚基的过表达和 α6 整合素亚基的敲低抑制了细胞增殖、迁移和侵袭。我们的体内发现表明,过表达整合素 α5 亚基和敲低 α6 亚基降低了 4T1 细胞的肺转移特性。我们的数据还表明,通过上调 p27,α5 整合素亚基的过表达和 α6 整合素亚基的抑制抑制了细胞进入 S 期,从而下调了细胞周期蛋白 E/CDK2 复合物,这表明这些整合素通过对细胞周期蛋白调节蛋白的影响来调节细胞生长。我们还发现,这些整合素的调节上调了 E2F,这可能诱导 chk1 的表达以通过反馈环机制调节 cdc25A/细胞周期蛋白 E/CDK2/Rb。
这项研究表明,整合素 α5 亚基作为潜在的转移抑制因子起作用,而 α6 亚基作为转移促进因子起作用。整合素的调节降低了 cdc25A,这是下调 CDK2 的另一种可能机制。综上所述,我们证明了整合素与 chk1-cdc25-cyclin E/CDK2-Rb 途径之间存在联系。