Sgambato A, Di Salvatore M A, De Paola B, Rettino A, Faraglia B, Boninsegna A, Graziani C, Camerini A, Proietti G, Cittadini A
Centro di Ricerche Oncologiche "Giovanni XXIII", Istituto di Patologia Generale, Catholic University, Rome, Italy.
J Cell Physiol. 2006 May;207(2):520-9. doi: 10.1002/jcp.20600.
Abnormalities in the interactions of cells with the extracellular matrix (ECM) play an important role in the development and progression of many types of cancer and are a hallmark of malignant transformation. The dystroglycan (DG) complex is a transmembrane glycoprotein that forms a continuous link from the ECM to the actin cytoskeleton, providing structural integrity and perhaps transducing signal, in a manner similar to integrins. Deregulated expression of DG has been reported in a variety of human malignancies and related to tumor differentiation and aggressiveness. In breast cancer, reduced DG expression has been associated with patient survival and with loss of differentiation of tumor cells. Limited data are available on DG physiology in epithelial cells. In this study, we used the HC11 spontaneously immortalized murine mammary epithelial cells to study DG function(s) and regulation in normal cells. We found that expression of DG protein and mRNA is cell-cycle and cell-density regulated in these cells. Moreover, expression of both DG subunits increased upon lactogenic differentiation of the HC11 cells. The turnover of cell-surface-expressed DG was evaluated in the same cells and half-life of DG subunits was evaluated to be about 12 h. DG-specific small inhibitory RNAs were used to analyze the effects of a reduced expression of DG in these cells. Cells in which DG expression was suppressed were growth inhibited, accumulated in the S-phase of the cell cycle, failed to undergo lactogenic differentiation, and displayed an increase in the percentage of apoptotic cells. Moreover, changes were observed in the expression and/or activity of several molecules involved in cell growth control. These results demonstrate that DG expression is tightly regulated in normal mammary epithelial cells and support the hypothesis that DG is involved in several functions other than structural integrity in these cells. This finding provides new insight into the roles played by DG in epithelial cell physiology and will contribute to our understanding of its involvement in the process of epithelial cell transformation.
细胞与细胞外基质（ECM）相互作用的异常在多种癌症的发生和发展中起着重要作用，是恶性转化的一个标志。肌营养不良聚糖（DG）复合体是一种跨膜糖蛋白，它形成了从ECM到肌动蛋白细胞骨架的连续连接，以类似于整合素的方式提供结构完整性并可能转导信号。DG的表达失调已在多种人类恶性肿瘤中报道，并与肿瘤分化和侵袭性相关。在乳腺癌中，DG表达降低与患者生存率以及肿瘤细胞分化丧失有关。关于上皮细胞中DG生理学的可用数据有限。在本研究中，我们使用HC11自发永生化小鼠乳腺上皮细胞来研究正常细胞中DG的功能及其调控。我们发现，在这些细胞中，DG蛋白和mRNA的表达受细胞周期和细胞密度调节。此外，HC11细胞在泌乳分化时，两种DG亚基的表达均增加。我们在相同细胞中评估了细胞表面表达的DG的周转率，并评估了DG亚基的半衰期约为12小时。使用DG特异性小干扰RNA来分析这些细胞中DG表达降低的影响。DG表达被抑制的细胞生长受到抑制，积聚在细胞周期的S期，无法进行泌乳分化，并且凋亡细胞百分比增加。此外，还观察到参与细胞生长控制的几种分子的表达和/或活性发生了变化。这些结果表明，在正常乳腺上皮细胞中，DG表达受到严格调控，并支持了DG除了在这些细胞中的结构完整性之外还参与多种功能的假说。这一发现为DG在上皮细胞生理学中的作用提供了新的见解，并将有助于我们理解其在上皮细胞转化过程中的参与情况。
