Loss of α-Dystroglycan Laminin Binding in Epithelium-derived Cancers Is Caused by Silencing of LARGE

Abstract

The interaction between epithelial cells and the extracellular matrix is crucial for tissue architecture and function and is compromised during cancer progression. Dystroglycan is a membrane receptor that mediates interactions between cells and basement membranes in various epithelia. In many epithelium-derived cancers, ␤-dystroglycan is expressed, but ␣-dystroglycan is not detected. Here we report that ␣-dystroglycan is correctly expressed and trafficked to the cell membrane but lacks laminin binding as a result of the silencing of the like-acetylglucosaminyltransferase (LARGE) gene in a cohort of highly metastatic epithelial cell lines derived from breast, cervical, and lung cancers. Exogenous expression of LARGE in these cancer cells restores the normal glycosylation and laminin binding of ␣-dystroglycan, leading to enhanced cell adhesion and reduced cell migration in vitro. Our findings demonstrate that LARGE repression is responsible for the defects in dystroglycan-mediated cell adhesion that are observed in epithelium-derived cancer cells and point to a defect of dystroglycan glycosylation as a factor in cancer progression.Normal epithelial cells are tightly associated with one another and with the underlying basement membrane to maintain tissue architecture and function. During cancer progression, primitive cancer cells escape from this control by modifying the binding affinities of their cell membrane receptors. Several receptors have been described as important for this process. Of these, the integrins are the best studied (1). The receptor dystroglycan has been reported to be required for the development and maintenance of epithelial tissues (2, 3). A direct requirement for dystroglycan in epithelia is further demonstrated by the profound effect that loss of dystroglycan expression has on cell polarity and laminin binding in cultured mammary epithelial cells (4, 5). However, dystroglycan is not only important in the establishment and maintenance of epithelial structure. Associations have also been made between the loss of ␣-dystroglycan immunoreactivity and cancer progression in tumors of epithelial origin, including breast, colon, cervix, and prostate cancers (4, 6 -9). The dystroglycan loss of function could thus serve as an effective means by which cancerous cells modify their adhesion to the extracellular matrix (ECM). 2Dystroglycan is a ubiquitously expressed cell membrane protein that plays a key function in cellular integrity, linking the intracellular cytoskeleton to the extracellular matrix. The dystroglycan gene encodes a preprotein that is cleaved into two peptides (10). The C-terminal component, known as ␤-dystroglycan, is embedded within the cell membrane, whereas the N-terminal component, ␣-dystroglycan, is present within the extracellular periphery but remains associated with ␤-dystroglycan through non-covalent bonds. ␤-Dystroglycan binds to actin (11), dystrophin (11), utrophin (11), and Grb2 (12) through its C-terminal intracellular domain. ␣-Dystroglycan, on the other hand, binds to E...

Human Natural Killer-1 Sulfotransferase (HNK-1ST)-induced Sulfate Transfer Regulates Laminin-binding Glycans on α-Dystroglycan

“…Hence, ␣-DG-dependent migration controlled by HNK-1ST might predominate in HNK-1-negative melanomas. The unique glycan structure expressed on ␣-DG has been shown to have a close relationship to tumor-related phenotypes such as invasiveness (32,33). Previous studies reported that the IIH6 mAb-reactive glycan of ␣-DG had a suppressive effect on tumor invasion in cases of breast, prostate, and lung carcinoma (32,33), although we obtained the opposite results using melanoma cells (Figs.…”

“…It has been demonstrated that ␣-DG, especially the glycan attached to it, is involved in tumor invasiveness in various cancer types such as breast, prostate, and lung carcinomas (32,33). Because HNK-1ST associates with the modification of glycans, up-regulation of HNK-1ST expression might affect the glycosylation in cells.…”

“…These observations indicate that O-mannosyl modification is essential for the functional glycosylation of ␣-DG. Furthermore, altered glycosylation of ␣-DG is also implicated in epithelium-derived cancer progression, demonstrating the involvement of ␣-DG in tumorigenic phenotypes (32,33).…”

Absence of Post-phosphoryl Modification in Dystroglycanopathy Mouse Models and Wild-type Tissues Expressing Non-laminin Binding Form of α-Dystroglycan

“…This situation is exemplified in studies using cancer cells. It has been reported that several malignant cancer cell types lose the laminin-binding glycan of ␣-DG due to epigenetic down-regulation of LARGE or defects in the LARGE-binding protein ␤3GnT1, raising the possibility of defects in post-phosphoryl modification of ␣-DG in those cells (31,33).…”

Tumor suppressor function of laminin-binding α-dystroglycan requires a distinct β3- N -acetylglucosaminyltransferase

“…These results demonstrated antimigratory activity of laminin-binding glycans attached to ␣-DG. While we were preparing our article, a report appeared showing that downregulation of LARGE resulted in higher migration of carcinoma cells (29).…”