Cancer Malignancy Is Correlated with Upregulation of PCYT2-Mediated Glycerol Phosphate Modification of α-Dystroglycan.

The dystrophin-glycoprotein complex connects the cytoskeleton with base membrane components such as laminin through unique O-glycans displayed on α-dystroglycan (α-DG). Genetic impairment of elongation of these glycans causes congenital muscular dystrophies. We previously identified that glycerol phosphate (GroP) can cap the core part of the α-DG O-glycans and terminate their further elongation. This study examined the possible roles of the GroP modification in cancer malignancy, focusing on colorectal cancer. We found that the GroP modification critically depends on PCYT2, which serves as cytidine 5'-diphosphate-glycerol (CDP-Gro) synthase. Furthermore, we identified a significant positive correlation between cancer progression and GroP modification, which also correlated positively with PCYT2 expression. Moreover, we demonstrate that GroP modification promotes the migration of cancer cells. Based on these findings, we propose that the GroP modification by PCYT2 disrupts the glycan-mediated cell adhesion to the extracellular matrix and thereby enhances cancer metastasis. Thus, the present study suggests the possibility of novel approaches for cancer treatment by targeting the PCYT2-mediated GroP modification.

Establishment of a novel monoclonal antibody against truncated glycoforms of α-dystroglycan lacking matriglycans.

α-Dystroglycan (α-DG) is a glycoprotein specifically modified with O-mannosyl glycans bearing long polysaccharides, termed matriglycans, which comprise repeating units of glucuronic acid and xylose. The matriglycan is linked to the O-mannosyl glycan core through two ribitol phosphate units that can be replaced with glycerol phosphate (GroP) units synthesized by fukutin and fukutin-related protein that transfer GroP from CDP-Gro. Here, we found that forced expression of the bacterial CDP-Gro synthase, TagD, from Bacillus subtilis could result in the overproduction of CDP-Gro in human colon carcinoma HCT116 cells. Western blot and liquid chromatography-tandem mass spectrometry analyses indicated that α-DG prepared from the TagD-expressing HCT116 cells contained abundant GroP and lacked matriglycans. Using the GroP-containing recombinant α-DG-Fc, we developed a novel monoclonal antibody, termed DG2, that reacts with several truncated glycoforms of α-DG, including GroP-terminated glycoforms lacking matriglycans; we verified the reactivity of DG2 against various types of knockout cells deficient in the biosynthesis of matriglycans. Accordingly, forced expression of TagD in HCT116 cells resulted in the reduction of matriglycans and an increase in DG2 reactivity. Collectively, our results indicate that DG2 could serve as a useful tool to determine tissue distribution and function of α-DG lacking matriglycans under physiological and pathophysiological conditions.