Identification of Global DNA Methylation Signatures in Glioblastoma-Derived Cancer Stem Cells

Glioblastoma （GBM） is the most common and most aggressive primary brain tumor in adults. The existence of a small population of stem-like tumor cells that efficiently propagate tumors and resist cytotoxic therapy is one proposed mechanism leading to the resilient behavior of tumor cells and poor prognosis. In this study, we performed an in-depth analysis of the DNA methylation landscape in GBM- derived cancer stem ceils （GSCs）. Parallel comparisons of primary tumors and GSC lines derived from these tumors with normal controls （a neural stem cell （NSC） line and normal brain tissue） identified groups of hyper- and hypomethylated genes that display a trend of either increasing or decreasing methylation levels in the order of controls, primary GBMs, and their counterpart GSC lines, respectively. Interestingly, concurrent promoter hypermethylation and gene body hypomethylation were observed in a subset of genes including MGMT, AJAP1 and PTPRN2. These unique DNA methylation signatures were also found in primary GBM-derived xenograft tumors indicating that they are not tissue culture-related epigenetic changes. Integration of GSC-specific epigenetic signatures with gene expression analysis further identified candidate tumor suppressor genes that are frequently down-regulated in GBMs such as SPINT2, NEFM and PENK. Forced re-expression of SPINT2 reduced glioma cell proliferative capacity, anchorage independent growth, cell motility, and tumor sphere formation in vitro. The results from this study demonstrate that GSCs possess unique epigenetic signatures that may play important roles in the pathogenesis of GBM.

Sox2 induces glioblastoma cell sternness and tumor propagation by repressing TET2 and deregulating 5hmC and 5mC DNA modifications

DNA methylation is a reversible process catalyzed by the ten-eleven translocation(TET)family of enzymes(TET1,TET2,TET3)that convert 5-methylcytosine(5mC)to 5-hydroxymethylcytosine(5hmC).Altered patterns of 5hmC and 5mC are widely reported in human cancers and loss of 5hmC correlates with poor prognosis.

Targeting UDP-α-D-glucose 6-dehydrogenase alters the CNS tumor immune microenvironment and inhibits glioblastoma growth

Glioblastoma(GBM,WHO grade IV glioma)is the most common and lethal malignant brain tumor in aduts with a dismal prognosis.The extracellular matrix(ECM)supports GBM progression by promoting tumor cell proliferation,migration,and immune escape.Uridine diphosphate(UDP)-glucose 6-dehydrogenase(UGDH)is the rate-limiting enzyme that catalyzes the biosynthesis of glycosaminoglycans that are the principal component of the CNS ECM.We investigated how targeting UGDH in GBM infuence$the GBM immune microenvironment,including tumor-associated microglia/macrophages(TAMs)and T cells.TAMs are the main im-mune effector cells in GBM and can directly target tumor cells if properly activated.In co-cultures of GBM cells and human primary macrophages,UGDH knockdown in GBM cells pro-moted macrophage phagocytosis and M-like polarization.In orthotropic human GBM xeno-grafts and syngeneic mouse glioma models,targeting UGDH decreased ECM deposition,increased TAM phagocytosis marker expression,reduced M2-like TAMS and inhibited tumor growth.UGDH knockdown in GBM cells also promoted cytotoxic T cell ifltration and activa-tion in orthotopic syngeneic mouse glioma models.The potent and in-human-use small mole-cule GAG synthesis inhibitor 4-methylumbelliferone(4-MU)was found to inhibit GBM cell proliferation and migration in vitro,mimic the macrophage and T-cell responses to UGDH knockdown in vitro and in vivo and inhibit growth of orthotopic murine GBM.Our study shows that UGDH supports GBM growth through multiple mechanisms and supports the development of ECM-based therapeutic strategies to simultaneously target tumor cells and their microenvi-ronment.