DR7 encoded by human herpesvirus 6 promotes glioma development and progression

We previously identified human herpesvirus 6 (HHV-6) infection in the pathogenesis of glioma. Direct repeat (DR)7, encoded by HHV-6, has been reported to possess malignant transforming activity and involved in Hodgkin's lymphoma carcinogenesis. Here, we aimed to determine the role of DR7 in the development and progression of glioma.

A total of 27 glioma and 30 normal brain tissues were collected for detection of DR7. Glioma cell proliferation, colony formation, cell cycle, migration, invasion and angiogenesis were evaluated by Cell Counting Kit-8 (CCK-8), soft agar, propidium iodide staining, wound healing, Transwell and chick embryo chorioallantoic membrane assays, respectively. The potential mRNA targets of DR7 were determined using mRNA microarray and validated via Western blot and ELISA.

DR7 could be detected in the 13 glioma tissues with a positive rate of 48.15%, but only the 5 normal brain tissues with a lower positive rate of 16.7%. The two strains of cells isolated from glioma tissues were also found to express DR7. CCK-8 and soft agar assays showed enhanced proliferation and colony formation in the cells expressing DR7 which might be in relation to acceleration of the G1/S phase transition by DR7. Further analyses showed that DR7 could promote glioma cell migration, invasion and angiogenesis. Expression profiles identified hundreds of differentially expressed mRNAs, among which P53, extracellular matrix (ECM) fibronectin, integrin receptor ITGβ5 and specific inhibitors of MMPs, tissue inhibitor of MMPs (TIMP)-2 and TIMP-4, were downregulated, whereas ECM-degrading proteinase MMP-3, proinflammatory cytokines IL-1β, IL-6 and IL-8, were upregulated by DR7, respectively.

We observed existence of DR7 in the glioma tissues, and overexpression of DR7 could promote glioma cell development and progression, which might be through creating an inflammatory microenvironment and enhancing degradation of ECM.