Retinoblastoma protein-interacting zinc-finger gene 1 (RIZ1) dysregulation in human malignant meningiomas.

Retinoblastoma protein-interacting zinc-finger gene 1 (RIZ1) expression is often silenced in many types of human tumors. However, the relationship between RIZ1 expression and malignant meningiomas remains unclear. Here we have found for the first time that the expression of RIZ1 genes are associated with meningiomas progression through extensive analyses of Affymetrix GeneChip microarray data. Further validation methods for gene expression included quantitative PCR (qPCR), western blot and immunohistochemistry analysis, and these methods confirmed that RIZ1 is significantly downregulated in malignant meningioma tissues, as compared with benign meningiomas. In addition, malignant meningioma cells were stably transfected with ectogenic RIZ1 using Lentivirus-mediated transfection, and the transfections were followed by an in vitro 5-bromo-2-deoxyuridin incorporation assay, colony formation assay, cell cycle analysis, invasive analysis, apoptotic assay and western blot analysis. Our results demonstrate that the forced expression of RIZ1 in a malignant meningioma cell line inhibited cellular proliferation and arrested the cells in the G2/M phase of the cell cycle. We also confirmed that overexpression of RIZ1 may induce apoptosis of malignant meningioma cells. Furthermore, RIZ1 overexpression in malignant meningioma cells was associated with the downregulation of c-myc expression. These results from our study indicate that RIZ1 expression is significantly downregulated as the formation of meningiomas progressed, and suggest that RIZ1 may represent a promising candidate tumor suppressor gene that contributes to malignant meningiomas.