MicroRNA-137 is downregulated in glioblastoma and inhibits the stemness of glioma stem cells by targeting RTVP-1

Abstract

// Ariel Bier, 1 Nis Giladi, 1 Noam Kronfeld, 1 Hae Kyung Lee, 2 Simona Cazacu, 2 Susan Finniss, 2 Cunli Xiang, 2 Laila Poisson, 3 Ana C. deCarvalho 2 , Shimon Slavin 4 , Elad Jacoby, 5 Michal Yalon, 5 Amos Toren, 5 Tom Mikkelsen 2 and Chaya Brodie 1,2 1 Everard and Mina Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel, 2 Davidson Laboratory of Cell Signaling and Tumorigenesis, Hermelin Brain Tumor Center, Department of Neurosurgery, Henry Ford Hospital, Detroit MI USA. 3 Department of Public Health Sciences, Tel Aviv, Israel 4 The International Center for Cell Therapy and Cancer Immunotherapy (CTCI), Tel Aviv, Israel, 5 Pediatric Hemato-Oncology, The Edmond and Lilly Safra Children’s Hospital, Sheba Medical Center, Tel-Hashomer and The Sackler School of Medicine, Tel-Aviv University, Israel. Correspondence: Chaya Brodie, email: // Keywords : Glioma stem cells, self renewal, miR-137, RTVP-1, CXCR4 Received : March 12, 2013 Accepted : April 7, 2013 Published : April 9, 2013 Abstract Glioblastomas (GBM), the most common and aggressive malignant astrocytic tumors, contain a small subpopulation of cancer stem cells (GSCs) that are implicated in therapeutic resistance and tumor recurrence. Here, we study the expression and function of miR-137, a putative suppressor miRNA, in GBM and GSCs. We found that the expression of miR-137 was significantly lower in GBM and GSCs compared to normal brains and neural stem cells (NSCs) and that the miR-137 promoter was hypermethylated in the GBM specimens. The expression of miR-137 was increased in differentiated NSCs and GSCs and overexpression of miR-137 promoted the neural differentiation of both cell types. Moreover, pre-miR-137 significantly decreased the self-renewal of GSCs and the stem cell markers Oct4, Nanog, Sox2 and Shh. We identified RTVP-1 as a novel target of miR-137 in GSCs; transfection of the cells with miR-137 decreased the expression of RTVP-1 and the luciferase activity of RTVP-1 3’-UTR reporter plasmid. Furthermore, overexpression of RTVP-1 plasmid lacking its 3’-UTR abrogated the inhibitory effect of miR-137 on the self-renewal of GSCs. Silencing of RTVP-1 decreased the self-renewal of GSCs and the expression of CXCR4 and overexpression of CXCR4 abrogated the inhibitory effect of RTVP-1 silencing on GSC self-renewal. These results demonstrate that miR-137 is downregulated in GBM probably due to promoter hypermethylation. miR-137 inhibits GSC self-renewal and promotes their differentiation by targeting RTVP-1 which downregulates CXCR4. Thus, miR-137 and RTVP-1 are attractive therapeutic targets for the eradication of GSCs and for the treatment of GBM.