Abstract 2845: PRMT5-PTEN molecular pathway regulates senescence and self-renewal of Glioblastoma stem-like cells

Abstract

Abstract PURPOSE: Glioblastoma (GBM) represents the most common and aggressive histologic subtype among malignant astrocytoma and is associated with poor outcomes because of heterogeneous tumor cell population including mature non-stem like cell and immature stem-like cells within the tumor. Thus, it is critical to find new target-specific therapeutic modalities. Protein arginine methyltransferase enzyme 5 (PRMT5) regulates many cellular processes through its methylation activity and its overexpression in GBM is associated with more aggressive disease. Previously, we have shown that silencing of PRMT5 expression in differentiated GBM cell lines results in apoptosis and reduced tumor growth in mice. Here we report the critical role of PRMT5 in differentiated GBM non-stem-like cells (non-GSC) grown in serum and undifferentiated GBM stem-like cells (GSC) grown as neurospheres in vitro. METHODS: GSC grown in stem-cell media and non-GSC grown in serum were transfected with specified siRNAs. At appropriate time, these cells were tested for in vitro proliferation, self-renewal capacity, apoptosis, cell cycle progression, mRNA expression and protein expression. Also, using intracranial mouse xenograft, tumor forming ability of PRMT5-intacta and depleted GSC and non-GSC was determined. RESULTS: Our results uncover a very significant role for PRMT5 in GSC self-renewal capacity and proliferation. PRMT5 knockdown in non-GSC led to apoptosis, knockdown in GSC led to G1 cell cycle arrest through upregulation of p27 and hypophoshorylation of Rb protein, leading to senescence. Comparison of impact of PRMT5 on cellular signaling by Human Phospho-Kinase Array and ChIP-PCR revealed that unlike non-GSC, PRMT5 controls both AKT and ERK activity by direct repression of PTEN in GSC. In vivo transient depletion of PRMT5 decreased intracranial tumor size and growth rate in mice implanted with both primary tumor derived GSC and non-GSC. CONCLUSION: This is the first study to identify PTEN as a potential downstream target of PRMT5 and vital to support both mature and immature GBM tumor cell populations. Citation Format: Yeshavanth Kumar Banasavadi-Siddegowda, Luke Russell, Jianying Zhang, Vrajesh A. Karkhanis, Jaime Imitola, Robert Baiocchi, Balveen Kaur. PRMT5-PTEN molecular pathway regulates senescence and self-renewal of Glioblastoma stem-like cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2845.