TRIB1 confers therapeutic resistance in GBM cells by activating the ERK and Akt pathways.

GBM (Glioblastoma) is the most lethal CNS (Central nervous system) tumor in adults, which inevitably develops resistance to standard treatments leading to recurrence and mortality. TRIB1 is a serine/threonine pseudokinase which functions as a scaffold platform that initiates degradation of its substrates like C/EBPα through the ubiquitin proteasome system and also activates MEK and Akt signaling. We found that increased TRIB1 gene expression associated with worse overall survival of GBM patients across multiple cohorts. Importantly, overexpression of TRIB1 decreased RT/TMZ (radiation therapy/temozolomide)-induced apoptosis in patient derived GBM cell lines in vitro. TRIB1 directly bound to MEK and Akt and increased ERK and Akt phosphorylation/activation. We also found that TRIB1 protein expression was maximal during G2/M transition of cell cycle in GBM cells. Furthermore, TRIB1 bound directly to HDAC1 and p53. Importantly, mice bearing TRIB1 overexpressing tumors had worse overall survival. Collectively, these data suggest that TRIB1 induces resistance of GBM cells to RT/TMZ treatments by activating the cell proliferation and survival pathways thus providing an opportunity for developing new targeted therapeutics.

MicroRNA-575 acts as a novel oncogene via targeting multiple signaling pathways in glioblastoma.

PURPOSE: Glioblastoma (GBM) patients currently face poor survival outcomes with an average survival period of <15 months, while only 3-5% of patients survive longer than 36 months. Although the mechanisms of tumorigenesis are still being elucidated, miRNAs are promising candidates to explore as novel and prognostic biomarkers in GBM. In this study, we identified the association between miR-575 expression and overall survival (OS) of primary GBM patients and undertook functional studies to discern the contribution of miR-575 to GBM tumorigenesis. METHODS: Total RNAs were isolated from 254 FFPE GBM tumor samples and miR expression was assayed (simultaneously) using NanoString Technologies. To determine the association between miR-575 and patients' prognosis, Kaplan-Meier, univariable and multivariable Cox regression analyses were performed. Cell proliferation, colony formation, migration assays were conducted to investigate the function of miR-575 in vitro and in vivo. In silico target gene network analysis was performed to identify the putative targets of miR-575 in GBM, which were further verified by luciferase reporter assay, as well as qPCR and immunoblotting. RESULTS: Our clinical data (n = 254) show that miR-575 is associated with worse GBM OS by univariable analysis (UVA, HR = 1.27, p-value<0.001) and multivariable (MVA, HR = 1.23, p = 0.007) analysis incorporating critical clinical variables. Functional studies indicated that overexpression of miR-575 significantly increased cell proliferation and migration of GBM cells in vitro, as well as tumor growth in vivo. Subsequent in silico target gene network and mechanistic studies identified CDKN1B/p27 and PTEN, as potential targets of miR-575 in GBM. MicroRNA-575 can also regulate the activity of AKT and ERK pathways in GBM. CONCLUSION: miR-575 has prognostic value in GBM, with higher expression associating with worse OS of patients, and contributes to GBM tumorigenesis by regulating multiple signaling pathways in GBM.

A Novel miR-146a-POU3F2/SMARCA5 Pathway Regulates Stemness and Therapeutic Response in Glioblastoma.

Rapid tumor growth, widespread brain-invasion, and therapeutic resistance critically contribute to glioblastoma (GBM) recurrence and dismal patient outcomes. Although GBM stem cells (GSC) are shown to play key roles in these processes, the molecular pathways governing the GSC phenotype (GBM-stemness) remain poorly defined. Here, we show that epigenetic silencing of miR-146a significantly correlated with worse patient outcome and importantly, miR-146a level was significantly lower in recurrent tumors compared with primary ones. Further, miR-146a overexpression significantly inhibited the proliferation and invasion of GBM patient-derived primary cells and increased their response to temozolomide (TMZ), both in vitro and in vivo. Mechanistically, miR-146a directly silenced POU3F2 and SMARCA5, two transcription factors that mutually regulated each other, significantly compromising GBM-stemness and increasing TMZ response. Collectively, our data show that miR-146a-POU3F2/SMARCA5 pathway plays a critical role in suppressing GBM-stemness and increasing TMZ-response, suggesting that POU3F2 and SMARCA5 may serve as novel therapeutic targets in GBM. IMPLICATIONS: miR-146a predicts favorable prognosis and the miR-146a-POU3F2/SMARCA5 pathway is important for the suppression of stemness in GBM.