SF3B1 inhibition disrupts malignancy and prolongs survival in glioblastoma patients through BCL2L1 splicing and mTOR/ß-catenin pathways imbalances

Abstract

Background Glioblastoma is one of the most devastating cancer worldwide based on its locally aggressive behavior and because it cannot be cured by current therapies. Defects in alternative splicing process are frequent in cancer. Recently, we demonstrated that dysregulation of the spliceosome is directly associated with glioma development, progression, and aggressiveness. Methods Different human cohorts and a dataset from different glioma mouse models were analyzed to determine the mutation frequency as well as the gene and protein expression levels between tumor and control samples of the splicing-factor-3B-subunit-1 (SF3B1), an essential and druggable spliceosome component. SF3B1 expression was also explored at the single-cell level across all cell subpopulations and transcriptomic programs. The association of SF3B1 expression with relevant clinical data (e.g., overall survival) in different human cohorts was also analyzed. Different functional (proliferation/migration/tumorspheres and colonies formation/VEGF secretion/apoptosis) and mechanistic (gene expression/signaling pathways) assays were performed in three different glioblastomas cell models (human primary cultures and cell lines) in response to SF3B1 blockade (using pladienolide B treatment). Moreover, tumor progression and formation were monitored in response to SF3B1 blockade in two preclinical xenograft glioblastoma mouse models. Results Our data provide novel evidence demonstrating that the splicing-factor-3B-subunit-1 (SF3B1, an essential and druggable spliceosome component) is low-frequency mutated in human gliomas (~ 1 %) but widely overexpressed in glioblastoma compared with control samples from the different human cohorts and mouse models included in the present study, wherein SF3B1 levels are associated with key molecular and clinical features (e.g., overall survival, poor prognosis and/or drug resistance). Remarkably, in vitro and in vivo blockade of SF3B1 activity with pladienolide B drastically altered multiple glioblastoma pathophysiological processes (i.e., reduction in proliferation, migration, tumorspheres formation, VEGF secretion, tumor initiation and increased apoptosis) likely by suppressing AKT/mTOR/ß-catenin pathways, and an imbalance of BCL2L1 splicing. Conclusions Together, we highlight SF3B1 as a potential diagnostic and prognostic biomarker and an efficient pharmacological target in glioblastoma, offering a clinically relevant opportunity worth to be explored in humans.

Dysregulation of CELF4 Splicing Factor in Pancreatic Neuroendocrine Tumors Enhances Aggressiveness and Alters Mtor Pathway and Everolimus Response

“…These results compare favorably with our recent ndings in PanNETs studying a related splicing factor, NOVA1 (19), but also in the most aggressive pancreatic adenocarcinoma cell models, where manipulation of SF3B1 caused these same effects (39). These parallel observations are in line with recent ndings from our group and other labs (51)(52)(53), and collectively argue in favor of the idea that not only mutations, but transcriptional (and epigenetic) alterations of speci c components of the splicing machinery can entail functionally relevant consequences for key cell processes. Remarkably, in vivo data with xenograft mice provides proof-ofconcept that CELF4 silencing in PanNET BON-1 cells-derived tumors can counteract cell proliferation and blunt tumor growth, paving the way to further explore the therapeutic potential of CELF4 in these rare tumors.…”

A Novel Splice Variant of BCAS1 Inhibits β-Arrestin 2 to Promote the Proliferation and Migration of Glioblastoma Cells, and This Effect Was Blocked by Maackiain

“…The overexpression of splicing-factor-3B-subunit-1 (SF3B1) in GBM results in shortened patient survival, increased drug resistance, and poor prognosis. The blockade of SF3B1 activity prevents the AKT/mTOR/ß-catenin pathway and BCL-X L splicing variant; lessens GBM proliferation, migration, tumorsphere formation, and VEGF secretion; and induces apoptosis [ 93 ]. Splicing factor Serine and arginine rich splicing factor 3 (SRSF3) affected more than 1000 AS events and induced self-renewal, cell proliferation, and tumorigenesis upregulation in GBM patients, which resulted in tumor progression and a poor prognosis [ 94 , 95 ].…”

A New Molecular (P)Layer in Pseudomyxoma Peritonei: The Splicing Machinery is Dysregulated and Linked to Low Survival

“…The RNA expression was adjusted by a normalization factor calculated using GeNorm 3.5 [16] by the expression of the control genes: ACTB (actin beta), GAPDH (glyceraldehyde 3-phosphate dehydrogenase) and HPRT1 (hypoxanthine phosphoribosyltransferase). Preampli cation, exonuclease treatment and qPCR dynamic array was implemented following manufacturer's instructions as previously reported by our group [11,12,14,17,18]. Biomark System and the FluidigmVR Real-Time PCR Analysis Software v3.0.2 and Data Collection Software v3.1.2 (Fluidigm, San Francisco, USA) were used to acquire RNA expression levels.…”