ABSTRACT
Most glioblastomas (GBMs) achieve cellular immortality by acquiring a mutation in the telomerase reverse transcriptase (TERT) promoter. TERT promoter mutations create a binding site for a GA binding protein (GABP) transcription factor complex, whose assembly at the promoter is associated with TERT reactivation and telomere maintenance. Here, we demonstrate increased binding of a specific GABPB1L-isoform-containing complex to the mutant TERT promoter. Furthermore, we find that TERT promoter mutant GBM cells, unlike wild-type cells, exhibit a critical near-term dependence on GABPB1L for proliferation, notably also posttumor establishment in vivo. Up-regulation of the protein paralogue GABPB2, which is normally expressed at very low levels, can rescue this dependence. More importantly, when combined with frontline temozolomide (TMZ) chemotherapy, inducible GABPB1L knockdown and the associated TERT reduction led to an impaired DNA damage response that resulted in profoundly reduced growth of intracranial GBM tumors. Together, these findings provide insights into the mechanism of cancer-specific TERT regulation, uncover rapid effects of GABPB1L-mediated TERT suppression in GBM maintenance, and establish GABPB1L inhibition in combination with chemotherapy as a therapeutic strategy for TERT promoter mutant GBM.
Subject(s)
Brain Neoplasms/genetics , GA-Binding Protein Transcription Factor/metabolism , Gene Expression Regulation, Neoplastic , Glioblastoma/genetics , Telomerase/genetics , Animals , Antineoplastic Agents, Alkylating/pharmacology , Antineoplastic Agents, Alkylating/therapeutic use , Astrocytes , Brain Neoplasms/drug therapy , Brain Neoplasms/pathology , Cell Line, Tumor , Cell Proliferation/genetics , DNA Damage/drug effects , Drug Resistance, Neoplasm/genetics , Female , GA-Binding Protein Transcription Factor/genetics , Gene Knockdown Techniques , Gene Knockout Techniques , Glioblastoma/drug therapy , Glioblastoma/pathology , HEK293 Cells , Humans , Mice , Mutation , Promoter Regions, Genetic/genetics , Protein Isoforms/metabolism , Temozolomide/pharmacology , Xenograft Model Antitumor AssaysABSTRACT
The ability to engineer natural proteins is pivotal to a future, pragmatic biology. CRISPR proteins have revolutionized genome modification, yet the CRISPR-Cas9 scaffold is not ideal for fusions or activation by cellular triggers. Here, we show that a topological rearrangement of Cas9 using circular permutation provides an advanced platform for RNA-guided genome modification and protection. Through systematic interrogation, we find that protein termini can be positioned adjacent to bound DNA, offering a straightforward mechanism for strategically fusing functional domains. Additionally, circular permutation enabled protease-sensing Cas9s (ProCas9s), a unique class of single-molecule effectors possessing programmable inputs and outputs. ProCas9s can sense a wide range of proteases, and we demonstrate that ProCas9 can orchestrate a cellular response to pathogen-associated protease activity. Together, these results provide a toolkit of safer and more efficient genome-modifying enzymes and molecular recorders for the advancement of precision genome engineering in research, agriculture, and biomedicine.
Subject(s)
CRISPR-Cas Systems/physiology , Clustered Regularly Interspaced Short Palindromic Repeats/physiology , Gene Editing/methods , CRISPR-Associated Proteins/chemistry , DNA/chemistry , Genome , Models, Molecular , RNA/chemistry , RNA, Guide, Kinetoplastida/geneticsABSTRACT
Cas12a (Cpf1) is a CRISPR-associated nuclease with broad utility for synthetic genome engineering, agricultural genomics, and biomedical applications. Although bacteria harboring CRISPR-Cas9 or CRISPR-Cas3 adaptive immune systems sometimes acquire mobile genetic elements encoding anti-CRISPR proteins that inhibit Cas9, Cas3, or the DNA-binding Cascade complex, no such inhibitors have been found for CRISPR-Cas12a. Here we use a comprehensive bioinformatic and experimental screening approach to identify three different inhibitors that block or diminish CRISPR-Cas12a-mediated genome editing in human cells. We also find a widespread connection between CRISPR self-targeting and inhibitor prevalence in prokaryotic genomes, suggesting a straightforward path to the discovery of many more anti-CRISPRs from the microbial world.
