Biology subjects

Fareh, M.

Publications and source records attributed to Fareh, M..

8 recordsLinked to original sources

bioRxiv2026

METTL1 gene dosage and catalytic activity define a targetable vulnerability in pediatric cancers

METTL1 is responsible for catalyzing N7-methylguanosine (m7G) methylation of tRNAs. METTL1-dependent oncogenic mechanisms include both its methyltransferase catalytic activity and, in specific instances, non-catalytic interactions that maintain aminoacylated tRNA levels in malignant cells. We show that METTL1 copy number gain and elevated expression are a feature of pediatric tumors that are METTL1 dependent, using Cas13-mediated RNA to reduce the threshold of METTL1 mRNA and protein, which disrupts both catalytic and non-catalytic functions. In cell lines with METTL1 gene amplification, specific degradation of METTL1 mRNA impaired colony formation, triggered cell death, and decreased the translation efficiency of a subset of genes enriched for codons decoded m7G-modified tRNAs. METTL1 inhibition was accompanied by downregulation of c-MYC, n-MYC and MCL-1 protein expression. METTL1 silencing synergizes with drugs targeting anti-apoptotic members of the BCL2 family, notably BCL-xL. Importantly, the catalytic activity of METTL1 was required to rescue cells from the deleterious consequences of METTL1 silencing. We conclude that inhibiting the catalytic activity of METTL1 has potential therapeutic efficacy, particularly in tumors with METTL1 amplification. Synergistic combinations with BH3-mimetic drugs may be a promising therapeutic combination.

cancer biology↗

bioRxiv2026

Addressing viral genomic variability towards developing a Cas13b-based therapy

Viral genome diversity may limit the effectiveness of antiviral RNA-editing tools such as CRISPR-Cas13 that can be used to destroy specific mRNA targets, by introducing mismatches between viral RNA targets and CRISPR guide RNAs (crRNAs). These mismatches can reduce target recognition and cleavage efficiency, diminishing antiviral activity and increasing the risk of viral escape. The extent to which natural viral genomic variability limits CRISPR-Cas13 efficacy remains unclear. Here, we used hepatitis B virus (HBV), which has substantial genetic diversity, as a model to assess the impact of viral genome variation on Cas13b activity in vitro. The efficacy of PspCas13b was examined across six HBV genotypes and sub-genotypes using five crRNAs that had up to five mismatches to the target region. We showed that crRNAs with one mismatch to the target strongly suppressed viral antigen expression for all genotypes tested, while some crRNAs with three or more mismatches were less effective. Restoring complementarity using spacer-target mutagenesis improved the level of knockdown for some but not all HBV genotypes, suggesting that sequence specificity alone did not control PspCas13b efficacy. Our findings show that a "one size fits all" approach for PspCas13b-mediated treatment of HBV is unlikely to be effective, but the impact of sequence variability on PspCas13b efficacy can be readily addressed through appropriate design of crRNAs. This approach will likely be necessary for all viral pathogens with highly variant genomes. IMPORTANCECRISPR-Cas13 is being explored as a novel antiviral for several viral infections. Viral sequence divergence can compromise CRISPR-Cas13 efficacy by introducing mismatches between therapeutic guide RNAs and viral targets. However, the impact of naturally occurring viral genomic variation on CRISPR-Cas13 efficacy remains poorly understood. Using hepatitis B virus (HBV) as a model, we showed that the effect of mismatches on Cas13b efficacy was context-dependent and varied for different crRNAs, HBV genotypes and target sites. Restoring complementarity improved the efficacy for some, but not all crRNAs, suggesting that Cas13b efficacy was not solely influenced by the number of mismatches. As the target sequence may differ between viral variants, this study advances our understanding of the impact of mismatches on Cas13b efficacy and provides further insights into using Cas13b as a novel antiviral.

microbiology↗

bioRxiv2026

Phase-Separated RNA Condensates Govern Cas13 Target Accessibility and Cleavage

RNA-guided CRISPR-Cas13 nucleases must efficiently locate and target specific transcripts amidst the millions of other RNA molecules that are spatially regulated in the cell. Yet the mechanisms by which Cas13 finds its targets within this crowded, compartmentalized environment remain elusive. Here, we show that diverse Cas13 orthologs assemble into distinct cytoplasmic granules in a crRNA-concentration dependent manner. These granules exhibit hallmark features of phase-separated condensates, displaying liquid-like viscoelasticity and dynamic molecular exchange with the cytoplasm, as demonstrated by FRAP analysis in both human and bacterial cells. Molecular profiling revealed that Cas13 co-localizes with polyadenylated RNAs and noncoding RNAs within condensates that display markers of canonical RNA granules. Biochemical purification coupled with RNA sequencing shows Cas13 associated with thousands of transcripts within condensates, likely mediated by electrostatic interactions with its positively charged surface. Notably, Cas13 retains catalytic activity within these condensates, efficiently cleaving co-localized targets, whereas RNA species excluded from the condensates remain largely protected from Cas13 cleavage. This data indicates that condensate-based spatial organization facilitates efficient sampling and binding of diverse RNA targets by concentrating Cas13 and its substrates within a confined, liquid-like compartment. Together, our findings uncover a conserved spatial mechanism regulating Cas13 activity across bacterial and mammalian cells, where localization within RNA dense granules governs Cas13 activity in cells.

molecular biology↗

bioRxiv2026

Target RNA abundance controls the collateral activity of RfxCas13d in human cells and zebrafish embryos

Collateral RNA cleavage by CRISPR-Cas13 effectors presents a critical obstacle to their application in biological research and therapeutics, yet the molecular determinants of this activity remain poorly understood. Here, we systematically investigate the collateral activity of various Cas13 variants in human cells in vitro and zebrafish embryos in vivo. Among these nucleases, RfxCas13d displays robust collateral activity that is highly dependent on target abundance. Targeting moderately expressed RNAs activates only a limited subset of RfxCas13d molecules, resulting in selective degradation of ectopically expressed transcripts, while endogenous RNAs remain largely protected. This selectivity indicates higher accessibility to exogenous RNAs through spatial proximity and temporal colocalization with activated RfxCas13d nuclease domains. In contrast, the recognition of highly abundant RNA targets drives simultaneous activation of a large fraction of cellular RfxCas13d, leading to widespread collateral cleavage of cellular RNAs, disruption of proteome homeostasis, and consequent cell toxicity and developmental defects in zebrafish embryos. Notably, transgenic zebrafish with target RNA expression restricted to endothelial or neuronal cell lineages exhibit localized collateral activity, leading to tissue-specific developmental abnormalities and motility deficits. These findings reveal that RfxCas13ds collateral activity is threshold-dependent, with abundant target RNA acting as a molecular switch for widespread collateral RNA degradation. This work underscores the need for careful consideration of target abundance when deploying RfxCas13d, and highlights PspCas13b as an alternative for RNA silencing free of collateral activity.

molecular biology↗

bioRxiv2025

Systematic silencing of oncogenic fusion transcripts with ultra-precise CRISPR-Cas13b

Oncogenic gene fusions are key drivers of cancer, yet most remain untargetable by current therapies. Here, we establish CRISPR-PspCas13b as a personalizable platform for systematic silencing of various fusion transcripts. We reveal that recognition and cleavage of the breakpoint sequence by PspCas13b disrupts the fusion transcript, resulting in unexpected RNA nicking and ligation near the cleavage site, which generates out-of-frame, translation-incompetent transcripts. This approach efficiently degrades canonical and drug-resistant BCR::ABL1 mutants (e.g., T315I), a primary cause of resistance to tyrosine kinase inhibitors (TKIs) and relapse in chronic myeloid leukemia (CML). Silencing T315I BCR::ABL1 mRNA in drug-resistant CML cells triggers extensive transcriptomic, proteomic, and phosphoproteomic remodelling, causing erythroid differentiation and apoptosis. Beyond BCR-ABL1 mutants, personalized design of PspCas13b effectively silences other undruggable fusions, including RUNX1::RUNX1T1 and EWSR1::FLI1, key drivers in acute myeloid leukemia and in Ewing sarcoma, respectively. Collectively, this study establishes a framework for systematic, precise, and personalizable targeting of otherwise undruggable or drug-resistant oncogenic transcripts.

molecular biology↗

bioRxiv2023

Molecular principles of CRISPR-Cas13 mismatch intolerance enable selective silencing of point-mutated oncogenic RNA with single-base precision

Single nucleotide variants (SNVs) are extremely prevalent in human cancers. For instance, KRAS mutations occur in over 90% of pancreatic cancers and [~]40% of colorectal cancers. Virtually all KRAS mutations are SNVs, most of which remain clinically unactionable. The programmable RNA nuclease CRISPR-Cas13 has been deployed to specifically target RNAs such as overexpressed oncogenes and fusion transcripts. However, silencing oncogenic SNVs with single-base precision remains extremely challenging due to the intrinsic mismatch tolerance of Cas13. Here, we developed a comprehensive mutagenesis analysis of target-spacer interactions at single-nucleotide resolution, which revealed key spacer nucleotide positions intolerant to mismatches. We show that introducing synthetic mismatches at these precise positions enables de nova design of CRISPR RNA (crRNA) with strong preferential silencing of SNV transcripts. We demonstrate that our top-performing crRNAs possess prominent SNV-selectivity with dose-dependent silencing activity against all KRAS G12 variants at both the RNA and protein levels with minimal off-target silencing of wildtype KRAS. We applied these design principles to effectively silence oncogenic NRAS G12D and BRAF V600E transcripts, underscoring the adaptability of this platform to silence various SNVs. These findings demonstrate that the CRISPR Cas13 system can be reprogrammed to target mutant transcripts with single-base precision, showcasing the tremendous potential of this tool in personalized transcriptome editing. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=176 SRC="FIGDIR/small/557083v1_ufig1.gif" ALT="Figure 1"> View larger version (58K): org.highwire.dtl.DTLVardef@20a7b3org.highwire.dtl.DTLVardef@1e1f79corg.highwire.dtl.DTLVardef@4724c1org.highwire.dtl.DTLVardef@be3063_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2022

Single-base precision design of CRISPR-Cas13b enables systematic silencing of oncogenic fusions

Precision oncology programs can rapidly identify oncogenic gene fusions in individual patients1-3. However, despite their established oncogenic status, the vast majority of gene fusions remain undruggable due to the lack of specific inhibitory molecules4, 5. Here, we establish PspCas13b, a poorly characterized programmable RNA nuclease, as a versatile tool to silence various oncogenic fusion transcripts. Our Single-Base Tiled crRNA screens (SiBTil), unbiased computational analysis, and comprehensive spacer-target mutagenesis revealed key determinants of PspCas13b activity. De novo design of crRNAs harbouring basepaired or mismatched guanosine bases at key spacer positions greatly enhances the silencing efficacy of otherwise inefficient crRNAs, expanding the targeting spectrum of this enzyme. We also reveal the interface between mismatch tolerance and intolerance, which unlocks an unexpected single-base precision targeting capability of this RNA nuclease. Notably, our de novo design principles enable potent and selective silencing of various gene fusion transcripts and their downstream oncogenic networks, without off-targeting of non-translocated variants that share extensive sequence homology. We demonstrate that PspCas13b targeting the breakpoint of fusion transcripts enables efficient suppression of ancestral and single-nucleotide mutants (e.g. BCR-ABL1 T315I) that often drive clinical cancer relapse. Collectively, this study provides new design principles for PspCas13b programming to specifically recognise and degrade any undruggable fusion oncogenic transcript, thus providing a new conceptual framework for personalized oncology.

molecular biology↗

bioRxiv2020

Reprogrammed CRISPR-Cas13b suppresses SARS-CoV-2 replication and circumvents its mutational escape through mismatch tolerance

Mutation-driven evolution of SARS coronavirus-2 (SARS-CoV-2) highlights the need for innovative approaches that simultaneously suppress viral replication and circumvent viral escape routes from host immunity and antiviral therapeutics. Here, we employed genome-wide computational prediction and singlenucleotide resolution screening to reprogram CRISPR-Cas13b against SARS-CoV-2 genomic and subgenomic RNAs. Reprogrammed Cas13b effectors targeting accessible regions of Spike and Nucleocapsid transcripts achieved >98% silencing efficiency in virus free-models. Further, optimized and multiplexed gRNAs suppressed viral replication by up to 90% in mammalian cells infected with replication-competent SARS-CoV-2. Unexpectedly, the comprehensive mutagenesis of guide-target interaction demonstrated that single-nucleotide mismatches do not impair the capacity of a potent single gRNA to simultaneously suppress ancestral and mutated SARS-CoV-2 in infected mammalian cells, including the highly infectious and globally disseminated Spike D614G mutant. The specificity, efficiency and rapid deployment properties of reprogrammed Cas13b described here provide a molecular blueprint of antiviral therapeutics to simultaneously suppress a wide range of SARS-CoV-2 mutants, and is readily adaptable to other emerging pathogenic viruses.

microbiology↗