Compound C inhibits nonsense-mediated RNA decay independently of AMPK

Identification of nonsense-mediated decay inhibitors that alter the tumor immune landscape

Despite exciting developments in cancer immunotherapy, its broad application is limited by the paucity of targetable antigens on the tumor cell surface. As an intrinsic cellular pathway, nonsense-mediated decay (NMD) conceals neoantigens through the destruction of the RNA products from genes harboring truncating mutations. We developed and conducted a high-throughput screen, based on the ratiometric analysis of transcripts, to identify critical mediators of NMD in human cells. This screen implicated disruption of kinase SMG1's phosphorylation of UPF1 as a potential disruptor of NMD. This led us to design a novel SMG1 inhibitor, KVS0001, that elevates the expression of transcripts and proteins resulting from human and murine truncating mutations in vitro and murine cells in vivo. Most importantly, KVS0001 concomitantly increased the presentation of immune-targetable human leukocyte antigens (HLA) class I-associated peptides from NMD-downregulated proteins on the surface of human cancer cells. KVS0001 provides new opportunities for studying NMD and the diseases in which NMD plays a role, including cancer and inherited diseases.

4-Hexylresorcinol Enhances Glut4 Expression and Glucose Homeostasis via AMPK Activation and Histone H3 Acetylation

This study investigates the potential of 4-hexylresorcinol (4HR) as a novel antidiabetic agent by assessing its effects on blood glucose levels, Glut4 expression, AMPK phosphorylation, and Histone H3 acetylation (Ac-H3) in the liver. In vitro experiments utilized Huh7 and HepG2 cells treated with varying concentrations of 4HR. Glut4, p-AMPK, and Ac-H3 expression levels were quantified via Western blotting. Additionally, GAPDH activity and glucose uptake were evaluated. In vivo experiments employed streptozotocin (STZ)-induced diabetic rats, with or without 4HR treatment, monitoring blood glucose, body weight, and hepatic levels of Glut4, p-AMPK, and Ac-H3. In vitro, 4HR treatment increased GAPDH activity and glucose uptake. Elevated Glut4, p-AMPK, and Ac-H3 levels were observed 8 h after 4HR administration. Inhibition of p-AMPK using compound C reduced 4HR-mediated Glut4 expression. In STZ-induced diabetic rats, 4HR significantly upregulated Glut4, p-AMPK, and Ac-H3 expression in the liver. Periodic 4HR injections mitigated weight loss and lowered blood glucose levels in STZ-injected animals. Histological analysis revealed increased glycogen storage in hepatocytes of the 4HR-treated group. Overall, 4HR enhanced Glut4 expression through upregulation of AMPK activity and histone H3 acetylation in vitro and in vivo, improving hepatic glucose homeostasis and suggesting potential as a candidate for diabetes treatment.

Identification of nonsense-mediated decay inhibitors that alter the tumor immune landscape

Despite exciting developments in cancer immunotherapy, its broad application is limited by the paucity of targetable antigens on the tumor cell surface. As an intrinsic cellular pathway, nonsense-mediated decay (NMD) conceals neoantigens through the destruction of the RNA products from genes harboring truncating mutations. We developed and conducted a high throughput screen, based on the ratiometric analysis of transcripts, to identify critical mediators of NMD. This screen implicated disruption of kinase SMG1's phosphorylation of UPF1 as a potential disruptor of NMD. This led us to design a novel SMG1 inhibitor, KVS0001, that elevates the expression of transcripts and proteins resulting from truncating mutations in vivo and in vitro . Most importantly, KVS0001 concomitantly increased the presentation of immune-targetable HLA class I-associated peptides from NMD-downregulated proteins on the surface of cancer cells. KVS0001 provides new opportunities for studying NMD and the diseases in which NMD plays a role, including cancer and inherited diseases.

One Sentence Summary

Disruption of the nonsense-mediated decay pathway with a newly developed SMG1 inhibitor with in-vivo activity increases the expression of T-cell targetable cancer neoantigens resulting from truncating mutations.

Nonsense-Mediated RNA Decay Is a Unique Vulnerability of Cancer Cells Harboring SF3B1 or U2AF1 Mutations

Nonsense-mediated RNA decay (NMD) is recognized as an RNA surveillance pathway that targets aberrant mRNAs with premature translation termination codons (PTC) for degradation, however, its molecular mechanisms and roles in health and disease remain incompletely understood. In this study, we developed a novel reporter system to accurately measure NMD activity in individual cells. A genome-wide CRISPR-Cas9 knockout screen using this reporter system identified novel NMD-promoting factors, including multiple components of the SF3B complex and other U2 spliceosome factors. Interestingly, cells with mutations in the spliceosome genes SF3B1 and U2AF1, which are commonly found in myelodysplastic syndrome (MDS) and cancers, have overall attenuated NMD activity. Compared with wild-type (WT) cells, SF3B1- and U2AF1-mutant cells were more sensitive to NMD inhibition, a phenotype that is accompanied by elevated DNA replication obstruction, DNA damage, and chromosomal instability. Remarkably, the sensitivity of spliceosome mutant cells to NMD inhibition was rescued by overexpression of RNase H1, which removes R-loops in the genome. Together, these findings shed new light on the functional interplay between NMD and RNA splicing and suggest a novel synthetic lethal strategy for the treatment of MDS and cancers with spliceosome mutations. SIGNIFICANCE: This study has developed a novel NMD reporter system and identified a potential therapeutic approach of targeting the NMD pathway to treat cancer with spliceosome gene mutations.

Repression of TERRA Expression by Subtelomeric DNA Methylation Is Dependent on NRF1 Binding

Chromosome ends are transcribed into long noncoding telomeric repeat-containing RNA (TERRA) from subtelomeric promoters. A class of TERRA promoters are associated with CpG islands embedded in repetitive DNA tracts. Cytosines in these subtelomeric CpG islands are frequently methylated in telomerase-positive cancer cells, and demethylation induced by depletion of DNA methyltransferases is associated with increased TERRA levels. However, the direct evidence and the underlying mechanism regulating TERRA expression through subtelomeric CpG islands methylation are still to establish. To analyze TERRA regulation by subtelomeric DNA methylation in human cell line (HeLa), we used an epigenetic engineering tool based on CRISPR-dCas9 (clustered regularly interspaced short palindromic repeats - dead CRISPR associated protein 9) associated with TET1 (ten-eleven 1 hydroxylase) to specifically demethylate subtelomeric CpG islands. This targeted demethylation caused an up-regulation of TERRA, and the enhanced TERRA production depended on the methyl-sensitive transcription factor NRF1 (nuclear respiratory factor 1). Since AMPK (AMP-activated protein kinase) is a well-known activator of NRF1, we treated cells with an AMPK inhibitor (compound C). Surprisingly, compound C treatment increased TERRA levels but did not inhibit AMPK activity in these experimental conditions. Altogether, our results provide new insight in the fine-tuning of TERRA at specific subtelomeric promoters and could allow identifying new regulators of TERRA.