UPF1: From mRNA Surveillance to Protein Quality Control

Advances in molecular function of UPF1 in Cancer

It is known that more than 10 % of genetic diseases are caused by a mutation in protein-coding mRNA (premature termination codon; PTC). mRNAs with an early stop codon are degraded by the cellular surveillance process known as nonsense-mediated mRNA decay (NMD), which prevents the synthesis of C-terminally truncated proteins. Up-frameshift-1 (UPF1) has been reported to be involved in the downregulation of various cancers, and low expression of UPF1 was shown to correlate with poor prognosis. It is known that UPF1 is a master regulator of nonsense-mediated mRNA decay (NMD). UPF1 may also function as an E3 ligase and degrade target proteins without using mRNA decay mechanisms. Increasing evidence indicates that UPF1 could serve as a good biomarker for cancer diagnosis and treatment for future therapeutic applications. Long non-coding RNAs (lncRNAs) have the ability to bind different proteins and regulate gene expression; this role in cancer cells has already been identified by different studies. This article provides an overview of the aberrant expression of UPF1, its functional properties, and molecular processes during cancer for clinical applications in cancer. We also discussed the interactions of lncRNA with UPF1 for cell growth during tumorigenesis.

Opportunistic pathogens increased and probiotics or short-chain fatty acid-producing bacteria decreased in the intestinal microbiota of pneumonia inpatients during SARS-CoV-2 Omicron variant epidemic

The global pandemic of COVID-19 has been over four years, and the role of intestinal microbiota in the occurrence and development of COVID-19 needs to be further clarified. During the outbreak of SARS-CoV-2 Omicron variant in China, we analyzed the intestinal microbiome in fecal samples from inpatients with pneumonia and normal individuals in January 2023. The microbiota composition, alpha diversity, beta diversity, differential microbial community, co-occurrence networks, and functional abundance were analyzed. The results showed significant differences in microbiota composition between the two groups. In pneumonia group, the abundance of Bifidobacterium, Blautia, Clostridium, and Coprococcus decreased, while the abundance of Enterococcus, Lactobacillus, and Megamonas increased. Through LEfSe analysis, 37 marker microbiota were identified in pneumonia group. Co-occurrence network analysis found that Lachnospiraceae was critical for the interaction of intestinal microbiota, and the anti-inflammatory bacteria Blautia was negatively correlated with the pro-inflammatory bacteria Ruminococcus. Functional prediction found the up-regulation of steroid biosynthesis, geraniol degradation, and mRNA surveillance pathway in pneumonia group. In conclusion, opportunistic pathogens increased and probiotics, or short-chain fatty acid-producing bacteria, decreased in the intestinal microbiota of pneumonia inpatients during the Omicron epidemic. Blautia could be used as a probiotic in the treatment of pneumonia patients in the future.

Messenger RNA Surveillance: Current Understanding, Regulatory Mechanisms, and Future Implications

Nonsense-mediated mRNA decay (NMD) is an evolutionarily conserved surveillance mechanism in eukaryotes primarily deployed to ensure RNA quality control by eliminating aberrant transcripts and also involved in modulating the expression of several physiological transcripts. NMD, the mRNA surveillance pathway, is a major form of gene regulation in eukaryotes. NMD serves as one of the most significant quality control mechanisms as it primarily scans the newly synthesized transcripts and differentiates the aberrant and non-aberrant transcripts. The synthesis of truncated proteins is restricted, which would otherwise lead to cellular dysfunctions. The up-frameshift factors (UPFs) play a central role in executing the NMD event, largely by recognizing and recruiting multiple protein factors that result in the decay of non-physiological mRNAs. NMD exhibits astounding variability in its ability across eukaryotes in an array of pathological and physiological contexts. The detailed understanding of NMD and the underlying molecular mechanisms remains blurred. This review outlines our current understanding of NMD, in regulating multifaceted cellular events during development and disease. It also attempts to identify unanswered questions that deserve further investigation.

Characterization of the mIF4G Domains in the RNA Surveillance Protein Upf2p

Thirty percent of all mutations causing human disease generate mRNAs with premature termination codons (PTCs). Recognition and degradation of these PTC-containing mRNAs is carried out by the mechanism known as nonsense-mediated mRNA decay (NMD). Upf2 is a scaffold protein known to be a central component of the NMD surveillance pathway. It harbors three middle domains of eukaryotic initiation factor 4G (mIF4G-1, mIF4G-2, mIF4G-3) in its N-terminal region that are potentially important in regulating the surveillance pathway. In this study, we defined regions within the mIF4G-1 and mIF4G-2 that are required for proper function of Upf2p in NMD and translation termination in Saccharomyces cerevisiae. In addition, we narrowed down the activity of these regions to an aspartic acid (D59) in mIF4G-1 that is important for NMD activity and translation termination accuracy. Taken together, these studies suggest that inherently charged residues within mIF4G-1 of Upf2p play a role in the regulation of the NMD surveillance mechanism in S. cerevisiae.

The Role of mRNA Quality Control in the Aging of Caenorhabditis elegans

The proper maintenance of mRNA quality that is regulated by diverse surveillance pathways is essential for cellular homeostasis and is highly conserved among eukaryotes. Here, we review findings regarding the role of mRNA quality control in the aging and longevity of Caenorhabditis elegans, an outstanding model for aging research. We discuss the recently discovered functions of the proper regulation of nonsense-mediated mRNA decay, ribosome-associated quality control, and mRNA splicing in the aging of C. elegans. We describe how mRNA quality control contributes to longevity conferred by various regimens, including inhibition of insulin/insulin-like growth factor 1 (IGF-1) signaling, dietary restriction, and reduced mechanistic target of rapamycin signaling. This review provides valuable information regarding the relationship between the mRNA quality control and aging in C. elegans, which may lead to insights into healthy longevity in complex organisms, including humans.

Cutting through the stress: RNA decay pathways at the endoplasmic reticulum

The endoplasmic reticulum (ER) is central to the processing of luminal, transmembrane, and secretory proteins, and maintaining a functional ER is essential for organismal physiology and health. Increased protein-folding load on the ER causes ER stress, which activates quality control mechanisms to restore ER function and protein homeostasis. Beyond protein quality control, mRNA decay pathways have emerged as potent ER fidelity regulators, but their mechanistic roles in ER quality control and their interrelationships remain incompletely understood. Herein, we review ER-associated RNA decay pathways - including regulated inositol-requiring enzyme 1α (IRE1α)-dependent mRNA decay (RIDD), nonsense-mediated mRNA decay (NMD), and Argonaute-dependent RNA silencing - in ER homeostasis, and highlight the intricate coordination of ER-targeted RNA and protein decay mechanisms and their association with antiviral defense.

YTHDF2 facilitates aggresome formation via UPF1 in an m6A-independent manner

YTHDF2 has been extensively studied and typified as an RNA-binding protein that specifically recognizes and destabilizes RNAs harboring N6-methyladenosine (m6A), the most prevalent internal modification found in eukaryotic RNAs. In this study, we unravel the m6A-independent role of YTHDF2 in the formation of an aggresome, where cytoplasmic protein aggregates are selectively sequestered upon failure of protein homeostasis mediated by the ubiquitin-proteasome system. Downregulation of YTHDF2 in HeLa cells reduces the circularity of aggresomes and the rate of movement of misfolded polypeptides, inhibits aggresome formation, and thereby promotes cellular apoptosis. Mechanistically, YTHDF2 is recruited to a misfolded polypeptide-associated complex composed of UPF1, CTIF, eEF1A1, and DCTN1 through its interaction with UPF1. Subsequently, YTHDF2 increases the interaction between the dynein motor protein and the misfolded polypeptide-associated complex, facilitating the diffusion dynamics of the movement of misfolded polypeptides toward aggresomes. Therefore, our data reveal that YTHDF2 is a cellular factor involved in protein quality control.

Advancement of targeted protein degradation strategies as therapeutics for undruggable disease targets

Targeted protein degradation (TPD) aids in developing novel bifunctional small-molecule degraders and eliminates proteins of interest. The TPD approach shows promising results in oncological, neurogenerative, cardiovascular and gynecological drug development. We provide an overview of technology advancements in TPD, including molecular glues, proteolysis-targeting chimeras (PROTACs), lysosome-targeting chimeras, antibody-based PROTAC, GlueBody PROTAC, autophagy-targeting chimera, autophagosome-tethering compound, autophagy-targeting chimera and chaperone-mediated autophagy-based degraders. Here we discuss the development and evolution of the TPD field, the variety of proteins that PROTACs target and the biological repercussions of their degradation. We particularly highlight the recent improvements in TPD research that utilize autophagy or the endolysosomal pathway, which enables the targeting of undruggable targets.

Recoding of Nonsense Mutation as a Pharmacological Strategy

Approximately 11% of genetic human diseases are caused by nonsense mutations that introduce a premature termination codon (PTC) into the coding sequence. The PTC results in the production of a potentially harmful shortened polypeptide and activation of a nonsense-mediated decay (NMD) pathway. The NMD pathway reduces the burden of unproductive protein synthesis by lowering the level of PTC mRNA. There is an endogenous rescue mechanism that produces a full-length protein from a PTC mRNA. Nonsense suppression therapies aim to increase readthrough, suppress NMD, or are a combination of both strategies. Therefore, treatment with translational readthrough-inducing drugs (TRIDs) and NMD inhibitors may increase the effectiveness of PTC suppression. Here we discuss the mechanism of PTC readthrough and the development of novel approaches to PTC suppression. We also discuss the toxicity and bioavailability of therapeutics used to stimulate PTC readthrough.

ABT1 modifies SMARD1 pathology via interactions with IGHMBP2 and stimulation of ATPase and helicase activity

SMA with respiratory distress type 1 (SMARD1) and Charcot-Marie-Tooth type 2S (CMT2S) are results of mutations in immunoglobulin mu DNA binding protein 2 (IGHMBP2). IGHMBP2 is a UPF1-like helicase with proposed roles in several cellular processes, including translation. This study examines activator of basal transcription 1 (ABT1), a modifier of SMARD1-nmd disease pathology. Microscale thermophoresis and dynamic light scattering demonstrate that IGHMBP2 and ABT1 proteins directly interact with high affinity. The association of ABT1 with IGHMBP2 significantly increases the ATPase and helicase activity as well as the processivity of IGHMBP2. The IGHMBP2/ABT1 complex interacts with the 47S pre-rRNA 5' external transcribed spacer and U3 small nucleolar RNA (snoRNA), suggesting that the IGHMBP2/ABT1 complex is important for pre-rRNA processing. Intracerebroventricular injection of scAAV9-Abt1 decreases FVB-Ighmbp2nmd/nmd disease pathology, significantly increases lifespan, and substantially decreases neuromuscular junction denervation. To our knowledge, ABT1 is the first disease-modifying gene identified for SMARD1. We provide a mechanism proposing that ABT1 decreases disease pathology in FVB-Ighmbp2nmd/nmd mutants by optimizing IGHMBP2 biochemical activity (ATPase and helicase activity). Our studies provide insight into SMARD1 pathogenesis, suggesting that ABT1 modifies IGHMBP2 activity as a means to regulate pre-rRNA processing.

RBM47 inhibits hepatocellular carcinoma progression by targeting UPF1 as a DNA/RNA regulator

The mechanisms by which the tumor behaviors of hepatocellular carcinoma (HCC) support growth and metastasis remain largely unknown, and it has become increasingly apparent that molecular dysregulation is of considerable importance for cellular signaling pathways. Recently, RNA-binding motif protein 47 (RBM47) has been suggested to function as a tumor regulator by acting as an RNA binding protein (RBP), but its role in HCC remains ambiguous. Here, in HCC, we identified that RBM47 had an inhibitory influence on tumor behaviors in vitro and accordingly suppressed the growth and metastasis of xenograft tumors in vivo. Additionally, RBM47 was verified to positively regulate Upframeshift 1 (UPF1), which is a crucial protein involved in the nonsense-mediated RNA decay (NMD) process and was previously determined to be an HCC suppressor. Mechanistically, the stability of UPF1 mRNA was demonstrated to be enhanced with its 3’UTR bound by RBM47, which acted as an RNA binding protein. Meanwhile, RBM47 was also proven to promote the transcription of UPF1 as a transcription factor. Taken together, we concluded that RBM47 functioned as a tumor suppressor by upregulating UPF1, acting as a DNA/RNA binding protein at the transcriptional and posttranscriptional levels.

Nonsense-Mediated mRNA Decay, a Finely Regulated Mechanism

Nonsense-mediated mRNA decay (NMD) is both a mechanism for rapidly eliminating mRNAs carrying a premature termination codon and a pathway that regulates many genes. This implies that NMD must be subject to regulation in order to allow, under certain physiological conditions, the expression of genes that are normally repressed by NMD. Therapeutically, it might be interesting to express certain NMD-repressed genes or to allow the synthesis of functional truncated proteins. Developing such approaches will require a good understanding of NMD regulation. This review describes the different levels of this regulation in human cells.

Prognostic and Genomic Analysis of Proteasome 20S Subunit Alpha (PSMA) Family Members in Breast Cancer

The complexity of breast cancer includes many interacting biological processes, and proteasome alpha (PSMA) subunits are reported to be involved in many cancerous diseases, although the transcriptomic expression of this gene family in breast cancer still needs to be more thoroughly investigated. Consequently, we used a holistic bioinformatics approach to study the PSMA genes involved in breast cancer by integrating several well-established high-throughput databases and tools, such as cBioPortal, Oncomine, and the Kaplan–Meier plotter. Additionally, correlations of breast cancer patient survival and PSMA messenger RNA expressions were also studied. The results demonstrated that breast cancer tissues had higher expression levels of PSMA genes compared to normal breast tissues. Furthermore, PSMA2, PSMA3, PSMA4, PSMA6, and PSMA7 showed high expression levels, which were correlated with poor survival of breast cancer patients. In contrast, PSMA5 and PSMA8 had high expression levels, which were associated with good prognoses. We also found that PSMA family genes were positively correlated with the cell cycle, ubiquinone metabolism, oxidative stress, and immune response signaling, including antigen presentation by major histocompatibility class, interferon-gamma, and the cluster of differentiation signaling. Collectively, these findings suggest that PSMA genes have the potential to serve as novel biomarkers and therapeutic targets for breast cancer. Nevertheless, the bioinformatic results from the present study would be strengthened with experimental validation in the future by prospective studies on the underlying biological mechanisms of PSMA genes and breast cancer.