Heightened protein-translation activities in mammalian cells and the disease/treatment implications

In vitro pharmacokinetic behavior in lung of harringtonine, an antagonist of SARS-CoV-2 associated proteins: New insights of inhalation therapy for COVID-19

BACKGROUND

Recent studies have shown that harringtonine (HT) could specifically bind with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein and host cell transmembrane serine protease 2 (TMPRSS2) to block membrane fusion, which is an effective antagonist for SARS-CoV-2.

PURPOSE

Our study focused on in-depth exploration of in vitro pharmacokinetic characteristics of HT in lung.

METHODS

HPLC-fluorescence detection method was used to detect changes of HT content. Incubation systems of lung microsomes for phase I metabolism and UGT incubation systems for phase II metabolism were performed to elucidate metabolites and metabolic mechanisms of HT, and then the metabolic enzyme phenotypes for HT were clarified by chemical inhibition method and recombinant enzyme method. Through metabolomics, we comprehensively evaluated the physiological dynamic changes in SD rat and human lung microsomes, and revealed the relationship between metabolomics and pharmacological activity of HT.

RESULTS

HPLC-fluorescence detection method showed strong specificity, high accuracy, and good stability for rapid quantification of HT. We confirmed that HT mainly underwent phase I metabolism, and the metabolites of HT in different species were all identified as 4'-demethyl HT, with metabolic pathway being hydrolysis reaction. CYP1A2 and CYP2E1 participated in HT metabolism, but as HT metabolism was not NADPH dependent, the esterase HCES1 in lung also played a role. The main KEGG pathways in SD rat and human lung microsomes were cortisol synthesis and secretion, steroid hormone biosynthesis and linoleic acid metabolism, respectively. The downregulated key biomarkers of 11-deoxycortisol, 21-deoxycortisol and 9(10)-EpOME suggested that HT could prevent immunosuppression and interfere with infection and replication of SARS-CoV-2.

CONCLUSION

HT was mainly metabolized into 4'-demethyl HT through phase I reactions, which was mediated by CYP1A2, CYP2E1, and HCES1. The downregulation of 11-deoxycortisol, 21-deoxycortisol and 9(10)-EpOME were key ways of HT against SARS-CoV-2. Our study was of great significance for development and clinical application of HT in the treatment of COVID-19.

Subcellular functions of tau mediates repair response and synaptic homeostasis in injury

Injury responses in terminally differentiated cells such as neurons is tightly regulated by pathways aiding homeostatic maintenance. Cancer patients subjected to neuronal injury in brain radiation experience cognitive declines similar to those seen in primary neurodegenerative diseases. Numerous studies have investigated the effect of radiation in proliferating cells of the brain, yet the impact in differentiated, post-mitotic neurons, especially the structural and functional alterations remain largely elusive. We identified that microtubule-associated tau is a critical player in neuronal injury response via compartmentalized functions in both repair-centric and synaptic regulatory pathways. Ionizing radiation-induced injury acutely induces increase in phosphorylated tau in the nucleus and directly interacts with histone 2AX (H2AX), a DNA damage repair (DDR) marker. Loss of tau significantly reduced H2AX after irradiation, indicating that tau may play an important role in neuronal DDR response. We also observed that loss of tau increases eukaryotic elongation factor levels after irradiation, the latter being a positive regulator of protein translation. This cascades into a significant increase in synaptic proteins, resulting in disrupted homeostasis. Consequently, novel object recognition test showed decrease in learning and memory in tau-knockout mice after irradiation, and electroencephalographic activity showed increase in delta and theta band oscillations, often seen in dementia patients. Our findings demonstrate tau's previously undefined, multifunctional role in acute responses to injury, ranging from DDR response in the nucleus to synaptic function within a neuron. Such knowledge is vital to develop therapeutic strategies targeting neuronal injury in cognitive decline for at risk and vulnerable populations.

Shiftless Is a Novel Member of the Ribosome Stress Surveillance Machinery That Has Evolved to Play a Role in Innate Immunity and Cancer Surveillance

A longstanding paradox in molecular biology has centered on the question of how very long proteins are synthesized, despite numerous measurements indicating that ribosomes spontaneously shift reading frame at rates that should preclude their ability completely translate their mRNAs. Shiftless (SFL; C19orf66) was originally identified as an interferon responsive gene encoding an antiviral protein, indicating that it is part of the innate immune response. This activity is due to its ability to bind ribosomes that have been programmed by viral sequence elements to shift reading frame. Curiously, Shiftless is constitutively expressed at low levels in mammalian cells. This study examines the effects of altering Shiftless homeostasis, revealing how it may be used by higher eukaryotes to identify and remove spontaneously frameshifted ribosomes, resolving the apparent limitation on protein length. Data also indicate that Shiftless plays a novel role in the ribosome-associated quality control program. A model is proposed wherein SFL recognizes and arrests frameshifted ribosomes, and depending on SFL protein concentrations, either leads to removal of frameshifted ribosomes while leaving mRNAs intact, or to mRNA degradation. We propose that SFL be added to the growing pantheon of proteins involved in surveilling translational fidelity and controlling gene expression in higher eukaryotes.

Ancistrocladinium A Induces Apoptosis in Proteasome Inhibitor-Resistant Multiple Myeloma Cells: A Promising Therapeutic Agent Candidate

The N,C-coupled naphthylisoquinoline alkaloid ancistrocladinium A belongs to a novel class of natural products with potent antiprotozoal activity. Its effects on tumor cells, however, have not yet been explored. We demonstrate the antitumor activity of ancistrocladinium A in multiple myeloma (MM), a yet incurable blood cancer that represents a model disease for adaptation to proteotoxic stress. Viability assays showed a potent apoptosis-inducing effect of ancistrocladinium A in MM cell lines, including those with proteasome inhibitor (PI) resistance, and in primary MM cells, but not in non-malignant blood cells. Concomitant treatment with the PI carfilzomib or the histone deacetylase inhibitor panobinostat strongly enhanced the ancistrocladinium A-induced apoptosis. Mass spectrometry with biotinylated ancistrocladinium A revealed significant enrichment of RNA-splicing-associated proteins. Affected RNA-splicing-associated pathways included genes involved in proteotoxic stress response, such as PSMB5-associated genes and the heat shock proteins HSP90 and HSP70. Furthermore, we found strong induction of ATF4 and the ATM/H2AX pathway, both of which are critically involved in the integrated cellular response following proteotoxic and oxidative stress. Taken together, our data indicate that ancistrocladinium A targets cellular stress regulation in MM and improves the therapeutic response to PIs or overcomes PI resistance, and thus may represent a promising potential therapeutic agent.

A multi-targeting drug design strategy for identifying potent anti-SARS-CoV-2 inhibitors

The COVID-19, caused by SARS-CoV-2, is threatening public health, and there is no effective treatment. In this study, we have implemented a multi-targeted anti-viral drug design strategy to discover highly potent SARS-CoV-2 inhibitors, which simultaneously act on the host ribosome, viral RNA as well as RNA-dependent RNA polymerases, and nucleocapsid protein of the virus, to impair viral translation, frameshifting, replication, and assembly. Driven by this strategy, three alkaloids, including lycorine, emetine, and cephaeline, were discovered to inhibit SARS-CoV-2 with EC50 values of low nanomolar levels potently. The findings in this work demonstrate the feasibility of this multi-targeting drug design strategy and provide a rationale for designing more potent anti-virus drugs.