c-Mpl-del, a c-Mpl alternative splicing isoform, promotes AMKL progression and chemoresistance.

Acute megakaryocytic leukemia (AMKL) is a clinically heterogeneous subtype of acute myeloid leukemia characterized by unrestricted megakaryoblast proliferation and poor prognosis. Thrombopoietin receptor c-Mpl is a primary regulator of megakaryopoeisis and a potent mitogenic receptor. Aberrant c-Mpl signaling has been implicated in a myriad of myeloid proliferative disorders, some of which can lead to AMKL, however, the role of c-Mpl in AMKL progression remains largely unexplored. Here, we identified increased expression of a c-Mpl alternative splicing isoform, c-Mpl-del, in AMKL patients. We found that c-Mpl-del expression was associated with enhanced AMKL cell proliferation and chemoresistance, and decreased survival in xenografted mice, while c-Mpl-del knockdown attenuated proliferation and restored apoptosis. Interestingly, we observed that c-Mpl-del exhibits preferential utilization of phosphorylated c-Mpl-del C-terminus Y607 and biased activation of PI3K/AKT pathway, which culminated in upregulation of GATA1 and downregulation of DDIT3-related apoptotic responses conducive to AMKL chemoresistance and proliferation. Thus, this study elucidates the critical roles of c-Mpl alternative splicing in AMKL progression and drug resistance, which may have important diagnostic and therapeutic implications for leukemia accelerated by c-Mpl-del overexpression.

Platelet-derived extracellular vesicles inhibit ferroptosis and promote distant metastasis of nasopharyngeal carcinoma by upregulating ITGB3.

Nasopharyngeal carcinoma (NPC) is a malignancy with high metastatic and invasive nature. Distant metastasis contributes substantially to treatment failure and mortality in NPC. Platelets are versatile blood cells and the number of platelets is positively associated with the distant metastasis of tumor cells. However, the role and underlying mechanism of platelets responsible for the metastasis of NPC cells remain unclear. Here we found that the distant metastasis of NPC patients was positively correlated with the expression levels of integrin ß3 (ITGB3) in platelet-derived extracellular vesicles (EVs) from NPC patients (P-EVs). We further revealed that EVs transfer occurred from platelets to NPC cells, mediating cell-cell communication and inducing the metastasis of NPC cells by upregulating ITGB3 expression. Mechanistically, P-EVs-upregulated ITGB3 increased SLC7A11 expression by enhancing protein stability and activating the MAPK/ERK/ATF4/Nrf2 axis, which suppressed ferroptosis, thereby facilitating the metastasis of NPC cells. NPC xenografts in mouse models further confirmed that P-EVs inhibited the ferroptosis of circulating NPC cells and promoted the distant metastasis of NPC cells. Thus, these findings elucidate a novel role of platelet-derived EVs in NPC metastasis, which not only improves our understanding of platelet-mediated tumor distant metastasis, but also has important implications in diagnosis and treatment of NPC.

SARS-CoV-2 spike promotes inflammation and apoptosis through autophagy by ROS-suppressed PI3K/AKT/mTOR signaling.

BACKGROUND: Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection-induced inflammatory responses are largely responsible for the death of novel coronavirus disease 2019 (COVID-19) patients. However, the mechanism by which SARS-CoV-2 triggers inflammatory responses remains unclear. Here, we aimed to explore the regulatory role of SARS-CoV-2 spike protein in infected cells and attempted to elucidate the molecular mechanism of SARS-CoV-2-induced inflammation. METHODS: SARS-CoV-2 spike pseudovirions (SCV-2-S) were generated using the spike-expressing virus packaging system. Western blot, mCherry-GFP-LC3 labeling, immunofluorescence, and RNA-seq were performed to examine the regulatory mechanism of SCV-2-S in autophagic response. The effects of SCV-2-S on apoptosis were evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), Western blot, and flow cytometry analysis. Enzyme-linked immunosorbent assay (ELISA) was carried out to examine the mechanism of SCV-2-S in inflammatory responses. RESULTS: Angiotensin-converting enzyme 2 (ACE2)-mediated SCV-2-S infection induced autophagy and apoptosis in human bronchial epithelial and microvascular endothelial cells. Mechanistically, SCV-2-S inhibited the PI3K/AKT/mTOR pathway by upregulating intracellular reactive oxygen species (ROS) levels, thus promoting the autophagic response. Ultimately, SCV-2-S-induced autophagy triggered inflammatory responses and apoptosis in infected cells. These findings not only improve our understanding of the mechanism underlying SARS-CoV-2 infection-induced pathogenic inflammation but also have important implications for developing anti-inflammatory therapies, such as ROS and autophagy inhibitors, for COVID-19 patients.

EGFR-rich extracellular vesicles derived from highly metastatic nasopharyngeal carcinoma cells accelerate tumour metastasis through PI3K/AKT pathway-suppressed ROS.

Nasopharyngeal carcinoma (NPC) is the most common cancer with high metastatic potential that occurs in the epithelial cells of the nasopharynx. Distant metastases are the primary cause for treatment failure and mortality of NPC patients. However, the underlying mechanism responsible for the initiation of tumour cell dissemination and tumour metastasis in NPC is not well understood. Here, we demonstrated that epidermal growth factor receptor (EGFR) was highly expressed in tumour tissues of NPC patients with distant metastases and was associated with a decrease in reactive oxygen species (ROS). We also revealed that extracellular vesicles (EVs) transfer occurred from highly to poorly metastatic NPC cells, mediating cell-cell communication and enhancing the metastatic potential of poorly metastatic NPC cells. Further experiments indicated that EVs derived from highly metastatic NPC cells induced the up-regulation of EGFR and down-regulation of ROS in low metastatic NPC cells. Mechanistically, EGFR-rich EVs-mediated EGFR overexpression down-regulated intracellular ROS levels through the PI3K/AKT pathway, thus promoting the metastatic potential of poorly metastatic NPC cells. Strikingly, treatment with EVs secreted from highly metastatic NPC cells was significantly associated with rapid NPC progression and shorter survival in xenografted mice. These findings not only improve our understanding of EVs-mediated NPC metastatic mechanism but also have important implications for the detection and treatment of NPC patients accompanied by aberrant EGFR-rich EVs transmission.

MiR-199b represses porcine muscle satellite cells proliferation by targeting JAG1.

Pig is a useful medical model for humans due to its similarity in size and physiology. Skeletal muscle plays an essential role in body movement. However, the skeletal muscle injuries are common. Skeletal muscle function maintenance largely depends on preserving the regenerative capacity of muscle. Muscle satellite cells proliferation plays an essential role in postnatal muscle growth and regeneration. Therefore, understanding the mechanisms associated with muscle satellite cells proliferation is essential for devising the alternative treatments for muscle injury. Previous studies showed JAG1-Notch1 signaling pathway and miRNAs regulate the skeletal muscle development. JAG1-Notch1 signal pathway regulates the transcription of certain types of miRNAs which further affects target gene expression. However, the specific relationship between JAG1-Notch1 signal pathway and miRNAs during muscle development has not been established. We found overexpression of intracellular domain of the Notch1 protein (N1ICD) in porcine muscle satellite cells (PSCs) decreased miR-199b level. We demonstrated that miR-199b inhibits PSCs proliferation using the overexpression and inhibition of miR-199b experiment. We also found JAG1, the miR-199b target gene, promotes PSCs proliferation through activating the Notch1 signal pathway. Furthermore, we demonstrated miR-199b forms a feedback loop with the JAG1-Notch1 signal pathway to maintain the PSCs niche homeostasis. Our results of miRNAs and genes work collaboratively in regulating PSCs proliferation expand our understanding in PSCs proliferation mechanism. Furthermore, this finding indicates miR-199b is a potential therapeutic target for muscle atrophy.

MiR-34c represses muscle development by forming a regulatory loop with Notch1.

Since pork accounts for about 40% of global meat consumption, the pig is an important economic animal for meat production. Pig is also a useful medical model for humans due to its similarity in size and physiology. Understanding the mechanism of muscle development has great implication for animal breeding and human health. Previous studies showed porcine muscle satellite cells (PSCs) are important for postnatal skeletal muscle growth, and Notch1 signaling pathway and miRNAs regulate the skeletal muscle development. Notch1 signal pathway regulates the transcription of certain types of miRNAs which further affects target gene expression. However, the specific relationship between Notch1 and miRNAs during muscle development has not been established. We found miR-34c is decreased in PSCs overexpressed N1ICD. Through the overexpression and inhibition of mi-34c, we demonstrated that miR-34c inhibits PSCs proliferation and promotes PSCs differentiation. Using dual-luciferase reporter assay and Chromatin immunoprecipitation, we demonstrate there is a reciprocal regulatory loop between Notch1 and miR-34c. Furthermore, injection of miR-34c lentivirus into mice caused repression of gastrocnemius muscle development. In summary, our data revealed that miR-34c can form a regulatory loop with Notch1 to repress muscle development, and this result expands our understanding of muscle development mechanism.

Characterization of the porcine epidemic diarrhea virus codon usage bias.

Porcine epidemic diarrhea virus (PEDV) has been responsible for several recent outbreaks of porcine epidemic diarrhea (PED) and has caused great economic loss in the swine-raising industry. Considering the significance of PEDV, a systemic analysis was performed to study its codon usage patterns. The relative synonymous codon usage value of each codon revealed that codon usage bias exists and that PEDV tends to use codons that end in T. The mean ENC value of 47.91 indicates that the codon usage bias is low. However, we still wanted to identify the cause of this codon usage bias. A correlation analysis between the codon compositions (A3s, T3s, G3s, C3s, and GC3s), the ENC values, and the nucleotide contents (A%, T%, G%, C%, and GC%) indicated that mutational bias plays role in shaping the PEDV codon usage bias. This was further confirmed by a principal component analysis between the codon compositions and the axis values. Using the Gravy, Aroma, and CAI values, a role of natural selection in the PEDV codon usage pattern was also identified. Neutral analysis indicated that natural selection pressure plays a more important role than mutational bias in codon usage bias. Natural selection also plays an increasingly significant role during PEDV evolution. Additionally, gene function and geographic distribution also influence the codon usage bias to a degree.