mTORC1/S6K1 signaling promotes sustained oncogenic translation through modulating CRL3IBTK-mediated ubiquitination of eIF4A1 in cancer cells.

Enhanced protein synthesis is a crucial molecular mechanism that allows cancer cells to survive, proliferate, metastasize, and develop resistance to anti-cancer treatments, and often arises as a consequence of increased signaling flux channeled to mRNA-bearing eukaryotic initiation factor 4F (eIF4F). However, the post-translational regulation of eIF4A1, an ATP-dependent RNA helicase and subunit of the eIF4F complex, is still poorly understood. Here, we demonstrate that IBTK, a substrate-binding adaptor of the Cullin 3-RING ubiquitin ligase (CRL3) complex, interacts with eIF4A1. The non-degradative ubiquitination of eIF4A1 catalyzed by the CRL3IBTK complex promotes cap-dependent translational initiation, nascent protein synthesis, oncogene expression, and cervical tumor cell growth both in vivo and in vitro. Moreover, we show that mTORC1 and S6K1, two key regulators of protein synthesis, directly phosphorylate IBTK to augment eIF4A1 ubiquitination and sustained oncogenic translation. This link between the CRL3IBTK complex and the mTORC1/S6K1 signaling pathway, which is frequently dysregulated in cancer, represents a promising target for anti-cancer therapies.

Asialoglycoprotein receptor 1 promotes SARS-CoV-2 infection of human normal hepatocytes.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes multi-organ damage, which includes hepatic dysfunction, as observed in over 50% of COVID-19 patients. Angiotensin I converting enzyme (peptidyl-dipeptidase A) 2 (ACE2) is the primary receptor for SARS-CoV-2 entry into host cells, and studies have shown the presence of intracellular virus particles in human hepatocytes that express ACE2, but at extremely low levels. Consequently, we asked if hepatocytes might express receptors other than ACE2 capable of promoting the entry of SARS-CoV-2 into cells. To address this question, we performed a genome-wide CRISPR-Cas9 activation library screening and found that Asialoglycoprotein receptor 1 (ASGR1) promoted SARS-CoV-2 pseudovirus infection of HeLa cells. In Huh-7 cells, simultaneous knockout of ACE2 and ASGR1 prevented SARS-CoV-2 pseudovirus infection. In the immortalized THLE-2 hepatocyte cell line and primary hepatic parenchymal cells, both of which barely expressed ACE2, SARS-CoV-2 pseudovirus could successfully establish an infection. However, after treatment with ASGR1 antibody or siRNA targeting ASGR1, the infection rate significantly dropped, suggesting that SARS-CoV-2 pseudovirus infects hepatic parenchymal cells mainly through an ASGR1-dependent mechanism. We confirmed that ASGR1 could interact with Spike protein, which depends on receptor binding domain (RBD) and N-terminal domain (NTD). Finally, we also used Immunohistochemistry and electron microscopy to verify that SARS-CoV-2 could infect primary hepatic parenchymal cells. After inhibiting ASGR1 in primary hepatic parenchymal cells by siRNA, the infection efficiency of the live virus decreased significantly. Collectively, these findings indicate that ASGR1 is a candidate receptor for SARS-CoV-2 that promotes infection of hepatic parenchymal cells.

Preoperative and postoperative clinical signatures of postgastrectomy venous thromboembolism in patients with gastric cancer: A retrospective cohort study.

BACKGROUND: This study aimed to identify preoperative and postoperative risk factors of venous thromboembolism (VTE) after gastrectomy in gastric cancer (GC) patients. METHODS: 757 GC patients underwent gastrectomy at our institution and 246 patients with elevated postoperative D-dimer levels who received Doppler ultrasonography of lower/upper extremity veins were enrolled. Clinicopathological factors data were collected, and the differences in clinicopathological factors between postoperative VTE (+) and VTE (-) groups were analyzed. Univariate and multivariate logistic regression analyses were performed to identify independent risk factors of postgastrectomy VTE. RESULTS: Of 246 patients with elevated postgastrectomy D-dimer concentrations, 74 patients showed thrombosis in lower/upper extremity veins. Among preoperative factors, age, WBC level, D-dimer concentration, and blood glucose level were significantly higher in the postoperative VTE (+) group. Among the postoperative factors, hemoglobin level was significantly lower in the postoperative VTE (+) group. Among the pathological factors, tumor stage, depth of invasion and TNM classification indicated higher malignancy in the postoperative VTE (+) group. Univariate logistic regression analysis indicated age, preoperative blood glucose level, postoperative hemoglobin level, tumor stage, depth of invasion, and TNM classification as the independent risk factors for postgastrectomy VTE, whereas multivariate logistic regression analysis revealed age and tumor stage as independent risk factors for postgastrectomy VTE. CONCLUSION: Our study revealed that age, preoperative blood glucose level, postoperative anemia, and tumor malignancy were independent risk factors for GC patients exhibiting postgastrectomy VTE. Therefore, the perioperative monitoring, assessment and management of risk factors are important in achieving better outcomes after gastrectomy.

FBXO34 promotes latent HIV-1 activation by post-transcriptional modulation.

ABSTRACTAcquired immunodeficiency syndrome (AIDS) cannot be completely cured, mainly due to the existence of a latent HIV-1 reservoir. However, our current understanding of the molecular mechanisms underlying the establishment and maintenance of HIV-1 latent reservoir is not comprehensive. Here, using a genome-wide CRISPR-Cas9 activation library screening, we identified E3 ubiquitin ligase F-box protein 34 (FBXO34) and the substrate of FBXO34, heterogeneous nuclear ribonucleoprotein U (hnRNP U) was identified by affinity purification mass spectrometry, as new host factors related to HIV-1 latent maintenance. Overexpression of FBXO34 or knockout of hnRNP U can activate latent HIV-1 in multiple latent cell lines. FBXO34 mainly promotes hnRNP U ubiquitination, which leads to hnRNP U degradation and abolishment of the interaction between hnRNP U and HIV-1 mRNA. In a latently infected cell line, hnRNP U interacts with the ReV region of HIV-1 mRNA through amino acids 1-339 to hinder HIV-1 translation, thereby, promoting HIV-1 latency. Importantly, we confirmed the role of the FBXO34/hnRNP U axis in the primary CD4+ T lymphocyte model, and detected differences in hnRNP U expression levels in samples from patients treated with antiretroviral therapy (ART) and healthy people, which further suggests that the FBXO34/hnRNP U axis is a new pathway involved in HIV-1 latency. These results provide mechanistic insights into the critical role of ubiquitination and hnRNP U in HIV-1 latency. This novel FBXO34/hnRNP U axis in HIV transcription may be directly targeted to control HIV reservoirs in patients in the future.

Neutralization of five SARS-CoV-2 variants of concern by convalescent and BBIBP-CorV vaccinee serum.

The prevalence of SARS-CoV-2 variants of concern (VOCs) is still escalating throughout the world. However, the level of neutralization of the inactivated viral vaccine recipients' sera and convalescent sera against all VOCs, including B.1.1.7 (Alpha), B.1.351 (Beta), P.1 (Gamma), B.1.617.2 (Delta), and B.1.1.529 (Omicron) remains to be lack of comparative analysis. Therefore, we constructed pseudoviruses of five VOCs using a lentiviral-based system and analyzed their viral infectivity and neutralization resistance to convalescent and BBIBP-CorV vaccinee serum at different times. Our results show that, compared with the wild-type strain (WT), five VOC pseudoviruses showed higher infection, of which B.1.617.2 and B.1.1.529 variant pseudoviruses exhibited higher infection rates than wild-type or other VOC strains, respectively. Sera from 10 vaccinated individuals at the 1, 3 and 5-month post second dose or from 10 convalescent at 14 and 200 days after discharge retained neutralizing activity against all strains but exhibited decreased neutralization activity significantly against the five VOC variant pseudoviruses over time compared to WT. Notably, 100% (30/30) of the vaccinee serum samples showed more than a 2.5-fold reduction in neutralizing activity against B.1.1.529, and 90% (18/20) of the convalescent serum samples showed more than 2.5-fold reduction in neutralization against B.1.1.529. These findings demonstrate the reduced protection against the VOCs in vaccinated and convalescent individuals over time, indicating that it is necessary to have a booster shot and develop new vaccines capable of eliciting broad neutralization antibodies.

The neutralization of B.1.617.1 and B.1.1.529 sera from convalescent patients and BBIBP-CorV vaccines.

The SARS-CoV-2 variants B.1.617.1 (Kappa) contain multiple mutations in the spike protein. However, the effect of B.1.617.1 lineage-related mutants on viral infectivity and inactivated-virus vaccine efficacy remains to be defined. We therefore constructed 12 B.1.617.1-related pseudoviruses and systematically studied the effects of mutations on virus infectivity and neutralization resistance to convalescent and inactivated virus vaccine sera. Our results show that the B.1.617.1 variant exhibited both higher infectivity and neutralization resistance in sera at 1 or 3 months after vaccination of 28 individuals and at 14 and 200 days after discharge of 15 convalescents. Notably, 89% of vaccines and 100% of the convalescent serum samples showed more than 2.5-fold reduction in neutralization against one single mutation: E484Q. Besides, we found a significant decrease in neutralizing activity in convalescent patients and BBIBP-CorV vaccines for B.1.1.529. These findings demonstrate that inactivated-virus vaccination or convalescent sera showed reduced, but still significant, neutralization against the B.1.617.1 variant.

DCAF12 promotes apoptosis and inhibits NF-κB activation by acting as an endogenous antagonist of IAPs.

Members of the Inhibitor of Apoptosis Protein (IAP) family are essential for cell survival and appear to neutralize the cell death machinery by binding pro-apoptotic caspases. dcaf12 was recently identified as an apoptosis regulator in Drosophila. However, the underlying molecular mechanisms are unknown. Here we revealed that human DCAF12 homolog binds multiple IAPs, including XIAP, cIAP1, cIAP2, and BRUCE, through recognition of BIR domains in IAPs. The pro-apoptotic function of DCAF12 is dependent on its capacity to bind IAPs. In response to apoptotic stimuli, DCAF12 translocates from the nucleus to the cytoplasm, where it blocks the interaction between XIAP and pro-apoptotic caspases to facilitate caspase activation and apoptosis execution. Similarly, DCAF12 suppresses NF-κB activation in an IAP binding-dependent manner. Moreover, DCAF12 acts as a tumor suppressor to restrict the malignant phenotypes of cancer cells. Together, our results suggest that DCAF12 is an evolutionarily conserved IAP antagonist.

SPOP mutations promote p62/SQSTM1-dependent autophagy and Nrf2 activation in prostate cancer.

p62/SQSTM1 is a selective autophagy receptor that drives ubiquitinated cargos towards autophagic degradation. This receptor is also a stress-induced scaffold protein that helps cells to cope with oxidative stress through activation of the Nrf2 pathway. Functional disorders of p62 are closely associated with multiple neurodegenerative diseases and cancers. The gene encoding the E3 ubiquitin ligase substrate-binding adapter SPOP is frequently mutated in prostate cancer (PCa), but the molecular mechanisms underlying how SPOP mutations contribute to PCa tumorigenesis remain poorly understood. Here, we report that cytoplasmic SPOP binds and induces the non-degradative ubiquitination of p62 at residue K420 within the UBA domain. This protein modification decreases p62 puncta formation, liquid phase condensation, dimerization, and ubiquitin-binding capacity, thereby suppressing p62-dependent autophagy. Moreover, we show that SPOP relieves p62-mediated Keap1 sequestration, which ultimately decreases Nrf2-mediated transcriptional activation of antioxidant genes. We further show that PCa-associated SPOP mutants lose the capacity to ubiquitinate p62 and instead promote autophagy and the redox response in a dominant-negative manner. Thus, our findings indicate oncogenic roles of autophagy and Nrf2 activation in the tumorigenesis of SPOP-mutated PCa.

CRL2-KLHDC3 E3 ubiquitin ligase complex suppresses ferroptosis through promoting p14ARF degradation.

The cystine/glutamate antiporter SLC7A11 (commonly known as xCT) functions to import cystine for glutathione biosynthesis, thereby protecting cells from oxidative stress and ferroptosis, a regulated form of non-apoptotic cell death driven by the accumulation of lipid-based reactive oxygen species (ROS). p14ARF, a well-established tumor suppressor, promotes ferroptosis by inhibiting NRF2-mediated SLC7A11 transcription. Here, we demonstrate the crucial role of Cullin 2 RING E3 ligase (CRL2)-KLHDC3 E3 ubiquitin ligase complex in regulating p14ARF protein stability. KLHDC3 acts as a CRL2 adaptor that specifically recognizes a C-terminal degron in p14ARF and triggers p14ARF for ubiquitin-proteasomal degradation. This regulation mode is absent in the murine p14ARF homolog, p19arf which lacks the C-terminal degron. We also show that KLHDC3 suppresses ferroptosis in vitro and supports tumor growth in vivo by relieving p14ARF-mediated suppression of SLC7A11 transcription. Overall, these findings reveal that the protein stability and pro-ferroptotic function of p14ARF are controlled by a CRL2 E3 ubiquitin ligase complex, and suggest that suppression of the p14ARF-NRF2-SLC7A11 regulatory pathway by KLHDC3 overexpression likely contributes to cancer progression.

FKBP3 Induces Human Immunodeficiency Virus Type 1 Latency by Recruiting Histone Deacetylase 1/2 to the Viral Long Terminal Repeat.

Human immunodeficiency virus type 1 (HIV-1) cannot be completely eliminated because of existence of the latent HIV-1 reservoir. However, the facts of HIV-1 latency, including its establishment and maintenance, are incomplete. FKBP3, encoded by the FKBP3 gene, belongs to the immunophilin family of proteins and is involved in immunoregulation and such cellular processes as protein folding. In a previous study, we found that FKBP3 may be related to HIV-1 latency using CRISPR screening. In this study, we knocked out the FKBP3 gene in multiple latently infected cell lines to promote latent HIV-1 activation. We found that FKBP3 could indirectly bind to the HIV-1 long terminal repeat through interaction with YY1, thereby recruiting histone deacetylase 1/2 to it. This promotes histone deacetylation and induces HIV-1 latency. Finally, in a primary latent cell model, we confirmed the effect of FKBP3 knockout on the latent activation of HIV-1. Our results suggest a new mechanism for the epigenetic regulation of HIV-1 latency and a new potential target for activating latent HIV-1. IMPORTANCE The primary reason why AIDS cannot be completely cured is the existence of a latent HIV-1 reservoir. Currently, the facts of HIV-1 latency, including its establishment and maintenance, are incomplete. Using a CRISPR library in our earlier screening of genes related to HIV-1 latency, we identified FBKP3 as a candidate gene related to HIV-1 latency. Therefore, in this mechanistic study, we first confirmed the HIV-1 latency-promoting effect of FKBP3 and determined that FKBP3 promotes histone deacetylation by recruiting histone deacetylase 1/2 to the HIV-1 long terminal repeat. We also confirmed, for the first time, that FKBP3 can act as a transcription factor (TF) recruitment scaffold and participate in epigenetic regulation of HIV-1 latency. These findings suggest a new mechanism for the epigenetic regulation of HIV-1 latency and a new potential target for activating latent HIV-1.

Mitochondrial STAT5A promotes metabolic remodeling and the Warburg effect by inactivating the pyruvate dehydrogenase complex.

Signal transducer and activator 5a (STAT5A) is a classical transcription factor that plays pivotal roles in various biological processes, including tumor initiation and progression. A fraction of STAT5A is localized in the mitochondria, but the biological functions of mitochondrial STAT5A remain obscure. Here, we show that STAT5A interacts with pyruvate dehydrogenase complex (PDC), a mitochondrial gatekeeper enzyme connecting two key metabolic pathways, glycolysis and the tricarboxylic acid cycle. Mitochondrial STAT5A disrupts PDC integrity, thereby inhibiting PDC activity and remodeling cellular glycolysis and oxidative phosphorylation. Mitochondrial translocation of STAT5A is increased under hypoxic conditions. This strengthens the Warburg effect in cancer cells and promotes in vitro cell growth under hypoxia and in vivo tumor growth. Our findings indicate distinct pro-oncogenic roles of STAT5A in energy metabolism, which is different from its classical function as a transcription factor.

PEBP1 suppresses HIV transcription and induces latency by inactivating MAPK/NF-κB signaling.

The latent HIV-1 reservoir is a major barrier to viral eradication. However, our understanding of how HIV-1 establishes latency is incomplete. Here, by performing a genome-wide CRISPR-Cas9 knockout library screen, we identify phosphatidylethanolamine-binding protein 1 (PEBP1), also known as Raf kinase inhibitor protein (RKIP), as a novel gene inducing HIV latency. Depletion of PEBP1 leads to the reactivation of HIV-1 in multiple models of latency. Mechanistically, PEBP1 de-phosphorylates Raf1/ERK/IκB and IKK/IκB signaling pathways to sequestrate NF-κB in the cytoplasm, which transcriptionally inactivates HIV-1 to induce latency. Importantly, the induction of PEBP1 expression by the green tea compound epigallocatechin-3-gallate (EGCG) prevents latency reversal by inhibiting nuclear translocation of NF-κB, thereby suppressing HIV-1 transcription in primary CD4+ T cells isolated from patients receiving antiretroviral therapy (ART). These results suggest a critical role for PEBP1 in the regulation of upstream NF-κB signaling pathways governing HIV transcription. Targeting of this pathway could be an option to control HIV reservoirs in patients in the future.

CRL3-SPOP ubiquitin ligase complex suppresses the growth of diffuse large B-cell lymphoma by negatively regulating the MyD88/NF-κB signaling.

Recurrent oncogenic mutations of MyD88 have been identified in a variety of lymphoid malignancies. Gain-of-function mutations of MyD88 constitutively activate downstream NF-κB signaling pathways, resulting in increased cellular proliferation and survival. However, whether MyD88 activity can be aberrantly regulated in MyD88-wild-type lymphoid malignancies remains poorly understood. SPOP is an adaptor protein of CUL3-based E3 ubiquitin ligase complex and frequently mutated genes in prostate and endometrial cancers. In this study, we reveal that SPOP binds to and induces the nondegradative ubiquitination of MyD88 by recognizing an atypical SPOP-binding motif in MyD88. This modification blocks Myddosome assembly and downstream NF-κB activation. SPOP is mutated in a subset of lymphoid malignancies, including diffuse large B-cell lymphoma (DLBCL). Lymphoid malignancies-associated SPOP mutants exhibited impaired binding to MyD88 and suppression of NF-κB activation. The DLBCL-associated, SPOP-binding defective mutants of MyD88 escaped from SPOP-mediated ubiquitination, and their effect on NF-κB activation is stronger than that of wild-type MyD88. Moreover, SPOP suppresses DLBCL cell growth in vitro and tumor xenograft in vivo by inhibiting the MyD88/NF-κB signaling. Therefore, SPOP acts as a tumor suppressor in DLBCL. Mutations in the SPOP-MyD88 binding interface may disrupt the SPOP-MyD88 regulatory axis and promote aberrant MyD88/NF-κB activation and cell growth in DLCBL.

Prostate Cancer-associated SPOP mutations enhance cancer cell survival and docetaxel resistance by upregulating Caprin1-dependent stress granule assembly.

BACKGROUND: The gene encoding the E3 ubiquitin ligase substrate-binding adaptor SPOP is frequently mutated in primary prostate cancer, but how SPOP mutations contribute to prostate cancer pathogenesis remains poorly understood. Stress granules (SG) assembly is an evolutionarily conserved strategy for survival of cells under stress, and often upregulated in human cancers. We investigated the role of SPOP mutations in aberrant activation of the SG in prostate cancer and explored the relevanve of the mechanism in therapy resistance. METHODS: We identified SG nucleating protein Caprin1 as a SPOP interactor by using the yeast two hybrid methods. A series of functional analyses in cell lines, patient samples, and xenograft models were performed to investigate the biological significance and clinical relevance of SPOP regulation of SG signaling in prostate cancer. RESULTS: The cytoplasmic form of wild-type (WT) SPOP recognizes and triggers ubiquitin-dependent degradation of Caprin1. Caprin1 abundance is elevated in SPOP-mutant expressing prostate cancer cell lines and patient specimens. SPOP WT suppresses SG assembly, while the prostate cancer-associated mutants enhance SG assembly in a Caprin1-dependent manner. Knockout of SPOP or expression of prostate cancer-associated SPOP mutants conferred resistance to death caused by SG inducers (e.g. docetaxel, sodium arsenite and H2O2) in prostate cancer cells. CONCLUSIONS: SG assembly is aberrantly elevated in SPOP-mutated prostate cancer. SPOP mutations cause resistance to cellular stress induced by chemtherapeutic drug such as docetaxel in prostate cancer.

Critical role of Spns2, a sphingosine-1-phosphate transporter, in lung cancer cell survival and migration.

The sphingosine-1-phosphate (S1P) transporter Spns2 regulates myocardial precursor migration in zebrafish and lymphocyte trafficking in mice. However, its function in cancer has not been investigated. We show here that ectopic Spns2 expression induced apoptosis and its knockdown enhanced cell migration in non-small cell lung cancer (NSCLC) cells. Metabolically, Spns2 expression increased the extracellular S1P level while its knockdown the intracellular. Pharmacological inhibition of S1P synthesis abolished the augmented cell migration mediated by Spns2 knockdown, indicating that intracellular S1P plays a key role in this process. Cell signaling studies indicated that Spns2 expression impaired GSK-3ß and Stat3 mediated pro-survival pathways. Conversely, these pathways were activated by Spns2 knockdown, which explains the increased cell migration since they are also crucial for migration. Alterations of Spns2 were found to affect several enzymes involved in S1P metabolism, including sphingosine kinases, S1P phosphatases, and S1P lyase 1. Genetically, Spns2 mRNA level was found to be reduced in advanced lung cancer (LC) patients as quantified by using a small scale qPCR array. These data show for the first time that Spns2 plays key roles in regulating the cellular functions in NSCLC cells, and that its down-regulation is a potential risk factor for LC.

Low dose Hsp90 inhibitor 17AAG protects neural progenitor cells from ischemia induced death.

Stress adaptation effect provides cell protection against ischemia induced apoptosis. Whether this mechanism prevents other types of cell death in stroke is not well studied. This is an important question for regenerative medicine to treat stroke since other types of cell death such as necrosis are also prominent in the stroke brain apart from apoptosis. We report here that treatment with 17-N-Allylamino-17-demethoxygeldanamycin (17AAG), an Hsp90 inhibitor, protected neural progenitor cells (NPCs) against oxygen glucose deprivation (OGD) induced cell death in a dose dependent fashion. Cell death assays indicated that 17AAG not only ameliorated apoptosis, but also necrosis mediated by OGD. This NPC protection was confirmed by exposing cells to oxidative stress, a major stress signal prevalent in the stroke brain. Mechanistic studies demonstrated that 17AAG activated PI3K/Akt and MAPK cell protective pathways. More interestingly, these two pathways were activated in vivo by 17AAG and 17AAG treatment reduced infarct volume in a middle cerebral artery occlusion (MCAO) stroke model. These data suggest that 17AAG protects cells against major cell death pathways and thus might be used as a pharmacological conditioning agent for regenerative medicine for stroke.