The temporal association of CapZ with early endosomes regulates endosomal trafficking and viral entry into host cells.

BACKGROUND: Many viruses enter host cells by hijacking endosomal trafficking. CapZ, a canonical actin capping protein, participates in endosomal trafficking, yet its precise role in endocytosis and virus infection remains elusive. RESULTS: Here, we showed that CapZ was transiently associated with early endosomes (EEs) and was subsequently released from the matured EEs after the fusion of two EEs, which was facilitated by PI(3)P to PI(3,5)P2 conversion. Vacuolin-1 (a triazine compound) stabilized CapZ at EEs and thus blocked the transition of EEs to late endosomes (LEs). Likewise, artificially tethering CapZ to EEs via a rapamycin-induced protein-protein interaction system blocked the early-to-late endosome transition. Remarkably, CapZ knockout or artificially tethering CapZ to EEs via rapamycin significantly inhibited flaviviruses, e.g., Zika virus (ZIKV) and dengue virus (DENV), or beta-coronavirus, e.g., murine hepatitis virus (MHV), infection by preventing the escape of RNA genome from endocytic vesicles. CONCLUSIONS: These results indicate that the temporal association of CapZ with EEs facilitates early-to-late endosome transition (physiologically) and the release of the viral genome from endocytic vesicles (pathologically).

Anti-PD1 does not improve pyroptosis induced by γδ T cells but promotes tumor regression in a pleural mesothelioma mouse model.

Introduction: Mesothelioma is an aggressive tumor in the pleural cavity that is difficult to treat. Diagnosis is usually late with minimal treatment options available for the patients and with unfavorable outcomes. However, recent advances in immunotherapy using γδ T cells may have potential against mesothelioma, given its ample tumoricidal and tumor-migratory properties could allow its infiltration to the widespread tumor mass. Thus, we hypothesize that Vδ2 T cells can perform cytotoxic activities against mesothelioma especially when combined with immune checkpoint blocker against PD-1. Methods: Human Vδ2 T cells were expanded from peripheral blood mononuclear cells using Tetrakis-pivaloyloxymethyl 2-(thiazole-2-ylamino) ethylidene-1,1-bisphosphonate (PTA) plus IL-2 for 13 days, before used to test for cytotoxicity against mesothelioma cell lines. Mesothelioma-bearing mice was established by Intrapleural administration of mesothelioma cell lines to test for the efficacy of Vδ2 T cells plus anti-PD-1 antibody combination treatment. Pyroptosis was evaluated by cell morphology, western blot analysis, and ELISA experiments. Flow cytometry was used to examine expression of BTN2A1, BTN3A1, PD-L1, PD-L2 on mesothelioma cell lines. Immunofluorescence staining was performed to detect Vδ2 T cells post adoptive transfer and characteristics of pyroptosis in ex vivo mesothelioma tissue sections. Results: Indeed, our data demonstrated that Vδ2 T cells killing mesothelioma can be enhanced by anti-PD-1 antibody in vitro, especially for high PD-1 expressing cells, and in vivo in the intrapleural mesothelioma mice model established by us. Adoptive transfer of Vδ2 T cells into these mice leads to tumor regression by 30-40% compared to control. Immunofluorescence of the tumor section confirmed infiltration of Vδ2 T cells into the tumor, especially to cells with BTN2A1 expression (a Vδ2 T cell activating molecule) despite PD-L1 co-localization. Interestingly, these cells co-expressed cleaved gasdermin D, suggesting that pyroptosis was induced by Vδ2 T cells. This was verified by Vδ2 T/mesothelioma co-culture experiments demonstrating membrane ballooning morphology, increased cleaved caspase-3 and gasdermin E, and upregulated IL-1ß and IL-18. Discussion: Vδ2 T cells plus anti-PD1 exhibited cytotoxicity against mesothelioma in vivo. However, we found no advantage for anti-PD-1 against PD-1 high expressing Vδ2 T cells in promoting pyroptosis. Taken together, our work demonstrated that Vδ2 T cells combined with anti-PD-1 antibody can be developed as a potential combination immunotherapy for mesothelioma.

EBV latent membrane protein 1 augments γδ T cell cytotoxicity against nasopharyngeal carcinoma by induction of butyrophilin molecules.

Nasopharyngeal carcinoma (NPC) is a diverse cancer with no well-defined tumor antigen, associated with oncogenic Epstein-Barr Virus (EBV), and with usually late-stage diagnosis and survival <40%. Current radiotherapy and chemotherapy have low effectiveness and cause adverse effects, which calls for the need of new therapy. In this regard, adoptive immunotherapy using γδ T cells has potential, but needs to be coupled with butyrophilin 2A1 and 3A1 protein expression to achieve tumoricidal effect. Methods: Human γδ T cells were expanded (with Zol or PTA) and used for cytotoxicity assay against NPC cells, which were treated with the EBV EBNA1-targeting peptide (L2)P4. Effect of (L2)P4 on BTN2A1/BTN3A1 expression in NPC cells was examined by flow cytometry and Western blot. An NPC-bearing NSG mice model was established to test the effectiveness of P4 and adoptive γδ T cells. Immunofluorescence was performed on NPC tissue sections to examine the presence of γδ T cells and expression of BTN2A1 and BTN3A1. EBV gene expression post-(L2)P4 treatment was assessed by qRT-PCR, and the relationship of LMP1, NLRC5 and BTN2A1/BTN3A1 was examined by transfection, reporter assay, Western blot, and inhibition experiments. Results: Zol- or PTA-expanded the Vδ2 subset of γδ T cells that exerted killing against certain NPC cells. (L2)P4 reactivates latent EBV, which increased BTN2A1 and BTN3A1 expression and conferred higher susceptibility towards Vδ2 T cells cytotoxicity in vitro, as well as enhanced tumor regression in vivo by adoptive transfer of Vδ2 T cells. Mechanistically, (L2)P4 induced EBV LMP1, leading to IFN-γ/p-JNK and NLRC5 activation, and subsequently stimulated the expression of BTN2A1 and BTN3A1. Conclusions: This study demonstrated the effectiveness of using the EBV-targeting probe (L2)P4 and adoptive γδ T cells as a promising combinatorial immunotherapy against NPC. The identification of the LMP1-IFN-γ/p-JNK-NLRC5-BTN2A1/BTN3A1 axis may lead to new insight and therapeutic targets against NPC and other EBV+ tumors.

Manipulation of PD-L1 Endosomal Trafficking Promotes Anticancer Immunity.

The aberrant regulation of PD-L1 in tumor cells remains poorly understood. Here, the authors systematically investigate the endosomal trafficking of plasma membrane PD-L1 in tumor cells. They show that plasma membrane PD-L1 is continuously internalized, and then trafficked from early endosomes to multivesicular bodies/late endosomes, recycling endosomes, lysosomes, and/or extracellular vesicles (EVs). This constitutive endocytic trafficking of PD-L1 is Rab5- and clathrin-dependent. Triazine compound 6J1 blocks the endosomal trafficking of PD-L1 and induces its accumulation in endocytic vesicles by activating Rab5. 6J1 also promotes exosomal PD-L1 secretion by activating Rab27. Together, these effects result in a decrease in the membrane level of PD-L1 in 6J1-treated tumor cells and enables tumor cells to be more susceptible to the tumor-killing activity of T cells in vitro. 6J1 also increases tumor-infiltrating cytotoxic T cells and promotes chemokines secretion in the tumor microenvironment. Rab27 knockdown abolishes 6J1-induced PD-L1 secretion in EVs and revokes the exhausted tumor-infiltrating T cells in tumors, thereby improving the anticancer efficacy of 6J1. Furthermore, a combination of 6J1 and an anti-PD-1 antibody significantly improves the anticancer immune response. Therefore, manipulating PD-L1 endosomal trafficking provides a promising means to promote an anticancer immune response in addition to the immune checkpoint-blocking antibody therapy.

The phosphorylation and dephosphorylation switch of VCP/p97 regulates the architecture of centrosome and spindle.

The proper orientation of centrosome and spindle is essential for genome stability; however, the mechanism that governs these processes remains elusive. Here, we demonstrated that polo-like kinase 1 (Plk1), a key mitotic kinase, phosphorylates residue Thr76 in VCP/p97 (an AAA-ATPase), at the centrosome from prophase to anaphase. This phosphorylation process recruits VCP to the centrosome and in this way, it regulates centrosome orientation. VCP exhibits strong co-localization with Eg5 (a mitotic kinesin motor), at the mitotic spindle, and the dephosphorylation of Thr76 in VCP is required for the enrichment of both VCP and Eg5 at the spindle, thus ensuring proper spindle architecture and chromosome segregation. We also showed that the phosphatase, PTEN, is responsible for the dephosphorylation of Thr76 in VCP; when PTEN was knocked down, the normal spread of VCP from the centrosome to the spindle was abolished. Cryo-EM structures of VCPT76A and VCPT76E, which represent dephosphorylated and phosphorylated states of VCP, respectively, revealed that the Thr76 phosphorylation modulates VCP by altering the inter-domain and inter-subunit interactions, and ultimately the nucleotide-binding pocket conformation. Interestingly, the tumor growth in nude mice implanted with VCPT76A-reconstituted cancer cells was significantly slower when compared with those implanted with VCPWT-reconstituted cancer cells. Collectively, our findings demonstrate that the phosphorylation and dephosphorylation switch of VCP regulates the architecture of centrosome and spindle for faithful chromosome segregation.

Capping protein regulates endosomal trafficking by controlling F-actin density around endocytic vesicles and recruiting RAB5 effectors.

Actin filaments (F-actin) have been implicated in various steps of endosomal trafficking, and the length of F-actin is controlled by actin capping proteins, such as CapZ, which is a stable heterodimeric protein complex consisting of α and ß subunits. However, the role of these capping proteins in endosomal trafficking remains elusive. Here, we found that CapZ docks to endocytic vesicles via its C-terminal actin-binding motif. CapZ knockout significantly increases the F-actin density around immature early endosomes, and this impedes fusion between these vesicles, manifested by the accumulation of small endocytic vesicles in CapZ-knockout cells. CapZ also recruits several RAB5 effectors, such as Rabaptin-5 and Rabex-5, to RAB5-positive early endosomes via its N-terminal domain, and this further activates RAB5. Collectively, our results indicate that CapZ regulates endosomal trafficking by controlling actin density around early endosomes and recruiting RAB5 effectors.

Berbamine inhibits Japanese encephalitis virus (JEV) infection by compromising TPRMLs-mediated endolysosomal trafficking of low-density lipoprotein receptor (LDLR).

Japanese encephalitis virus (JEV), a member of the Flavivirus genus, is an important pathogen that causes human and animal infectious diseases in Asia. So far, no effective antiviral agents are available to treat JEV infection. Here, we found that LDLR is a host factor required for JEV entry. Berbamine significantly decreases the level of LDLR at the plasma membrane by inducing the secretion of LDLR via extracellular vesicles (EVs), thereby inhibiting JEV infection. Mechanistically, berbamine blocks TRPMLs (Ca2+ permeable non-selective cation channels in endosomes and lysosomes) to compromise the endolysosomal trafficking of LDLR. This leads to the increased secretion of LDLR via EVs and the concomitant decrease in its level at the plasma membrane, thereby rendering cells resistant to JEV infection. Berbamine also protects mice from the lethal challenge of JEV. In summary, these results indicate that berbamine is an effective anti-JEV agent by preventing JEV entry.

Vacuolin-1 inhibits endosomal trafficking and metastasis via CapZß.

Metastasis is the fundamental cause of cancer mortality, but there are still very few anti-metastatic drugs available. Endosomal trafficking has been implicated in tumor metastasis, and we have previously found that small chemical vacuolin-1 (V1) potently inhibits autophagosome-lysosome fusion and general endosomal-lysosomal degradation. Here, we assessed the anti-metastatic activity of V1 both in vitro and in vivo. V1 significantly inhibits colony formation, migration, and invasion of various cancer cells in vitro. It also compromises the assembly-disassembly dynamics of focal adhesions (FAs) by inhibiting the recycling and degradation of integrins. In various experimental or transgenic mouse models, V1 significantly suppresses the metastasis and/or tumor growth of breast cancer or melanoma. We further identified capping protein Zß (CapZß) as a V1 binding protein and showed that it is required for the V1-mediated inhibition of migration and metastasis of cancer cells. Collectively, our results indicate that V1 targets CapZß to inhibit endosomal trafficking and metastasis.

VCP/p97 targets the nuclear export and degradation of p27Kip1 during G1 to S phase transition.

One of the critical regulatory mechanisms for cell cycle progression is the timely degradation of CDK inhibitors, including p21Cip1 and p27Kip1 . VCP/p97, an AAA-ATPase, is reported to be overexpressed in many types of cancers. Here, we found that treatment of MCF-7 human breast cancer cells with DBeQ, a VCP inhibitor, or VCP knockdown in MCF-7 cells arrested cells at G1 phase, accompanied with the blockage of both p21 and p27 degradation. Whereas, double knockdown of p21 and p27 in MCF-7 cells rendered cells refractory to DBeQ-induced G1 arrest. Moreover, inhibition or knockdown of VCP or UFD1, one of VCP's co-factors, in MCF-7, NIH3T3, or HEK293T cells blocked the nuclear export of p27 during earlier G1 phase after mitogen stimulation. We also identified the nuclear localization sequence (NLS) of VCP, and found that adding back wild-type VCP, not the NLS-deleted VCP mutant, restored the nuclear export and degradation of p27 in VCP knockout MCF-7 cells. Importantly, we found that VCP inhibition sensitized breast cancer cells to the treatment of several anticancer therapeutics both in vitro and in vivo. Taken together, our study not only uncovers the mechanisms underlying VCP-mediated cell proliferation control but also provides potential therapeutic option for cancer treatment.

Retraction note to: Lentivirus-Mediated Short-Hairpin RNA Targeting Protein Phosphatase 4 Regulatory Subunit 1 Inhibits Growth in Breast Cancer.

[This retracts the article on p. 218 in vol. 18, PMID: 26472971.].

Absence of autophagy promotes apoptosis by modulating the ROS-dependent RLR signaling pathway in classical swine fever virus-infected cells.

A growing number of studies have demonstrated that both macroautophagy/autophagy and apoptosis are important inner mechanisms of cell to maintain homeostasis and participate in the host response to pathogens. We have previously reported that a functional autophagy pathway is trigged by infection of classical swine fever virus (CSFV) and is required for viral replication and release in host cells. However, the interplay of autophagy and apoptosis in CSFV-infected cells has not been clarified. In the present study, we demonstrated that autophagy induction with rapamycin facilitates cellular proliferation after CSFV infection, and that autophagy inhibition by knockdown of essential autophagic proteins BECN1/Beclin 1 or MAP1LC3/LC3 (microtubule-associated protein 1 light chain 3) promotes apoptosis via fully activating both intrinsic and extrinsic mechanisms in CSFV-infected cells. We also found that RIG-I-like receptor (RLR) signaling was amplified in autophagy-deficient cells during CSFV infection, which was closely linked to the activation of the intrinsic apoptosis pathway. Moreover, we discovered that virus infection of autophagy-impaired cells results in an increase in copy number of mitochondrial DNA and in the production of reactive oxygen species (ROS), which plays a significant role in enhanced RLR signaling and the activated extrinsic apoptosis pathway in cultured cells. Collectively, these data indicate that CSFV-induced autophagy delays apoptosis by downregulating ROS-dependent RLR signaling and thus contributes to virus persistent infection in host cells.

Erratum: Lentivirus-Mediated Short-Hairpin RNA Targeting Protein Phosphatase 4 Regulatory Subunit 1 Inhibits Growth in Breast Cancer.

[This corrects the article on p. 218 in vol. 18, PMID: 26472971.].

Lentivirus-Mediated Short-Hairpin RNA Targeting Protein Phosphatase 4 Regulatory Subunit 1 Inhibits Growth in Breast Cancer.

PURPOSE: Protein phosphatase 4 regulatory subunit 1 (PP4R1), as an interaction partner of the catalytic serine/threonine-protein phosphatase 4 catalytic subunit has been shown to involve in cellular processes and nuclear factor κB signaling. However, the functions of PP4R1 in human breast cancers remain unclear. This study is designed to explore the effect of PP4R1 knockdown on the biological characteristics of breast cancer cells. METHODS: A lentivirus-mediated short hairpin RNA (shRNA) was designed to knockdown the expression of PP4R1 in ZR-75-30 breast cancer cells. The efficiency of lentivirus-mediated shRNA infection was determined using fluorescence microscopy to observe lentivirus-mediated green fluorescent protein expression and confirmed to be over 80%. PP4R1 expression in infected ZR-75-30 cells was detected by quantitative real-time polymerase chain reaction and western blot analysis. Cell proliferation and colony formation ability were measured by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay and colony formation assay, respectively. Flow cytometry was used to measure cell cycle progression and cell apoptosis. In addition, apoptosis makers, including poly-ADP-ribose polymerase (PARP) and caspase-3, were investigated in PP4R1-silenced ZR-75-30 cells by western blot assay. RESULTS: We successfully constructed lentivirus-mediated shRNA to target PP4R1 in ZR-75-30 cells. MTT assay and colony formation assay showed the loss of PP4R1 suppressed the proliferation of ZR-75-30 cells. Flow cytometry analysis indicated cell cycle arrest and increased cell apoptosis in PP4R1 knockdown cells. Further, the apoptosis response in cells depleted of PP4R1 was illustrated by downregulation of PARP and upregulation of caspase-3. CONCLUSION: Our results suggest that PP4R1 could promote breast cancer cell proliferation and might play a vital role in breast cancer occurrence.

Rapid and simple detection of Japanese encephalitis virus by reverse transcription loop-mediated isothermal amplification combined with a lateral flow dipstick.

Japanese encephalitis virus (JEV) is a major cause of viral encephalitis in geographical areas, such as Asia and Western Pacific, where it is a threat to human and animal health. To control this disease, it is necessary to develop a rapid, simple, accurate method for diagnosis. In this study, a method based on reverse transcription loop-mediated isothermal amplification (RT-LAMP) coupled with a lateral flow dipstick (LFD) has been developed to detect JEV (JEV RT-LAMP-LFD). The entire assay can be completed within 70 min, and in this study, no false positive results were observed when other pathogens were tested, indicating that the assay is a highly specific method for the detection of JEV. Additionally, the sensitivity of the RT-LAMP-LFD assay for SA14-14-2 strain was 50 pg of RNA, which was similar to that of RT-PCR and RT-LAMP combined with gel electrophoresis, and was 10-fold more sensitive than RT-LAMP combined with calcein. The limit of detection for this assay was 5 pg of RNA. In addition, no false positive results were obtained with 14 serum samples. Our results indicate that this RT-LAMP-LFD assay will be of great value for JEV infection testing due to its rapid and highly specific and sensitive properties.

Autophagy enhances the replication of classical swine fever virus in vitro.

Autophagy plays an important role in cellular responses to pathogens. However, the impact of the autophagy machinery on classical swine fever virus (CSFV) infection is not yet confirmed. In this study, we showed that CSFV infection significantly increases the number of autophagy-like vesicles in the cytoplasm of host cells at the ultrastructural level. We also found the formation of 2 ubiquitin-like conjugation systems upon virus infection, including LC3-I/LC3-II conversion and ATG12-ATG5 conjugation, which are considered important indicators of autophagy. Meanwhile, high expression of ATG5 and BECN1 was detected in CSFV-infected cells; conversely, degradation of SQSTM1 was observed by immunoblotting, suggesting that CSFV infection triggered a complete autophagic response, most likely by the NS5A protein. Furthermore, by confocal immunofluorescence analysis, we discovered that both envelope protein E2 and nonstructural protein NS5A colocalized with LC3 and CD63 during CSFV infection. Examination by immunoelectron microscopy further confirmed the colocalization of both E2 and NS5A proteins with autophagosome-like vesicles, indicating that CSFV utilizes the membranes of these vesicles for replication. Finally, we demonstrated that alteration of cellular autophagy by autophagy regulators and shRNAs affects progeny virus production. Collectively, these findings provide strong evidence that CSFV infection needs an autophagy pathway to enhance viral replication and maturity in host cells.