Ting Pan

Expansion of Monocytic Myeloid-Derived Suppressor Cells Dampens T Cell Function in HIV-1-Seropositive Individuals

ABSTRACT T lymphocyte dysfunction contributes to human immunodeficiency virus type 1 (HIV-1) disease progression by impairing antivirus cellular immunity. However, the mechanisms of HIV-1 infection-mediated T cell dysfunction are not completely understood. Here, we provide evidence that expansion of monocytic myeloid-derived suppressor cells (M-MDSCs) suppressed T cell function in HIV-1-infected individuals. We observed a dramatic elevation of M-MDSCs (HLA-DR−/low CD11b+ CD33+/high CD14+ CD15− cells) in the peripheral blood of HIV-1-seropositive subjects (n = 61) compared with healthy controls (n = 51), despite efficacious antiretroviral therapy for nearly 2 years. The elevated M-MDSC frequency in HIV-1+ subjects correlated with prognostic HIV-1 disease markers, including the HIV-1 load (r = 0.5957; P < 0.0001), CD4+ T cell loss (r = −0.5312; P < 0.0001), and activated T cells (r = 0.4421; P = 0.0004). Functional studies showed that M-MDSCs from HIV-1+ subjects suppressed T cell responses in both HIV-1-specific and antigen-nonspecific manners; this effect was dependent on the induction of arginase 1 and required direct cell-cell contact. Further investigations revealed that direct HIV-1 infection or culture with HIV-1-derived Tat protein significantly enhanced human MDSC generation in vitro, and MDSCs from healthy donors could be directly infected by HIV-1 to facilitate HIV-1 replication and transmission, indicating that a positive-feedback loop between HIV-1 infection and MDSC expansion existed. In summary, our studies revealed a novel mechanism of T cell dysfunction in HIV-1-infected individuals and suggested that targeting MDSCs may be a promising strategy for HIV-1 immunotherapy.

An Lnc RNA (GAS5)/SnoRNA-derived piRNA induces activation of TRAIL gene by site-specifically recruiting MLL/COMPASS-like complexes

PIWI-interacting RNA (piRNA) silences the transposons in germlines or induces epigenetic modifications in the invertebrates. However, its function in the mammalian somatic cells remains unknown. Here we demonstrate that a piRNA derived from Growth Arrest Specific 5, a tumor-suppressive long non-coding RNA, potently upregulates the transcription of tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a proapoptotic protein, by inducing H3K4 methylation/H3K27 demethylation. Interestingly, the PIWIL1/4 proteins, which bind with this piRNA, directly interact with WDR5, resulting in a site-specific recruitment of the hCOMPASS-like complexes containing at least MLL3 and UTX (KDM6A). We have indicated a novel pathway for piRNAs to specially activate gene expression. Given that MLL3 or UTX are frequently mutated in various tumors, the piRNA/MLL3/UTX complex mediates the induction of TRAIL, and consequently leads to the inhibition of tumor growth.

Necroptosis Takes Place in Human Immunodeficiency Virus Type-1 (HIV-1)-Infected CD4+ T Lymphocytes

Human immunodeficiency virus type 1 (HIV-1) infection is characterized by progressive depletion of CD4+ T lymphocytes and dysfunction of the immune system. The numbers of CD4+ T lymphocytes in the human body are maintained constantly by homeostatic mechanisms that failed during HIV-1 infection, resulting in progressive loss of CD4+ T cells mainly via apoptosis. Recently, a non-apoptotic form of necrotic programmed cell death, named necroptosis, has been investigated in many biological and pathological processes. We then determine whether HIV-1-infected cells also undergo necroptosis. In this report, we demonstrate that HIV-1 not only induces apoptosis, but also mediates necroptosis in the infected primary CD4+ T lymphocytes and CD4+ T-cell lines. Necroptosis-dependent cytopathic effects are significantly increased in HIV-1-infected Jurkat cells that is lack of Fas-associated protein-containing death domain (FADD), indicating that necroptosis occurs as an alternative cell death mechanism in the absence of apoptosis. Unlike apoptosis, necroptosis mainly occurs in HIV-infected cells and spares bystander damage. Treatment with necrostatin-1(Nec-1), a RIP1 inhibitor that specifically blocks the necroptosis pathway, potently restrains HIV-1-induced cytopathic effect and interestingly, inhibits the formation of HIV-induced syncytia in CD4+ T-cell lines. This suggests that syncytia formation is mediated, at least partially, by necroptosis-related processes. Furthermore, we also found that the HIV-1 infection-augmented tumor necrosis factor-alpha (TNF-α) plays a key role in inducing necroptosis and HIV-1 Envelope and Tat proteins function as its co-factors. Taken together,necroptosis can function as an alternative cell death pathway in lieu of apoptosis during HIV-1 infection, thereby also contributing to HIV-1-induced cytopathic effects. Our results reveal that in addition to apoptosis, necroptosis also plays an important role in HIV-1-induced pathogenesis.

DDX5 Facilitates HIV-1 Replication as a Cellular Co-Factor of Rev

HIV-1 Rev plays an important role in the late phase of HIV-1 replication, which facilitates export of unspliced viral mRNAs from the nucleus to cytoplasm in infected cells. Recent studies have shown that DDX1 and DDX3 are co-factors of Rev for the export of HIV-1 transcripts. In this report, we have demonstrated that DDX5 (p68), which is a multifunctional DEAD-box RNA helicase, functions as a new cellular co-factor of HIV-1 Rev. We found that DDX5 affects Rev function through the Rev-RRE axis and subsequently enhances HIV-1 replication. Confocal microscopy and co-immunoprecipitation analysis indicated that DDX5 binds to Rev and this interaction is largely dependent on RNA. If the DEAD-box motif of DDX5 is mutated, DDX5 loses almost all of its ability to bind to Rev, indicating that the DEAD-box motif of DDX5 is required for the interaction between DDX5 and Rev. Our data indicate that interference of DDX5-Rev interaction could reduce HIV-1 replication and potentially provide a new molecular target for anti-HIV-1 therapeutics.

A SnoRNA-derived piRNA interacts with human interleukin-4 pre-mRNA and induces its decay in nuclear exosomes

PIWI interacting RNAs (piRNAs) are highly expressed in germline cells and are involved in maintaining genome integrity by silencing transposons. These are also involved in DNA/histone methylation and gene expression regulation in somatic cells of invertebrates. The functions of piRNAs in somatic cells of vertebrates, however, remain elusive. We found that snoRNA-derived and C (C′)/D′ (D)-box conserved piRNAs are abundant in human CD4 primary T-lymphocytes. piRNA (piR30840) significantly downregulated interleukin-4 (IL-4) via sequence complementarity binding to pre-mRNA intron, which subsequently inhibited the development of Th2 T-lymphocytes. Piwil4 and Ago4 are associated with this piRNA, and this complex further interacts with Trf4-Air2-Mtr4 Polyadenylation (TRAMP) complex, which leads to the decay of targeted pre-mRNA through nuclear exosomes. Taken together, we demonstrate a novel piRNA mechanism in regulating gene expression in highly differentiated somatic cells and a possible novel target for allergy therapeutics.

Glycopeptide Antibiotics Potently Inhibit Cathepsin L in the Late Endosome/Lysosome and Block the Entry of Ebola Virus, Middle East Respiratory Syndrome Coronavirus (MERS-CoV), and Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)

Ebola virus infection can cause severe hemorrhagic fever with a high mortality in humans. The outbreaks of Ebola viruses in 2014 represented the most serious Ebola epidemics in history and greatly threatened public health worldwide. The development of additional effective anti-Ebola therapeutic agents is therefore quite urgent. In this study, via high throughput screening of Food and Drug Administration-approved drugs, we identified that teicoplanin, a glycopeptide antibiotic, potently prevents the entry of Ebola envelope pseudotyped viruses into the cytoplasm. Furthermore, teicoplanin also has an inhibitory effect on transcription- and replication-competent virus-like particles, with an IC50 as low as 330 nm. Comparative analysis further demonstrated that teicoplanin is able to block the entry of Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS) envelope pseudotyped viruses as well. Teicoplanin derivatives such as dalbavancin, oritavancin, and telavancin can also inhibit the entry of Ebola, MERS, and SARS viruses. Mechanistic studies showed that teicoplanin blocks Ebola virus entry by specifically inhibiting the activity of cathepsin L, opening a novel avenue for the development of additional glycopeptides as potential inhibitors of cathepsin L-dependent viruses. Notably, given that teicoplanin has routinely been used in the clinic with low toxicity, our work provides a promising prospect for the prophylaxis and treatment of Ebola, MERS, and SARS virus infection.

17β-Oestradiol enhances the expansion and activation of myeloid-derived suppressor cells via signal transducer and activator of transcription (STAT)-3 signalling in human pregnancy.

During a successful pregnancy, the maternal immune system plays a critical role in maintaining immunotolerance towards semi‐allogeneic fetal antigens. Recent studies have indicated that myeloid‐derived suppressor cells (MDSCs) are active players in establishing fetal–maternal tolerance; however, the underlying mechanism remains poorly understood. In this study, we observed a significant expansion of monocytic MDSCs (M‐MDSCs) in the peripheral blood of pregnant women, which suppressed T cell responses in a reactive oxygen species‐dependent manner and required cell–cell contact. The number of M‐MDSCs correlated positively with serum oestrogen and progesterone levels. Administration of 17β‐oestradiol, but not progesterone, enhanced both the expansion and suppressive activity of M‐MDSCs through signal transducer and activator of transcription (STAT)‐3. Pretreatment with STAT‐3 inhibitor JSI‐124 almost completely abrogated the effects of 17β‐oestradiol on MDSCs. Collectively, these results demonstrate that 17β‐oestradiol‐induced STAT‐3 signalling plays an important role in both the expansion and activation of MDSCs during human pregnancy, which may benefit the development of novel therapeutic strategies for prevention of immune‐related miscarriage.

Identification of an HIV-1 replication inhibitor which rescues host restriction factor APOBEC3G in Vif–APOBEC3G complex

HIV-1 Vif protein is one of the most crucial accessory proteins for viral replication. It efficiently counteracts the important host restriction factor APOBEC3G (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G, A3G) which is lethal to HIV-1 by causing G to A mutation of viral genome. Vif protein mediates degradation of APOBEC3G via the complicated protein-protein interactions of Vif, APOBEC3G, Elongin C/B and Cullin 5. The importance of Vif-APOBEC3G complex makes it a good potential target to develop new therapeutics of HIV-1. We identified a potent HIV-1 replication inhibitor (ZBMA-1, IC50 = 1.01 μM) that efficiently protected APOBEC3G protein by targeting Vif-APOBEC3G complex. The co-immunoprecipitation and docking studies indicated that compound ZBMA-1 affected the binding of Elongin C with Vif protein.

Myeloid‐derived suppressor cells are essential for maintaining feto‐maternal immunotolerance via STAT3 signaling in mice

Maternal immune system tolerance to the semiallogeneic fetus is essential for a successful pregnancy; however, the mechanisms underlying this immunotolerance have not been fully elucidated. Here, we demonstrate that myeloid‐derived suppressor cells play an important role in maintaining feto‐maternal tolerance. A significant expansion of granulocytic myeloid‐derived suppressor cells was observed in multiple immune organs and decidual tissues from pregnant mice. Pregnancy‐derived granulocytic myeloid‐derived suppressor cells suppressed T cell responses in a reactive oxygen species‐dependent manner and required direct cell–cell contact. Mechanistic studies showed that progesterone facilitated differentiation and activation of granulocytic myeloid‐derived suppressor cells, mediated through STAT3 signaling. The STAT3 inhibitor JSI‐124 and a specific short hairpin RNA completely abrogated the effects of progesterone on granulocytic myeloid‐derived suppressor cells. More importantly, granulocytic myeloid‐derived suppressor cell depletion dramatically enhanced the abortion rate in normal pregnant mice, whereas adoptive transfer of granulocytic myeloid‐derived suppressor cells clearly reduced the abortion rate in the CBA/J X DBA/2J mouse model of spontaneous abortion. These observations collectively demonstrate that granulocytic myeloid‐derived suppressor cells play an essential role in the maintenance of fetal immunotolerance in mice. Furthermore, our study supports the notion that in addition to their well‐recognized roles under pathologic conditions, myeloid‐derived suppressor cells perform important functions under certain physiologic circumstances.

17β‐estradiol enhances the expansion and activation of myeloid‐derived suppressor cells via STAT3 signaling in human pregnancy

During a successful pregnancy, the maternal immune system plays a critical role in maintaining immunotolerance towards semi‐allogeneic fetal antigens. Recent studies have indicated that myeloid‐derived suppressor cells (MDSCs) are active players in establishing fetal–maternal tolerance; however, the underlying mechanism remains poorly understood. In this study, we observed a significant expansion of monocytic MDSCs (M‐MDSCs) in the peripheral blood of pregnant women, which suppressed T cell responses in a reactive oxygen species‐dependent manner and required cell–cell contact. The number of M‐MDSCs correlated positively with serum oestrogen and progesterone levels. Administration of 17β‐oestradiol, but not progesterone, enhanced both the expansion and suppressive activity of M‐MDSCs through signal transducer and activator of transcription (STAT)‐3. Pretreatment with STAT‐3 inhibitor JSI‐124 almost completely abrogated the effects of 17β‐oestradiol on MDSCs. Collectively, these results demonstrate that 17β‐oestradiol‐induced STAT‐3 signalling plays an important role in both the expansion and activation of MDSCs during human pregnancy, which may benefit the development of novel therapeutic strategies for prevention of immune‐related miscarriage.