Transcriptome-wide analysis uncovers the targets of the RNA-binding protein MSI2 and effects of MSI2's RNA-binding activity on IL-6 signaling.

The RNA-binding protein Musashi 2 (MSI2) has emerged as an important regulator in cancer initiation, progression, and drug resistance. Translocations and deregulation of the MSI2 gene are diagnostic of certain cancers, including chronic myeloid leukemia (CML) with translocation t(7;17), acute myeloid leukemia (AML) with translocation t(10;17), and some cases of B-precursor acute lymphoblastic leukemia (pB-ALL). To better understand the function of MSI2 in leukemia, the mRNA targets that are bound and regulated by MSI2 and their MSI2-binding motifs need to be identified. To this end, using photoactivatable ribonucleoside cross-linking and immunoprecipitation (PAR-CLIP) and the multiple EM for motif elicitation (MEME) analysis tool, here we identified MSI2's mRNA targets and the consensus RNA-recognition element (RRE) motif recognized by MSI2 (UUAG). Of note, MSI2 knockdown altered the expression of several genes with roles in eukaryotic initiation factor 2 (eIF2), hepatocyte growth factor (HGF), and epidermal growth factor (EGF) signaling pathways. We also show that MSI2 regulates classic interleukin-6 (IL-6) signaling by promoting the degradation of the mRNA of IL-6 signal transducer (IL6ST or GP130), which, in turn, affected the phosphorylation statuses of signal transducer and activator of transcription 3 (STAT3) and the mitogen-activated protein kinase ERK. In summary, we have identified multiple MSI2-regulated mRNAs and provided evidence that MSI2 controls IL6ST activity that control oncogenic signaling networks. Our findings may help inform strategies for unraveling the role of MSI2 in leukemia to pave the way for the development of targeted therapies.

Tumor Necrosis Factor-Mediated Survival of CD169+ Cells Promotes Immune Activation during Vesicular Stomatitis Virus Infection.

Innate immune activation is essential to mount an effective antiviral response and to prime adaptive immunity. Although a crucial role of CD169+ cells during vesicular stomatitis virus (VSV) infections is increasingly recognized, factors regulating CD169+ cells during viral infections remain unclear. Here, we show that tumor necrosis factor is produced by CD11b+ Ly6C+ Ly6G+ cells following infection with VSV. The absence of TNF or TNF receptor 1 (TNFR1) resulted in reduced numbers of CD169+ cells and in reduced type I interferon (IFN-I) production during VSV infection, with a severe disease outcome. Specifically, TNF triggered RelA translocation into the nuclei of CD169+ cells; this translocation was inhibited when the paracaspase MALT-1 was absent. Consequently, MALT1 deficiency resulted in reduced VSV replication, defective innate immune activation, and development of severe disease. These findings indicate that TNF mediates the maintenance of CD169+ cells and innate and adaptive immune activation during VSV infection.IMPORTANCE Over the last decade, strategically placed CD169+ metallophilic macrophages in the marginal zone of the murine spleen and lymph nodes (LN) have been shown to play a very important role in host defense against viral pathogens. CD169+ macrophages have been shown to activate innate and adaptive immunity via "enforced virus replication," a controlled amplification of virus particles. However, the factors regulating the CD169+ macrophages remain to be studied. In this paper, we show that after vesicular stomatitis virus infection, phagocytes produce tumor necrosis factor (TNF), which signals via TNFR1, and promote enforced virus replication in CD169+ macrophages. Consequently, lack of TNF or TNFR1 resulted in defective immune activation and VSV clearance.

RAIDD Mediates TLR3 and IRF7 Driven Type I Interferon Production.

BACKGROUND/AIMS: Viral infections represent a global health problem with the need for new viral therapies and better understanding of the immune response during infection. The most immediate and potent anti-viral defense mechanism is the production of type I interferon (IFN-I) which are activated rapidly following recognition of viral infection by host pathogen recognition receptors (PRR). The mechanisms of innate cellular signaling downstream of PRR activation remain to be fully understood. In the present study, we demonstrate that CASP2 and RIPK1 domain-containing adaptor with death domain (CRADD/RAIDD) is a critical component in type I IFN production. METHODS: The role of RAIDD during IFN-I production was investigated using western blot, shRNA mediated lentiviral knockdown, immunoprecipitation and IFN-I driven dual luciferase assay. RESULTS: Immunoprecipitation analysis revealed the molecular interaction of RAIDD with interferon regulatory factor 7 (IRF7) and its phosphorylating kinase IKKε. Using an IFN-4α driven dual luciferase analysis in RAIDD deficient cells, type I IFN activation by IKKε and IRF7 was dramatically reduced. Furthermore, deletion of either the caspase recruitment domain (CARD) or death domain (DD) of RAIDD inhibited IKKε and IRF7 mediated interferon-4α activation. CONCLUSION: We have identified that the adaptor molecule RAIDD coordinates IKKε and IRF7 interaction to ensure efficient expression of type I interferon.

Deficiency of the B cell-activating factor receptor results in limited CD169+ macrophage function during viral infection.

UNLABELLED: The B cell-activating factor (BAFF) is critical for B cell development and humoral immunity in mice and humans. While the role of BAFF in B cells has been widely described, its role in innate immunity remains unknown. Using BAFF receptor (BAFFR)-deficient mice, we characterized BAFFR-related innate and adaptive immune functions following infection with vesicular stomatitis virus (VSV) and lymphocytic choriomeningitis virus (LCMV). We identified a critical role for BAFFR signaling in the generation and maintenance of the CD169(+) macrophage compartment. Consequently, Baffr(-) (/) (-) mice exhibited limited induction of innate type I interferon production after viral infection. Lack of BAFFR signaling reduced virus amplification and presentation following viral infection, resulting in highly reduced antiviral adaptive immune responses. As a consequence, BAFFR-deficient mice showed exacerbated and fatal disease after viral infection. Mechanistically, transient lack of B cells in Baffr(-) (/) (-) animals resulted in limited lymphotoxin expression, which is critical for maintenance of CD169(+) cells. In conclusion, BAFFR signaling affects both innate and adaptive immune activation during viral infections. IMPORTANCE: Viruses cause acute and chronic infections in humans resulting in millions of deaths every year. Innate immunity is critical for the outcome of a viral infection. Innate type I interferon production can limit viral replication, while adaptive immune priming by innate immune cells induces pathogen-specific immunity with long-term protection. Here, we show that BAFFR deficiency not only perturbed B cells, but also resulted in limited CD169(+) macrophages. These macrophages are critical in amplifying viral particles to trigger type I interferon production and initiate adaptive immune priming. Consequently, BAFFR deficiency resulted in reduced enforced viral replication, limited type I interferon production, and reduced adaptive immunity compared to BAFFR-competent controls. As a result, BAFFR-deficient mice were predisposed to fatal viral infections. Thus, BAFFR expression is critical for innate immune activation and antiviral immunity.

CEACAM1 induces B-cell survival and is essential for protective antiviral antibody production.

B cells are essential for antiviral immune defence because they produce neutralizing antibodies, present antigen and maintain the lymphoid architecture. Here we show that intrinsic signalling of CEACAM1 is essential for generating efficient B-cell responses. Although CEACAM1 exerts limited influence on the proliferation of B cells, expression of CEACAM1 induces survival of proliferating B cells via the BTK/Syk/NF-κB-axis. The absence of this signalling cascade in naive Ceacam1(-/-) mice limits the survival of B cells. During systemic infection with cytopathic vesicular stomatitis virus, Ceacam1(-/-) mice can barely induce neutralizing antibody responses and die early after infection. We find, therefore, that CEACAM1 is a crucial regulator of B-cell survival, influencing B-cell numbers and protective antiviral antibody responses.

Tricin 4'-O-(erythro-ß-guaiacylglyceryl) ether and tricin 4'-O-(threo-ß-guaiacylglyceryl) ether isolated from Njavara (Oryza sativa L. var. Njavara), induce apoptosis in multiple tumor cells by mitochondrial pathway.

Njavara is an important medicinal rice variety of Kerala, India widely used in Ayurveda for the treatment of rheumatoid arthritis, paralysis, neurodegenerative diseases and in rejuvenation therapy. The study evaluated, for the first time, antitumor effects of the two rare flavonolignans, tricin 4'-O-(erythro-ß-guaiacylglyceryl) ether (compound 1) and tricin 4'-O-(threo-ß-guaiacylglyceryl) ether (compound 2), isolated from 'Njavara' black. Both the compounds induced apoptosis in three cancer cell lines colon adenocarcinoma cell line HCT 116, ovarian cancer cell line SKOV3 and breast cancer cell line MCF-7. Chromatin condensation in the three cancer cell lines by Hoechst staining showed >50 % of apoptosis by compounds 1 and 2 at concentration 40 and 30 µg/ml, respectively after 48 h. Further studies substantiated that both the compounds targeted cancer cells through mitochondrial membrane potential loss and subsequent chromatin condensation. Both compounds significantly increased the Annexin V binding thus confirming compounds 1 and 2 to be potential apoptotic agents.

iRhom2 regulation of TACE controls TNF-mediated protection against Listeria and responses to LPS.

Innate immune responses are vital for pathogen defense but can result in septic shock when excessive. A key mediator of septic shock is tumor necrosis factor-α (TNFα), which is shed from the plasma membrane after cleavage by the TNFα convertase (TACE). We report that the rhomboid family member iRhom2 interacted with TACE and regulated TNFα shedding. iRhom2 was critical for TACE maturation and trafficking to the cell surface in hematopoietic cells. Gene-targeted iRhom2-deficient mice showed reduced serum TNFα in response to lipopolysaccharide (LPS) and could survive a lethal LPS dose. Furthermore, iRhom2-deficient mice failed to control the replication of Listeria monocytogenes. Our study has identified iRhom2 as a regulator of innate immunity that may be an important target for modulating sepsis and pathogen defense.

Effect of apoptosis-inducing antitumor agents on endocardial endothelial cells.

Chemotherapy is one of the common treatment modalities for cancer. Some of the antineoplastic drugs have, however, been found to be toxic for vascular endothelium, resulting in complications such as endothelial dysfunction, thromboembolism, heart failure, and cardiomyopathy. In this study, we investigated the cytotoxic effect of widely used antitumor agents doxorubicin, camptothecin, and thapsigargin on primary and immortalized porcine endocardial endothelial cells and compared with the effects of these agents on human umbilical vein endothelial cells, human aortic endothelial cells, and EA.hy926 cells. Our study revealed that endocardial endothelial cells are relatively resistant to apoptosis induced by these drugs. Interestingly, our study indicates that response to antitumor agents greatly differs depending on the site of origin of endothelial cells. Doxorubicin, camptothecin, and thapsigargin induce mitochondrial-dependent cell death following loss of mitochondrial membrane potential (MMP) in vascular endothelial cells, with subsequent increase in sub-G0 population. In endocardial endothelial cells, there was no MMP loss; and only cell cycle arrest either at G1 or S phases was observed when the cells were treated with doxorubicin, camptothecin, and thapsigargin.

Endoplasmic reticulum targeted Bcl2 confers long term cell survival through phosphorylation of heat shock protein 27.

Overexpression of anti-apoptotic Bcl2 family proteins is often seen in cancers rendering them insensitive to apoptosis inducing anticancer strategies. Anti-apoptotic Bcl2 family proteins are associated with different organelles like mitochondria and endoplasmic reticulum (ER) and exert their anti-apoptotic activity by inhibiting the release of Cyt.C from mitochondria irrespective of its localization. Here, we have identified a long term survival function for Bcl2 targeted at ER in mammalian system compared to wild type Bcl2 that is mediated by enhanced phosphorylation of heat shock protein 27 at ser 15, 78 and 82 sites with inhibition of caspase9 activity. Phosphorylation of hsp27 was prevented and the survival of ER-Bcl2 cells was reversed by inhibiting p38 and MEK suggesting that these kinases can act as the upstream targets for hsp27 phosphorylation. The results suggest that Bcl2 possess additional survival function in the regulation of apoptosis which is primarily regulated by its association with the ER in an hsp27 dependent manner. The interplay of both hsp27 and ER-Bcl2 in providing long term survival to cancer cells is interesting since both of these proteins are overexpressed in tumors with aggressive phenotype. The results suggest that spatial localization of Bcl2 family proteins also play a key role in long term survival of cancers indicating another level of functional regulation of Bcl2 in cancer cell survival.

Bax deficiency mediated drug resistance can be reversed by endoplasmic reticulum stress induced death signaling.

Tumors often acquire drug resistance due to functional loss of pro apoptotic gene Bax, a critical and essential component of cell death rendering them insensitive to most anti-tumor agents. Compounds that can induce Bax independent apoptotic cell death are expected to overcome such drug resistance. We have employed a live cell based screening platform to identify potential compounds that can induce programmed cell death in Bax deficiency. Release of cytochrome C from mitochondria into the cytosol is a decisive initial event required for the caspase dependent cell death. We have engineered both wild type and Bax knock out colon cancer cells stably expressing cytochrome C with EGFP fusion protein to identify compounds that can trigger cytochrome C release in both cells with equal efficiency. In the fluorescent translocation assay, most of the drugs tested failed to induce cytochrome C release in Bax deficient cells validating the sensitivity of the assay. This study identified five lead compounds such as thapsigargin, tunicamycine, MG132, kaempferol and camptothecin that could induce cytochrome C release in both wild type and Bax deficient cells with equal potency. All the positive hits induced ER stress signaling as evidenced by up-regulation of Grp78. Studies with a Bak deficient cells indicate that Bak deficiency confers protection to cells from ER stress through autophagy. Further studies revealed that ER stress inducing agents are capable of triggering classical mitochondrial apoptotic cell death through the conformational activation of Bak, substantiating the potential of this pathway in designing drugs against Bax deficiency mediated drug resistance.