Retraction: Non-epigenetic function of HDAC8 in regulating breast cancer stem cells by maintaining Notch1 protein stability.

[This retracts the article DOI: 10.18632/oncotarget.6427.].

Targeting breast cancer stem cells by novel HDAC3-selective inhibitors.

Although histone deacetylase (HDAC) inhibitors have been known to suppress the cancer stem cell (CSC) population in multiple types of cancer cells, it remains unclear which HDAC isoforms and corresponding mechanisms contribute to this anti-CSC activity. Pursuant to our previous finding that HDAC8 regulates CSCs in triple-negative breast cancer (TNBC) cells by targeting Notch1 stability, we investigated related pathways and found HDAC3 to be mechanistically linked to CSC homeostasis by increasing ß-catenin expression through the Akt/GSK3ß pathway. Accordingly, we used a pan-HDAC inhibitor, AR-42 (1), as a scaffold to develop HDAC3-selective inhibitors, obtaining the proof-of-concept with 18 and 28. These two derivatives exhibited high potency and isoform selectivity in HDAC3 inhibition. Equally important, they showed in vitro and/or in vivo efficacy in suppressing the CSC subpopulation of TNBC cells via the downregulation of ß-catenin.

Thymidine Kinase-Negative Herpes Simplex Virus 1 Can Efficiently Establish Persistent Infection in Neural Tissues of Nude Mice.

Herpes simplex virus 1 (HSV-1) establishes latency in neural tissues of immunocompetent mice but persists in both peripheral and neural tissues of lymphocyte-deficient mice. Thymidine kinase (TK) is believed to be essential for HSV-1 to persist in neural tissues of immunocompromised mice, because infectious virus of a mutant with defects in both TK and UL24 is detected only in peripheral tissues, but not in neural tissues, of severe combined immunodeficiency mice (T. Valyi-Nagy, R. M. Gesser, B. Raengsakulrach, S. L. Deshmane, B. P. Randazzo, A. J. Dillner, and N. W. Fraser, Virology 199:484-490, 1994, https://doi.org/10.1006/viro.1994.1150). Here we find infiltration of CD4 and CD8 T cells in peripheral and neural tissues of mice infected with a TK-negative mutant. We therefore investigated the significance of viral TK and host T cells for HSV-1 to persist in neural tissues using three genetically engineered mutants with defects in only TK or in both TK and UL24 and two strains of nude mice. Surprisingly, all three mutants establish persistent infection in up to 100% of brain stems and 93% of trigeminal ganglia of adult nude mice at 28 days postinfection, as measured by the recovery of infectious virus. Thus, in mouse neural tissues, host T cells block persistent HSV-1 infection, and viral TK is dispensable for the virus to establish persistent infection. Furthermore, we found 30- to 200-fold more virus in neural tissues than in the eye and detected glycoprotein C, a true late viral antigen, in brainstem neurons of nude mice persistently infected with the TK-negative mutant, suggesting that adult mouse neurons can support the replication of TK-negative HSV-1. IMPORTANCE: Acyclovir is used to treat herpes simplex virus 1 (HSV-1)-infected immunocompromised patients, but treatment is hindered by the emergence of drug-resistant viruses, mostly those with mutations in viral thymidine kinase (TK), which activates acyclovir. TK mutants are detected in brains of immunocompromised patients with persistent infection. However, answers to the questions as to whether TK-negative (TK-) HSV-1 can establish persistent infection in brains of immunocompromised hosts and whether neurons in vivo are permissive for TK- HSV-1 remain elusive. Using three genetically engineered HSV-1 TK- mutants and two strains of nude mice deficient in T cells, we found that all three HSV-1 TK- mutants can efficiently establish persistent infection in the brain stem and trigeminal ganglion and detected glycoprotein C, a true late viral antigen, in brainstem neurons. Our study provides evidence that TK- HSV-1 can persist in neural tissues and replicate in brain neurons of immunocompromised hosts.

Non-epigenetic function of HDAC8 in regulating breast cancer stem cells by maintaining Notch1 protein stability.

Here, we report a novel non-epigenetic function of histone deacetylase (HDAC) 8 in activating cancer stem cell (CSC)-like properties in breast cancer cells by enhancing the stability of Notch1 protein. The pan-HDAC inhibitors AR-42 and SAHA, and the class I HDAC inhibitor depsipeptide, suppressed mammosphere formation and other CSC markers by reducing Notch1 expression in MDA-MB-231 and SUM-159 cells. Interrogation of individual class I isoforms (HDAC1-3 and 8) using si/shRNA-mediated knockdown, ectopic expression and/or pharmacological inhibition revealed HDAC8 to be the primary mediator of this drug effect. This suppression of Notch1 in response to HDAC8 inhibition was abrogated by the proteasome inhibitor MG132 and siRNA-induced silencing of Fbwx7, indicating Notch1 suppression occurred through proteasomal degradation. However, co-immunoprecipitation analysis indicated that HDAC8 did not form complexes with Notch1 and HDAC inhibition had no effect on Notch1 acetylation. In a xenograft tumor model, the tumorigenicity of breast cancer cells was decreased by HDAC8 knockdown. These findings suggest the therapeutic potential of HDAC8 inhibition to suppress Notch1 signaling in breast cancer.

Proteasome inhibitor bortezomib suppresses nuclear factor-kappa B activation and ameliorates eye inflammation in experimental autoimmune uveitis.

Bortezomib is a proteasome inhibitor used for hematologic cancer treatment. Since it can suppress NF-κB activation, which is critical for the inflammatory process, bortezomib has been found to possess anti-inflammatory activity. In this study, we evaluated the effect of bortezomib on experimental autoimmune uveitis (EAU) in mice and investigated the potential mechanisms related to NF-κB inactivation. High-dose bortezomib (0.75 mg/kg), low-dose bortezomib (0.15 mg/kg), or phosphate buffered saline was given after EAU induction. We found that the EAU is ameliorated by high-dose bortezomib treatment when compared with low-dose bortezomib or PBS treatment. The DNA-binding activity of NF-κB was suppressed and expression of several key inflammatory mediators including TNF-α, IL-1α, IL-1ß, IL-12, IL-17, and MCP-1 was lowered in the high-dose bortezomib-treated group. These results suggest that proteasome inhibition is a promising treatment strategy for autoimmune uveitis.

Early dexamethasone treatment exacerbates enterovirus 71 infection in mice.

Enterovirus 71 (EV71) infection can induce encephalitis. Overt immune responses is suspected to cause severe symptoms, so anti-inflammatory agents, corticosteroids have been recommended for treatment. However, one clinical study reported that treatment with glucocorticoids, dexamethasone (Dex) exacerbates disease severity. Here we investigated Dex treatment on EV71 infection using the murine model and found that both long-term (14-day) and short-term (4-day) Dex treatment starting from 1 or 3 days postinfection increased the mortality and disease severity of infected mice. Dex treatment starting from 4 or 8 days postinfection did not affect mouse mortality and disease severity. Early Dex treatment starting from 1 day postinfection caused atrophy and enhanced apoptosis in lymphoid organs to decrease the numbers of lymphocytes (CD4(+) T cells, CD8(+) T cells, and CD19(+) B cells) and to increase viral loads in infected tissues of mice. Our results demonstrate that Dex treatment has no beneficial effect on EV71 infection.

Tranylcypromine reduces herpes simplex virus 1 infection in mice.

Herpes simplex virus 1 (HSV-1) infects the majority of the human population and establishes latency by maintaining viral genomes in neurons of sensory ganglia. Latent virus can undergo reactivation to cause recurrent infection. Both primary and recurrent infections can cause devastating diseases, including encephalitis and corneal blindness. Acyclovir is used to treat patients, but virus resistance to acyclovir is frequently reported. Recent in vitro findings reveal that pretreatment of cells with tranylcypromine (TCP), a drug widely used in the clinic to treat neurological disorders, restrains HSV-1 gene transcription by inhibiting the histone-modifying enzyme lysine-specific demethylase 1. The present study was designed to examine the anti-HSV-1 efficacy of TCP in vivo because of the paucity of reports on this issue. Using the murine model, we found that TCP decreased the severity of wild-type-virus-induced encephalitis and corneal blindness, infection with the acyclovir-resistant (thymidine kinase-negative) HSV-1 mutant, and tissue viral loads. Additionally, TCP blocked in vivo viral reactivation in trigeminal ganglia. These results support the therapeutic potential of TCP for controlling HSV-1 infection.

Absence of CXCL10 aggravates herpes stromal keratitis with reduced primary neutrophil influx in mice.

Herpes simplex virus 1 (HSV-1) replication initiates inflammation and angiogenesis responses in the cornea to result in herpetic stromal keratitis (HSK), which is a leading cause of infection-induced vision impairment. Chemokines are secreted to modulate HSK by recruiting leukocytes, which affect virus growth, and by influencing angiogenesis. The present study used a murine infection model to investigate the significance of the chemokine CXC chemokine ligand 10 (CXCL10; gamma interferon-inducible protein 10 [IP-10]) in HSK. Here, we show that HSV-1 infection of the cornea induced CXCL10 protein expression in epithelial cells. The corneas of mice with a targeted disruption of the gene encoding CXCL10 displayed decreases in levels of neutrophil-attracting cytokine (interleukin-6), primary neutrophil influx, and viral clearance 2 or 3 days postinfection. Subsequently, absence of CXCL10 aggravated HSK with elevated levels of interleukin-6, chemokines for CD4(+) T cells and/or neutrophils (macrophage inflammatory protein-1α and macrophage inflammatory protein-2), angiogenic factor (vascular endothelial growth factor A), and secondary neutrophil influx, as well as infiltration of CD4(+) T cells to exacerbate opacity and angiogenesis in the cornea at 14 and up to 28 days postinfection. Our results collectively show that endogenous CXCL10 contributes to recruit the primary neutrophil influx and to affect the expression of cytokines, chemokines, and angiogenic factors as well as to reduce the viral titer and HSK severity.

Enterovirus 71 infection increases expression of interferon-gamma-inducible protein 10 which protects mice by reducing viral burden in multiple tissues.

Enterovirus 71 (EV71) infection has induced fatal encephalitis in thousands of young children in the Asia-Pacific region over the last decade. EV71 infection continues to cause serious problems in areas with outbreaks, because vaccines and antiviral therapies are not available. Lymphocytes are present in the brains of infected patients and mice, and they protect mice from infection by decreasing the viral burden. The chemokines responsible for recruiting lymphocytes to infected organs are yet to be identified. Among the lymphocyte chemokines detected, high levels of interferon-gamma-inducible protein-10 (IP-10) are found in the plasma and cerebral spinal fluid of patients with brainstem encephalitis as compared with the levels of a monokine induced by gamma interferon (Mig). Using a murine model to investigate the induction of IP-10 by EV71 infection, we observed that EV71 infection significantly enhanced IP-10 protein expression in the serum and brain, with kinetics similar to viral titres in the blood and brain. Brain neurons of infected mice expressed IP-10. Using wild-type mice and IP-10 gene knockout mice to investigate the role of IP-10 in EV71 infection, we found that IP-10 deficiency significantly reduced levels of Mig in serum, and levels of gamma interferon and the number of CD8 T cells in the mouse brain. Absence of IP-10 significantly increased the mortality of infected mice by 45%, with slow virus clearance in several vital tissues. Our observations are consistent with a model where EV71 infection boosts IP-10 expression to increase gamma interferon and Mig levels, infiltration of CD8 T cells, virus clearance in tissues and the survival of mice.

Ribavirin reduces mortality in enterovirus 71-infected mice by decreasing viral replication.

Enterovirus 71 (EV71) causes fatal encephalitis in young children. However, there is no effective antiviral drug available for infected patients. Ribavirin is currently used for the treatment of several RNA virus infections clinically, so its anti-EV71 efficacy was evaluated. In vitro results showed that ribavirin effectively reduced the viral yields (with an IC50 of 65 microg/mL) and virus-induced cytopathic effect in human and mouse cell lines. In vivo results showed that ribavirin reduced the mortality, morbidity, and subsequent paralysis sequelae in infected mice by decreasing viral loads in tissues. Thus, ribavirin could be a potential anti-EV71 drug.