Weiguo Zou

UBP43 is a novel regulator of interferon signaling independent of its ISG15 isopeptidase activity

Interferons (IFNs) regulate diverse cellular functions through activation of the Janus kinase–signal transducer and activator of transcription (JAK–STAT) pathway. Lack of Ubp43, an IFN‐inducible ISG15 deconjugating enzyme, leads to IFN hypersensitivity in ubp43−/− mice, suggesting an important function of Ubp43 in downregulation of IFN responses. Here, we show that Ubp43 negatively regulates IFN signaling independent of its isopeptidase activity towards ISG15. Ubp43 functions specifically for type I IFN signaling by downregulating the JAK–STAT pathway at the level of the IFN receptor. Using molecular, biochemical, and genetic approaches, we demonstrate that Ubp43 specifically binds to the IFNAR2 receptor subunit and inhibits the activity of receptor‐associated JAK1 by blocking the interaction between JAK and the IFN receptor. These data implicate Ubp43 as a novel in vivo inhibitor of signal transduction pathways that are specifically triggered by type I IFN.

The p38 MAPK pathway is essential for skeletogenesis and bone homeostasis in mice

Nearly every extracellular ligand that has been found to play a role in regulating bone biology acts, at least in part, through MAPK pathways. Nevertheless, much remains to be learned about the contribution of MAPKs to osteoblast biology in vivo. Here we report that the p38 MAPK pathway is required for normal skeletogenesis in mice, as mice with deletion of any of the MAPK pathway member-encoding genes MAPK kinase 3 (Mkk3), Mkk6, p38a, or p38b displayed profoundly reduced bone mass secondary to defective osteoblast differentiation. Among the MAPK kinase kinase (MAP3K) family, we identified TGF-beta-activated kinase 1 (TAK1; also known as MAP3K7) as the critical activator upstream of p38 in osteoblasts. Osteoblast-specific deletion of Tak1 resulted in clavicular hypoplasia and delayed fontanelle fusion, a phenotype similar to the cleidocranial dysplasia observed in humans haploinsufficient for the transcription factor runt-related transcription factor 2 (Runx2). Mechanistic analysis revealed that the TAK1-MKK3/6-p38 MAPK axis phosphorylated Runx2, promoting its association with the coactivator CREB-binding protein (CBP), which was required to regulate osteoblast genetic programs. These findings reveal an in vivo function for p38beta and establish that MAPK signaling is essential for bone formation in vivo. These results also suggest that selective p38beta agonists may represent attractive therapeutic agents to prevent bone loss associated with osteoporosis and aging.

The Interferon-inducible Ubiquitin-protein Isopeptide Ligase (E3) EFP Also Functions as an ISG15 E3 Ligase

The expression of the ubiquitin-like protein ISG15 and protein modification by ISG15 (ISGylation) are strongly activated by interferons. Accordingly, ISG15 expression and protein ISGylation are strongly activated upon viral and bacterial infections and during other stress conditions, suggesting important roles for the ISG15 system in innate immune responses. Here, we report the identification of the ubiquitin-protein isopeptide ligase (E3) EFP (estrogen-responsive finger protein) as the ISG15 E3 ligase for 14-3-3σ protein. Like other known components of the protein ISGylation system (ISG15, UBE1L, UBP43, and UBC8), EFP is also an interferon-inducible protein. Expression of EFP small interfering RNA decreased the ISGylation of 14-3-3σ in the 293T cell ISGylation system as well as in MCF-7 cells upon interferon treatment. Furthermore, the ISGylation enzyme activity of EFP was RING domain-dependent. These findings indicate that EFP is an ISG15 E3 ligase for 14-3-3σ in vivo. The fact that both UBC8 and EFP are common components in the ubiquitin and ISG15 conjugation pathways suggests a mechanism whereby a limited set of enzymes accomplishes diverse post-translational modifications of their substrates in response to changes in environmental stimulations.

Cobalt chloride induces PC12 cells apoptosis through reactive oxygen species and accompanied by AP-1 activation.

Reactive oxygen species (ROS) are supposed to play an important role in hypoxia‐ and ischemia/reperfusion‐mediated neuronal injury with the characteristics of apoptosis. There are many reports showing that cobalt chloride (CoCl2) could mimic the hypoxic responses in some aspects including production of ROS in cultured cells. The cytotoxicity of CoCl2 and its molecular mechanisms have yet to be elucidated. We report that CoCl2 triggered neuronal PC12 cells apoptosis in a dose‐ and time‐dependent manner. Apoptosis was demonstrated by morphological changes and DNA fragmentation, and was dependent on macromolecular synthesis. Apoptosis was also confirmed by the decrease of the expression of Bcl‐XL. To our knowledge, this is the first documentation of the apoptotic induction of CoCl2 on PC12 cells. Furthermore, ROS production in PC12 cells was increased during CoCl2 treatment. Antioxidants, which could inhibit ROS production, significantly blocked CoCl2‐induced apoptosis, suggesting that apoptosis is mediated by ROS production. We also observed a significant increase of the DNA‐binding activity of AP‐1 in response to CoCl2 and this increase was blocked by antioxidants, showing that CoCl2‐induced apoptosis is accompanied by ROS‐activated AP‐1. CoCl2‐treated PC12 cells may serve as an in vitro model for studies of molecular mechanisms in ROS‐linked neuronal disorders. J. Neurosci. Res. 64:646–653, 2001.

An oncolytic adenoviral vector of Smac increases antitumor activity of TRAIL against HCC in human cells and in mice.

Hepatocellular carcinoma (HCC) displays a high resistance to tumor necrosis factor–related apoptosis–inducing ligand (TRAIL)–mediated cell death. To increase sensitivity of HCC cells to TRAIL, we have constructed an oncolytic adenoviral vector (ZD55) and used this vector to deliver second mitochondria‐derived activator of caspases (Smac) and TRAIL genes (ZD55‐Smac and ZD55‐TRAIL, respectively) into HCC cells. Our data showed that human HCC cells express high levels of inhibitor of apoptosis proteins (IAPs). Transfected HCC cells expressing exogenous X‐linked IAPs (XIAPs) displayed more resistance to TRAIL. The expression of Smac led to rapid and potent activation of apoptosis in HCC cells after infection with ZD55‐Smac. The activation of caspases and induction of apoptosis could be enhanced further through coinfection with ZD55‐TRAIL. The combined treatment of ZD55‐Smac and ZD55‐TRAIL resulted in significant reduction of XIAP expression levels. In addition, our in vivo data in mice showed only a partial response in the established tumor treated either by ZD55‐Smac or ZD55‐TRAIL alone. By contrast, complete tumor regression was observed by combination of ZD55‐Smac and ZD55‐TRAIL in all treated animals. This strong antitumoral activity achieved by this combination was due to a dramatic induction of tumor cell apoptosis in the treated tumors. In conclusion, our data indicate that Smac antagonizes the IAPs in HCC tumor cells and enhances tumor cell death induced by TRAIL in the oncolytic adenoviral vector. The combination of Smac and TRAIL delivered by way of the oncolytic adenoviral vector would provide a useful strategy for therapy of HCC and might also be applied to other IAPs abundant in cancers. (HEPATOLOGY 2004;39:1371–1381.)

Ube1L and protein ISGylation are not essential for alpha/beta interferon signaling.

ABSTRACT The expression of ubiquitin-like modifier ISG15 and its conjugation to target proteins are highly induced by interferon (IFN) stimulation and during viral and bacterial infections. However, the biological significance of this modification has not been clearly understood. To investigate the function of protein modification by ISG15, we generated a mouse model deficient in UBE1L, an ISG15-activating enzyme. Ube1L−/− mice did not produce ISG15 conjugates but expressed free ISG15 normally. ISGylation has been implicated in the reproduction and innate immunity. However, Ube1L−/− mice were fertile and exhibited normal antiviral responses against vesicular stomatitis virus and lymphocytic choriomeningitis virus infection. Our results indicate that UBE1L and protein ISGylation are not critical for IFN-α/β signaling via JAK/STAT activation. Moreover, using Ube1L/Ubp43 double-deficient mice, we showed that lack of UBP43, but not the increase of protein ISGylation, is related to the increased IFN signaling in Ubp43-deficient mice.

An armed oncolytic adenovirus system, ZD55-gene, demonstrating potent antitumoral efficacy

ABSTRACTONYX-015 is an attractive therapeutic adenovirus for cancer because it can selectively replicate in tumor cells and kill them. To date, clinical trials of this adenovirus have demonstrated marked safety but not potent enough when it was used alone. In this paper, we put forward a novel concept of Gene-ViroTherapy strategy and in this way, we constructed an armed therapeutic oncolytic adenovirus system, ZD55-gene, which is not only deleted of E1B 55-kD gene similar to ONYX-015, but also armed with foreign antitumor gene. ZD55-gene exhibited similar cytopathic effects and replication kinetics to that of ONYX-015 in vitro. Importantly, the carried gene is expressed and the expression level can increase with the replication of virus. Consequently, a significant antitumoral efficacy was observed when ZD55-CD/5-FU was used as an example in nude mice with subcutaneous human SW620 colon cancer. Our data demonstrated that ZD55-gene, which utilizing the Gene-ViroTherapy strategy, is more efficacious than each individual component in vivo.

The E3 ubiquitin ligase Wwp2 regulates craniofacial development through mono-ubiquitylation of Goosecoid

Craniofacial anomalies (CFAs) are the most frequently occurring human congenital disease, and a major cause of infant mortality and childhood morbidity. Although CFAs seems to arise from a combination of genetic factors and environmental influences, the underlying gene defects and pathophysiological mechanisms for most CFAs are currently unknown. Here we reveal a role for the E3 ubiquitin ligase Wwp2 in regulating craniofacial patterning. Mice deficient in Wwp2 develop malformations of the craniofacial region. Wwp2 is present in cartilage where its expression is controlled by Sox9. Our studies demonstrate that Wwp2 influences craniofacial patterning through its interactions with Goosecoid (Gsc), a paired-like homeobox transcription factor that has an important role in craniofacial development. We show that Wwp2-associated Gsc is a transcriptional activator of the key cartilage regulatory protein Sox6. Wwp2 interacts with Gsc to facilitate its mono-ubiquitylation, a post-translational modification required for optimal transcriptional activation of Gsc. Our results identify for the first time a physiological pathway regulated by Wwp2 in vivo, and also a unique non-proteolytic mechanism through which Wwp2 controls craniofacial development.

Cdh1 Regulates Osteoblast Function through an APC/C-Independent Modulation of Smurf1

The APC/Cdh1 E3 ubiquitin ligase plays an essential role in both mitotic exit and G1/S transition by targeting key cell-cycle regulators for destruction. There is mounting evidence indicating that Cdh1 has other functions in addition to cell-cycle regulation. However, it remains unclear whether these additional functions depend on its E3 ligase activity. Here, we report that Cdh1, but not Cdc20, promotes the E3 ligase activity of Smurf1. This is mediated by disruption of an autoinhibitory Smurf1 homodimer and is independent of APC/Cdh1 E3 ligase activity. As a result, depletion of Cdh1 leads to reduced Smurf1 activity and subsequent activation of multiple downstream targets, including the MEKK2 signaling pathway, inducing osteoblast differentiation. Our studies uncover a cell-cycle-independent function of Cdh1, establishing Cdh1 as an upstream component that governs Smurf1 activity. They further suggest that modulation of Cdh1 is a potential therapeutic option for treatment of osteoporosis.

A novel oncolytic adenovirus targeting to telomerase activity in tumor cells with potent

Telomerase is a therapeutic target for cancer. Human telomerase reverse transcriptase (hTERT), the catalytic subunit of the telomerase, is transcriptionaly upregulated exclusively in about 90% of cancer cells. Previous studies have demonstrated that hTERT promoter can control the expression of exogenous genes to the telomerase-positive cancer cells, thus hTERT promoter is an excellent candidate for generating cancer-specific oncolytic adenovirus. In this study, we devised a novel oncolytic adenovirus (Ad.TERT) by replacing the normal E1A regulatory elements with hTERT promoter. Ad.TERT displays cancer-specific E1A expression, virus replication and cytolysis in in vitro experiments. In animal experiments, intratumoral administration of Ad.TERT demonstrates potent antitumoral efficacy at least in two xenograft models (Bcap37 and BEL7404). Ad.TERT was targeted by the telomerase activity in cancer cells and has potent antitumoral efficacy in vivo, and since telomerase activity is a wide-ranged tumor marker, Ad.TERT could be a powerful therapeutic agent for a variety of cancers.