Yuejun Fu

β-catenin as a potential key target for tumor suppression.

β‐catenin is a multifunctional protein identified to be pivotal in embryonic patterning, organogenesis and adult homeostasis. It plays a critical structural role in mediating cadherin junctions and is also an essential transcriptional co‐activator in the canonical Wnt pathway. Evidence has been documented that both the canonical Wnt pathway and cadherin junctions are deregulated or impaired in a plethora of human malignancies. In the light of this, there has been a recent surge in elucidating the mechanisms underlying the etiology of cancer development from the perspective of β‐catenin. Here, we focus on the emerging roles of β‐catenin in the process of tumorigenesis by discussing novel functions of old players and new proteins, mechanisms identified to mediate or interact with β‐catenin and the most recently unraveled clinical implications of β‐catenin regulatory pathways toward tumor suppression.

Therapeutic potential of chlorotoxin-like neurotoxin from the Chinese scorpion for human gliomas

Chlorotoxin, one of the key toxins in scorpion Leiurus quinquestriatus venom, has been shown to bind specifically to glioma cell surface as a specific chloride channel blocker. In this study, a purified, recombinant chlorotoxin-like peptide from the scorpion Buthus martensii Karsch (named rBmK CTa) was characterized by in vivo and in vitro studies. The results from cell proliferation assay with human glioma (SHG-44) cells showed that rBmK CTa inhibits the growth of glioma cells in a dose-dependent manner, with an IC(50) value of approximately 0.28microM. Under the same conditions, the IC(50) value for normal astrocytes increased to 8microM. This clearly indicated that rBmK CTa had specific toxicity against glioma cells but not astrocytes. Results from whole-cell patch-clamp recording showed that chloride current in SHG-44 was inhibited by rBmK CTa in a voltage-dependent manner and percent inhibitions for the blocking action of rBmK CTa (0.07 and 0.14microM) on I(Cl) was 17.64+/-3.06% and 55.86+/-2.83%, respectively. Histological analysis of rBmK CTa treated mice showed that brain, leg muscle and cardiac muscle were the target organs of this toxin. These results suggest that rBmK CTa may have potential therapeutic application in clinical treatment of human glioma. It represents an approach for developing a novel therapeutic agent.

Glioma-derived mutations in IDH: From mechanism to potential therapy

Heterozygous mutations in either the R132 residue of isocitrate dehydrogenase I (IDH1) or the R172 residue of IDH2 in human gliomas were recently highlighted. Heterozygous mutations in the IDH1 occur in the majority of grade II and grade III gliomas and secondary glioblastomas and change the structure of the enzyme, which diminishes its ability to convert isocitrate (ICT) to alpha-ketoglutarate (alpha-KG) and provides it with a newly acquired ability to convert alpha-KG to R(-)-2-hydroxyglutarate [R(-)-2HG]. The IDH1 and IDH2 mutations are relevant to the progression of gliomas, the prognosis and treatment of the patients with gliomas harboring the mutation. In this paper, we reviewed these recent findings which were essential for the further exploration of human glioma cancer and might be responsible for developing a newer and more effective therapeutic approach in clinical treatment of this cancer.

Glioma derived isocitrate dehydrogenase-2 mutations induced up-regulation of HIF-1α and β-catenin signaling: possible impact on glioma cell metastasis and chemo-resistance.

The identification of heterozygous mutations (with an incidence up to 85%) in either the R132 residue of isocitrate dehydrogenase-1 (IDH1) or the R172 residue of IDH2 in human low-grade diffuse gliomas was remarkable because no oncogenic pathway had been previously documented correlated with these enzymes. In spite of a recent surge in elucidating the tumorigenic activity of IDH mutations in glioblastoma, the underlying biological mechanisms remain poorly understood. We showed here that C6 glioma cells transiently over-expressing IDH2(R172G) induced nuclear accumulation of β-catenin, up-regulation of HIF-1α signaling and corresponding proteins expression that were closely related with tumor invasion and chemo-resistance. These results demonstrated a functional model in which IDH mutations were closely interrelated with glioma progression and could hold some therapeutic implications for future human glioma treatment.

Effect of location of the His-tag on the production of soluble and functional Buthus martensii Karsch insect toxin.

The low yield and poor folding efficiency in vivo of soluble and active recombinant cysteine-rich proteins expressed in Escherichia coli are a major challenge for large-scale protein production and purification. Expression vectors containing Buthus martensii Karsch insect toxin (BmK IT) fused to the C terminus of the intein Ssp DnaB were constructed in an attempt to overcome this problem. Following purification and intein self-cleavage, the fusion protein His(6)-intein-IT produced insoluble BmK IT, while intein-IT-His(6) generated soluble and properly folded BmK IT. This result indicated that the positioning of the His(6) tag has a key role in the production of soluble and functional BmK IT.

Chlorotoxin-conjugated nanoparticles as potential glioma-targeted drugs.

Development of glioma-specific nanoparticles has been an area of intense research over the past several years. Iron oxide, multifunctional superparamagnetic, and NaYF4:Yb,rare-earth upconversion nanoparticles, conjugated with chlorotoxin (CTX, a key toxin in scorpion venom which has been shown to bind specifically to glioma cell surface as a specific chloride channel and matrix metalloproteinase-2 blocker), exhibit high affinity for glioma and direct tumor visualization. We review the latest improvements of CTX-modified nanoparticle platforms which might enable development of more effective therapeutic agents in clinical treatment of glioma.

Mutations in isocitrate dehydrogenase 2 accelerate glioma cell migration via matrix metalloproteinase-2 and 9

The gene encoding isocitrate dehydrogenase (IDH) is somatically mutated predominantly in secondary glioblastoma multiforme. Glioma-specific mutations in IDH1 always produced a single amino acid substitution at R132, but mutations in IDH2 were exclusively at R172 which was the analogous site to R132 in IDH1. Mutations of IDH1 and IDH2 led to simultaneous loss and gain of activities in the production of α-ketoglutarate and 2-hydroxyglutarate, respectively. Matrix metalloproteinases (MMPs) are zinc-dependent endoproteinases involved in the degradation of the extracellular matrix. The exact role of IDH2 mutant on MMPs activity and cell migration has not been fully studied. Here, we show that in response to IDH2 mutations, low levels of α-ketoglutarate increased the stabilization of HIF-1α which can contribute to tumor growth. Moreover, mutant IDH2-induced HIF-1α improved the secretion levels of pro-MMP-2 and pro-MMP-9 as well as the conversion from pro-MMP-2 to its active form, giving C6 glioma cells a higher migration potential. The HIF-1α pathway is probably a critical pathway for release of MMPs in the glioma cancer harboring IDH mutant.

A potential strategy for high-grade gliomas: combination treatment with lithium chloride and BmK CT

Therapies for high-grade gliomas (HHG) that have strong tendency of infiltration and resistance to chemotherapies are currently unavailable. Here, we report that lower-dose combination therapy of Buthusmartensii Karsch (BmK) CT, a type of scorpion toxin peptide, and LiCl, clinically used as mood stabilizer, could synergistically inhibit the migration, invasion and proliferation of C6 glioma cells. The decreased invasiveness of C6 glioma cells was accompanied by inhibited activation, catalytic activity and/or expression of matrix metalloproteinase-2. Moreover, TOPfalsh luciferase reporter and immunofluorescence staining showed altered localization pattern of β-catenin at the leading edge of 2D scratch. Our results suggested that the combination treatment of lithium and BmK CT may constitute a novel and potential strategy for HHG therapy.

Potential adenovirus-mediated gene therapy of glioma cancer

Malignant gliomas are typically characterized by rapid cell proliferation and a marked propensity to invade and damage surrounding tissues. They are the main brain tumors notoriously resistant to currently available therapies, since they fail to undergo apoptosis upon anticancer treatments. With recent advances in neuroscience and improved understanding of the molecular mechanisms of invasive migration, gene therapy provides a new strategy for treating glioma cancer. Brain tumor gene therapy using viral vectors and stem cells has shown promise in animal model and human patient studies. Here, we review recent studies on engineering adenoviral vectors that can be used as therapy for brain tumors. The new findings presented in this study are essential for the further exploration of this cancer and they represent an approach for developing a newer and more effective therapeutic approach in the clinical treatment of human glioma cancer.

Enzymology and thermal stability of phytase appA mutants

Escherichia coli phytase appA which hydrolyzes phytate has been widely applied as an important feed supplement, but the need to improve the thermal tolerance remains. Here, ten residue substitutions (W46E, Q62W, A73P, K75C, S146E, R159Y, N204C, Y255D, Q258N and Q349N) were introduced to enhance its thermal tolerance. Results showed the purified appAM10 had a specific activity of 3022 U mg−1 with an MW of approximately 53–55 kDa. Compared with the non-engineered enzyme produced by appA (GenBank Accession DQ513832), appAM10 showed an enhancement in thermal tolerance and 7.5 °C increased in the melting temperatures (Tm). To understand the mechanism of the improvement in its thermal tolerance, conformational changes between appA and its mutant appAM10 have been investigated in detail by means of fluorescence spectroscopy. The results indicated that appAM10 had enhancement of α-helix content and displayed greater exposed hydrophobic surface than appA. These conformational changes made the appAM10 more stable against heat treatment. This study provided a biotechnologically useful mutant and expanded our knowledge about the mechanisms of phytase thermal tolerance.