MEX3A Impairs DNA Mismatch Repair Signaling and Mediates Acquired Temozolomide Resistance in Glioblastoma.

MutS protein homolog 2 (MSH2) is a key element involved in the DNA mismatch repair (MMR) system, which is responsible for recognizing and repairing mispaired bases. Simultaneously, MSH2 identifies DNA adducts induced by temozolomide (TMZ) and triggers apoptosis and autophagy in tumor cells. Previous work has revealed that reduced MSH2 expression is often observed in patients with glioblastoma (GBM) who relapse after chemotherapy. Elucidation of the mechanism behind TMZ-mediated reduction of MSH2 could help improve GBM treatment. Here, we report significant upregulation of Mex-3 RNA binding family member A (MEX3A) in GBM tissues and cell lines following TMZ treatment. MEX3A bound to the MEX3 recognition element (MRE) of MSH2 mRNA, which in turn recruited CCR4-NOT complexes to target MSH2 mRNA for deadenylation and degradation. In addition, ectopic expression of MEX3A significantly decreased cellular DNA MMR activities and reduced the chemosensitivity of GBM cells via downregulation of MSH2, while depletion of MEX3A sensitized GBM cells to TMZ. In MGMT-deficient patients with GBM, MEX3A expression correlated with MSH2 levels, and high MEX3A expression was associated with poor prognosis. Overall, these findings reveal a potential mechanism by which MSH2 expression is reduced in post-TMZ recurrent GBM. SIGNIFICANCE: A MEX3A/CCR4-NOT/MSH2 axis plays a crucial role in promoting temozolomide resistance, providing new insights into the function of MEX3A and suggesting MEX3A as a potential therapeutic target in therapy-resistant glioblastoma.

Improved Durability of High-Performance Intermediate-Temperature Solid Oxide Fuel Cells with a Ba-Doped La0.6Sr0.4Co0.2Fe0.8O3-δ Cathode.

As a device for direct conversion of chemical energy into electrical energy, the solid oxide fuel cell (SOFC) contributes positively to the sustainable development strategy. However, the commercialization of fuel cells is still impeded by severe cathode degradation caused by its limited stability at operating temperatures and being prone to Cr-poisoning from Cr-containing alloy interconnectors commonly used in these cells. This paper reports the development of a high-durability Ba-doped LSCF(La0.6Sr0.4Co0.2Fe0.8O3-δ) cathode material under realistic fuel cell operating conditions in the presence of the Cr alloy. In particular, when tested in a symmetrical cell constructed of Ba-doped LSCF, the polarization resistance of the cell remains very low at 0.06 Ω cm2 after being tested at 800 °C for 120 h exposed to Cr in 3% humidified air. In contrast, for the undoped LSCF under the same testing conditions, the polarization resistance of the cell increases ∼10 times from 0.22 Ω cm2 of the pristine cell to 2.18 Ω cm2 after Cr-exposure testing. Furthermore, when tested in an anode-supported complete cell as a cathode under typical SOFC operation conditions at 750 °C, the cell with the Ba-doped LSCF cathode displays significantly low degradation rates of 0.00056% h-1 (without Cr) and 0.00310% h-1 (with Cr); both are much lower than that of the cell using the undoped LSCF cathode (0.00124% h-1 without Cr and 0.01082% h-1 with Cr). This enhanced durability and Cr-tolerance exhibited by the Ba-doped LSCF cathode stem from its higher crystal structure stability and improved chemical resistance compared to undoped LSCF.

The Grain Growth Control of ZnO-V2O5 Based Varistors by PrMnO3 Addition.

In this study, the grain growth behaviour of ZnO-V2O5-based ceramics with 0.25-0.75 mol% additions of PrMnO3 was systematically investigated during sintering from 850 °C to 925 °C. with the aim to control the ZnO grain size for their application as varistors. It was found that with the increased addition of PrMnO3, in addition to the decrease in the average grain size, the grain size distribution also narrowed and eventually changed from a bimodal to unimodal distribution after a 0.75 mol% PrMnO3 addition. The grain growth control was achieved by a pinning effect of the secondary ZnCr2O4 and PrVO4 phases at the ZnO grain boundaries. The apparent activation energy of the ZnO grain growth in these ceramics was found to increase with increased additions of PrVO4, hence the observed reduction in the ZnO grain sizes.

TGF-ß1 modulates temozolomide resistance in glioblastoma via altered microRNA processing and elevated MGMT.

BACKGROUND: Our previous studies have indicated that miR-198 reduces cellular methylguanine DNA methyltransferase (MGMT) levels to enhance temozolomide sensitivity. Transforming growth factor beta 1 (TGF-ß1) switches off miR-198 expression by repressing K-homology splicing regulatory protein (KSRP) expression in epidermal keratinocytes. However, the underlying role of TGF-ß1 in temozolomide resistance has remained unknown. METHODS: The distribution of KSRP was detected by western blotting and immunofluorescence. Microarray analysis was used to compare the levels of long noncoding RNAs (lncRNAs) between TGF-ß1-treated and untreated cells. RNA immunoprecipitation was performed to verify the relationship between RNAs and KSRP. Flow cytometry and orthotopic and subcutaneous xenograft tumor models were used to determine the function of TGF-ß1 in temozolomide resistance. RESULTS: Overexpression of TGF-ß1 contributed to temozolomide resistance in MGMT promoter hypomethylated glioblastoma cells in vitro and in vivo. TGF-ß1 treatment reduced cellular MGMT levels through suppressing the expression of miR-198. However, TGF-ß1 upregulation did not affect KSRP expression in glioma cells. We identified and characterized 2 lncRNAs (H19 and HOXD-AS2) that were upregulated by TGF-ß1 through Smad signaling. H19 and HOXD-AS2 exhibited competitive binding to KSRP and prevented KSRP from binding to primary miR-198, thus decreasing miR-198 expression. HOXD-AS2 or H19 upregulation strongly promoted temozolomide resistance and MGMT expression. Moreover, KSRP depletion abrogated the effects of TGF-ß1 and lncRNAs on miR-198 and MGMT. Finally, we found that patients with low levels of TGF-ß1 or lncRNA expression benefited from temozolomide therapy. CONCLUSIONS: Our results reveal an underlying mechanism by which TGF-ß1 confers temozolomide resistance. Furthermore, our findings suggest that a novel combination of temozolomide with a TGF-ß inhibitor may serve as an effective therapy for glioblastomas.

PHAP1 promotes glioma cell proliferation by regulating the Akt/p27/stathmin pathway.

PHAP1 (Putative HLA-DR-associated protein 1), also termed acidic leucine-rich nuclear phosphoprotein 32A (ANP32A), Phosphoprotein 32 (pp32) or protein phosphatase 2A inhibitor (I1PP2A), is a multifunctional protein aberrantly expressed in multiple types of human cancers. However, its expression pattern and clinical relevance in human glioma remain unknown. In this study, Western blotting and immunohistochemistry analysis demonstrated PHAP1 protein was highly expressed in glioma patients, especially in those with high-grade disease. Publicly available data also revealed high levels of PHAP1 were associated with poor prognosis in glioma patients. The functional studies showed that knock-down of PHAP1 suppressed the proliferation of glioma cells, while overexpression of PHAP1 facilitated it. The iTRAQ proteomic analysis suggested that stathmin might be a potential downstream target of PHAP1. Consistently, PHAP1 knock-down significantly decreased the expression of stathmin, while overexpression of PHAP1 increased it. Also, the upstream negative regulator, p27, expression levels increased upon PHAP1 knock-down and decreased when PHAP1 was overexpressed. As a result, the phosphorylated Akt (S473), an upstream regulator of p27, expression levels decreased upon silencing of PHAP1, but elevated after PHAP1 overexpression. Importantly, we demonstrate the p27 down-regulation, stathmin up-regulation and cell proliferation acceleration induced by PHAP1 overexpression were dependent on Akt activation. In conclusion, the above results suggest that PHAP1 expression is elevated in glioma patients, which may accelerate the proliferation of glioma cells by regulating the Akt/p27/stathmin pathway.

Loss of SH3GL2 promotes the migration and invasion behaviours of glioblastoma cells through activating the STAT3/MMP2 signalling.

SH3GL2 (Src homology 3 (SH3) domain GRB2-like 2) is mainly expressed in the central nervous system and regarded as a tumour suppressor in human glioma. However, the molecular mechanism of the SH3GL2 protein involved in malignant behaviours of human glioma has not been elucidated. In this study, we tried to investigate the role of SH3GL2 in glioma cell migration and invasion and explore its underlined molecular mechanism. Firstly, we discovered that the protein level of SH3GL2 was widely decreased in the human glioma patients, especially in high-grade glioma tissues. Then, we determined the role of SH3GL2 in migration and invasion of glioma cells upon SH3GL2 knocking down and overexpressing. It was showed that knocking down of SH3GL2 promoted the migration and invasion of glioma cells, whereas overexpression of SH3GL2 inhibited them. Further study on molecular mechanism disclosed that silencing of SH3GL2 obviously activated the STAT3 (signal transducer and activator of transcription 3) signalling thereby promoting the expression and secretion of MMP2. On the contrary, overexpression of SH3GL2 had opposite effect. Taken together, the above results suggest that SH3GL2 suppresses migration and invasion behaviours of glioma cells through negatively regulating STAT3/MMP2 signalling and that loss of SH3GL2 may intensify the STAT3/MMP2 signalling thereby contributing to the migration and invasion of glioma cells.

The Ubiquitin Ligase COP1 Promotes Glioma Cell Proliferation by Preferentially Downregulating Tumor Suppressor p53.

Human glioma causes substantial morbidity and mortality worldwide. However, the molecular mechanisms underlying glioma progression are still largely unknown. COP1 (constitutively photomorphogenic 1), an E3 ubiquitin ligase, is important in cell survival, development, cell growth, and cancer biology by regulating different substrates. As is well known, both tumor suppressor p53 and oncogenic protein c-JUN could be ubiquitinated and degraded by ubiquitin ligase COP1, which may be the reason that COP1 serves as an oncogene or a tumor suppressor in different cancer types. Up to now, the possible role of COP1 in human glioma is still unclear. In the present study, we found that the expression of COP1 was upregulated in human glioma tissues. The role of COP1 in glioma cell proliferation was investigated using COP1 loss- and gain-of-function. The results showed that downregulation of COP1 by short hairpin RNA (shRNA) inhibited glioma cell proliferation, while overexpression of COP1 significantly promoted it. Furthermore, we demonstrated that COP1 only interacted with and regulated p53, but not c-JUN. Taken together, these results indicate that COP1 may play a role in promoting glioma cell proliferation by interacting with and downregulating tumor suppressor p53 rather than oncogenic protein c-JUN.