Laurey Comeau

microRNA-7 Inhibits the Epidermal Growth Factor Receptor and the Akt Pathway and Is Down-regulated in Glioblastoma

microRNAs are noncoding RNAs inhibiting expression of numerous target genes, and a few have been shown to act as oncogenes or tumor suppressors. We show that microRNA-7 (miR-7) is a potential tumor suppressor in glioblastoma targeting critical cancer pathways. miR-7 potently suppressed epidermal growth factor receptor expression, and furthermore it independently inhibited the Akt pathway via targeting upstream regulators. miR-7 expression was down-regulated in glioblastoma versus surrounding brain, with a mechanism involving impaired processing. Importantly, transfection with miR-7 decreased viability and invasiveness of primary glioblastoma lines. This study establishes miR-7 as a regulator of major cancer pathways and suggests that it has therapeutic potential for glioblastoma.

The neuronal microRNA miR-326 acts in a feedback loop with Notch and has therapeutic potential against brain tumors

Little is known of microRNA interactions with cellular pathways. Few reports have associated microRNAs with the Notch pathway, which plays key roles in nervous system development and in brain tumors. We previously implicated the Notch pathway in gliomas, the most common and aggressive brain tumors. While investigating Notch mediators, we noted microRNA-326 was upregulated following Notch-1 knockdown. This neuronally expressed microRNA was not only suppressed by Notch but also inhibited Notch proteins and activity, indicating a feedback loop. MicroRNA-326 was downregulated in gliomas via decreased expression of its host gene. Transfection of microRNA-326 into both established and stem cell-like glioma lines was cytotoxic, and rescue was obtained with Notch restoration. Furthermore, miR-326 transfection reduced glioma cell tumorigenicity in vivo. Additionally, we found microRNA-326 partially mediated the toxic effects of Notch knockdown. This work demonstrates a microRNA-326/Notch axis, shedding light on the biology of Notch and suggesting microRNA-326 delivery as a therapy.

Pyruvate kinase M2 is a target of the tumor-suppressive microRNA-326 and regulates the survival of glioma cells

Emerging studies have identified microRNAs (miRNAs) as possible therapeutic tools for the treatment of glioma, the most aggressive brain tumor. Their important targets in this tumor are not well understood. We recently found that the Notch pathway is a target of miRNA-326. Ectopic expression of miRNA-326 in glioma and glioma stem cells induced their apoptosis and reduced their metabolic activity. Computational target gene prediction revealed pyruvate kinase type M2 (PKM2) as another target of miRNA-326. PKM2 has recently been shown to play a key role in cancer cell metabolism. To investigate whether it might be a functionally important target of miR-326, we used RNA interference to knockdown PKM2 expression in glioma cells. Transfection of the established glioma and glioma stem cells with PKM2 siRNA reduced their growth, cellular invasion, metabolic activity, ATP and glutathione levels, and activated AMP-activated protein kinase. The cytotoxic effects exhibited by PKM2 knockdown in glioma and glioma stem cells were not observed in transformed human astrocytes. Western blot analysis of human glioblastoma specimens showed high levels of PKM2 protein, but none was observed in normal brain samples. Strikingly, cells with high levels of PKM2 expressed lower levels of miR-326, suggestive of endogenous regulation of PKM2 by miR-326. Our data suggest PKM2 inhibition as a therapy for glioblastoma, with the potential for minimal toxicity to the brain.

Structural and functional evidence for the role of the TLR2 DD loop in TLR1/TLR2 heterodimerization and signaling.

The Toll/Interleukin-1 receptor (TIR) domain of the Toll-like receptors (TLRs) plays an important role in innate host defense signaling. The TIR-TIR platform formed by the dimerization of two TLRs promotes homotypic protein-protein interactions with additional cytoplasmic adapter molecules to form an active signaling complex resulting in the expression of pro- and anti-inflammatory cytokine genes. To generate a better understanding of the functional domains of TLR2 we performed a random mutagenesis analysis of the human TLR2 TIR domain and screened for TLR2/1 signaling-deficient mutants. Based upon the random mutagenesis results, we performed an alanine scanning mutagenesis of the TLR2 DD loop and part of the αD region. This resulted in the identification of four residues crucial for TLR2/1 signaling: Arg-748, Phe-749, Leu-752, and Arg-753. Computer-assisted energy minimization and docking studies indicated three regions of interaction in the TLR2/1 TIR-docked heterodimer. In Region I, residues Arg-748 and Phe-749 in TLR2 DD loop were involved in close contacts with Gly-676 in the TLR1 BB loop. Because this model suggested that steric hindrance would significantly alter the binding interactions between DD loop of TLR2 and BB loop of TLR1, Gly-676 in TLR1 was rationally mutated to Ala and Leu. As expected, in vitro functional studies involving TLR1 G676A and TLR1 G676L resulted in reduced PAM3CSK4 mediated NF-κB activation lending support to the computerized predictions. Additionally, mutation of an amino acid residue (TLR2 Asp-730) in Region II also resulted in decreased activity in agreement with our model, providing new insights into the structure-function relationship of TLR2/1 TIR domains.

Notch-1 regulates transcription of the epidermal growth factor receptor through p53

The Notch pathway plays a key role in the development and is increasingly recognized for its importance in cancer. We demonstrated previously the overexpression of Notch-1 and its ligands in gliomas and showed that their knockdown inhibits glioma cell proliferation and survival. To elucidate the mechanisms downstream of Notch-1 in glioma cells, we performed microarray profiling of glioma cells transfected with Notch-1 small interfering RNA. Notable among downregulated transcripts was the epidermal growth factor receptor (EGFR), known to be overexpressed or amplified in gliomas and prominent in other cancers as well. Further studies confirmed that Notch-1 inhibition decreased EGFR messenger RNA (mRNA) and EGFR protein in glioma and other cell lines. Transfection with Notch-1 increased EGFR expression. Additionally, we found a significant correlation in levels of EGFR and Notch-1 mRNA in primary high-grade human gliomas. Subsequent experiments showed that p53, an activator of the EGFR promoter, is regulated by Notch-1. Experiments with p53-positive and -null cell lines confirmed that p53 partially mediates the effects of Notch-1 on EGFR expression. These results show for the first time that Notch-1 upregulates EGFR expression and also demonstrate Notch-1 regulation of p53 in gliomas. These observations have significant implications for understanding the mechanisms of Notch in cancer and development.

Role of endogenous IL-10 in LPS-induced STAT3 activation and IL-1 receptor antagonist gene expression

The regulation of secretory interleukin (IL)‐1 receptor antagonist (sIL‐1Ra) in response to IL‐10 is unique. In contrast to most cytokines, the lipopolysaccharide (LPS)‐induced expression of the sIL‐1Ra gene is enhanced by concomitant treatment with IL‐10. Cotreatment of RAW 264.7 cells with IL‐10 + LPS resulted in at least a twofold increase in sIL‐1Ra promoter activity and mRNA expression compared with LPS alone; IL‐10 alone had no effect on promoter activity or mRNA expression. Examination of sIL‐1Ra mRNA expression in bone marrow‐derived macrophages (BMDM) resulted in identical results. Transfection of RAW 264.7 cells with the sIL‐1Ra/luc reporter and a dominant‐negative signal transducer and activator of transcripton (STAT)3 (Y705A) expression plasmid inhibited the enhanced response induced by exogenous IL‐10 in the presence of LPS. The presence of a functional STAT3‐bininding site within the proximal sIL‐1Ra promoter was demonstrated. As IL‐10 is produced by LPS‐stimulated macrophages, a role for endogenously produced IL‐10 in the response of the sIL‐1Ra gene to LPS was suggested. This was confirmed in IL‐10‐deficient BMDM, which when compared with normal BMDM, had significantly decreased LPS‐induced sIL‐1Ra mRNA levels that could be restored by exogenously provided IL‐10, which induced a fivefold increase of LPS‐induced IL‐1Ra mRNA in cells from IL‐10−/− BMDM. Western blot analysis of phosphorylated STAT3 from wild‐type and IL‐10−/− BMDM and IL‐10 neutralization experiments demonstrated a role for endogenously produced IL‐10 in the LPS‐induced STAT3 activity. Together, these results demonstrate that endogenously produced IL‐10 plays a significant role in LPS‐induced sIL‐1Ra gene expression via the activation of STAT3.

Usp18 Regulates Epidermal Growth Factor (EGF) Receptor Expression and Cancer Cell Survival via MicroRNA-7

Epidermal growth factor receptor (EGFR) is involved in development and progression of many human cancers. We have previously demonstrated that the ubiquitin-specific peptidase Usp18 (Ubp43) is a potent regulator of EGFR protein expression. Here we report that the 3′-untranslated region (3′-UTR) of the EGFR message modulates RNA translation following cell treatment with Usp18 siRNA, suggesting microRNA as a possible mediator. Given earlier evidence of EGFR regulation by the microRNA miR-7, we assessed whether miR-7 mediates Usp18 siRNA effects. We found that Usp18 depletion elevates miR-7 levels in several cancer cell lines because of a transcriptional activation and/or mRNA stabilization of miR-7 host genes and that miR-7 acts downstream of Usp18 to regulate EGFR mRNA translation via the 3′-UTR. Also, depletion of Usp18 led to a decrease in protein levels of other known oncogenic targets of miR-7, reduced cell proliferation and soft agar colony formation, and increased apoptosis. Notably, all of these phenotypes were reversed by a specific inhibitor of miR-7. Thus, our findings support a model in which Usp18 inhibition promotes up-regulation of miR-7, which in turn inhibits EGFR expression and the tumorigenic activity of cancer cells.

Abstract 3316: An alpha-secretase inhibitor decreases glioma stem cell growth by inhibiting the Notch pathway and LMW Cyclin E

The Notch pathway is deregulated in glioblastoma. Previous work suggests the inhibition of this pathway will have therapeutic benefits. The only inhibitors of Notch available block the gamma-secretase enzymatic complex necessary for processing Notch into the active form. However, Notch is also cleaved by alpha-secretase outside the plasma membrane, with the sheddases ADAM10 and 17. INCB3619 is a potent inhibitor of both ADAM10 and 17, and has been shown to inhibit growth of MCF-7 breast tumor cells when used with lapatinib. In this work, INCB3619 was used to inhibit endogenous Notch cleavage and downstream CBF-1 reporter activity in 0308 and 0822 human glioma stem cell lines. A microarray analysis of INCB3619 vs. DMSO treatment of 0308 cells identified many downregulated Notch pathway targets, but also identified new targets of INCB3619, such as CHI3L1/YKL40, an important prognostic indicator of many inflammatory diseases. Treatment of 0308 and 0822 glioma stem lines with INCB3619 inhibited their growth in culture due to a cell cycle arrest in G1 and a decrease in S phase cells. Growth inhibition by INCB3619 can be rescued with transfection of the active form of two Notch family members, NICD1 and 2. The growth inhibition of INCB3619 treated glioma stem cells is also stems from a shift in Cyclin E expression from a hyperactive low-molecular-weight form to the usual high-molecular-weight form. Also, INCB3619 induces higher expression of both p53 and p21, which can inhibit Cyclin E. Unlike with INCB3619, The treatment of glioma stem cells with DAPT, a well-known and potent gamma secretase inhibitor that cleaves Notch downstream of ADAM10 and 17, does not have a noticeable effect on Cyclin E processing or p21/p53 expression. INCB3619 therefore decreases glioma stem cell growth partly through a mechanism of Notch inhibition and also through inhibition of production of the hyperactive low-molecular-weight form of Cyclin E. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3316. doi:10.1158/1538-7445.AM2011-3316