- Open Access
High level of miR-221/222 confers increased cell invasion and poor prognosis in glioma
- Chunzhi Zhang†1, 2, 3,
- Junxia Zhang†2, 3, 4,
- Jianwei Hao†2, 3,
- Zhendong Shi†2, 3,
- Yingyi Wang4,
- Lei Han2,
- Shizhu Yu3,
- Yongping You4,
- Tao Jiang5,
- Jinhuan Wang1,
- Meili Liu6,
- Peiyu Pu2, 3 and
- Chunsheng Kang2, 3, 7Email author
© Zhang et al.; licensee BioMed Central Ltd. 2012
- Received: 23 November 2011
- Accepted: 8 June 2012
- Published: 8 June 2012
MiR-221 and miR-222 (miR-221/222), upregulated in gliomas, can regulate glioma cell cycle progression and apoptosis, respectively. However, the association of miR-221/222 with glioma cell invasion and survival remains unknown.
Invasion capability of miR-221/222 was detected by mutiple analyses, including diffusion tensor imaging (DTI), transwell, wound healing and nude mouse tumor xenograft model assay. Further, the target of miR-221/222 was determined by luciferase reporter, western blot and gene rescue assay. The association of miR-221/222 with outcome was examined in fifty glioma patients.
MiR-221/222 expression was significantly increased in high-grade gliomas compared with low-grade gliomas, and positively correlated with the degree of glioma infiltration. Over-expression of miR-221/222 increased cell invasion, whereas knockdown of miR-221/222 decreased cell invasion via modulating the levels of the target, TIMP3. Introduction of a TIMP3 cDNA lacking 3’ UTR abrogated miR-221/222-induced cell invasion. In addition, knockdown of miR-221/222 increased TIMP3 expression and considerably inhibited tumor growth in a xenograft model. Finally, the increased level of miR-221/222 expression in high-grade gliomas confers poorer overall survival.
The present data indicate that miR-221 and miR-222 directly regulate cell invasion by targeting TIMP3 and act as prognostic factors for glioma patients.
- Cell invasion
Glioblastoma multiforme (GBM) is the most frequent malignant primary brain tumor in adults. The hallmark of GBM is the widespread diffuse invasion of tumor cells into brain tissues. Owing to the aggressive infiltration into the surrounding normal brain, current therapies fail to control GBM [1, 2]. With standard treatment, GBM patients have a median survival of 15.6 months, despite of surgery, radiation therapy and chemotherapy . Thus, there is an urgent need to develop novel therapeutic approaches that focus on controlling the invasion of this malignancy.
MicroRNAs (miRNAs), a recently identified class of endogenous, small (~22 nt), non-protein coding, single-stranded RNA molecules, negatively regulate protein-coding genes by base-pair matching with the 3’ UTRs of mRNAs. MiRNAs are dysregulated in tumors and function as oncogenic miRNAs or as tumor suppressor miRNAs . Growing evidence has indicated important roles for miRNAs in tumor invasion. MiR-21 is an important oncogenic miRNA that promotes cell invasion by regulating multiple genes, including PTEN, RECK and MARCKS in several kinds of cancers, such as glioma, ovarian epithelial carcinoma and prostate cancer [5–7]. In pancreatic cancer cells, miR-146a inhibits the invasive capacity with concomitant down-regulation of EGFR and the NF-kappaB regulatory kinase, interleukin 1 receptor-associated kinase 1 (IRAK-1) . In addition, in glioma cells, miR-7 binds to the EGFR 3’UTR and decreases cell invasiveness by suppressing translation of EGFR . Over-expression of miR-146b inhibits glioma cell invasion by targeting matrix metalloproteinases (MMPs) . However, there is little direct evidence to show the mechanism by which miR-221/222 controls glioma invasion.
In the current study, we demonstrate that high levels of miR-221/222 expression in gliomas confer highly aggressive invasion and poorer overall survival. Furthermore, knockdown of miR-221/222 decreased invasion capability, reduced tumor growth and up-regulated the expression of the target, TIMP3, whereas ectopic expression of miR-221/222 exhibited the opposite effects. These findings indicate that TIMP3 is a critical target of miR-221 and miR-222 and that these two miRNAs could be critical therapeutic targets and survival predictors in glioma.
Tissue samples and clinical data
All patients underwent complete or partial surgical resection at Tianjin Huanhu Hospital and Beijing Tiantan Hospital. Fifty paraffin-embedded glioma specimens with clinical data were collected from January 2006 to June 2006, including 14 grade I-II tumors, 18 grade III tumors and 18 grade IV tumors. Twenty-two frozen glioma specimens, stored in liquid nitrogen, were collected from October 2009 to May 2010, including 9 grade I-II tumors, 6 grade III tumors and 7 grade IV tumors. Paraffin-embedded glioma specimens were used for MiRNA locked nucleic acid (LNA) in situ hybridization and immunohistochemistry, and frozen glioma specimen were used for Real-time PCR. This study was approved by the institutional review boards of the hospitals (the Ethics Committees of Tianjin Medical University, TMUhMEC 2009016) and written informed consent was obtained from all patients. Patients were followed by clinical and laboratory monitoring on a regular basis starting at definitive diagnosis. Disease-specific survival time was defined as the time from definitive diagnosis to disease-specific death.
MR data acquisition
Patients were scanned with a 3.0 T clinical MR imaging scanner (Magnetom Sonata; Siemens, Erlangen, Germany) equipped with the standard head coil according to a standardized hospital brain tumor imaging protocol. The scans used for this study included diffusion tensor imaging (DTI) and axial contrast-enhanced T1-weighted spin-echo scans. In low-grade gliomas, peritumoral edematous regions were selected by T2 and FLAIR. In every patient, we measure three times in peritumoral edematous different regions with the volume of ROI (5 pixels). DTI data were transferred to a workstation (Inspiron 8200; Dell, Round Rock, TX, USA) for analysis. Data processing was performed using DTIStudio (version 2.4; Johns Hopkins University, Baltimore, MD, USA).
Cell culture and transfection
Human U251 and LN229 glioblastoma cells, were obtained from the China Academia Sinica Cell Repository, Shanghai, China. The cells were maintained in Dulbecco’s modified Eagle’s medium (Gibco, Los Angeles, CA, USA) supplemented with 10% fetal bovine serum (Gibco), and were incubated at 37°C in a 5% CO2 atmosphere. Cell transfection was performed using Lipofectamine 2000 (Invitrogen) according to the manufacturer’s instructions.
Plasmids and oligonucleotides
2′-OMe-oligonucleotides were chemically synthesized and purified by high-performance liquid chromatography (GenePharma, Shanghai, China). The sequences are: 2'-OMe -miR-221 (miR-221), 5'-AGCUACAUUGUCUGCUGGGUUUC-3'; 2'-OMe -miR-222 (miR-222), 5'-AGCUACAUCUGGCUACUGGGU-3'; 2'-OMe-As-miR-221 (As-miR-221), 5'-AGCUACAUUGUCUGCUGGGUUUC-3'; 2'-OMe-As-miR-222 (As-miR-222), 5'-AGCUACAUCUGGCUACUGGGU-3'. Then As-miR-221 and/or As-miR-222 (200 pmol) were transfected using Lipofectamine 2000 (Invitrogen). Cells transfected with scrambled 2'-OMe oligonucleotides (scramble) were used as control. Wild-type TIMP3 lacking its 3′ UTR in pCDNA3 was provided by Dr. J.Q. Cheng (Molecular Oncology, H. Lee Moffitt Cancer Center, Tampa, FL, USA).
MiRNA expression was analyzed using a Hairpin-itTM miRNA qPCR Quantitation Kit (GenePharma, Shanghai, China) and a DNA Engine Opticon 2 Two-color Real-time PCR Detection System (Bio-Rad, USA), according to the manufacturer’s instructions. Cycle threshold (CT value) was acquired using the software provided by the manufacturer. U6 is used as the normalization gene in Real-time PCR. The real-time PCR data were analyzed using the ddCT method.
Cells were detached and resuspended in serum-free medium. Cells (1 × 105 cells/well) were then plated into Matrigel coated invasion chambers (Becton Dickinson) and allowed to invade for 24 hours. The remaining cells in the chambers were removed by cotton swabs and the invading cells on the lower surface of the chambers were fixed with 70% ethanol and then stained with hematoxylin. The number of invading cells was calculated by counting three different fields under a phase-contrast microscope.
Wound healing assay
Cells were optimized to ensure a homogeneous and viable cell monolayer prior to wounding. Equal numbers of cells were seeded into six-well culture plates. According to the above methods, cells were transfected with As-miR-221/222 or miR-221/222. When the cell confluence reached about 90% at 48 h post-transfection, an artificial homogenous wound was created on the monolayer with a sterile plastic 100 μL micropipette tip. After wounding, the debris was removed by washing the cells with serum-free medium. Migration of cells into the wound was observed after 36 h. Cells that migrated into the wounded area or cells with extended protrusions from the border of the wound were photographed. A total of three areas were selected from each well at random, and three wells of each group were quantified in each experiment.
Parental and transfected cells were washed with pre-chilled phosphate-buffered saline (PBS) three times. The cells were then solubilized in 1% Nonidet P-40 lysis buffer (20 mM Tris, pH 8.0, 137 mM NaCl, 1% Nonidet P-40, 10% glycerol, 1 mM CaCl2, 1 mM MgCl2, 1 mM phenylmethylsulfonyl fluoride, 1 mM sodium fluoride, 1 mM sodium orthovanadate, and a protease inhibitor mixture). Total protein lysates were separated by SDS-PAGE. The separated proteins were transferred to PVDF membranes. Blots were incubated with MMP2, MMP9 and TIMP3 (Santa Cruz) primary antibodies, followed by incubation with HRP-conjugated secondary antibody. The specific protein was detected using a super signal protein detection kit (Pierce). After washing with stripping buffer, PVDF membranes were reprobed with antibody against β-actin.
Twenty-four hours post-transfection, cell culture media were collected and quantified for MMP2 and MMP9 levels using an MMP2 and MMP9-specific ELISA kit (R&D Systems, Minneapolis, MN, USA), according to the manufacturer’s protocol.
MiRNA locked nucleic acid (LNA) in situ hybridization and immunohistochemistry
Using an antisense locked nucleic acid (LNA/DNA) modified oligonucleotide probe, in situ hybridization was performed with fluorescence in situ hybridization kit (CYBRDI, China). MiR-221 and miR-222-LNA oligonucleotides with digoxigenin modification contained LNAs at five locations (underlined): 5′-GAAAC CCA GCA GACA ATGTAG CT-3′ (miR-221); 5′-GAGAC CCA GTAG CCAG ATGT AGCT-3′ (miR-222). LNA-miR-221 uses DIG modification and LNA-miR-222 uses BIO modification in 3' distal end. Sections were deparaffinized and deproteinated, and then prehybridized for 2 h in hybridization liquid in a humidified chamber (50% formamide, 5 x SSC). The probes were added to the sections and incubated overnight at 40°C in a water bath. After washing 3 times, anti-digoxigenin-rhodamine solution was added and incubated for 2 h at room temperature in the dark. Nuclei were counterstained with a DAPI karyotyping kit (Genmed, USA). After washing 3 times, sections were sealed and detected under a fluorescence microscope. In immunohistochemistry assay, sections were incubated with primary antibody (1:100 dilution) overnight at 4°C, then incubated with a biotinylated secondary antibody (1:200 dilution) at room temperature for 1 h, followed by incubation with ABC-peroxidase reagent for an additional 1 h. After washing with Tris-buffer, the sections were stained with DAB (30 mg 3,3 diaminobenzidine dissolved in 100 ml Tris-buffer containing 0.03% H2O2) for 5 min, rinsed in water and counterstained with hematoxylin. The antibodies used in this study were to MMP2, MMP9 and TIMP3. The quantity and intensity scores were calculated such that a final score of 0–1 indicated negative expression (−), 2–3 indicated weak expression (+), 4–5 indicated moderate expression (++) and 6 indicated strong expression (+++).
Luciferase reporter assay
The pGL3-WT-TIMP3-3’UTR-Luc reporter was created by the ligation of TIMP3 3’ UTR PCR products into the XbaI site of the pGL3 control vector (Promega, USA). For the reporter assay, cells were cultured in 96-well plates and transfected with pGL3-TIMP3-3’UTR-Luc, and As-miR-221 and/or As-miR-221. Following 48 h incubation, luciferase activity was measured using a dual-luciferase reporter system (Promega).
Nude mouse tumor xenograft model and treatment
U251 glioma cells were subcutaneously injected into 5-week-old female nude mice (Cancer Institute of the Chinese Academy of Medical Science). When the tumor volume reached 50 mm3, the mice were randomly divided into four groups (eight mice per group). Each group was treated with 200 pmol scramble oligo, As-miR-221/222 in 10 μl Lipofectamine, miR-221/222 or PBS through local injection of the xenograft tumor at multiple sites (3–4 injected sites). The treatment was performed once every 3 days for 15 days. On day 28, tumors were harvested, fixed embedded in paraffin. The tumor volume was measured with a caliper twice a week, using the formula: volume = length × width2/2.
Descriptive statistics, including mean and ± SE, along with independent sample t-tests, and the Pearson correlation were used to determine significant differences. Kaplan-Meier analysis was employed to assess the survival rate of patients relative to expression levels of miR-221 and miR-222. P < 0.05 was considered a significant difference.
Correlation of miR-221/222 expression levels and glioma invasion
Critical role of miR-221/222 in glioma cell invasion
TIMP3 is a direct target of miR-221 and miR-222
Expression of TIMP3 overrides miR-221/222-induced invasion
As-miR-221/222 inhibits glioblastoma xenograft growth and induces TIMP3 up-regulation
Inverse correlation of expression of miR-221/222 and TIMP3 in glioma tissues
Significant prognostic value of miR-221/222 in high-grade glioma
Our present data and previous studies have shown that miR-221/222 affects the behavior of glioma cells including invasion, proliferation, apoptosis and radioresistance, by regulating multiple targets, including TIMP3, p27, PUMA, and PTEN [13–15]. Thus, we reasoned that miR-221/222 should have a critical prognostic value for glioma patients (Figure 6B). We analyzed the overall survival of patients and found significant differences between the low positive group and the high positive group in high-grade gliomas. Kaplan-Meier survival curve analysis showed that a highly statistically significant correlation was observed between the overall survival and the expression levels of miR-221 (P = 0.011) and miR-222 (P = 0.020) in high-grade gliomas (Figure 6C). These data indicate that the miR-221/222 high positive cases have a markedly worse outcome.
Glioma cell invasion along white matter tracts is believed to be one of the major reasons for the resistance to treatment. A quantitative analysis of glioma cell invasion would be of value for clinical applications and experimental studies. However, in clinical studies, measurements of tumor cell invasion remain controversial. DTI is a new MRI technique that can reveal abnormalities and destruction of white matter fibers and has been used to measure the degree of white matter damage in brain regions, thus providing the potential for quantitative analysis of tumor invasion . Notably, we found that miR-221 and miR-222 are associated with glioma cell invasion by integrating expression and DTI data. In high-grade glioma, DTI indicated a decrease and deflection of the fibers surrounding the glioma that was associated with high levels of miR-221/222. To our knowledge, this is the first report combining analysis of a glioma invasion maker with DTI data.
MiR-221 and miR-222 share the same seed sequence, which are short, evolutionarily conserved regions through which miRNAs bind their target sites in mRNA 3' UTRs, indicating an important role in coordinated regulation and function. Several genes have been found to be common targets of these two miRNAs, such as p27, Bmf and PTEN [13, 17, 18]. Our recent data have shown that miR-221/222 inhibit cell apoptosis in human glioma cells by targeting the proapoptotic gene, PUMA. Here, we demonstrated that miR-221/222 play an important role in the regulation of glioma invasion by directly targeting TIMP3, an inhibitor of MMPs. Among the MMPs, attention in human gliomas has focused on gelatinases (MMP2 and MMP9) . A major mechanism for controlling the activity of MMPs in the pericellular space is mediated by the action of tissue inhibitors of metalloproteinases (TIMPs), which bind to active MMPs . There are four metalloproteinase family members: TIMP1, TIMP2, TIMP3 and TIMP4. TIMP3 is unique within the TIMP family as it remains closely associated to the extracellular matrix after being secreted by the cell . In our study, down-regulation of TIMP3 correlated with increasing malignancy in human gliomas. TIMP3 was also inversely correlated with miR-221/222 expression. Ectopic expression of TIMP3 inhibited U251 and LN229 glioma cell invasion through the inhibition of MMP2 and MMP9 expression and activity. Furthermore, expression of TIMP3 could largely override miR-221/222-mediated invasion. These results demonstrate that TIMP3 is a core target of miR-221/222 in glioma cell invasion.
The significance of miRNAs in prognostic determination has been shown in a variety of human cancers, such as lung cancer, pancreatic cancer, neuroblastomas and colon cancers [22–25]. However, few studies addressing the correlation between miRNA expression and glioma patient survival have been reported. Zhi et al. screened the expression profile of 200 miRNAs in a sample set consisting of 84 astrocytoma samples and 20 normal adjacent tissue samples and found that low level of miR-181b or miR-106a, or high level of miR-21, was significantly associated with poor patient survival . Another study reported that the cumulative 5 year survival rate of glioma patients was 51.54% in the low miR-182-expression group, whereas it was only 7.23% in the high miR-182-expression group. Moreover, multivariate Cox regression analysis indicated that miR-182 expression was an independent prognostic indicator for the survival of glioma patients . In this study, our data suggest that a high miR-221/222 expression level is a valuable marker for pathological diagnosis and prognosis prediction in high-grade glioma; high miR-221/222 expression levels were significantly associated with poor survival in high-grade glioma patients as determined by Kaplan-Meier analysis. However, recent data showed that miR-221 and miR-222 were downregulated in GBM and neither prognostic nor predictive associations were found for miR-221or miR-222 . Thus, these controversial data needs to be further investigation.
In summary, our data demonstrate that miR-221/222 regulate glioma cell invasion by directly targeting TIMP3. We also provide direct evidence that high levels of miR-221/222 expression are significantly associated with poorer overall survival. To conclude, our data suggest that miR-221/222 could be intrinsic regulators of progression in glioma cells and could be used as potential targets and predictors of survival in this devastating disease.
Chunzhi Zhang, Junxia Zhang, Jianwei Hao and Zhendong Shi contributed equally to this work.
This work is supported by the National Basic Research Project of China (2009CB918903 and 2010CB529406), National High Technology Research and Development Program 863 (2012AA02A508), the China National Natural Scientific Foundation (30901772), and the Natural Science Foundation of Tianjin Municipal Science and Technology Commission (10SYSYJC28800).
- Tate MC, Aghi MK: Biology of angiogenesis and invasion in glioma. Neurotherapeutics. 2009, 6: 447-457. 10.1016/j.nurt.2009.04.001.View ArticlePubMedGoogle Scholar
- Chi A, Norden AD, Wen PY: Inhibition of angiogenesis and invasion in malignant gliomas. Expert Rev Anticancer Ther. 2007, 7: 1537-1560. 10.1586/14737184.108.40.2067.View ArticlePubMedGoogle Scholar
- Stupp R, Hegi ME, Mason WP, van den Bent MJ, Taphoorn MJ, Janzer RC, Ludwin SK, Allgeier A, Fisher B, Belanger K: Effects of radiotherapy with concomitant and adjuvant temozolomide versus radiotherapy alone on survival in glioblastoma in a randomised phase III study: 5-year analysis of the EORTC-NCIC trial. Lancet Oncol. 2009, 10: 459-466. 10.1016/S1470-2045(09)70025-7.View ArticlePubMedGoogle Scholar
- Calin GA, Croce CM: MicroRNA signatures in human cancers. Nat Rev Cancer. 2006, 6: 857-866. 10.1038/nrc1997.View ArticlePubMedGoogle Scholar
- Lou Y, Yang X, Wang F, Cui Z, Huang Y: MicroRNA-21 promotes the cell proliferation, invasion and migration abilities in ovarian epithelial carcinomas through inhibiting the expression of PTEN protein. Int J Mol Med. 2010, 26: 819-827.View ArticlePubMedGoogle Scholar
- Gabriely G, Wurdinger T, Kesari S, Esau CC, Burchard J, Linsley PS, Krichevsky AM: MicroRNA 21 promotes glioma invasion by targeting matrix metalloproteinase regulators. Mol Cell Biol. 2008, 28: 5369-5380. 10.1128/MCB.00479-08.View ArticlePubMedPubMed CentralGoogle Scholar
- Li T, Li D, Sha J, Sun P, Huang Y: MicroRNA-21 directly targets MARCKS and promotes apoptosis resistance and invasion in prostate cancer cells. Biochem Biophys Res Commun. 2009, 383: 280-285. 10.1016/j.bbrc.2009.03.077.View ArticlePubMedGoogle Scholar
- Li Y, Vandenboom TG, Wang Z, Kong D, Ali S, Philip PA, Sarkar FH: miR-146a suppresses invasion of pancreatic cancer cells. Cancer Res. 2010, 70: 1486-1495. 10.1158/0008-5472.CAN-09-2792.View ArticlePubMedPubMed CentralGoogle Scholar
- Kefas B, Godlewski J, Comeau L, Li Y, Abounader R, Hawkinson M, Lee J, Fine H, Chiocca EA, Lawler S, Purow B: microRNA-7 inhibits the epidermal growth factor receptor and the Akt pathway and is down-regulated in glioblastoma. Cancer Res. 2008, 68: 3566-3572. 10.1158/0008-5472.CAN-07-6639.View ArticlePubMedGoogle Scholar
- Xia H, Qi Y, Ng SS, Chen X, Li D, Chen S, Ge R, Jiang S, Li G, Chen Y: microRNA-146b inhibits glioma cell migration and invasion by targeting MMPs. Brain Res. 2009, 1269: 158-165.View ArticlePubMedGoogle Scholar
- Deng Z, Yan Y, Zhong D, Yang G, Tang W, Lu F, Xie B, Liu B: Quantitative analysis of glioma cell invasion by diffusion tensor imaging. J Clin Neurosci. 2010, 17: 1530-1536. 10.1016/j.jocn.2010.03.060.View ArticlePubMedGoogle Scholar
- Garofalo M, Di Leva G, Romano G, Nuovo G, Suh SS, Ngankeu A, Taccioli C, Pichiorri F, Alder H, Secchiero P: miR-221&222 regulate TRAIL resistance and enhance tumorigenicity through PTEN and TIMP3 downregulation. Cancer Cell. 2009, 16: 498-509. 10.1016/j.ccr.2009.10.014.View ArticlePubMedPubMed CentralGoogle Scholar
- Zhang C, Kang C, You Y, Pu P, Yang W, Zhao P, Wang G, Zhang A, Jia Z, Han L, Jiang H: Co-suppression of miR-221/222 cluster suppresses human glioma cell growth by targeting p27kip1 in vitro and in vivo. Int J Oncol. 2009, 34: 1653-1660.View ArticlePubMedGoogle Scholar
- Zhang CZ, Zhang JX, Zhang AL, Shi ZD, Han L, Jia ZF, Yang WD, Wang GX, Jiang T, You YP: MiR-221 and miR-222 target PUMA to induce cell survival in glioblastoma. Mol Cancer. 2010, 9: 229-10.1186/1476-4598-9-229.View ArticlePubMedPubMed CentralGoogle Scholar
- Zhang C, Kang C, Wang P, Cao Y, Lv Z, Yu S, Wang G, Zhang A, Jia Z, Han L: MicroRNA-221 and −222 regulate radiation sensitivity by targeting the PTEN pathway. Int J Radiat Oncol Biol Phys. 2011, 80: 240-248. 10.1016/j.ijrobp.2010.12.049.View ArticlePubMedGoogle Scholar
- Cruz Junior LC, Sorensen AG: Diffusion tensor magnetic resonance imaging of brain tumors. Neurosurg Clin N Am. 2005, 16: 115-134. 10.1016/j.nec.2004.07.007.View ArticlePubMedGoogle Scholar
- Gramantieri L, Fornari F, Ferracin M, Veronese A, Sabbioni S, Calin GA, Grazi GL, Croce CM, Bolondi L, Negrini M: MicroRNA-221 targets Bmf in hepatocellular carcinoma and correlates with tumor multifocality. Clin Cancer Res. 2009, 15: 5073-5081. 10.1158/1078-0432.CCR-09-0092.View ArticlePubMedPubMed CentralGoogle Scholar
- Chun-Zhi Z, Lei H, An-Ling Z, Yan-Chao F, Xiao Y, Guang-Xiu W, Zhi-Fan J, Pei-Yu P, Qing-Yu Z, Chun-Sheng K: MicroRNA-221 and microRNA-222 regulate gastric carcinoma cell proliferation and radioresistance by targeting PTEN. BMC Cancer. 2010, 10: 367-10.1186/1471-2407-10-367.View ArticlePubMedPubMed CentralGoogle Scholar
- Levicar N, Nuttall RK, Lah TT: Proteases in brain tumour progression. Acta Neurochir (Wien). 2003, 145: 825-838. 10.1007/s00701-003-0097-z.View ArticleGoogle Scholar
- Jiang Y, Goldberg ID, Shi YE: Complex roles of tissue inhibitors of metalloproteinases in cancer. Oncogene. 2002, 21: 2245-2252. 10.1038/sj.onc.1205291.View ArticlePubMedGoogle Scholar
- Lamfers ML, Gianni D, Tung CH, Idema S, Schagen FH, Carette JE, Quax PH, Van Beusechem VW, Vandertop WP, Dirven CM: Tissue inhibitor of metalloproteinase-3 expression from an oncolytic adenovirus inhibits matrix metalloproteinase activity in vivo without affecting antitumor efficacy in malignant glioma. Cancer Res. 2005, 65: 9398-9405. 10.1158/0008-5472.CAN-04-4264.View ArticlePubMedGoogle Scholar
- Yanaihara N, Caplen N, Bowman E, Seike M, Kumamoto K, Yi M, Stephens RM, Okamoto A, Yokota J, Tanaka T: Unique microRNA molecular profiles in lung cancer diagnosis and prognosis. Cancer Cell. 2006, 9: 189-198. 10.1016/j.ccr.2006.01.025.View ArticlePubMedGoogle Scholar
- Bloomston M, Frankel WL, Petrocca F, Volinia S, Alder H, Hagan JP, Liu CG, Bhatt D, Taccioli C, Croce CM: MicroRNA expression patterns to differentiate pancreatic adenocarcinoma from normal pancreas and chronic pancreatitis. JAMA. 2007, 297: 1901-1908. 10.1001/jama.297.17.1901.View ArticlePubMedGoogle Scholar
- Chen Y, Stallings RL: Differential patterns of microRNA expression in neuroblastoma are correlated with prognosis, differentiation, and apoptosis. Cancer Res. 2007, 67: 976-983. 10.1158/0008-5472.CAN-06-3667.View ArticlePubMedGoogle Scholar
- Schetter AJ, Leung SY, Sohn JJ, Zanetti KA, Bowman ED, Yanaihara N, Yuen ST, Chan TL, Kwong DL, Au GK: MicroRNA expression profiles associated with prognosis and therapeutic outcome in colon adenocarcinoma. JAMA. 2008, 299: 425-436. 10.1001/jama.299.4.425.PubMedPubMed CentralGoogle Scholar
- Zhi F, Chen X, Wang S, Xia X, Shi Y, Guan W, Shao N, Qu H, Yang C, Zhang Y: The use of hsa-miR-21, hsa-miR-181b and hsa-miR-106a as prognostic indicators of astrocytoma. Eur J Cancer. 2010, 46: 1640-1649. 10.1016/j.ejca.2010.02.003.View ArticlePubMedGoogle Scholar
- Jiang L, Mao P, Song L, Wu J, Huang J, Lin C, Yuan J, Qu L, Cheng SY, Li J: miR-182 as a prognostic marker for glioma progression and patient survival. Am J Pathol. 2010, 177: 29-38. 10.2353/ajpath.2010.090812.View ArticlePubMedPubMed CentralGoogle Scholar
- Lakomy R, Sana J, Hankeova S, Fadrus P, Kren L, Lzicarova E, Svoboda M, Dolezelova H, Smrcka M, Vyzula R: MiR-195, miR-196b, miR-181c, miR-21 expression levels and O-6-methylguanine-DNA methyltransferase methylation status are associated with clinical outcome in glioblastoma patients. Cancer Sci. 2011, 102: 2186-2190. 10.1111/j.1349-7006.2011.02092.x.View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.