miR-27a regulates cisplatin resistance and metastasis by targeting RKIP in human lung adenocarcinoma cells
© Li et al.; licensee BioMed Central Ltd. 2014
Received: 15 May 2014
Accepted: 12 August 2014
Published: 16 August 2014
MicroRNAs (miRNAs) have been identified as important posttranscriptional regulators involved in various biological and pathological processes of cells, but their association with tumor chemoresistance has not been fully understood.
We detected miR-27a expression in two lung adenocarcinoma cell lines, A549 and A549/CDDP, and then investigated the effects of miR-27a on the metastasis and the chemosensitivity of cancer cells, using both gain- and loss-of-function studies. The correlation between miR-27a level and chemoresistance was further investigated in clinical lung adenocarcinoma specimens.
miR-27a was significantly up-regulated in cisplatin-resistant lung adenocarcinoma A549/CDDP cells compared with parental A549 cells. miR-27a regulates epithelial-mesenchymal transition (EMT) and cisplatin resistance in vitro and modulates response of lung adenocarcinoma cells to cisplatin in vivo. Further studies identified Raf Kinase Inhibitory Protein (RKIP) as a direct and functional target of miR-27a. Small interfering RNA-mediated RKIP knockdown revealed similar effects as that of ectopic miR-27a expression, while overexpression of RKIP attenuated the function of miR-27a in lung adenocarcinoma cells. Increased miR-27a expression was also detected in tumor tissues sampled from lung adenocarcinoma patients treated with cisplatin-based chemotherapy and was proved to be correlated with low expression of RKIP, decreased sensitivity to cisplatin, and poor prognosis.
Our results suggest that up-regulation of miR-27a could suppress RKIP expression and in turn contribute to chemoresistance of lung adenocarcinoma cells to cisplatin.
KeywordsmiR-27a RKIP Lung adenocarcinoma Cisplatin Chemoresistance
Lung cancer is the leading cause of cancer-related death among men and women worldwide, Approximately 70%-80% of lung cancers are non-small cell lung cancer (NSCLC), including squamous cell carcinoma, adenocarcinoma, and large cell carcinoma [1, 2]. In NSCLC, the leading death cause is chemotherapy resistance and metastasis, yet the underlying mechanisms of them remain largely unclear [3–6]. Previous studies in ovarian carcinoma, breast cancer, colorectal cancer and tongue cancer have demonstrated that the drug-resistant cancer cells display features of epithelial-mesenchymal transition (EMT), characterized by the loss of the epithelial marker E-cadherin, an increase in the mesenchymal markers vimentin and N-cadherin, and an increase in the invasion and metastasis behavior [7–11]. Therefore, chemotherapy-induced EMT in tumor cells has been linked to chemotherapeutic resistance and metastasis.
MicroRNAs (miRNAs) are a class of small noncoding RNA molecules that negatively regulate the expression of target genes by either mRNA degradation or translational inhibition. miRNAs are involved in various biological and pathological processes such as differentiation, morphogenesis, and carcinogenesis [12–14]. Accumulating evidence has demonstrated that miRNAs have a key role in drug resistance and EMT. For example, miR-141 is reported to enhance cisplatin resistance through repression of KEAP1 in ovarian cancer cells , miR-106a induces multidrug resistance in gastric cancer by targeting RUNX3 . In contrast, MiR-200b and miR-15b reverse chemotherapy-induced EMT in human tongue cancer cells by targeting BMI1 . The involvement of miRNAs in drug resistance is just beginning to emerge, and more studies are needed to identify other miRNAs, their molecular targets and the processes they affect.
In this study, we observed that miR-27a is significantly upregulated in cisplatin-resistant human lung adenocarcinoma A549/CDDP cells compared with parental A549 cells. Next we explored the roles of miR-27a and its target Raf Kinase Inhibitory Protein (RKIP) in regulating cisplatin resistance and metastasis in lung adenocarcinoma. Finally, we correlated the expression of miR-27a and RKIP with the chemotherapeutic status and prognosis of lung adenocarcinoma patients. Our results show that miR-27a has the potential as key regulatory factors for the chemotherapy resistance and metastasis of lung adenocarcinoma.
Parental A549 cells and cisplatin-resistant A549/CDDP cells differ in morphology, physiology, and miRNA expression
Based on the miRNA microarray data, 13 miRNAs were found to be differentially expressed (>2-fold change) in A549/CDDP cells compared with A549 cells (Additional file 1: Table S1), among which miR-27a was the most up-regulated one (5.6-fold change). The result was validated via real-time quantitative RT-PCR (Figure 1E).
miR-27a promotes EMT and cisplatin resistance in vitro
miR-27a regulates response of lung adenocarcinoma cells to cisplatin in vivo
miR-27a directly targets RKIP
RKIP is involved in miR-27a-induced EMT and cisplatin resistance
High expression of miR-27a in lung adenocarcinoma tissues is associated with decreased RKIP expression, chemotherapeutic resistance, and poor prognosis
In the current study, we demonstrate that upregulation of miR-27a is critical for cisplatin resistance and tumor metastasis of lung adenocarcinoma cells both in vitro and in vivo, and miR-27a induces mesenchymal features and promotes tumor metastasis of chemoresistant lung adenocarcinoma via silencing RKIP. Furthermore, upregulation of miR-27a is correlated with cisplatin resistance and poor prognosis of lung adenocarcinoma patients. These findings provide new insights into the molecular functions of miR-27a as well as the role of RKIP in chemotherapeutic resistance.
MiR-27a is located at chromosome 19 and has been shown to be overexpressed in breast cancer, gastric cancer and cervical cancer [17–19]. In gastric cancer cells, miR-27a promots cell growth and metastasis both in vitro and in vivo[20, 21]. In addition, it could regulate endothelial differentiation of breast cancer stem like cells . Moreover, miR-27a plays an important role in mediating drug resistance by targeting multiple drug-resistance related genes. MiR-27a modulated MDR1/P-glycoprotein expression in human ovarian cancer cells by targeting HIPK2  and Down-regulation of miR-27a might reverse multidrug resistance of esophageal squamous cell carcinoma through regulation of MDR1 and apoptosis . Despite the oncogenic role of miR-27a has been implicated by previous studies, the role of miR-27a in lung cancer chemotherpy and molecular mechanisms are not known. Here we identified RKIP as the functional target, through which miR-27a regulates metastasis and chemoresistance.
Raf Kinase Inhibitory Protein (RKIP), a member of the phosphatidylethanolamine binding protein (PEBP) family, is widely expressed in normal human tissues, highlighting its role in various physiologic processes , but is considered to be a metastasis suppressor in cancer, being its loss or reduced expression associated with malignancy and prognosis in many types of metastatic and aggressive cancers [26–29]. Recently, a study showed that snail, a mediator of the EMT, can inhibit RKIP transcription and negatively correlates with RKIP levels in tumors . Additionally, another study reported that RKIP inhibition in cervical cancer is associated with higher tumor aggressive behavior and resistance to cisplatin therapy . Our finding showed that downregulation of RKIP induces EMT and contributes to cisplatin resistance. We further establish miR-27a-RKIP as another important pathway regulating EMT and chemoresistance of lung adenocarcinoma cells.
Chemoresistance is a major issue of treatment in the majority of human tumors, including lung cancer. Thus, detecting rationale biomarkers to predict chemotherapy sensitivity and screening for targets to overcome resistance are significant for cancer therapy. A specific miRNA can affect simultaneously the expression of proteins involved in multiple cellular pathways, potentially serving as better therapeutic target or biomarker for clinical outcome than single proteins. In fact, several miRNAs, including miR-21, miR-10b and miR-125b, have been used as predictors of chemoresistance in cancers [32–34]. Herein, our observation that increased miR-27a expression is associated with chemotherapy resistance, and poor patient prognosis may provide surrogates to predict the chemotherapeutic sensitivity for lung adenocarcinoma.
In conclusion, we have reported the altered expression of miR-27a in human lung adenocarcinoma cell lines with different sensitivities to cisplatin, and have shown that miR-27a could modulate cisplatin resistance and metastasis in these cells by targeting RKIP. Therefore, targeting miR-27a-RKIP interaction may be a potential strategy for reversing chemoresistance in human lung adenocarcinoma.
Materials and methods
Cell culture and transfection
Human lung adenocarcinoma A549 cells were purchased from the American Type Culture Collection and cultured in RPMI 1640 medium containing 10% fetal bovine serum (FBS) with 100 μg/ml penicillin /streptomycin at 37°C with 5% CO2. The cisplatin-resistant A549 cell line (A549/CDDP) was established and preserved in a 40 μmol/L final concentration of cisplatin in our laboratory.
miR-27a mimics and negative control mimics (NC), miR-27a inhibitors (anti-miR-27a) and negative control inhibitors (anti-NC) and RKIP siRNAs were synthesized by GenePharma Company (Shanghai, China). Transfection was performed with Lipofectamine 2000 (Invitrogen, CA, USA) according to the manufacturer’s protocol. Total RNA and protein were prepared 48 h after transfection and were used for qRT-PCR or Western blot analysis.
A total of 30 lung adenocarcinoma tissues were collected from patients with advanced lung adenocarcinoma who received chemotherapy at Yinzhou People’s Hospital (Ningbo, China) between January 2009 and March 2010. Informed consent was obtained from all subjects and this study was approved by the Clinical Research Ethics Committee of Yinzhou People’s Hospital. Patients met all of the following criteria: primary lung adenocarcinoma; histological diagnosis of lung adenocarcinoma with at least 1 measurable lesion; clinical stage IIIB-IV; first-line chemotherapy either with cisplatin 100 mg/m2 and docetaxel 75 mg/m2 or cisplatin 100 mg/m2 and gemcitabine 1000 mg/m2 administered every 3 weeks for a maximum of 5 cycles. Samples were divided into “sensitive” (complete response or partial response) and “insensitive” (stable disease or progressive disease) groups according to the patient’s responses assessed via medical image analysis and detection of serum tumor markers after 4 or 5 cycles of cisplatin-based chemotherapy.
RNA extraction and qRT–PCR
Total RNA was extracted from the cultured cells and the lung adenocarcinoma tissue specimens using Trizol Reagent (Invitrogen, CA, USA) according to the manufacturer’s protocol. The expression level of mature miR-27a was measured by TaqMan miRNA assays (Applied Biosystems, CA, USA) according to the provided protocol, U6 snRNA levels were used for normalization. RKIP expression was measured by SYBR green qPCR assay (Takara, Dalian, China) and GAPDH was used as an endogenous control.
Western blot analysis
Protein extracts were prepared by a modified RIPA buffer with 0.5% sodium dodecyl sulfate (SDS) in the presence of proteinase inhibitor cocktail (Complete mini, Roche, Indianapolis, IN, USA). Polyacrylamide gel electrophoresis, tank-based transfer to Immobilon Hybond-C membranes (Amersham Biosciences) and immunodetection were performed with standard techniques. Antibodies to RKIP (catalog no. sc-28837), E-cadherin (catalog no. sc-8426), vimentin (catalog no. sc-32322) and β-actin (catalog no. sc-1616) were purchased from Santa Cruz Biotechnology, Inc. (Santa Cruz, CA). Signals were visualized with SuperSignal® West Pico chemoluminescent substrate (Pierce, Rockford, III, USA) by exposure to films.
Cell viability assay
Cells were seeded into 96-well plates (2 × 103 cells/well) directly or 24 hours after transfection and allowed to attach overnight. Freshly prepared cisplatin was then added with different final concentrations. Forty-eight hours later, cell viability was assessed via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay as described previously .
Transwell invasion assay
2 × 105 cells were added into the upper chamber of the insert precoated with Matrigel (ECM gel, Sigma-Aldrich, St. Louis, MO). Cells were plated in medium without serum, and medium containing 10% fetal bovine serum in the lower chamber served as chemoattractant. After several hours of incubation, the cells that did not invade through the pores were carefully wiped out with cotton wool, and the filters were fixed by treatment with 95% ethanol for 30 minutes and stained with 0.2% crystal violet solution for 30 minutes. Invasive cells adhering to the undersurface of the filter were counted (five fields/chamber; 0.24 mm2/field) using an inverted microscope, and each experiment was repeated three times.
Plasmid construction and luciferase reporter assay
Wild-type 3′untranslated region (3′UTR) of RKIP containing predicted miR-27a target sites were amplified by PCR from A549 cell genomic DNA. Primers used: Forward: GAT CTG CAG GGG TTA GCT TGG GGA CCT GAA C; Reverse: GAT CAT ATG AGA GTG ACA TAC TGA TGC CTA C. Mutant 3′UTRs were generated by overlap-extension PCR method. Both wild-type and mutant 3′UTR fragments were subcloned into the pGL3-control vector (Promega, Madison, WI) immediately downstream of the stop codon of the luciferase gene. DNA fragment coding RKIP protein was amplified by PCR from A549 cell cDNA, and cloned into pCMV-Myc expression vector (Clonetech, Mountain View, CA). Primers used: Forward: GCT GAA TTC ATG CCG GTG GAC CTC AGC AAG T; Reverse: CTG CTC GAG CTA CTT CCC AGA CAG CTG CTC G. For luciferase assay, the reporter plasmid was cotransfected with a control Renilla luciferase vector into A549 cells in the presence of either miR-27a or NC. After 48 h, cells were harvested, and the luciferase activity was measured using the Dual-Luciferase Reporter Assay System (Promega, Madison, WI, USA).
Five-week-old female BALB/c nude mice were purchased from the Animal Center of Zhejiang University (Hangzhou, China). For in vivo chemosensitivity and metastasis assays, A549 cells ( infected with either the miR-27a-overexpressing lentivirus or the mock lentivirus) and A549/CDDP cells (infected with either the miR-27a-knockdown lentivirus-mediated antagomir or the antagomir-NC) were subcutaneously inoculated into nude mice (six per group, 1 × 106 cells for each mouse). Tumor growth was examined every other day, and tumor volumes were calculated using the equation V = A × B2/2 (mm3), where A is the largest diameter and B is the perpendicular diameter. When the average tumor size reached ≈ 50 mm3, cisplatin was administered via intraperitoneal injection at a dose of 5 mg/kg, 1 dose every other day, with 3 doses in total. After 2 weeks, all mice were sacrificed. Transplanted tumors were excised, and tumor tissues were used to perform hematoxylin & eosin (H&E) staining. All research involving animal complied with protocols approved by the Zhejiang medical experimental animal care commission.
Statistical analyses were performed using SPSS 16.0 software (SPSS Inc.). All data from 3 independent experiments were expressed as mean ± SD. Differences were assessed by two-tailed Student’s t test. P < 0.05 was considered statistically significant.
This work was supported by Zhejiang Provincial Natural Science Foundation of China (Grant No. LY14H160002), Zhejiang Provincial Medicine and Health Science Research Foundation of China (Grant No. 2014KYB248), Ningbo Municipal Medical Science and Technique Foundation (Grant No. 2013A30) and Yinzhou Science and Technology bureau (2011–111, 2013–107).
- Jemal A, Thun MJ, Ries LA, Howe HL, Weir HK, Center MM, Ward E, Wu XC, Eheman C, Anderson R, Ajani UA, Kohler B, Edwards BK: Annual report to the nation on the status of cancer, 1975–2005, featuring trends in lung cancer, tobacco use, and tobacco control. J Natl Cancer Inst. 2008, 100: 1672-1694.PubMed CentralView ArticlePubMedGoogle Scholar
- Jemal A, Siegel R, Xu J, Ward E: Cancer statistics, 2010. CA Cancer J Clin. 2010, 60: 277-300.View ArticlePubMedGoogle Scholar
- Gupta GP, Massague J: Cancer metastasis: building a framework. Cell. 2006, 127: 679-695.View ArticlePubMedGoogle Scholar
- Goldman B: Multidrug resistance: can new drugs help chemotherapy score against cancer?. J Natl Cancer Inst. 2003, 95: 255-257.View ArticlePubMedGoogle Scholar
- Gao D, Vahdat LT, Wong S, Chang JC, Mittal V: Microenvironmental regulation of epithelial-mesenchymal transitions in cancer. Cancer Res. 2012, 72: 4883-4889.PubMed CentralView ArticlePubMedGoogle Scholar
- Sato M, Shames DS, Gazdar AF, Minna JD: A translational view of the molecular pathogenesis of lung cancer. J Thorac Oncol. 2007, 2: 327-343.View ArticlePubMedGoogle Scholar
- Kajiyama H, Shibata K, Terauchi M, Yamashita M, Ino K, Nawa A, Kikkawa F: Chemoresistance to paclitaxel induces epithelialmesenchymal transition and enhances metastatic potential for epithelial ovarian carcinoma cells. Int J Oncol. 2007, 31: 277-283.PubMedGoogle Scholar
- Hiscox S, Jiang WG, Obermeier K, Taylor K, Morgan L, Burmi R, Barrow D, Nicholson RI: Tamoxifen resistance in MCF7 cells promotes EMT-like behaviour and involves modulation of beta-catenin phosphorylation. Int J Cancer. 2006, 118: 290-301.View ArticlePubMedGoogle Scholar
- Yang AD, Fan F, Camp ER, van Buren G, Liu W, Somcio R, Gray M, Cheng H, Hoff PM, Ellis LM: Chronic oxaliplatin resistance induces epithelial-to-mesenchymal transition in colorectal cancer cell lines. Clin Cancer Res. 2006, 12: 4147-4153.View ArticlePubMedGoogle Scholar
- Sun L, Yao Y, Liu B, Lin L, Yang M, Zhang W, Chen W, Pan C, Liu Q, Song E, Li J: miR-200b and miR-15b regulate chemotherapy-induced epithelial-mesenchymal transition in human tonge cancer cells by targeting BMI1. Oncogene. 2012, 31: 432-445.View ArticlePubMedGoogle Scholar
- Singh A, Settleman J: EMT, cancer stem cells and drug resistance: an emerging axis of evil in the war on cancer. Oncogene. 2010, 29: 4741-4751.PubMed CentralView ArticlePubMedGoogle Scholar
- Gordeladze JO, Djouad F, Brondello JM, Duroux-Richard I, Apparailly F, Jorgensen C: Concerted stimuli regulating osteo-chondral differentiation from stem cells: phenotype acquisition regulated by microRNAs. Acta Pharmacol Sin. 2009, 30: 1369-1384.PubMed CentralView ArticlePubMedGoogle Scholar
- Wu F, Yang Z, Li G: Role of specific microRNAs for endothelial function and angiogenesis. Biochem Biophys Res Commun. 2009, 386: 549-553.PubMed CentralView ArticlePubMedGoogle Scholar
- Skaftnesmo KO, Prestegarden L, Micklem DR, Lorens JB: MicroRNAs in tumorigenesis. Curr Pharm Biotechnol. 2007, 8: 320-325.View ArticlePubMedGoogle Scholar
- Van Jaarsveld MT, Helleman J, Boersma AW, Van Kuijk PF, Van Ljchen WF, Despierre E, Vergote I, Mathijssen RH, Berns EM, Verweij J, Pothof J, Wiemer EA: miR-141 regulates KEAP1 and modulates cisplatin sensitivity in ovarian cancer cells. Oncogene. 2013, 32: 4284-4293.View ArticlePubMedGoogle Scholar
- Zhang Y, Lu Q, Cai X: MicroRNA-106a induces multidrug resistance in gastric cancer by targeting RUNX3. FEBS Lett. 2013, 587: 3069-3075.View ArticlePubMedGoogle Scholar
- Mertens-Talcott SU, Chintharlapalli S, Li X, Safe S: The oncogenic microRNA-27a targets genes that regulate specificity protein transcription factors and the G2-M checkpoint in MDA-MB-231 breast cancer cells. Cancer Res. 2007, 67: 11001-11011.View ArticlePubMedGoogle Scholar
- Huang D, Wang H, Liu R, Li H, Ge S, Bai M, Deng T, Yao G, Ba Y: miR-27a is a biomarker for predicting chemosensitivity and prognosis in metastatic or recurrent gastric cancer. J Cell Biochem. 2014, 15: 549-556.View ArticleGoogle Scholar
- Wang X, Tang S, Le SY, Lu R, Rader JS, Meyers C, Zheng ZM: Aberrant expression of oncogenic and tumor-suppressive microRNAs in cervical cancer is required for cancer cell growth. PLoS One. 2008, 3: e2557-PubMed CentralView ArticlePubMedGoogle Scholar
- Zhao X, Yang L, Hu J: Down-regulation of miR-27a might inhibit proliferation and drug resistance of gastric cancer cells. J Exp Clin Cancer Res. 2011, 30: 55-PubMed CentralView ArticlePubMedGoogle Scholar
- Zhang Z, Liu S, Shi R, Zhao G: miR-27 promotes human gastric cancer cell metastasis by inducing epithelial-to-mesenchymal transition. Cancer Genet. 2011, 204: 486-491.View ArticlePubMedGoogle Scholar
- Tang W, Yu F, Yao H, Cui X, Jiao Y, Lin L, Chen J, Yin D, Song E, Liu Q: miR-27a regulates endothelial differentiation of breast cancer stem like cells. Oncogene. 2014, 33: 2629-2638.View ArticlePubMedGoogle Scholar
- Li Z, Hu S, Wang J, Cai J, Xiao L, Yu L, Wang Z: MiR-27a modulates MDR1/Pglycoprotein expression by targeting HIPK2 in human ovarian cancer cells. Gynecol Oncol. 2010, 119: 125-130.View ArticlePubMedGoogle Scholar
- Zhang H, Li M, Han Y, Hong L, Gong T, Sun L, Zheng X: Down-regulation of miR-27a might reverse multidrug resistance of esophageal squamous cell carcinoma. Dig Dis Sci. 2010, 55: 2545-2551.View ArticlePubMedGoogle Scholar
- Granovsky AE, Rosner MR: Raf kinase inhibitory protein: a signal transduction modulator and metastasis suppressor. Cell Res. 2008, 18: 452-457.View ArticlePubMedGoogle Scholar
- Escara-Wilke J, Yeung K, Keller ET: Raf kinase inhibitor protein (RKIP) in cancer. Cancer Metastasis Rev. 2012, 31: 615-620.View ArticlePubMedGoogle Scholar
- Das SK, Bhutia SK, Sokhi UK, Azab B, Su ZZ, Boukerche H, Anwar T, moen EL, Chatterjee D, Pellecchia M, Sarkar D, Fiser PB: Raf kinase inhibitor RKIP inhibits MDA-9/syntenin-mediated metastasis in melanoma. Cancer Res. 2012, 72: 6217-6226.PubMed CentralView ArticlePubMedGoogle Scholar
- Zhang XM, Gu H, Yan L, Zhang GY: RKIP inhibits the malignant phenotypes of gastric cancer cells. Neoplasma. 2013, 60: 196-202.View ArticlePubMedGoogle Scholar
- Koelzer VH, Karamitopoulou E, Dawson H, Kondi-Pafiti A, Zlobec I, Lugli A: Geographic analysis of RKIP expression and its clinical relevance in colorectal cancer. Br J Cancer. 2013, 108: 2088-2096.PubMed CentralView ArticlePubMedGoogle Scholar
- Beach S, Tang H, Park S, Dhillon AS, Keller ET, Kolch W, Yeung KC: Snail is a repressor of RKIP transcription in metastatic prostate cancer cells. Oncogene. 2008, 27: 2243-2248.PubMed CentralView ArticlePubMedGoogle Scholar
- Martinho O, Pinto F, Granja S, Miranda-Goncalves V, Moreira MA, Ribeiro LF, di Loreto C, Rosner MR, Longatto-Filho A, Reis RM: RKIP inhibition in cervical cancer is associated with higher tumor aggressive behavior and resistance to cisplatin therapy. PLoS One. 2013, 8 (3): e59104-PubMed CentralView ArticlePubMedGoogle Scholar
- Hwang JH, Voortman J, Giovannetti E, Steinberg SM, Leon LG, Kim YT, Funel N, Park JK, Kim MA, Kang GH, Kim SW, Del Chiaro M, Peters GJ, Giaccone G: Identification of microRNA-21as a biomarker for chemoresistance and clinical outcome following adjuvant therapy in resectable pancreatic cancer. PLoS One. 2010, 5: e10630-PubMed CentralView ArticlePubMedGoogle Scholar
- Nishida N, Yamashita S, Mimori K, Sudo T, Tanaka F, Shibata K, Yamamoto H, Ishii H, Doki Y, Mori M: MicroRNA-10b is a prognostic indicator in colorectal cancer and confers resistance to the chemotherapeutic agent 5-fluorouracil in colorectal cancer cells. Ann Surg Oncol. 2012, 19: 3065-3071.View ArticlePubMedGoogle Scholar
- Wang H, Tan G, Dong L, Cheng L, Li K, Wang Z, Luo H: Circulating miR-125b as a marker predicting chemoresistance in breast cancer. PLoS One. 2012, 7: e34210-PubMed CentralView ArticlePubMedGoogle Scholar
- Tsang WP, Kwok TT: The miR-18a* microRNA functions as a potential tumor suppressor by targeting on K-Ras. Carcinogenesis. 2009, 30: 953-959.View ArticlePubMedGoogle Scholar
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