Unknown,Transcriptomics,Genomics,Proteomics

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Identification of Oncogenic Potential of SIRT7 and Its Regulatory MicroRNAs in Liver Tumorigenesis

ABSTRACT: To investigate the specific roles of SIRT7 in the development of HCC, we employed large-scale gene expression analysis to identify the molecular signature that may affect enabling characteristics of cancer cells. Differentially expressed genes were analyzed on the Hep3B cells transfected with SIRT7 shRNAs, and recapitulated molecular signatures that related to hallmarks of cancer. For each of the experimental conditions, total RNA was extracted from three independent sets of the corresponding cell lines using TRIzol Reagent (Invitrogen), followed by clean up on Ambion columns (Illumina Total-Prep RNA Amplification Kit, Ambion). For each experimental condition, an RNA pool was then obtained by mixing equal quantities of total RNA from each of the three independent RNA extractions. Biotin-labelled cRNA targets were synthesized starting from 1.5 µg of total RNA. Double stranded cDNA synthesis was performed with Illumina® TotalPrep RNA Amplification Kit (Ambion), and biotin-UTP-labelled antisense RNA was transcribed in vitro using Ambion’s Kit. All steps of the labelling protocol were performed as suggested by Ambion (http://www.ambion.com/techlib/prot/ fm_IL1791.pdf). The size and the accuracy of quantitation of targets were checked by Experion (Bio-rad Laboratories., Hercules, CA) electrophoresis system, prior to and after cRNA purification. After purification, targets were diluted in hybridization buffer at a concentration of 240 ng/µl, and hybridization was allowed to proceed at 58°C for 20 h. For microarray analysis, the Illumina HumanHT-12 v4 Sentrix Expression BeadChip was used (Illumina, San Diego, CA). Hybridization of labelled cRNA to the BeadChip, washing, and scanning were performed according to the Illumina BeadStation 500× manual. The array signal was developed via 10-min incubation with streptavidin-Cy3. The HumanHT-12 v4 Sentrix Expression BeadChip was washed and subsequently dried via centrifugation for 4 min at a setting of 275 xg. The arrays were scanned on the Illumina BeadArray reader, a confocal-type imaging system with 532 (Cy3) nm laser illumination. Data from each sample was extracted with Genome Studio software (Illumina) using default parameters and then analyzed using GenPlex 3.0.

ORGANISM(S): Homo sapiens

SUBMITTER: JUNGWOO EUN

PROVIDER: E-GEOD-33234 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Background: Cancers are commonly characterised by hypoxia and also by global reductions in the levels of mature microRNAs. We have examined the hypothesis that hypoxia might mediate this reduction through repressive effects on microRNA biogenesis proteins. Methods: Breast cancer cell lines were exposed to hypoxia and manipulations of hypoxia inducible factor (HIF) and HIF hydroxylase activity. The effects of hypoxia on the mRNA and protein levels of enzymes involved in microRNA biogenesis (Dicer, Drosha, TARPB2, DCGR8, XPO5) was determined by RT PCR and immunoblotting. The effect of hypoxia on microRNAs was determined with microarray studies, RT PCR and reporter assays. Results: In breast cancer lines there was significant reduction of Dicer mRNA and protein levels in cells exposed to hypoxia. This effect was independent of HIF but dependent on the HIF hydroxylase PHD2 and was partly mediated by feedback effects via microRNAs. Furthermore, several other proteins with critical roles in microRNA biogenesis (Drosha, TARBP2 and DCGR8) also showed significant and co-ordinated repression under hypoxic conditions. Despite these substantial alterations no, or modest, changes were observed in mature microRNA production Conclusion: These observations provide further and important interfaces between oxygen availability and gene expression and a potential mechanistic explanation for the reduced levels of microRNAs observed in some cancers. They provide further support for the existence of feedback mechanisms in the regulation of the microRNA biogenesis pathway and the relative stability of microRNAs. MCF7 cells were treated with three different conditions. Treatment-1: MCF7 cells were exposed to hypoxia (0.1% O2) for 48 h and harvested for RNA extraction (n=3). Treatment-2: MCF7 cells were exposed to normoxia for 48 h and harvested for RNA extraction (n=3). Treatment-3: Dicer inhibition in MCF7 cells by transient transfection of siRNAs targeting Dicer. Cells were transfected with 20 nM siRNA duplexes (Shanghai GenePharma Co., Ltd, China), using Lipofectamine 2000 reagent (Invitrogen) following the manufacturerM-bM-^@M-^Ys protocol. A second transfection was carried out after 24 h following the same protocol. Cells were harvested 24 h after the second transfection and used for RNA extraction (n=3). RNA integrity was assessed using the Agilent 2100 Bioanalyzer. Affymetrix miRNA 3.1 Array Strip was used for RNA analysis. This array consisted probe sets unique to human mature and pre-miRNA hairpins. A detailed protocol can be found in the miRNA 3.1 Array Strips technical manual (Affymetrix). In summary, 100-300 ng of total RNA was used to synthesise double stranded cDNA using random hexamers. The cDNA was then amplified to produce antisense cRNA, which was then reverse transcribed in a second cycle of cDNA synthesis. The second cycle incorporates dUTP into the cDNA sequence, which allows it to be fragmented using uracil DNA glycosylase and apurinic/apyrimidic endonuclease I. Following biotinylation, these fragments were hybridised overnight to a Affymetrix miRNA 3.1 array. The arrays were then washed, stained using a fluorescently-labelled antibody, and scanned using a high-resolution scanner. Intensity data were analysed using PartekM-BM-. software (Partek Inc.). Data were normalised by quantile normalisation and log 2 transformed. Differential expression was determined by ANOVA and corrected for false discovery.

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Identification of Oncogenic Potential of SIRT7 and Its Regulatory MicroRNAs in Liver Tumorigenesis

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