miR-152-3p Modulates hepatic carcinogenesis by targeting cyclin-dependent kinase 8.

BACKGROUND: Cyclin-dependent kinase 8 (CDK8) as a Mediator complex-associated transcriptional regulator has been shown to play important role in the initiation and progression of various cancers. The present study aimed to explore miR-152-3p-modulated post-transcriptional repression of CDK8 in hepatic carcinogenesis. METHODS: Eighty-nine pairs of hepatocellular carcinoma (HCC) and adjacent non-tumor tissues were collected for molecular biological analysis. Cell viability and apoptosis assays were detected using CCK8 and Annexin V-fluorescein isothiocyanate/propidium iodide (Annexinv-FITC) double staining, respectively. Bioinformatics algorithms and luciferase reporter assay were performed to validate CDK8 as a direct target of miR-152-3p. Gene and protein expression levels were monitored using RT-qPCR, western blotting or immunohistochemical (IHC) staining. RESULTS: CDK8 expression levels were up-regulated and miR-152-3p was down-regulated in HCC tissues. The correlation analysis had documented a significant negative correlation between miR-152-3p and CDK8 in the HCC tissues. Both CDK8 and miR-152-3p could serve as the independent prognostic factors for predicting the OS and DFS in HCC patients. Bioinformatics and experimental measurement revealed that CDK8 was a direct target of miR-152-3p. After co-transfection with the miR-152-3p mimics and the CDK8 overexpressed plasmids, the anti-proliferative and pro-apoptotic roles of miR-152-3p were restricted by CDK8. CONCLUSION: The present results obtained forcefully proved that miR-152-3p exhibited an antineoplastic activity via targeting CDK8 and might be served as a potential therapeutic target for the treatment of HCC.

mTORC1 Down-Regulates Cyclin-Dependent Kinase 8 (CDK8) and Cyclin C (CycC).

In non-alcoholic fatty liver disease (NAFLD) and insulin resistance, hepatic de novo lipogenesis is often elevated, but the underlying mechanisms remain poorly understood. Recently, we show that CDK8 functions to suppress de novo lipogenesis. Here, we identify the mammalian target of rapamycin complex 1 (mTORC1) as a critical regulator of CDK8 and its activating partner CycC. Using pharmacologic and genetic approaches, we show that increased mTORC1 activation causes the reduction of the CDK8-CycC complex in vitro and in mouse liver in vivo. In addition, mTORC1 is more active in three mouse models of NAFLD, correlated with the lower abundance of the CDK8-CycC complex. Consistent with the inhibitory role of CDK8 on de novo lipogenesis, nuclear SREBP-1c proteins and lipogenic enzymes are accumulated in NAFLD models. Thus, our results suggest that mTORC1 activation in NAFLD and insulin resistance results in down-regulation of the CDK8-CycC complex and elevation of lipogenic protein expression.

siRNA-mediated silencing of CDK8 inhibits proliferation and growth in breast cancer cells.

UNLABELLED: CDK8 is a cyclin-dependent kinase (CDK) member of the mediator complex that couples transcriptional regulators to the basal transcriptional machinery, and it has been investigated for possible tumor promoting functions. However, it is unclear whether CDK8 is involved in breast tumor cells growth. The aim of this study was to determine whether the suppression of CDK8 by small interfering RNA (siRNA) inhibits the growth of human breast cancer cell. METHODS: CDK8-siRNA transfection was used to silencing the CDK8 gene in established breast cancer cell line, MDA-MB-231 and MCF-7, successful transfection being confirmed by Real-time PCR and could be shown by Western Blotting. CDK8 deletion caused significant decline in cell proliferation was observed in breast cancer cell lines as investigated by MTS assay, the number and size of the colonies formed were also significantly reduced in the absence of CDK8. Furthermore, transwell test were conducted to explore the migration of breast cancer cells. Moreover CDK8 gene knockdown arrested cell cycle. RESULTS: CDK8 mRNA expression was reduced after transfection with CDK8-siRNA, and protein expression had a similar trend. Transfection of CDK8-siRNA suppressed breast cancer cells proliferation and migration; meanwhile the cells were arrested at G0/G1 phase. CONCLUSIONS: CDK8 plays an essential role in breast cancer progression, which might inhibit the proliferation and migration in breast cancer cells.

Effects of cyclin-dependent kinase 8 specific siRNA on the proliferation and apoptosis of colon cancer cells.

BACKGROUND: To investigate the expression of cyclin-dependent kinase 8 (CDK8) and ß-catenin in colon cancer and evaluate the role of CDK8 in the proliferation, apoptosis and cell cycle progression of colon cancer cells, especially in HCT116 cell line. METHODS: Colon cancer cell line HCT116 was transfected with small interfering RNA (siRNA) targeting on CDK8. After CDK8-siRNA transfection, mRNA and protein expression levels of CDK8 and ß-catenin were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot assay in HCT116 cells. Cell proliferation was measured by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide Methylthiazolyl tetrazolium (MTT) assay, and cell cycle distribution and apoptosis were analyzed by flow cytometry analysis (FACS). CDK8 and ß-catenin protein levels were also examined by real-time PCR and immunohistochemistry (IHC) in colon cancer tissues and adjacent normal tissues. RESULTS: After CDK8 specific siRNA transfection, mRNA and protein expression levels of CDK8 and ß-catenin in HCT116 cells were noticeably decreased (P < 0.05). CDK8 specific siRNA transfection inhibited HCT116 cells' proliferation and facilitated their apoptosis significantly (P < 0.05). In addition, the proportion of HCT116 cells in the G0/G1 phase was remarkably increased after CDK8-siRNA transfection (P < 0.05). The expression levels of CDK8 and ß-catenin in adjacent normal tissues were lower than in tumor tissues (P < 0.05). Moreover, the expression of CDK8 was correlated with the expression of ß-catenin in both tumor and adjacent normal tissues (P < 0.05). CONCLUSIONS: CDK8 and ß-catenin were expressed in colon cancer at a high frequency. CDK8 specific siRNA transfection down-regulated the expression of CDK8 in colon cancer cells, which was also associated with a decrease in the expression of ß-catenin Moreover, CDK8 specific siRNA inhibited the proliferation of colon cancer cells, promoted their apoptosis and arrested these cells in the G0/G1 phase. Interference of CDK8 might be an effective strategy through ß-catenin regulation of colon cancer.

Expression of the Argonaute protein PiwiL2 and piRNAs in adult mouse mesenchymal stem cells.

Piwi (P-element-induced wimpy testis) first discovered in Drosophila is a member of the Argonaute family of micro-RNA binding proteins with essential roles in germ-cell development. The murine homologue of PiwiL2, also known as Mili is selectively expressed in the testes, and mice bearing targeted mutations of the PiwiL2 gene are male-sterile. PiwiL2 proteins are thought to protect the germ line genome by suppressing retrotransposons, stabilizing heterochromatin structure, and regulating target genes during meiosis and mitosis. Here, we report that PiwiL2 and associated piRNAs (piRs) may play similar roles in adult mouse mesenchymal stem cells. We found that PiwiL2 is expressed in the cytoplasm of metaphase mesenchymal stem cells from the bone marrow of adult and aged mice. Knockdown of PiwiL2 with a specific siRNA enhanced cell proliferation, significantly increased the number of cells in G1/S and G2/M cell cycle phases and was associated with increased expression of cell cycle genes CCND1, CDK8, microtubule regulation genes, and decreased expression of tumor suppressors Cables 1, LATS, and Cxxc4. The results suggest broader roles for Piwi in genome surveillance beyond the germ line and a possible role in regulating the cell cycle of mesenchymal stem cells.