Effects of cyclin-dependent kinase 8 specific siRNA on the proliferation and apoptosis of colon cancer cells
JOURNAL OF EXPERIMENTAL & CLINICAL CANCER RESEARCH
Authors: He, Song-Bing; Yuan, Yin; Wang, Lei; Yu, Min-Jing; Zhu, Yi-Bei; Zhu, Xing-Guo
Background: To investigate the expression of cyclin-dependent kinase 8 (CDK8) and beta-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 beta-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 beta-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 beta-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 beta-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 beta-catenin in both tumor and adjacent normal tissues (P < 0.05). Conclusions: CDK8 and beta-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 beta-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 beta-catenin regulation of colon cancer.
The transcriptional coactivator MAML1 regulates p300 autoacetylation and HAT activity
NUCLEIC ACIDS RESEARCH
Authors: Hansson, Magnus L.; Popko-Scibor, Anita E.; Ribeiro, Mariana Saint Just; Dancy, Beverley M.; Lindberg, Mikael J.; Cole, Philip A.; Wallberg, Annika E.
MAML1 is a transcriptional coregulator originally identified as a Notch coactivator. MAML1 is also reported to interact with other coregulator proteins, such as CDK8 and p300, to modulate the activity of Notch. We, and others, previously showed that MAML1 recruits p300 to Notch-regulated genes through direct interactions with the DNACSLNotch complex and p300. MAML1 interacts with the C/H3 domain of p300, and the p300MAML1 complex specifically acetylates lysines of histone H3 and H4 tails in chromatin in vitro. In this report, we show that MAML1 potentiates p300 autoacetylation and p300 transcriptional activation. MAML1 directly enhances p300 HAT activity, and this coincides with the translocation of MAML1, p300 and acetylated histones to nuclear bodies.