Cheng-Chieh Yang | PubMed Health

PubMed2006

Tyrosine phosphorylation controls PCNA function through protein stability.

The proliferating cell nuclear antigen (PCNA) is an essential protein for DNA replication and damage repair. How its function is controlled remains an important question. Here, we show that the chromatin-bound PCNA protein is phosphorylated on Tyr 211, which is required for maintaining its function on chromatin and is dependent on the tyrosine kinase activity of EGF receptor (EGFR) in the nucleus. Phosphorylation on Tyr 211 by EGFR stabilizes chromatin-bound PCNA protein and associated functions. Consistently, increased PCNA Tyr 211 phosphorylation coincides with pronounced cell proliferation, and is better correlated with poor survival of breast cancer patients, as well as nuclear EGFR in tumours, than is the total PCNA level. These results identify a novel nuclear mechanism linking tyrosine kinase receptor function with the regulation of the PCNA sliding clamp.

Cell Nucleus↗

PubMed2005

Akt-mediated phosphorylation of EZH2 suppresses methylation of lysine 27 in histone H3.

Enhancer of Zeste homolog 2 (EZH2) is a methyltransferase that plays an important role in many biological processes through its ability to trimethylate lysine 27 in histone H3. Here, we show that Akt phosphorylates EZH2 at serine 21 and suppresses its methyltransferase activity by impeding EZH2 binding to histone H3, which results in a decrease of lysine 27 trimethylation and derepression of silenced genes. Our results imply that Akt regulates the methylation activity, through phosphorylation of EZH2, which may contribute to oncogenesis.

3T3 Cells↗

PubMed2002

In vitro growth inhibition by indomethacin on human oral squamous cell carcinoma lines synergistically suppressed by all-trans retinoic acid correlating to apoptosis.

BACKGROUND: Indomethacin, an NSAID capable of inhibiting the effect of both cyclooxygenase and lipooxygenase, has been reported to repress the growth of breast cancer, skin cancer and head & neck cancer, etc. Inhibition in the some cell lines of oral squamous cell carcinoma (OSCC) has also been reported. The purpose of this study was primarily to explore the cellular response of human OSCC lines after indomethacin or retinoic acid (RA) treatment and its correlation to apoptosis phenomenon. METHODS: Five human OSCC cell lines--KB, SCC15, SCC25, OEC-M1 and OC2--were used for this in vitro study. By direct cell number counting, the cellular response was observed under incremental indomethacin concentrations of 50 microM, 100 microM, 200 microM and 400 microM, in order to select the most appropriate concentration for further study. Then 200 microM indomethacin and all-trans RA at 1 microM were used in the 2nd experiment to explore the intensity of their inhibitory effects individually and potential synergistic inhibition when exerted together. While in the 3rd part, TdT-mediated-dUTP nick-end labeling (TUNEL) method was used for in situ apoptosis assay to see if the apoptosis rate varied with these two agents. RESULTS: All 5 cell lines constantly showed growth suppression with positive dosage effect of indomethacin. Synergistic inhibition by combined treatment of indomethacin and RA was seen in RA responsive lines of SCC15 and SCC25, whereas other RA-resistant clones showed no synergism of this combined treatment. The in situ detection of apoptosis by TUNEL assay revealed a significantly higher ratio of apoptotic cells in the indomethacin/RA treated SCC15 and SCC25 than in controls. CONCLUSIONS: The study provides the value of further exploration on the mechanism of how indomethacin inhibiting cancer cell growth and how RA-sensitive OSCC cell lines are synergistically suppressed by conjoint treatment of RA and indomethacin. This study also highlights the value to see how the apoptotic pathway responds differently to the indomethacin/RA treatment.

Apoptosis↗