In this study, we elucidated anti-cancer activity and potential molecular mechanism of 70% ethanol extracts from Taxilli Ramulus (Taxillus chinensis (DC.) Danser) (TR-E70) against human colorectal cancer cells. Anti-cell proliferative effect of TR-E70 was evaluated by MTT assay. The effect of TR-E70 on the expression of cyclin D1 in the protein and mRNA level was evaluated by Western blot and RT-PCR, respectively. TR-E70 suppressed the proliferation of human colorectal cancer cell lines, HCT116 and SW480. Although TR-E70 decreased cyclin D1 expression in protein and mRNA level, decreased level of cyclin D1 protein by TR-E70 more dramatically occurred than that of cyclin D1 mRNA. Cyclin D1 downregulation by TR-E70 was attenuated in presence of MG132. In addition, TR-E70 phosphorylated threonine-286 (T286) of cyclin D1. TR-E70-mediated cyclin D1 degradation was blocked in presence of LiCl as an inhibitor GSK3β but not PD98059 as an ERK1/2 inhibitor and SB203580 as a p38 inhibitor. Our results suggest that TR-E70 may downregulate cyclin D1 as one of the potential anti-cancer targets through GSK3β-dependent cyclin D1 degradation. From these findings, TR-E70 has potential to be a candidate for the development of chemoprevention or therapeutic agents for human colorectal cancer.

Abstract
 Introduction
 Materials and Methods
  Materials
  Sample preparation
  Cell culture and treatment
  Cell proliferation assay
  SDS-PAGE and Western blot
  Reverse transcriptase-polymerase chain reaction (RT-PCR)
  Statistical analysis
 Results and Discussion
  Effect of TR-E70 on the cell proliferation in humancolorectal cancer cell
  Effect of TR-E70 on cyclin D1 level in human colorectalcancer cells
  Induction of cyclin D1 proteasomal degradation byTR-E70 in human colorectal cancer cells
  Dependency on GSK3β in TR-E70-mediated proteasomaldegradation of cyclin D1 in human colorectal cancer cells
 References

• Gwang Hun Park(Forest Medicinal Resources Research Center, National Institute of Forest Science)
• Hun Min Song(Department of Medicinal Plant Resources, Andong National University)
• Su Bin Park(Department of Medicinal Plant Resources, Andong National University)
• Ji Hye Park(Department of Medicinal Plant Resources, Andong National University)
• Myeong Su Shin(Department of Medicinal Plant Resources, Andong National University)
• Ho-Jun Son(Forest Medicinal Resources Research Center, National Institute of Forest Science)
• Yurry Um(Forest Medicinal Resources Research Center, National Institute of Forest Science)
• Jin Boo Jeong(Department of Medicinal Plant Resources, Andong National University) Corresponding author