[Synergistic effect of rapamycin (RPM) and PD98059 on cell cycle and mTOR signal transduction in human colorectal cancer cells].
OBJECTIVE
To investigate the synergistic effect of rapamycin (RPM) and PD98059 on human colorectal cancer cells and its potential mechanisms.


METHODS
Three human colorectal cancer cell lines SW480, HCT116 and HT29 were treated with RPM 10 nmol/L, PD98059 (10 micromol/L, 20 micromol/L, 40 micromol/L, 50 micromol/L), or RPM plus PD98059, respectively, and the sensitivity was analyzed by MTT assay. The cell cycle progression was evaluated by flow cytometry. Western blotting analysis was performed to examine the total and phosphorylated levels of mammalian target of rapamycin (mTOR) and its downstream translational signaling intermediates, 70 kDa ribosomal protein S6 kinase (p70s6k) and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1).


RESULTS
Both RPM and PD98059 could inhibit viability of the three cell lines. The anti-proliferative effect of PD98059 exhibited a time/dose dependent manner and was strengthen by RPM. All the treatment with RPM, PD98059, and RPM + PD98059 induced arrest of cell cycle, although the arrest was confined at different cell cycle phases. In addition to their effect on proliferation and cell cycle, both inhibitors also reduced phosphorylation levels of mTOR, p70s6k, and 4E-BP1, as well as total 4E-BP1 levels in SW480 and HCT116 cells. That effect was reinforced when cells were treated with RPM plus PD98059 simultaneously, whereas total protein levels of mTOR and p70s6k remained unchanged.


CONCLUSIONS
RPM and PD98059 inhibit proliferation of colorectal cancer cells synergistically, and induce cell cycle arrest. The modulation of mammalian target of rapamycin signaling pathway is involved in its potential mechanisms.
Zhang
Yan-Jie
YJ
Shanghai Institute of Digestive Diseases, Shanghai Jiaotong University, School of Medicine, Renji Hospital, Shanghai 200001, China.
Fang
Jing-Yuan
JY
Sun
Dan-Feng
DF
Zhao
Shu-Liang
SL
Shen
Guan-Feng
GF
Zheng
Qing
Q
Zhu
Hong-Yin
HY
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins; D049109:Cell Proliferation; D015179:Colorectal Neoplasms / Q000378:metabolism / Q000473:pathology*; D004357:Drug Synergism; D005419:Flavonoids / Q000494:pharmacology*; D045325:HCT116 Cells; D019073:HT29 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases
D048868:Adaptor Proteins, Signal Transducing; D000903:Antibiotics, Antineoplastic; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D005419:Flavonoids; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; C546842:MTOR protein, human; D017346:Protein Serine-Threonine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus