Ha-ras overexpression mediated cell apoptosis in the presence of 5-fluorouracil.
By using a mouse NIH3T3 derivate designed 7-4 harboring the inducible Ha-ras oncogene, we demonstrated the close relationship between Ha-ras expression level and sensitization of 5-flurouracil (5-FU)-treated cells. Further studies revealed that the cells susceptible to 5-FU treatment died of apoptosis, which was demonstrated by caspase-3 activation, loss of mitochondria membrane potential (MMP), and DNA fragmentation. The 7-4 cells coexpressing dominant negative Ras (Ras(Asn17)), dominant negative Raf-1 (Raf-1(CB4)), Bcl-2, or active form of phosphatidylinositol 3-kinase (PI3K) became resistant to 5-FU, and apoptosis was prevented. In contrast, the cells coexpressing dominant negative Rac 1 (Rac1(Asn17)) or dominant negative Rho A (RhoA(Asn19)) showed no change of sensitivity to 5-FU. These results indicate that Ras, Bcl-2, as well as Raf-1 and PI3K pathways play pivotal roles in 5-FU-induced apoptosis under Ha-ras-overexpressed condition. Aberrant levels of cyclin E and p21(Cip/WAF-1) expression as well as Cdc 2 phosphorylation at Tyrosine 15 suggest that perturbation of G1/S and G2/M transitions in cell cycle might be responsible for 5-FU triggered apoptosis. Sensitization of Ha-ras-related cells to 5-FU was also demonstrated in human bladder cancer cells. Through understanding the mechanism of 5-FU induced apoptosis in tumor cells, a new direction toward the treatment of Ha-ras oncogene-related cancers with 5-FU at more optimal dosages is possible and combinational therapy with other drugs that suppress PI3K and Bcl-2 activities can also be considered.
Tseng
Ya-Shih
YS
Department of Microbiology and Immunology, National Cheng Kung University, College of Medicine, Tainan, Taiwan.
Tzeng
Ching-Cherng
CC
Chiu
Allen Wen-Hsiang
AW
Lin
Chia-Hsiang
CH
Won
Shen-Jeu
SJ
Wu
I-Chien
IC
Liu
Hsiao-Sheng
HS
D016475:3T3 Cells; D000818:Animals; D000963:Antimetabolites / Q000378:metabolism*; D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology; D004789:Enzyme Activation; D005472:Fluorouracil / Q000378:metabolism*; D011905:Genes, ras; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000963:Antimetabolites; D019253:Proto-Oncogene Proteins c-bcl-2; D019908:Proto-Oncogene Proteins c-raf; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D005472:Fluorouracil