Insulin-like growth factor-I promotes multidrug resistance in MCLM colon cancer cells.
Insulin-like growth factor-I (IGF-I) is known as a potent mitogen for a variety of cell types, including colon cancer cell lines. The objective of this study was to determine the effect of IGF-I on cell death induced by cytotoxic agents actinomycin D (Act-D), lovastatin (LOV), and doxorubicin (DOX) in the MCLM mouse colon cancer cell line, and the mechanisms involved. Subconfluent monolayer MCLM cells were treated with IGF-I (25 ng/ml) for 12 h in serum-free media. Various concentrations of cytotoxic agents then were added to the cells that were incubated continually at 37 degrees C for 24 h. Cell survival was determined with the MTT (3-[4-5-dimenthylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay, which assesses mitochondrial function in living cells. The mRNA expression for multidrug resistance gene-1 (mdr-1), c-H-ras, and manganese superoxide dismutase (MnSOD) in cells treated with IGF-I was examined by Northern blot or RNase protection assays. The levels of p-glycoprotein, a drug efflux pump encoded by the mdr-1 gene, were assessed by Western immunoblotting. Results demonstrated that 1) IGF-I significantly inhibited the cell death and apoptosis of MCLM cells treated with Act-D, LOV, or DOX; 2) IGF-I increased mRNA expression for mdr-1, c-H-ras, and MnSOD; 3) the p-glycoproteins in cells treated with IGF-I or stably transfected with c-H-ras were elevated when compared with control. These results suggest that IGF-I protects MCLM cells against death induced by cytotoxic agents; this acquired drug resistance may be mediated by multiple mechanisms, including promoting expression of mdr-1, c-H-ras, and MnSOD; whereas, the p-glycoprotein level stimulated by IGF-I may result partly from the increase of c-H-ras in the cells.
Guo
Y S
YS
Department of Surgery, The University of Texas Medical Branch, Galveston 77555-0527, USA.
Jin
G F
GF
Houston
C W
CW
Thompson
J C
JC
Townsend
C M
CM
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects*; D003110:Colonic Neoplasms / Q000378:metabolism*; D003609:Dactinomycin / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects; D019450:Genes, MDR / Q000187:drug effects; D011905:Genes, ras / Q000187:drug effects; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008148:Lovastatin / Q000494:pharmacology; D051379:Mice; D008928:Mitochondria / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D013482:Superoxide Dismutase / Q000235:genetics; D013778:Tetrazolium Salts / Q000378:metabolism; D013844:Thiazoles / Q000378:metabolism; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D012333:RNA, Messenger; D013778:Tetrazolium Salts; D013844:Thiazoles; D003609:Dactinomycin; D007334:Insulin-Like Growth Factor I; D004317:Doxorubicin; D008148:Lovastatin; D013482:Superoxide Dismutase; C022616:thiazolyl blue