Inducible overexpression of cyclin D1 in breast cancer cells reverses the growth-inhibitory effects of antiestrogens.
The development of endocrine resistance in previously sensitive, estrogen receptor-positive breast cancers is a major limitation in the treatment of breast cancer. Because antiestrogens have a cell cycle-specific action on breast cancer cells and influence the expression and activity of several cell cycle-regulatory molecules, the development of aberrant cell cycle control mechanisms is a potential mechanism by which cells might develop resistance to antiestrogens. We postulated that overexpression of cyclin D1, which is a common feature of breast cancer, may confer antiestrogen resistance. We addressed this question in vitro by testing the ability of ectopic cyclin D1 overexpression to overcome the growth-inhibitory effects of tamoxifen and the pure steroidal antiestrogens, ICI 164384 and ICI 182780, in T-47D and MCF-7 human breast cancer cells. In cells stably transfected with a human cyclin D1 cDNA under the control of a metal-inducible metallothionein promoter, cyclin D1 expression was increased 2-4-fold following treatment with zinc. Despite the continued presence of antiestrogen, cyclin D1 induction resulted in the formation of active cyclin D1/Cdk4 complexes, concurrent hyperphosphorylation of the retinoblastoma protein, and entry into S phase of cells previously arrested in G1. Elevated cyclin D1 protein levels were first detected 3 h after treatment with zinc, and the proportion of cells in S phase began to increase 6 h later. The S-phase fraction increased 2-3-fold from 13 to 17% in cells treated with antiestrogen alone, to a peak of 33-38% 15 h after zinc treatment. Both the cyclin D1 protein level and the proportion of cells in S phase increased with increasing concentrations of zinc. We conclude that the ectopic overexpression of cyclin D1 reverses the growth-inhibitory effect of antiestrogens in estrogen receptor-positive breast cancer cells, providing a potential mechanism for clinical antiestrogen resistance.
Wilcken
N R
NR
Cancer Research Program, Garvan Institute of Medical Research, St. Vincent's Hospital, Darlinghurst, New South Wales 2010, Australia.
Prall
O W
OW
Musgrove
E A
EA
Sutherland
R L
RL
D000970:Antineoplastic Agents / Q000633:toxicity*; D001943:Breast Neoplasms; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D019938:Cyclin D1 / Q000235:genetics* / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004958:Estradiol / Q000031:analogs & derivatives* / Q000633:toxicity; D004965:Estrogen Antagonists / Q000633:toxicity*; D005260:Female; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D053284:Polyunsaturated Alkamides; D011518:Proto-Oncogene Proteins; D016196:S Phase; D013629:Tamoxifen / Q000633:toxicity*; D014407:Tumor Cells, Cultured; D019287:Zinc Sulfate / Q000494:pharmacology
D000970:Antineoplastic Agents; D004965:Estrogen Antagonists; D053284:Polyunsaturated Alkamides; D011518:Proto-Oncogene Proteins; D013629:Tamoxifen; D019938:Cyclin D1; D000077267:Fulvestrant; D004958:Estradiol; D019287:Zinc Sulfate; C051781:ICI 164384; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases