Acquisition of hormone-independent growth in MCF-7 cells is accompanied by increased expression of estrogen-regulated genes but without detectable DNA amplifications.
A hormone-independent but hormone-responsive subpopulation (MCF7/MIII) of the hormone-dependent MCF-7 human breast cancer cell line (R. Clarke et al., Proc. Natl. Acad. Sci. USA 86: 3649-3653, 1989) was further passaged in ovariectomized nude mice and re-established in vitro as the continuous cell line MCF7/LCC1. The lag time to the appearance of proliferating tumors in ovariectomized animals is significantly reduced in MCF7/LCC1 when compared with MCF7/MIII cells. In gel denaturation/renaturation analysis of tumor, genomic DNA does not reveal significant differences in the pattern of detectable DNA amplifications between parent MCF-7 cells and MCF7/LCC1 cells. In the absence of estrogen, steady-state levels of phosphoinositol turnover are similar in both MCF-7 and MCF7/LCC1 cells, but turnover is increased by estrogen only in MCF-7 cells. MCF7/MIII and MCF7/LCC1, but not MCF-7 cells, express a high baseline level of the estrogen-regulated pS2 mRNA. The baseline level of expression of progesterone receptor protein, but not mRNA, is higher in MCF7/LCC1 when compared with either MCF-7 or early passage MCF7/MIII cells. However, while the estrogen receptor is also an estrogen-regulated gene, MCF7/MIII and MCF7/LCC1 cells retain estrogen receptor levels equivalent to the parental MCF-7 cells. These data indicate that progression to hormone independence can occur without major gene amplifications or a high constitutive induction of phosphoinositide metabolism. Thus, DNA amplifications may be acquired during the early initiation and/or promotional events of carcinogenesis. Significantly, acquisition of a hormone-independent but responsive phenotype in human breast cancer is associated with perturbations in the expression of specific estrogen-regulated genes.
Vincent T. Lombardi Cancer Research Center, Georgetown University Medical School, Washington, DC 20007.
N
N
Brünner
V
V
Boulay
A
A
Fojo
C E
CE
Freter
M E
ME
Lippman
R
R
Clarke
D000818:Animals; D001943:Breast Neoplasms / Q000473:pathology*; D002455:Cell Division; D004965:Estrogen Antagonists / Q000494:pharmacology; D004967:Estrogens / Q000502:physiology; D005784:Gene Amplification; D015972:Gene Expression Regulation, Neoplastic; D007621:Karyotyping; D051379:Mice; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000235:genetics; D009368:Neoplasm Transplantation; D010716:Phosphatidylinositols / Q000378:metabolism; D011506:Proteins; D012334:RNA, Neoplasm / Q000235:genetics; D011960:Receptors, Estrogen / Q000235:genetics; D011980:Receptors, Progesterone / Q000235:genetics; D015398:Signal Transduction; D000071163:Trefoil Factor-1; D014407:Tumor Cells, Cultured / Q000166:cytology; D025521:Tumor Suppressor Proteins
D004965:Estrogen Antagonists; D004967:Estrogens; D009363:Neoplasm Proteins; D010716:Phosphatidylinositols; D011506:Proteins; D012334:RNA, Neoplasm; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C051838:TFF1 protein, human; D000071163:Trefoil Factor-1; D025521:Tumor Suppressor Proteins