Both autocrine and paracrine effects of transfected acidic fibroblast growth factor are involved in the estrogen-independent and antiestrogen-resistant growth of MCF-7 breast cancer cells.
To determine the extent to which autocrine effects of acidic fibroblast growth factor (FGF)-1 overexpression contribute to an increased malignant phenotype, FGF-1-transfected MCF-7 cells were retransfected with a FGF receptor (FGFR1) vector encoding a truncated dominant-negative receptor to inhibit autocrine FGF signal transduction. This transfection eliminated FGF signaling within the breast cancer cells without interfering with their ability to produce FGF-1, thereby allowing possible paracrine effects to still be observed in vivo. Truncated FGFR1 overexpression inhibited the acquired ability of FGF-1-overexpressing cells to form colonies in soft agar in estrogen-depleted or antiestrogen-containing medium. However, soft agar colony formation was still stimulated by estrogen treatment in cells expressing up to 6 x 10(5) truncated FGFR1 sites per cell. In vivo, truncated receptor expression severely inhibited the ability of the FGF-1-overexpressing cells to form tumors without estrogen in ovariectomized mice, indicating that the mitogenic effect of FGF-1 on the breast tumor cells was important in the estrogen-independent in vivo growth of these transfectants. However, rapid formation of large tumors was still observed in estrogen-supplemented mice injected with the truncated FGFR1-expressing cells, suggesting that the paracrine effects of FGF production could act in synergy with mitogenic effects mediated by estrogen. Truncated FGFR1-overexpressing cells also continued to form tumors in tamoxifen-treated mice, raising the possibility that the paracrine effects of FGF-1 expression may allow the partial agonist properties of this antiestrogen to be more readily observed. We conclude that autocrine effects of FGF-1 increase the ability of MCF-7 breast cancer cells to grow in vitro and in vivo under estrogen-depleted conditions but that paracrine effects of FGF-1 are also involved in the enhancement of tumor growth in estrogen-supplemented or tamoxifen-treated animals.
Zhang
L
L
Lombardi Cancer Center, Department of Biochemistry and Molecular Biology, Georgetown University Medical Center, Washington, DC 20007, USA.
Kharbanda
S
S
Hanfelt
J
J
Kern
F G
FG
D000818:Animals; D019898:Autocrine Communication / Q000502:physiology*; D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D017931:DNA Primers / Q000737:chemistry; D019008:Drug Resistance, Neoplasm; D004965:Estrogen Antagonists / Q000494:pharmacology*; D004967:Estrogens / Q000494:pharmacology / Q000502:physiology*; D005260:Female; D016220:Fibroblast Growth Factor 1 / Q000235:genetics / Q000378:metabolism*; D005822:Genetic Vectors; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000188:drug therapy / Q000473:pathology; D019899:Paracrine Communication / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D017468:Receptors, Fibroblast Growth Factor / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D017931:DNA Primers; D004965:Estrogen Antagonists; D004967:Estrogens; D012333:RNA, Messenger; D017468:Receptors, Fibroblast Growth Factor; D013629:Tamoxifen; D016220:Fibroblast Growth Factor 1; C496348:FGFR1 protein, human; C496349:Fgfr1 protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1