Heterogeneity of binding sites and bioeffects of raloxifene on the human leukemic cell line FLG 29.1.
The benzothiophene divarative raloxifene is known to mimic estrogen in human bone remodeling. To investigate the "in vitro" properties of raloxifene on osteoclast precursors, the human leukemic cell line FLG 29.1, which differentiates toward the osteoclastic phenotype, was examined for raloxifene binding and for evidence of its bioeffects. Scatchard and Hill analysis of binding data with the tritiated raloxifene demonstrated the presence of two classes of binding sites in both nuclear and cytosol fractions with Kd values of approximately 1 nM and approximately 5 nM, respectively. In addition, analysis of binding data using tritiated 17 beta E2 as ligand at high concentrations (10-40 nM) and either unlabeled 17 beta E2 or raloxifene as competitors gave similar results demonstrating the presence of type II EBS in these cells. Picomolar concentrations of raloxifene significantly (p < 0.05) inhibited cell proliferation. Moreover, the compound at nanomolar concentrations induced a significant dose- and time-dependent increase of progesterone receptor, and activated apoptotic cell death. These findings clearly demonstrate that raloxifene acts as an estrogen agonist in FLG 29.1 cells, acting through the estrogen receptor and, possibly, via multiple cooperative binding component(s).
Fiorelli
G
G
Department of Clinical Physiopathology, University of Florence, School of Medicine, Italy.
Martineti
V
V
Gori
F
F
Benvenuti
S
S
Frediani
U
U
Formigli
L
L
Zecchi
S
S
Brandi
M L
ML
D017209:Apoptosis / Q000187:drug effects; D001665:Binding Sites; D001667:Binding, Competitive; D002455:Cell Division / Q000187:drug effects; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D004229:Dithiothreitol / Q000494:pharmacology; D004587:Electrophoresis, Agar Gel; D004958:Estradiol / Q000378:metabolism; D000091344:Filaggrin Proteins; D006801:Humans; D007948:Leukemia, Monocytic, Acute; D008854:Microscopy, Electron; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010880:Piperidines / Q000378:metabolism* / Q000494:pharmacology*; D011397:Promegestone / Q000378:metabolism; D020849:Raloxifene Hydrochloride; D011960:Receptors, Estrogen / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000378:metabolism; D014407:Tumor Cells, Cultured
C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D010880:Piperidines; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D020849:Raloxifene Hydrochloride; D004958:Estradiol; D011397:Promegestone; D004229:Dithiothreitol