title: Molecular changes associated with the acquisition of oestrogen hypersensitivity in MCF-7 breast cancer cells on long-term oestrogen deprivation.
abstract: The growth dependence of many breast cancers on oestrogen has been exploited therapeutically by oestrogen deprivation, but almost all patients eventually develop resistance largely by unknown mechanisms. Wild-type (WT) MCF-7 cells were cultured in oestrogen-deficient medium for 90 weeks in order to establish a long-term oestrogen-deprived MCF-7 (LTED) which eventually became independent of exogenous oestrogen for growth. After 15 weeks of quiescence (LTED-Q), basal growth rate increased in parallel with increasing oestrogen sensitivity. While 10(-9)M oestradiol (E2) maximally stimulated WT growth, the hypersensitive LTED (LTED-H) were maximally growth stimulated by 10(-13)M E2. By week 50, hypersensitivity was apparently lost and the cells became oestrogen independent (LTED-I), although the pure antioestrogen ICI182780 still inhibited cell growth and reversed the inhibitory effect of 10(-9)M E2 at 10(-12) to 10(-7)M. Tamoxifen (10(-7) to 10(-6)M) had a partial agonist effect on WT, but had no stimulatory effect on LTED. Whilst LTED cells have a low progesterone receptor (PgR) expression in all phases, oestrogen receptor (ER) a expression was, on average, elevated five- and seven-fold in LTED-H and LTED-I, respectively, and serine118 was phosphorylated. ERbeta expression was up-regulated and the levels of insulin receptor substrate 1 (IRS-1) remained low throughout all phases. The levels of RIP140mRNA appeared to decrease to approximately 50% of the WT message in LTED-Q and remained constant into the hypersensitive phase. No significant changes were observed in the expression of SUG-1, TIF-1 and SMRT in LTED. The overall changes in nuclear receptor interacting proteins do not appear to be involved in the hypersensitivity. Thus, the resistance of these human breast cancer cells to oestrogen-deprivation appears to be due to acquired hypersensitivity which may be explained in part by increased levels of and phosphorylated ERalpha.
mesh_terms: D000074183:ATPases Associated with Diverse Cellular Activities; D048868:Adaptor Proteins, Signal Transducing; D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D004967:Estrogens / Q000172:deficiency / Q000494:pharmacology*; D005260:Female; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056985:Nuclear Receptor Co-Repressor 2; D000078723:Nuclear Receptor Interacting Protein 1; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex; D015800:Protozoan Proteins; D012333:RNA, Messenger / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology; D014157:Transcription Factors; D014407:Tumor Cells, Cultured / Q000187:drug effects* / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D004965:Estrogen Antagonists; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D004967:Estrogens; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; C539130:NCOR2 protein, human; D009687:Nuclear Proteins; D056985:Nuclear Receptor Co-Repressor 2; D000078723:Nuclear Receptor Interacting Protein 1; C092282:PSMC5 protein, human; D010750:Phosphoproteins; D015800:Protozoan Proteins; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D012097:Repressor Proteins; C106843:SUG1 protein, mammalian; C443134:TIF1 protein, Tetrahymena thermophila; D014157:Transcription Factors; D013629:Tamoxifen; D000077267:Fulvestrant; D004958:Estradiol; D046988:Proteasome Endopeptidase Complex; D000074183:ATPases Associated with Diverse Cellular Activities