Changes in the expression and binding properties of the estrogen receptor in MCF-7 breast cancer cells during growth inhibition by tamoxifen and cisplatin.
Most mammary carcinomas contain estrogen receptors (ER), which are an important factor in diagnosis and prognosis, and in deciding on the type of therapy. ER-positive tumors are most commonly treated with the antiestrogen tamoxifen or with a combination of chemotherapeutic drugs. An important aspect for further treatment and anticipating possible side effects is the fate of the ER during the course of therapy. To study the effect of drug-induced growth inhibition on ER expression and binding properties. human breast cancer MCF-7 cells were treated with tamoxifen and cisplatin. and also estradiol (E2) for 5 days. Following this incubation, intact cells were incubated with [3H]E2 to determine the dissociation constant (KD) and maximal number of binding sites (Bmax) of the ER. The amount of ER protein per cell was quantified using anti-ER antibodies. For analysis of ER mRNA, total cellular RNA was subjected to Northern blotting. The 5-day treatment with E2 reduced Bmax and the amount of ER protein by about 70%, while the cellular level of ER mRNA was reduced by 40%. Treatment with E2 did not affect the subsequent growth inhibitory response to tamoxifen or cisplatin. In contrast, tamoxifen reduced the capacity for E2 binding; it caused about a 30-fold increase in the KD value. At the same time, Bmax and ER protein content were increased (about 3.5- and 2-fold, respectively), but the cellular level of ER mRNA was again reduced by 40%. The growth of tamoxifen-treated cells remained sensitive to subsequent treatment with estradiol, tamoxifen or cisplatin. Treatment of MCF-7 cells with cisplatin likewise reduced E2 binding due to a 20-fold increase in KD value. In this case, both Bmax and the amount of ER protein were decreased when calculated per milligram of protein, but were increased on a cellular basis due to an increase in cell size. The ER mRNA content was not altered in cisplatin-treated cells. Growth of these cells also remained sensitive to tamoxifen and cisplatin. In conclusion, drug-induced changes in ER expression and binding capacity do not necessarily indicate a loss of sensitivity of breast cancer cells to a subsequent chemotherapeutic treatment.
Otto
A M
AM
Institute of Pharmacy, University of Regensburg, Germany. angela.otto@ei.tum.de
Schubert
S
S
Netzker
R
R
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001665:Binding Sites / Q000502:physiology; D001943:Breast Neoplasms / Q000473:pathology*; D002945:Cisplatin / Q000494:pharmacology*; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D012333:RNA, Messenger / Q000032:analysis; D011960:Receptors, Estrogen / Q000096:biosynthesis* / Q000502:physiology*; D013629:Tamoxifen / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D000972:Antineoplastic Agents, Phytogenic; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D013629:Tamoxifen; D004958:Estradiol; D002945:Cisplatin