Activation of the MAPK pathway enhances sensitivity of MCF-7 breast cancer cells to the mitogenic effect of estradiol.
Long-term estrogen deprivation causes human breast cancer cells to develop hypersensitivity to the mitogenic effect of estradiol (E(2)). Our prior studies demonstrated an association between enhanced MAPK activation and hypersensitivity in long-term estrogen-deprived (LTED) MCF-7 cells. Herein, we report that MAPK is constitutively activated in LTED cells and not dependent on serum factors. Additionally, activated MAPK levels fall upon reversion of the hypersensitivity. Importantly, we now provide direct evidence that enhanced MAPK causes hypersensitivity to E(2). We activated MAPK in wild-type MCF-7 cells using TGFalpha, and demonstrated a 2-3 log enhancement of sensitivity to E(2). PD98059 abrogated the TGFalpha-induced effect, indicating that MAPK activation is responsible for E(2) hypersensitivity. To determine the level at which MAPK activation enhanced E(2) sensitivity, we examined the dose-response effects of E(2) on several transcriptional readouts, including ERE-reporter activity and the levels of progesterone receptor and pS2. Wild-type and LTED cells exhibited nearly identical responses to E(2), suggesting that mechanisms downstream of estrogen receptor-mediated transcription are involved in inducing hypersensitivity. In support of this possibility, LTED and TGFalpha-treated wild-type cells were hypersensitive to the effects of E(2) on the key cell cycle regulator, E2F1.
Yue
Wei
W
Department of Internal Medicine, University of Virginia, Charlottesville, Virginia 22908, USA. wy9c@virginia.edu
Wang
Ji-Ping
JP
Conaway
Mark
M
Masamura
Shigeru
S
Li
Yuebai
Y
Santen
Richard J
RJ
D001943:Breast Neoplasms / Q000201:enzymology / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects*; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011506:Proteins / Q000032:analysis; D011960:Receptors, Estrogen / Q000502:physiology; D011980:Receptors, Progesterone / Q000032:analysis; D020218:Response Elements; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic; D016211:Transforming Growth Factor alpha / Q000494:pharmacology; D000071163:Trefoil Factor-1; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D004791:Enzyme Inhibitors; D005419:Flavonoids; D011506:Proteins; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C051838:TFF1 protein, human; D014157:Transcription Factors; D016211:Transforming Growth Factor alpha; D000071163:Trefoil Factor-1; D025521:Tumor Suppressor Proteins; D004958:Estradiol; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one