title: Estradiol abrogates apoptosis in breast cancer cells through inactivation of BAD: Ras-dependent nongenomic pathways requiring signaling through ERK and Akt.
abstract: Estrogens such as 17-beta estradiol (E(2)) play a critical role in sporadic breast cancer progression and decrease apoptosis in breast cancer cells. Our studies using estrogen receptor-positive MCF7 cells show that E(2) abrogates apoptosis possibly through phosphorylation/inactivation of the proapoptotic protein BAD, which was rapidly phosphorylated at S112 and S136. Inhibition of BAD protein expression with specific antisense oligonucleotides reduced the effectiveness of tumor necrosis factor-alpha, H(2)O(2), and serum starvation in causing apoptosis. Furthermore, the ability of E(2) to prevent tumor necrosis factor-alpha-induced apoptosis was blocked by overexpression of the BAD S112A/S136A mutant but not the wild-type BAD. BAD S112A/S136A, which lacks phosphorylation sites for p90(RSK1) and Akt, was not phosphorylated in response to E(2) in vitro(.) E(2) treatment rapidly activated phosphatidylinositol 3-kinase (PI-3K)/Akt and p90(RSK1) to an extent similar to insulin-like growth factor-1 treatment. In agreement with p90(RSK1) activation, E(2) also rapidly activated extracellular signal-regulated kinase, and this activity was down-regulated by chemical and biological inhibition of PI-3K suggestive of cross talk between signaling pathways responding to E(2). Dominant negative Ras blocked E(2)-induced BAD phosphorylation and the Raf-activator RasV12T35S induced BAD phosphorylation as well as enhanced E(2)-induced phosphorylation at S112. Chemical inhibition of PI-3K and mitogen-activated protein kinase kinase 1 inhibited E(2)-induced BAD phosphorylation at S112 and S136 and expression of dominant negative Ras-induced apoptosis in proliferating cells. Together, these data demonstrate a new nongenomic mechanism by which E(2) prevents apoptosis.
authors.affiliation: Department of Obstetrics and Gynecology, and the Comparative and Experimental Medicine Program, Graduate School of Medicine, University of Tennessee, Knoxville, Tennessee 37920, USA.
authors.forename: Romaine Ingrid
authors.initials: RI
authors.lastname: Fernando
authors.forename: Jay
authors.initials: J
authors.lastname: Wimalasena
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001943:Breast Neoplasms / Q000201:enzymology / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology* / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology*; D005260:Female; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000502:physiology; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D051025:bcl-Associated Death Protein; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D004958:Estradiol; D048049:Extracellular Signal-Regulated MAP Kinases; D006861:Hydrogen Peroxide; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D010744:Phosphoric Monoester Hydrolases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014409:Tumor Necrosis Factor-alpha; D025521:Tumor Suppressor Proteins; D051025:bcl-Associated Death Protein; D018631:ras Proteins; C494819:BAD protein, human; C494918:AKT1 protein, human; C494929:PTEN protein, human