title: c-Src modulates estrogen-induced stress and apoptosis in estrogen-deprived breast cancer cells.
abstract: The emergence of anti-estrogen resistance in breast cancer is an important clinical phenomenon affecting long-term survival in this disease. Identifying factors that convey cell survival in this setting may guide improvements in treatment. Estrogen (E2) can induce apoptosis in breast cancer cells that have been selected for survival after E2 deprivation for long periods (MCF-7:5C cells), but the mechanisms underlying E2-induced stress in this setting have not been elucidated. Here, we report that the c-Src kinase functions as a key adapter protein for the estrogen receptor (ER, ESR1) in its activation of stress responses induced by E2 in MCF-7:5C cells. E2 elevated phosphorylation of c-Src, which was blocked by 4-hydroxytamoxifen (4-OHT), suggesting that E2 activated c-Src through the ER. We found that E2 activated the sensors of the unfolded protein response (UPR), IRE1α (ERN1) and PERK kinase (EIF2AK3), the latter of which phosphorylates eukaryotic translation initiation factor-2α (eIF2α). E2 also dramatically increased reactive oxygen species production and upregulated expression of heme oxygenase HO-1 (HMOX1), an indicator of oxidative stress, along with the central energy sensor kinase AMPK (PRKAA2). Pharmacologic or RNA interference-mediated inhibition of c-Src abolished the phosphorylation of eIF2α and AMPK, blocked E2-induced ROS production, and inhibited E2-induced apoptosis. Together, our results establish that c-Src kinase mediates stresses generated by E2 in long-term E2-deprived cells that trigger apoptosis. This work offers a mechanistic rationale for a new approach in the treatment of endocrine-resistant breast cancer.
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Fan
authors.forename: Obi L
authors.initials: OL
authors.lastname: Griffith
authors.forename: Fadeke A
authors.initials: FA
authors.lastname: Agboke
authors.forename: Pavana
authors.initials: P
authors.lastname: Anur
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Zou
authors.forename: Russell E
authors.initials: RE
authors.lastname: McDaniel
authors.forename: Karen
authors.initials: K
authors.lastname: Creswell
authors.forename: Sung Hoon
authors.initials: SH
authors.lastname: Kim
authors.forename: John A
authors.initials: JA
authors.lastname: Katzenellenbogen
authors.forename: Joe W
authors.initials: JW
authors.lastname: Gray
authors.forename: V Craig
authors.initials: VC
authors.lastname: Jordan
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D001943:Breast Neoplasms / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D000081247:CSK Tyrosine-Protein Kinase; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004722:Endoribonucleases / Q000378:metabolism; D004967:Estrogens / Q000172:deficiency* / Q000378:metabolism*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D005260:Female; D051547:Heme Oxygenase-1 / Q000378:metabolism; D006801:Humans; D061986:MCF-7 Cells; D018384:Oxidative Stress / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D056811:Unfolded Protein Response / Q000502:physiology; D019892:eIF-2 Kinase / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D055372:AMP-Activated Protein Kinases; D000081247:CSK Tyrosine-Protein Kinase; D004722:Endoribonucleases; D004967:Estrogens; D015852:Eukaryotic Initiation Factor-2; D051547:Heme Oxygenase-1; D017346:Protein Serine-Threonine Kinases; D017382:Reactive Oxygen Species; D011960:Receptors, Estrogen; D019892:eIF-2 Kinase; D019061:src-Family Kinases; C496541:HMOX1 protein, human; C000631346:CSK protein, human; C528229:ERN1 protein, human