Ligand-independent antiapoptotic function of estrogen receptor-beta in lung cancer cells.
Recent studies have demonstrated the presence of estrogen receptor (ER)beta in the mitochondria in various cell types and tissues, but the exact function of this localization remains unclear. In this study, we have examined the function of mitochondrial ERbeta in non-small-cell lung cancer (NSCLC) cells. Down-regulation of ERbeta by short hairpin RNA constructs sensitized NSCLC cells to various apoptosis-inducing agents such as cisplatin, taxol, and etoposide. The increased growth inhibition and induction of apoptosis in ERbeta-knockdown cells was observed irrespective of estrogen treatment, suggesting a ligand-independent role of ERbeta in regulating the intrinsic apoptotic pathway. Further, ERbeta from the mitochondrial fraction physically interacted with the proapoptotic protein Bad, in a ligand-independent manner. Glutathione-S-transferase pull-down assays and molecular modeling studies revealed that the DNA-binding domain and hinge region of ERbeta, and the BH3 domain of Bad were involved in these interactions. Further investigations revealed that ERbeta inhibited Bad function by disrupting Bad-Bcl-X(L) and Bad-Bcl-2 interactions. Reintroduction of ERbeta in the mitochondria of ERbeta knockdown cells reversed their sensitivity to cisplatin. Overall, our results demonstrate a ligand-independent role of ERbeta in regulating apoptosis, revealing a novel function for ERbeta in the mitochondria.
Zhang
Guangfeng
G
Division of Endocrinology and Metabolism, University of Pittsburgh, E1115 Starzl Biomedical Science Tower, 200 Lothrop Street, Pittsburgh, PA 15261, USA.
Yanamala
Naveena
N
Lathrop
Kira L
KL
Zhang
Lin
L
Klein-Seetharaman
Judith
J
Srinivas
Harish
H
D017209:Apoptosis / Q000187:drug effects; D002289:Carcinoma, Non-Small-Cell Lung / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000494:pharmacology; D047629:Estrogen Receptor beta / Q000737:chemistry / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D047468:Immunoprecipitation; D020128:Inhibitory Concentration 50; D008024:Ligands; D008175:Lung Neoplasms / Q000378:metabolism* / Q000473:pathology*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D008958:Models, Molecular; D011485:Protein Binding / Q000187:drug effects; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D034741:RNA, Small Interfering / Q000378:metabolism; D051025:bcl-Associated Death Protein / Q000737:chemistry / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
D047629:Estrogen Receptor beta; D008024:Ligands; D034741:RNA, Small Interfering; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; D002945:Cisplatin