Premium
Bile Acid Binding Protein STARD5 Suppresses Doxorubicin‐mediated Apoptosis in H1792 Lung Adenocarcinoma Cells
Author(s) -
Clark Barbara J,
Dougherty Susan M,
Hill Bradford G,
Klinge Carolyn M
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.616.4
Subject(s) - apoptosis , chenodeoxycholic acid , cancer research , adenocarcinoma , mitochondrion , chemistry , viability assay , gene knockdown , biology , bile acid , microbiology and biotechnology , endocrinology , biochemistry , cancer , genetics
The bile acid chenodeoxycholic acid (CDCA) is a FXR ligand that has anti‐proliferative and pro‐apoptotic actions in gastrointestinal cancer cells. The cytotoxic actions of CDCA appear to be both FXR‐dependent and independent and cell‐type specific. Although FXR is expressed in lung and bile acid biosynthesis is associated with lung inflammation, the role of FXR in lung cancer is unknown. Herein, we have used non‐small cell carcinoma (NSCLC) cancer cell lines to test the effect of the bile acid binding protein, STARD5, on doxorubicin‐mediated apoptosis. Western blot analysis detected high levels of STARD5 protein in 5 lung adenocarcinoma cell lines compared to non‐detectable levels in normal human bronchial epithelial cells (HBEC). These lung adenocarcinoma cells have greater resistance to doxorubicin‐induced apoptosis, measured by caspase activation, compared to HBECs. Notably siRNA silencing of STARD5 in H1792 lung adenocarcinoma cells decreased cell viability and increased sensitivity to doxorubicin‐induced apoptosis. To address possible anti‐apoptotic mechanisms, we measured the mitochondrial function of H1792 cells after siRNA knockdown or transient overexpression of STARD5. Using the Seahorse XF24 analyzer we found that STARD5 knockdown had no effect on mitochondria function while STARD5 overexpression resulted in a 40% decrease in both the ATP‐linked oxygen consumption rate (OCR) and glycolytic reserve. The proton leak was unchanged, suggesting no change in the mitochondria permeability transition pore, an early marker of apoptosis. A decrease in ATP‐linked OCR mediated by STARD5, in the absence of proton leak, may reflect increased mitochondrial ROS production. Decreased mitochondria function and increased mitochondrial ROS would be consistent with suppressed FXR action. To test whether STARD5 affects FXR activity, we measured FXR‐luciferase reporter gene activity in siRNA‐STARD5 knockdown cells. STARD5 knockdown resulted in increased FXR activity, suggesting that STARD5 sequesters FXR ligands (CDCA) which contribute to FXR's pro‐apoptotic activity. Future studies will test the model that FXR signaling in NSCLC sensitizes cells to doxorubicin‐mediated apoptosis and that increased STARD5 in NSCLC mediates suppression of FXR signaling and contributes to acquired chemoresistance. Support or Funding Information This study was supported by a U of L SOM Collaborative Matching Grant to BJC and KY Lung Cancer Research Program to CMK.