title: Identification of novel molecular regulators of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in breast cancer cells by RNAi screening.
abstract: BACKGROUND
  Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) binds to its receptors, TRAIL-receptor 1 (TRAIL-R1) and TRAIL-receptor 2 (TRAIL-R2), leading to apoptosis by activation of caspase-8 and the downstream executioner caspases, caspase-3 and caspase-7 (caspase-3/7). Triple-negative breast cancer (TNBC) cell lines with a mesenchymal phenotype are sensitive to TRAIL, whereas other breast cancer cell lines are resistant. The underlying mechanisms that control TRAIL sensitivity in breast cancer cells are not well understood. Here, we performed small interfering RNA (siRNA) screens to identify molecular regulators of the TRAIL pathway in breast cancer cells.
  
  
  METHODS
  We conducted siRNA screens of the human kinome (691 genes), phosphatome (320 genes), and about 300 additional genes in the mesenchymal TNBC cell line MB231. Forty-eight hours after transfection of siRNA, parallel screens measuring caspase-8 activity, caspase-3/7 activity, or cell viability were conducted in the absence or presence of TRAIL for each siRNA, relative to a negative control siRNA (siNeg). A subset of genes was screened in cell lines representing epithelial TNBC (MB468), HER2-amplified breast cancer (SKBR3), and estrogen receptor-positive breast cancer (T47D). Selected putative negative regulators of the TRAIL pathway were studied by using small-molecule inhibitors.
  
  
  RESULTS
  The primary screens in MB231 identified 150 genes, including 83 kinases, 4 phosphatases, and 63 nonkinases, as potential negative regulators of TRAIL. The identified genes are involved in many critical cell processes, including apoptosis, growth factor-receptor signaling, cell-cycle regulation, transcriptional regulation, and DNA repair. Gene-network analysis identified four genes (PDPK1, IKBKB, SRC, and BCL2L1) that formed key nodes within the interaction network of negative regulators. A secondary screen of a subset of the genes identified in additional cell lines representing different breast cancer subtypes and sensitivities to TRAIL validated and extended these findings. Further, we confirmed that small-molecule inhibition of SRC or BCL2L1, in combination with TRAIL, sensitizes breast cancer cells to TRAIL-induced apoptosis, including cell lines resistant to TRAIL-induced cytotoxicity.
  
  
  CONCLUSIONS
  These data identify novel molecular regulators of TRAIL-induced apoptosis in breast cancer cells and suggest strategies for the enhanced application of TRAIL as a therapy for breast cancer.
authors.forename: Sireesha V
authors.initials: SV
authors.lastname: Garimella
authors.forename: Kristie
authors.initials: K
authors.lastname: Gehlhaus
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Dine
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Pitt
authors.forename: Magdalena
authors.initials: M
authors.lastname: Grandin
authors.forename: Sirisha
authors.initials: S
authors.lastname: Chakka
authors.forename: Marion M
authors.initials: MM
authors.lastname: Nau
authors.forename: Natasha J
authors.initials: NJ
authors.lastname: Caplen
authors.forename: Stanley
authors.initials: S
authors.lastname: Lipkowitz
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics*; D001713:Biphenyl Compounds / Q000494:pharmacology; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D053179:Caspase 7 / Q000235:genetics / Q000378:metabolism; D053181:Caspase 8 / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D015151:Immunoblotting; D009596:Nitrophenols / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D034622:RNA Interference; D013449:Sulfonamides / Q000494:pharmacology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D051020:bcl-X Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: C501332:ABT-737; C412373:AG 1879; C494811:BCL2L1 protein, human; D001713:Biphenyl Compounds; D015853:Cysteine Proteinase Inhibitors; D009596:Nitrophenols; D009842:Oligopeptides; D010879:Piperazines; D011743:Pyrimidines; D013449:Sulfonamides; D053221:TNF-Related Apoptosis-Inducing Ligand; C108637:aspartyl-glutamyl-valyl-aspartal; D051020:bcl-X Protein; D019061:src-Family Kinases; D053148:Caspase 3; D053179:Caspase 7; D053181:Caspase 8
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