title: Nelfinavir induces liposarcoma apoptosis through inhibition of regulated intramembrane proteolysis of SREBP-1 and ATF6.
abstract: OBJECTIVE
  We previously reported that nelfinavir (NFV) induces G(1) cell-cycle block and apoptosis selectively in liposarcoma cell lines due to increased SREBP-1 (sterol regulatory element binding protein-1) expression in the absence of increased transcription. We postulate that NFV interferes with regulated intramembrane proteolysis of SREBP-1 and ATF6 (activating transcription factor 6).
  
  
  METHODS
  Time-lapse, confocal microscopic studies show that NFV inhibits the nuclear translocation of full-length SREBP-1-EGFP and ATF6-EGFP fusion proteins. siRNA-mediated knockdown of site-1 protease (S1P) and/or site-2 protease (S2P) leads to inhibition of SREBP-1 intracellular trafficking to the nucleus and reduces liposarcoma cell proliferation. Treatment of LiSa-2 liposarcoma cells with 3,4-dichloroisocoumarin, a serine protease inhibitor of S1P, did not affect SREBP-1 processing. In contrast, 1,10-phenanthroline, an S2P-specific inhibitor, reproduces the molecular and biological phenotypes observed in NFV-treated cells, which implicates S2P as a target of NFV. In vivo evaluation of NFV in a murine liposarcoma xenograft model leads to inhibition of tumor growth without significant toxicity.
  
  
  RESULTS
  NFV-induced upregulation of SREBP-1 and ATF6 results from inhibition of S2P, which together with S1P mediates regulated intramembrane proteolysis from their precursor to their transcriptionally active forms. The resulting endoplasmic reticulum (ER) stress and concurrent inhibition of the unfolded protein response induce caspase-mediated apoptosis.
  
  
  CONCLUSIONS
  These results provide new insight into the mechanism of NFV-mediated induction of ER stress and cell death in liposarcomas and are the first to report targeting S2P for cancer therapy.
authors.affiliation: Department of Molecular Pharmacology, Beckman Research Institute of the City of Hope, Duarte, California 91010, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Guan
authors.forename: Kristen
authors.initials: K
authors.lastname: Fousek
authors.forename: Chunling
authors.initials: C
authors.lastname: Jiang
authors.forename: Song
authors.initials: S
authors.lastname: Guo
authors.forename: Tim
authors.initials: T
authors.lastname: Synold
authors.forename: Bixin
authors.initials: B
authors.lastname: Xi
authors.forename: Chu-Chih
authors.initials: CC
authors.lastname: Shih
authors.forename: Warren A
authors.initials: WA
authors.lastname: Chow
mesh_terms: D051702:Activating Transcription Factor 6 / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053178:Caspase 6 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003374:Coumarins / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000502:physiology; D004789:Enzyme Activation; D054890:Fatty Acid Synthase, Type I / Q000235:genetics / Q000378:metabolism; D005260:Female; D006801:Humans; D049934:Isocoumarins; D008080:Liposarcoma / Q000188:drug therapy / Q000473:pathology*; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors* / Q000235:genetics; D051379:Mice; D016513:Mice, SCID; D019888:Nelfinavir / Q000031:analogs & derivatives / Q000493:pharmacokinetics / Q000494:pharmacology*; D009368:Neoplasm Transplantation; D010618:Phenanthrolines / Q000494:pharmacology; D043484:Proprotein Convertases / Q000235:genetics / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism; D051780:Sterol Regulatory Element Binding Protein 1 / Q000378:metabolism*; D014158:Transcription, Genetic; D014183:Transplantation, Heterologous; D047368:Tumor Burden / Q000187:drug effects
chemical_list: C497111:ATF6 protein, human; D051702:Activating Transcription Factor 6; D000970:Antineoplastic Agents; D003374:Coumarins; D049934:Isocoumarins; D010618:Phenanthrolines; D011480:Protease Inhibitors; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; C497387:SREBF1 protein, human; D051780:Sterol Regulatory Element Binding Protein 1; C495123:hydroxy-t-butylamidenelfinavir; C046235:3,4-dichloroisocoumarin; C518729:FASN protein, human; D054890:Fatty Acid Synthase, Type I; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; C115575:membrane-bound transcription factor peptidase, site 1; D053178:Caspase 6; D053453:Caspase 9; D008666:Metalloendopeptidases; C120654:MBTPS2 protein, human; D019888:Nelfinavir; C025205:1,10-phenanthroline