title: Ceramide targets xIAP and cIAP1 to sensitize metastatic colon and breast cancer cells to apoptosis induction to suppress tumor progression.
abstract: BACKGROUND
  Ceramide is a bioeffector that mediates various cellular processes, including apoptosis. However, the mechanism underlying ceramide function in apoptosis is apparently cell type-dependent and is not well-understood. We aimed at identifying molecular targets of ceramide in metastatic human colon and breast cancer cells, and determining the efficacy of ceramide analog in suppression of colon and breast cancer metastasis.
  
  
  METHODS
  The activity of and mechanism underlying ceramide as a cytotoxic agent, and as a sensitizer for Fas-mediated apoptosis was analyzed in human cell lines established from primary or metastatic colon and breast cancers. The efficacy of ceramide analog LCL85 in suppression of metastasis was examined in preclinical mouse tumor models.
  
  
  RESULTS
  Exposure of human colon carcinoma cells to ceramide analog LCL85 results in apoptosis in a dose-dependent manner. Interestingly, a sublethal dose of LCL85 increased C16 ceramide content and overcame tumor cell resistance to Fas-mediated apoptosis. Subsequently, treatment of tumor cells with exogenous C16 ceramide resulted in increased tumor cell sensitivity to Fas-mediated apoptosis. LCL85 resembles Smac mimetic BV6 in sensitization of colon carcinoma cells to Fas-mediated apoptosis by inducing proteasomal degradation of cIAP1 and xIAP proteins. LCL85 also decreased xIAP1 and cIAP1 protein levels and sensitized metastatic human breast cancer cells to Fas-mediated apoptosis. Silencing xIAP and cIAP1 with specific siRNAs significantly increased the metastatic human colon carcinoma cell sensitivity to Fas-mediated apoptosis, suggesting that IAP proteins mediate apoptosis resistance in metastatic human colon carcinoma cells and ceramide induces IAP protein degradation to sensitize the tumor cells to apoptosis induction. Consistent with its apoptosis sensitization activity, subtoxic doses of LCL85 suppressed colon carcinoma cell metastatic potential in an experimental lung metastasis mouse model, as well as breast cancer growth and spontaneous lung metastasis in an orthotopic breast cancer mouse model.
  
  
  CONCLUSIONS
  We have identified xIAP and cIAP1 as molecular targets of ceramide and determined that ceramide analog LCL85 is an effective sensitizer in overcoming resistance of human cell lines established from metastatic colon and breast cancers to apoptosis induction to suppress metastasis in vivo.
authors.forename: Amy V
authors.initials: AV
authors.lastname: Paschall
authors.forename: Mary A
authors.initials: MA
authors.lastname: Zimmerman
authors.forename: Christina M
authors.initials: CM
authors.lastname: Torres
authors.forename: Dafeng
authors.initials: D
authors.lastname: Yang
authors.forename: May R
authors.initials: MR
authors.lastname: Chen
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.forename: Erhard
authors.initials: E
authors.lastname: Bieberich
authors.forename: Aiping
authors.initials: A
authors.lastname: Bai
authors.forename: Jacek
authors.initials: J
authors.lastname: Bielawski
authors.forename: Alicja
authors.initials: A
authors.lastname: Bielawska
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Georgia Regents University, Augusta, GA, USA. Kliu@gru.edu.
authors.forename: Kebin
authors.initials: K
authors.lastname: Liu
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000556:secondary; D045744:Cell Line, Tumor; D002518:Ceramides / Q000494:pharmacology*; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000556:secondary; D018450:Disease Progression; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D058990:Molecular Targeted Therapy; D011412:Propanolamines / Q000494:pharmacology*; D011726:Pyridinium Compounds / Q000494:pharmacology*; D034622:RNA Interference; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D044767:Ubiquitin-Protein Ligases; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000235:genetics / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays; D019014:fas Receptor / Q000378:metabolism
chemical_list: C560215:2-N-(16-(1'-pyridinium)hexadecanoylamino)-1-(4'-nitrophenyl)-1,3-propandiol; D000970:Antineoplastic Agents; C107521:Birc4 protein, mouse; D002518:Ceramides; C491901:FAS protein, human; C491899:Fas protein, mouse; D051034:Inhibitor of Apoptosis Proteins; D011412:Propanolamines; D011726:Pyridinium Compounds; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D019014:fas Receptor; C494833:BIRC2 protein, human; C494834:Birc2 protein, mouse; D044767:Ubiquitin-Protein Ligases