title: [Role of dysregulation of Bim in resistance of melanoma cells to endoplasmic reticulum stress-induced apoptosis].
abstract: OBJECTIVE
  To establish a model of ER stress-induced apoptosis with tunicamycin and to examine whether Bim is dysregulated and its potential role in resistance of melanoma cells to apoptosis under endoplasmic reticulum (ER) stress.
  
  
  METHODS
  A model of ER stress-induced apoptosis was established with tunicamycin. Apoptotic cells were quantitated using the annexin V/propidium iodide method by flow cytometry. Hoechst staining was also used to confirm the apoptotic cell death. Western blotting was used to measure the activation of caspase-3 and -9, and the expression of Bim, GRP78, CHOP, and Foxo1 at the protein level. The expression of Bim, CHOP and Foxo1 at the mRNA level was quantitated by qPCR. The siRNA technique was used to inhibit the expression of Bim.
  
  
  RESULTS
  Treatment of the melanoma cells with tunicamycin did not induce significant apoptosis and activation of caspase cascade, whereas it caused marked activation of caspase-3 and -9, and apoptosis in HEK293 cells which were used as a control. With exposure to tunicamycin (3 µmol/L) for 12, 24, 36 hours the Bim protein levels were not increased in Mel-RM and MM200 cells. Its mRNA levels were 0.37 ± 0.05, 0.13 ± 0.02 and 0.02 ± 0.01 in Mel-RM cells, while 0.41 ± 0.06, 0.16 ± 0.04 and 0.21 ± 0.03 in MM200 cells, respectively. The expression of Bim mRNA was significantly reduced compared with that in the control groups of the two cell lines (P < 0.01). siRNA knockdown of Bim protected HEK293 cells against activation of caspase-3. The cell apoptosis of Bim siRNA group was (5.69 ± 0.38)%, significantly lower than that of the siRNA control group (40.32 ± 1.64)% and blank control group (35.46 ± 2.01)% (P < 0.01). In the melanoma cells after exposure to tunicamycin (3 µmol/L) for 6, 12, 24, and 36 hours the transcription factor CHOP at mRNA level were significantly increased and the expressions at protein level were also up-regulated. The expressions of another transcription factor Foxo1 at mRNA level significantly decreased and the expressions at protein level were down-regulated, too.
  
  
  CONCLUSIONS
  The lack of Bim up-regulation contributes to the resistance of melanoma cells to ER stress-induced apoptosis and may be a mechanism by which melanoma cells adapt to ER stress conditions. Transcription factors CHOP and Foxo1 may be responsible for the dysregulation of Bim in melanoma cells upon ER stress.
authors.affiliation: Department of Immunology, Anhui Medical University, Hefei, China.
authors.forename: Li-li
authors.initials: LL
authors.lastname: Hou
authors.forename: Lei
authors.initials: L
authors.lastname: Jin
authors.forename: Chuan-chun
authors.initials: CC
authors.lastname: Han
authors.forename: Bing
authors.initials: B
authors.lastname: Cheng
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Xu-dong
authors.initials: XD
authors.lastname: Zhang
authors.forename: Lin-jie
authors.initials: LJ
authors.lastname: Zhang
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D045744:Cell Line, Tumor; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008545:Melanoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology*
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C497249:DDIT3 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D014415:Tunicamycin; D051742:Transcription Factor CHOP; D053148:Caspase 3; D053453:Caspase 9