title: Down-regulation of cellular FLICE-inhibitory protein (Long Form) contributes to apoptosis induced by Hsp90 inhibition in human lung cancer cells.
abstract: BACKGROUND
  Cellular FLICE-Inhibitory Protein (long form, c-FLIPL) is a critical negative regulator of death receptor-mediated apoptosis. Overexpression of c-FLIPL has been reported in many cancer cell lines and is associated with chemoresistance. In contrast, down-regulation of c-FLIP may drive cancer cells into cellular apoptosis. This study aims to demonstrate that inhibition of the heat shock protein 90 (Hsp90) either by inhibitors geldanamycin/17-N-Allylamino-17-demethoxygeldanamycin (GA/17-AAG) or siRNA technique in human lung cancer cells induces c-FLIPL degradation and cellular apoptosis through C-terminus of Hsp70-interacting protein (CHIP)-mediated mechanisms.
  
  
  METHODS
  Calu-1 and H157 cell lines (including H157-c-FLIPL overexpressing c-FLIPL and control cell H157-lacZ) were treated with 17-AAG and the cell lysates were prepared to detect the given proteins by Western Blot and the cell survival was assayed by SRB assay. CHIP and Hsp90 α/β proteins were knocked down by siRNA technique. CHIP and c-FLIPL plasmids were transfected into cells and immunoprecipitation experiments were performed to testify the interactions between c-FLIPL, CHIP and Hsp90.
  
  
  RESULTS
  c-FLIPL down-regulation induced by 17-AAG can be reversed with the proteasome inhibitor MG132, which suggested that c-FLIPL degradation is mediated by a ubiquitin-proteasome system. Inhibition of Hsp90α/β reduced c-FLIPL level, whereas knocking down CHIP expression with siRNA technique inhibited c-FLIPL degradation. Furthermore, c-FLIPL and CHIP were co-precipitated in the IP complexes. In addition, overexpression of c-FLIPL can rescue cancer cells from apoptosis. When 17-AAG was combined with an anti-cancer agent celecoxib(CCB), c-FLIPL level declined further and there was a higher degree of caspase activation.
  
  
  CONCLUSIONS
  We have elucidated c-FLIPL degradation contributes to apoptosis induced by Hsp90 inhibition, suggesting c-FLIP and Hsp90 may be the promising combined targets in human lung cancer treatment.
authors.affiliation: Key Laboratory for Experimental Teratology of the Ministry of Education and School of Life Sciences, Shandong University, Jinan, China.|Liaocheng University School of Life Sciences, Liaocheng, China.
authors.forename: Qilin
authors.initials: Q
authors.lastname: Wang
authors.affiliation: The Second Hospital, Shandong University, Jinan, China.
authors.forename: Wendong
authors.initials: W
authors.lastname: Sun
authors.affiliation: The Second Hospital, Shandong University, Jinan, China.
authors.forename: Xuexi
authors.initials: X
authors.lastname: Hao
authors.affiliation: Key Laboratory for Experimental Teratology of the Ministry of Education and School of Life Sciences, Shandong University, Jinan, China.
authors.forename: Tianliang
authors.initials: T
authors.lastname: Li
authors.affiliation: Key Laboratory for Experimental Teratology of the Ministry of Education and School of Life Sciences, Shandong University, Jinan, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Su
authors.affiliation: Key Laboratory for Experimental Teratology of the Ministry of Education and School of Life Sciences, Shandong University, Jinan, China.|Shandong University School of Life Sciences, Room103, South Building, 27 Shandananlu Road, Jinan, 250100, China.
authors.forename: Xiangguo
authors.initials: X
authors.lastname: Liu