Targeting Hsp90 with small molecule inhibitors induces the over-expression of the anti-apoptotic molecule, survivin, in human A549, HONE-1 and HT-29 cancer cells.
BACKGROUND
Survivin is a dual functioning protein. It inhibits the apoptosis of cancer cells by inhibiting caspases, and also promotes cancer cell growth by stabilizing microtubules during mitosis. Since the molecular chaperone Hsp90 binds and stabilizes survivin, it is widely believed that down-regulation of survivin is one of the important therapeutic functions of Hsp90 inhibitors such as the phase III clinically trialed compound 17-AAG. However, Hsp90 interferes with a number of molecules that up-regulate the intracellular level of survivin, raising the question that clinical use of Hsp90 inhibitors may indirectly induce survivin expression and subsequently enhance cancer anti-drug responses. The purpose of this study is to determine whether targeting Hsp90 can alter survivin expression differently in different cancer cell lines and to explore possible mechanisms that cause the alteration in survivin expression.


RESULTS
Here, we demonstrated that Hsp90 inhibitors, geldanamycin and 17-AAG, induced the over-expression of survivin in three different human cancer cell lines as shown by Western blotting. Increased survivin mRNA transcripts were observed in 17-AAG and geldanamycin-treated HT-29 and HONE-1 cancer cells. Interestingly, real-time PCR and translation inhibition studies revealed that survivin was over-expressed partially through the up-regulation of protein translation instead of gene transcription in A549 cancer cells. In addition, 17-AAG-treated A549, HONE-1 and HT-29 cells showed reduced proteasomal activity while inhibition of 26S proteasome activity further increased the amount of survivin protein in cells. At the functional level, down-regulation of survivin by siRNA further increased the drug sensitivity to 17-AAG in the tested cancer cell lines.


CONCLUSIONS
We showed for the first time that down-regulation of survivin is not a definite therapeutic function of Hsp90 inhibitors. Instead, targeting Hsp90 with small molecule inhibitors will induce the over-expression of survivin in certain cancer cell lines and subsequently enhances the ability of cell survival in drug-treated situations. The current study suggests that dual inhibition of Hsp90 and survivin may be warranted.
Cheung
Chun Hei Antonio
CH
National Institute of Cancer Research, National Health Research Institutes (NHRI), Tainan 70456, Taiwan ROC. a.cheung@nhri.org.tw
Chen
Huang-Hui
HH
Cheng
Li-Ting
LT
Lyu
Kevin W
KW
Kanwar
Jagat R
JR
Chang
Jang-Yang
JY
D000970:Antineoplastic Agents / Q000494:pharmacology*; D016227:Benzoquinones / Q000494:pharmacology; D015153:Blotting, Western; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects*; D018841:HSP90 Heat-Shock Proteins / Q000187:drug effects* / Q000378:metabolism; D019073:HT29 Cells; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D047029:Lactams, Macrocyclic / Q000494:pharmacology; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis* / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077022:Survivin
D000970:Antineoplastic Agents; C107489:BIRC5 protein, human; D016227:Benzoquinones; D004791:Enzyme Inhibitors; D018841:HSP90 Heat-Shock Proteins; D051034:Inhibitor of Apoptosis Proteins; D047029:Lactams, Macrocyclic; D008869:Microtubule-Associated Proteins; D034741:RNA, Small Interfering; D000077022:Survivin; C112765:tanespimycin; D046988:Proteasome Endopeptidase Complex; C001277:geldanamycin
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