Stabilization of SDF-2 by Hsp72 contributes to oxaliplatin resistance in human gastric cancer cells

[Speaker] Masako Tanaka:1
[Co-author] Katsuyuki Takahashi:2, Katsuyuki Miura:3, Shuhei Tomita:4, Nobuhito Goda:1, Masayuki Shiota:5
1:Dept. Life Sci. Med. BioSci., Sch. Sci. Eng., Waseda Univ., Japan, 2:Dept. Pharmacy, Osaka City Univ. Hosp., Japan, 3:Appl. Pharmacol. Ther., Osaka City Univ. Grad. Sch. Med., Japan, 4:Dept. Pharmacol., Osaka City Univ. Grad. Sch. Med., Japan, 5:Res. Sprt. Platf., Osaka City Univ. Grad. Sch. Med., Japan

Heat shock protein 72 (Hsp72), a molecular chaperone, is constitutively expressed at elevated levels in many cancers, resulting in enhanced stress tolerance. Following treatment with chemotherapeutic drugs, Hsp72 also increases and binds to misfolded proteins for proteostasis, by which cancer cells become highly resistant to the drugs. We therefore hypothesized that Hsp72 binding proteins may play a crucial role in chemoresistance.
Here, we aimed to identify Hsp72 interactors critical for oxaliplatin resistance in human gastric cancer cells, OCUM-2M. We performed the mass-spectrometry-based proteomic analysis utilizing the affinity purification with anti-Hsp72 antibodies. Identified Hsp72 interactors unique to oxaliplatin resistant cells then were subjected to RNAi screening for recovery drug sensitivity.
Stromal cell-derived factor 2 (SDF-2) was identified as an Hsp72 interactor unique to an OCUM-2M subline resistant to oxaliplatin (OCUM-2M/OXA). SDF-2 knockdown induced apoptosis selectively in the resistant cells, but not in the sensitive ones, resulting in a significant decrease in the IC50 values of oxaliplatin and consequent restoration of sensitivity to the chemotherapy. These results suggest that SDF-2 serves as a molecule determinant responsible for oxaliplatin resistance in OCUM-2M cells. SDF-2 increased at protein level in the resistant cells without any impacts on its mRNA level. Suppression of Hsp72 expression and its chaperon activity by VER155008 successfully decreased SDF-2 protein level without affecting mRNA level. This decrease was prevented by lactacystin, a proteasome inhibitor, suggesting that Hsp72 prevents SDF-2 degradation through the proteasome-mediated pathway.
Hsp72 prevents oxaliplatin-induced apoptosis by protecting SDF-2 degradation.

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