Hsp90B enhances MAST1-mediated cisplatin resistance by protecting MAST1 from proteosomal degradation
Chaoyun Pan, … , Lingtao Jin, Sumin Kang
Chaoyun Pan, … , Lingtao Jin, Sumin Kang
Published August 26, 2019
Citation Information: J Clin Invest. 2019;129(10):4110-4123. https://doi.org/10.1172/JCI125963.
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Hsp90B enhances MAST1-mediated cisplatin resistance by protecting MAST1 from proteosomal degradation

Abstract

Microtubule-associated serine/threonine kinase 1 (MAST1) is a central driver of cisplatin resistance in human cancers. However, the molecular mechanism regulating MAST1 levels in cisplatin-resistant tumors is unknown. Through a proteomics screen, we identified the heat shock protein 90 B (hsp90B) chaperone as a direct MAST1 binding partner essential for its stabilization. Targeting hsp90B sensitized cancer cells to cisplatin predominantly through MAST1 destabilization. Mechanistically, interaction of hsp90B with MAST1 blocked ubiquitination of MAST1 at lysines 317 and 545 by the E3 ubiquitin ligase CHIP and prevented proteasomal degradation. The hsp90B-MAST1-CHIP signaling axis and its relationship with cisplatin response were clinically validated in cancer patients. Furthermore, combined treatment with a hsp90 inhibitor and the MAST1 inhibitor lestaurtinib further abrogated MAST1 activity and consequently enhanced cisplatin-induced tumor growth arrest in a patient-derived xenograft model. Our study not only uncovers the regulatory mechanism of MAST1 in tumors but also suggests a promising combinatorial therapy to overcome cisplatin resistance in human cancers.

Authors

Chaoyun Pan, Jaemoo Chun, Dan Li, Austin C. Boese, Jie Li, JiHoon Kang, Anna Umano, Yunhan Jiang, Lina Song, Kelly R. Magliocca, Zhuo G. Chen, Nabil F. Saba, Dong M. Shin, Taofeek K. Owonikoko, Sagar Lonial, Lingtao Jin, Sumin Kang

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Figure 4

Ubiquitination of MAST1 at K317 and K545 induces MAST1 degradation and cisplatin-mediated cell death upon 17-AAG treatment.

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Ubiquitination of MAST1 at K317 and K545 induces MAST1 degradation and c...
(A) Effect of 17-AAG on MAST1 WT and K317R/K545R (2KR) degradation. Cells were treated with or without 17-AAG (200 nM) and sublethal doses of cisplatin as in Figure 2E. MAST1 expression and MEK1 activation was assessed by immunoblotting. (B) MAST1 in vitro kinase assay of MAST1 WT and 2KR. Kinase activity of GST-MAST1 variants. Kinase dead mutant D497A MAST1 was used as a negative control. (C) Cell viability and cisplatin sensitivity of cisplatin-resistant cells expressing MAST1 WT or 2KR. Cell viability was determined by trypan blue exclusion in cells treated with 200 nM of 17-AAG and sublethal doses of cisplatin for 48 hours. Cisplatin sensitivity is shown as cisplatin IC50, which was determined by CellTiter-Glo assay. (D) Effect of 17-AAG and cisplatin treatment on tumor volume and tumor weight of xenograft mice bearing KB-3-1cisR with MAST1 WT or 2KR overexpression. Mice were treated with cisplatin (5 mg/kg) and 17-AAG (50 mg/kg) from 5 days after xenograft. (E) MAST1 expression and MEK1 activation levels in tumor lysates. WT or 2KR MAST1 was overexpressed in MAST1 knockdown cells for functional assays. Data are mean ± SD from 3 technical replicates for B and C; n = 6 for D. Error bars represent SEM for tumor volume and SD for tumor weight. Data shown are representative of 3 (A and C [top]) and 2 (B–E) independent biological experiments. Data are mean ± SD from 3 technical replicates for B and C; n = 6 for D. Error bars represent SEM for tumor volume and SD for tumor weight. Statistical analysis was performed by 2-way ANOVA for D (left) and 1-way ANOVA for all the rest. **P < 0.01; ***P < 0.005; ****P < 0.0001.