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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Research Article Oncology

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 5

CHIP ubiquitinates and degrades MAST1 when unmasked by hsp90B.

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CHIP ubiquitinates and degrades MAST1 when unmasked by hsp90B. (A) MAST1...
(A) MAST1 interacts with CHIP in cells. GST-pull-down samples from 293T were applied to LC-MS/MS. Spectral counts of CHIP and MAST1 in samples treated with or without 17-AAG are shown. (B) Overexpressed CHIP and MAST1 interact in cancer cells. Effect of CHIP overexpression (C) or knockout (D) on MAST1 levels. (E) Comparison of MAST1 protein stability in cells with CHIP modulation was achieved by cycloheximide (CHX) chase assay. Cells with CHIP knockdown were transfected with shRNA-resistant CHIP variants followed by 5 μg/mL CHX treatment for the indicated time. MAST1 amount was determined by density analysis. Representative data are shown. (F) In vitro CHIP ubiquitination assay using purified MAST1 WT or 2KR. (G) Ubiquitination of MAST1 WT and 2KR in cells. GST pull-down samples from A549cisR cells treated with MG-132 (10 μM) were immunoblotted with anti-ubiquitin antibody. (H) Interaction of MAST1 WT or 2KR, hsp90B, and CHIP in the presence or absence of 17-AAG. MAST1 WT and 2KR protein stability in the absence (I) and presence (J) of 17-AAG was determined by cycloheximide chase assay. Data shown are representative of 3 (B–E, I, and J) and 2 (F, G, H) independent biological experiments. Data are mean ± SD from 3 technical replicates. Statistical analysis was performed by 2-way ANOVA for E and 1-way ANOVA for I and J. ***P < 0.005; ****P < 0.0001.