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 3

Inhibition of hsp90 induces ubiquitination of MAST1 at lysine 317/545 that leads to proteasomal degradation.

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Inhibition of hsp90 induces ubiquitination of MAST1 at lysine 317/545 th...
(A) Effect of 17-AAG on MAST1 ubiquitination. 293T cells with GST-MAST1 and HA-tagged ubiquitin (Ub) were treated with 17-AAG for 4 hours and subjected to GST pull down. Anti-HA antibody was used to detect ubiquitinated MAST1. (B and C) Effect of 17-AAG on MAST1 proteasomal degradation. Cells were treated with or without MG-132 (10 μM) before addition of 17-AAG (1 μM) in 293T (B) or cisplatin-resistant cancer cells (C), and exogenous or endogenous MAST1 levels were detected, respectively. cRaf and AKT levels are shown for comparison. (D) Effect of 17-AAG on MAST1 ubiquitination and proteasomal degradation in cisplatin-resistant cancer cells. (E) MS spectra of ubiquitinated peptide fragments of MAST1. 293T cells with GST-MAST1 were treated with 1 μM of 17-AAG for 4 hours. Ubiquitination at K317 and K545 in MAST1 was identified using LC/MS-MS. (F) Ubiquitination of MAST1 WT and K317R or/and K545R mutants upon 17-AAG treatment. (G) Degradation of MAST1 WT and K317R/K545R (2KR) upon 17-AAG treatment in KB-3-1cisR and A549cisR cells. MAST1 knockdown cells were transfected with shRNA-resistant MAST1 WT or 2KR and treated with indicated concentrations of 17-AAG for 24 hours. Data shown are representative of 2 (A, B, and F) and 3 (C, D, and G) independent biological experiments.