Bay 61-3606 Sensitizes TRAIL-Induced Apoptosis by Downregulating Mcl-1 in Breast Cancer Cells.

So-Young Kim,Dong-Hoon Jin,Kyung Kon Kim,Seong-Yun Jeong,Eun Kyung Choi,Inki Kim,Sojung Park,Jung Jin Hwang,Sang-Mi Shim,Sang Eun Park,Christopher Doosoon Chung,Dong-Gyu Jo

doi:10.1371/journal.pone.0146073

Abstract

Breast cancer cells generally develop resistance to TNF-Related Apoptosis-Inducing Ligand (TRAIL) and, therefore, assistance from sensitizers is required. In our study, we have demonstrated that Spleen tyrosine kinase (Syk) inhibitor Bay 61–3606 was identified as a TRAIL sensitizer. Amplification of TRAIL-induced apoptosis by Bay 61–3606 was accompanied by the strong activation of Bak, caspases, and DNA fragmentation. In mechanism of action, Bay 61–3606 sensitized cells to TRAIL via two mechanisms regulating myeloid cell leukemia sequence-1 (Mcl-1). First, Bay 61–3606 triggered ubiquitin-dependent degradation of Mcl-1 by regulating Mcl-1 phosphorylation. Second, Bay 61–3606 downregulates Mcl-1 expression at the transcription level. In this context, Bay 61–3606 acted as an inhibitor of Cyclin-Dependent Kinase (CDK) 9 rather than Syk. In summary, Bay 61–3606 downregulates Mcl-1 expression in breast cancer cells and sensitizes cancer cells to TRAIL-mediated apoptosis.

Highlights

TNF-Related Apoptosis-Inducing Ligand (TRAIL)/Apo2 ligand selectively kills cancer cells by initiating apoptotic signaling through the engagement of its pro-apoptotic receptors, Death Receptors-4 and -5 [1, 2]
Bay 61–3606 sensitized cells to death induced by TRAIL while exposure to TRAIL alone showed minimal reduction (Fig 1A, bars in far right)
To support the premise that Bay 61–3606 triggers ubiquitination of myeloid cell leukemia sequence-1 (Mcl-1), we investigated whether Bay 61–3606 could increase the ubiquitination of Mcl-1 protein (Fig 4B)

Summary

Introduction

TRAIL/Apo ligand selectively kills cancer cells by initiating apoptotic signaling through the engagement of its pro-apoptotic receptors, Death Receptors-4 and -5 [1, 2]. TRAIL binding to these receptors results in the formation of ‘death-inducing signaling complex (DISC)’ inducing caspase-8 activation [3]. The joint effort of the extrinsic and intrinsic apoptotic pathways leads to the activation of downstream caspases (-3 and -7) and apoptotic demise of cells [4]. TRAIL shows cancer-selective killing activity, a phase 2 clinical trial failed to demonstrate a clear benefit in a therapeutic window [5]. Parallel to this result, primary tumors were

Methods

Results

Conclusion