Activated ERK Signaling Is One of the Major Hub Signals Related to the Acquisition of Radiotherapy-Resistant MDA-MB-231 Breast Cancer Cells.

Anjugam Paramanantham,Eun Joo Jung,Soon Chan Hong,Se-IL Go,Jin-Myung Jung,Bae Kwon Jeong,Won Sup Lee,Gon Sup Kim

doi:10.3390/ijms22094940

Abstract

Breast cancer is one of the major causes of deaths due to cancer, especially in women. The crucial barrier for breast cancer treatment is resistance to radiation therapy, one of the important local regional therapies. We previously established and characterized radio-resistant MDA-MB-231 breast cancer cells (RT-R-MDA-MB-231 cells) that harbor a high expression of cancer stem cells (CSCs) and the EMT phenotype. In this study, we performed antibody array analysis to identify the hub signaling mechanism for the radiation resistance of RT-R-MDA-MB-231 cells by comparing parental MDA-MB-231 (p-MDA-MB-231) and RT-R-MDA-MB-231 cells. Antibody array analysis unveiled that the MAPK1 protein was the most upregulated protein in RT-R-MDA-MB-231 cells compared to in p-MDA-MB-231 cells. The pathway enrichment analysis also revealed the presence of MAPK1 in almost all enriched pathways. Thus, we used an MEK/ERK inhibitor, PD98059, to block the MEK/ERK pathway and to identify the role of MAPK1 in the radio-resistance of RT-R-MDA-MB-231 cells. MEK/ERK inhibition induced cell death in both p-MDA-MB-231 and RT-R-MDA-MB-231 cells, but the death mechanism for each cell was different; p-MDA-MB-231 cells underwent apoptosis, showing cell shrinkage and PARP-1 cleavage, while RT-R-MDA-MB-231 cells underwent necroptosis, showing mitochondrial dissipation, nuclear swelling, and an increase in the expressions of CypA and AIF. In addition, MEK/ERK inhibition reversed the radio-resistance of RT-R-MDA-MB-231 cells and suppressed the increased expression of CSC markers (CD44 and OCT3/4) and the EMT phenotype (β-catenin and N-cadherin/E-cadherin). Taken together, this study suggests that activated ERK signaling is one of the major hub signals related to the radio-resistance of MDA-MB-231 breast cancer cells.

Highlights

Breast cancer is one of the major causes of death due to cancer worldwide, especially in women [1]
To determine the key altered expressions of proteins involved in the radio-resistance of RT-R-MDA-MB 231 cells, we performed and analyzed antibody microarrays to assess the difference in protein expressions between p-MDA-MB-231 and RT-R-MDA-MB-231 cells
There was a difference in morphology of the cell death between p-MDA-MB-231 cells and RT-R-MDA-MB-231 cells (Figure 3A). These findings suggested that extracellular signal-regulated kinase (ERK) signaling should be important in the cell survival of RT-R-MDA-MB-231 cells, and that the inhibition of ERK signaling might reverse the radio-resistance of MDA-MB-231 cells

Summary

Introduction

Breast cancer is one of the major causes of death due to cancer worldwide, especially in women [1]. Many therapies are available such as surgical resection, with or without lymph node dissection, radiation, and chemotherapy [2]. Radiotherapy is applied for most breast cancer patients after surgical resection, but not all patients obtain the same benefits, because some of them suffer from a loco-regional relapse. Radio-resistance is the primary reason for this relapse [4]. Radio-resistance is a process in which the tumor cells or tissues adapt to radio therapyinduced damage [5] and survive irradiation (IR) [6,7]. The DDR may help the cells survive the IR-induced DNA damage, eventually developing radio-resistance by increasing the DDR rate. Repopulation, hypoxic tumor areas, and cancer stemness are involved in radio-resistance. In DDR to IR and cancer stemness, several signaling pathways are reportedly involved: phosphatidylinositol

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