J Breast Cancer.  2021 Apr;24(2):138-152. 10.4048/jbc.2021.24.e6.

Increased Melanoma-Associated Antigen C2 Expression Affords Resistance to Apoptotic Deathin Suspension-Cultured Tumor Cells

Affiliations
  • 1Department of Biological Sciences, Research Center for Cellular Heterogeneity, Research Institute of Women's Health, Sookmyung Women's University, Seoul, Korea
  • 2GC LabCell, Yongin, Korea
  • 3Department of Biological Sciences, Sookmyung Women's University, Seoul, Korea

Abstract

Purpose
Melanoma-associated antigen C2 (MAGEC2) is an oncogene associated with various types of cancers. However, the biological function of MAGEC2 in circulating tumor cells remains unclear. In this study, we investigated the role of MAGEC2 using adapted suspension cells (ASCs), which were previously developed to study circulating tumor cells (CTCs).
Methods
Differential gene expression in adherent cells (ADs) and ASCs was examined using RNA-seq analysis. MAGEC2 expression was assessed using reverse transcription quantitative polymerase chain reaction (RT-qPCR), immunoblotting, and ChIP-seq analysis. Depletion of MAGEC2 expression was performed using siRNA. MAGEC2-depleted ADs and ASCs were used to investigate changes in the proliferation rate and cell cycle. Then, the protein levels of signal transducer and activator of transcription 3 (STAT3), phosphorylated STAT3, and downstream of STAT3 were measured using control and MAGEC2-depleted ADs and ASCs. In ASCs, the direct effect of active STAT3 inhibition with Stattic, a STAT3 inhibitor, was assessed in terms of proliferation and apoptosis. Finally, an Annexin V/7-AAD assay was performed to determine the percentage of apoptotic cells in the Stattic-treated cells.
Results
MAGEC2 was highly expressed in ASCs when compared with ADs. Depletion of MAGEC2 reduced the proliferation rate and viability of ASCs. To elucidate the underlying mechanism, the level of STAT3 was examined owing to its oncogenic properties. Tyrosinephosphorylated active STAT3 was highly expressed in ASCs and decreased in MAGEC2-depleted ASCs. Furthermore, on treating ASCs with Stattic, an active STAT3 inhibitor, the cells were markedly sensitive to intrinsic pathway-mediated apoptosis.
Conclusions
High MAGEC2 expression may play an important role in the survival of ASCs by maintaining the expression of activated STAT3 to prevent apoptotic cell death.

Keyword

Breast neoplasms; Neoplasm proteins; Neoplastic cells; circulating; STAT3 transcription factor
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