Implication of IZUMO2 in the cell‐in‐cell phenomenon: A potential therapeutic target for triple‐negative breast cancer

• Published in: Thoracic cancer Vol. 15; no. 7; pp. 513 - 518
• Main Authors: Higashi, Toshiya, Saigo, Chiemi, Chikaishi, Wakana, Hayashi, Hirokatsu, Hanamatsu, Yuki, Futamura, Manabu, Matsuhashi, Nobuhisa, Takeuchi, Tamotsu
• Format: Journal Article
• Language: English
• Published: Melbourne John Wiley & Sons Australia, Ltd 01.03.2024; John Wiley & Sons, Inc; Wiley
• Subjects: adiponectin‐expressing Tregs; Antigens; Apoptosis; Breast cancer; Cells; cell‐in‐cell activity; Cloning; Cytokeratin; Cytoplasm; Estrogens; Gene expression; Immunoassay; IZUMO2; Lasers; Mesothelioma; Monoclonal antibodies; monoclonal antibody; Original; Peptides; Spectrum analysis; Targeted cancer therapy; triple‐negative breast cancer; adiponectin-expressing Tregs; IZUMO2; triple-negative breast cancer; cell-in-cell activity; monoclonal antibody
• ISSN: 1759-7706; 1759-7714
• DOI: 10.1111/1759-7714.15189

Background Triple‐negative breast cancer (TNBC) is characterized by the loss of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. The aggressive clinicopathological features and resistance to currently available therapeutics of the disease warrant an urgent need for the development of novel alternate therapeutic options. We have previously reported adiponectin‐expressing regulatory T cells (A‐Tregs), which can induce apoptosis in TNBC through the cell‐in‐cell phenomenon. In this study, we aimed to elucidate the molecule that allows TNBC cells to engulf A‐Tregs. Methods A monoclonal antibody, which repressed the engulfment of A‐Tregs by TNBC cells, was developed. Immunoprecipitation followed by mass spectrometry and small interfering RNAs‐mediated gene silencing was performed to characterize the antigen. Results We successfully generated a monoclonal antibody, designated G1D7, which abrogated the engulfment of A‐Tregs by TNBC and subsequent A‐Treg‐mediated apoptosis. G1D7 detected the immunoglobulin‐like type I membrane protein IZUMO2, a molecule related to IZUMO1 that is essential for cell–cell membrane binding and fusion of sperm to oocyte. Conclusion The findings highlight the importance of IZUMO2 on TNBC cells in facilitating the cell‐in‐cell phenomenon by A‐Tregs. (a) Several adiponectin‐expressing Tregs attached to MDA‐MB‐231 cells (red signal). Note the integration of adiponectin‐expressing Tregs into the cytoplasm (yellow, merging of red and green). (b and c) An angle of 45 degrees and vertical cell‐in‐cell images are shown in (b) and (c), respectively. Note the destruction (denoted by the white line) of MDA‐MB‐231 cells after the occurrence of the cell‐in‐cell phenomenon. (d) An antibody to IZUMO2, designated G1D7 (final concentration of 1 μg/mL) markedly reduced the occurrence of cell‐in‐cell phenomenon. (e) siRNA‐mediated silencing of the IZUMO2 gene also abrogated the cell‐in‐cell phenomenon.