The histogenesis of pleomorphic adenoma (PA) of the salivary glands remains controversial. PAs are characterized by the transition of epithelial cells to spindled mesenchymal cells, known as epithelial-mesenchymal transition (EMT). The present study aimed to identify a major EMT-inducing transcription factor (EMT-TF) in PAs. Real-time PCR analysis of SNAIL, SLUG, ZEB1, and TWIST1 demonstrated that only SLUG was significantly upregulated in normal salivary glands and PAs. Combined in situ hybridization for SLUG and multiplex immunohistochemistry for CK19 and P63 revealed that SLUG was specifically expressed in the myoepithelial cells of normal salivary glands. In PAs, SLUG was expressed in neoplastic myoepithelial cells and stromal cells but not in the luminal cells lining the inner layers of tumor glands. SLUG expression showed no correlation with PLAG1 expression, and in vitro experiments demonstrated that PLAG1 suppression in primary cultured PA cells or PLAG1 overexpression in HEK 293 T cells did not affect SLUG levels, indicating that PLAG1 was not involved in the upregulation of SLUG in PAs. The suppression of SLUG expression in cultured PA cells resulted in a morphology change to a less elongated shape and attenuated tumor growth. In addition, SLUG downregulation led to increased E-cadherin and decreased N-cadherin and vimentin expression levels along with decreased migratory activity in cultured PA cells. These findings suggest that SLUG is a major TF that can induce EMT in PAs. In summary, SLUG is specifically and highly expressed in the myoepithelial cells and stromal cells of PAs and is a key regulator of EMT in PAs.
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The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
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We sincerely appreciate Professor Woo Ho Kim of Superbiochips for his help with the combined RNA in situ hybridization and immunohistochemical analysis.
This research was supported by the Bio & Medical Technology Development Program of the National Research Foundation (NRF) funded by the Korean government (MSIT) (No. 2021R1C1C1011172) (to B.J.), (NO. 2020R1I1A1A01069168) (to H.K.) and research fund of Hanyang University (HY-202000000002704) (to J.K.M).
The authors declare no competing interests.
This study was approved by the Institutional Review Board of JNUH (2019–04–007). Institutional Review Board confirmed that informed consent for FFPE samples was waived because of the retrospective nature of the study, while informed consent was obtained for the primary culture of PA cells. All procedures were in accordance with the ethical standards of the Helsinki Declaration of 1964 and later versions.
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Kim, H., Lee, S.B., Myung, J.K. et al. SLUG is a key regulator of epithelial-mesenchymal transition in pleomorphic adenoma. Lab Invest 102, 631–640 (2022). https://doi.org/10.1038/s41374-022-00739-1