Transcription factors related to chondrogenesis in pleomorphic adenoma of the salivary gland: a mechanism of mesenchymal tissue formation

Abstract

In salivary gland pleomorphic adenoma, expression of extracellular matrix (ECM) substances indicates that tumor epithelial cells are becoming chondrogenic and will produce cartilage-like mesenchymal tissues. Sox9, the master transcription factor of chondrogenesis, is expressed in mouse salivary gland cells. To clarify the mechanism behind chondrogenesis in tumor epithelial cells, we examined the expression of transcription factors related to chondrogenesis in tumors and salivary glands. Reverse transcriptase-polymerase chain reaction (RT-PCR), quantitative real-time RT-PCR, and immunostaining were performed on pleomorphic adenoma tissues, salivary gland tissues, and human submandibular gland (HSG) cells. The mRNAs of essential transcription factors for chondrogenesis-Sox9, Sox6, and Sox5-were detected in both tumor and salivary gland tissues. The mRNAs of aggrecan and type II collagen-cartilage-specific ECM substances-were detected only in tumors. Sox9 and Sox6 proteins were colocalized in many epithelial cells in tumors and salivary glands. Tumor epithelial cells also possessed aggrecan protein and occasionally type II collagen protein. Moreover, mRNAs for transcription repressors of chondrogenesis δEF1 and AP-2α were detected in both tumors and salivary glands, whereas Twist1 mRNA was detected only in salivary glands and was at significantly low-to-undetectable levels in tumors. Twist1 protein was localized in the Sox9-expressing salivary gland cells. HSG cells expressed Sox9, Sox6, and Twist1, but not aggrecan or type II collagen, and thus were similar to salivary gland cells. Twist1 depletion by Twist1 siRNA led to the upregulation of aggrecan and type II collagen mRNA expression in HSG cells. In contrast, forced expression of Twist1, using Twist1 cDNA, resulted in the downregulation of both these genes. Taken together, these results indicate that salivary gland cells have a potential for chondrogenesis, and Twist1 depletion concomitant with neoplastic transformation, which would permit tumor epithelial cells to produce cartilage-like mesenchymal tissues in salivary gland pleomorphic adenoma. (2016) 96, 16-24; doi:10.1038/labinvest.2015 published online 26 October 2015 Pleomorphic adenoma is the most common tumor of the salivary gland. It is characterized by mixed appearance of epithelial and mesenchymal components. 1,2 A number of ultrastructural and immunohistochemical studies have shown that the mesenchymal component (typically composed of myxoid and chondroid tissues) is epithelial in origin (e.g., Dardick et al. 3,4 and Erlandson et al. 5 ). Immunohistochemical and in situ hybridization studies have shown the production of aggrecan and type II collagen, extracellular matrix (ECM) substances specific to cartilage, in the myxoid and chondroid tissues. [6][7][8][9] As aggrecan is also produced in the epithelial component, 6,9 epithelial cells of pleomorphic adenoma could conceivably become chondrogenic and produce mesenchymal tissues similar to cartilage. Laboratory InvestigationWhen forced to express ...

Pleomorphic Adenoma of the Salivary Glands and Epithelial–Mesenchymal Transition

“…In contrast, overexpression of Twist1 led to the downregulation of these two genes. These results supported our hypothesis [ 61 ].…”

“…The occurrence of EMT within PA has been demonstrated by immunohistochemical and ultrastructural analyses [ 48 , 58 , 59 ], but no specific TFs have been identified. To our knowledge, only four studies have investigated the expression of EMT-TFs in PAs through the examination of TWIST or SLUG expression by immunohistochemical or reverse transcription-quantitative polymerase chain reaction (RT–qPCR) analysis [ 60 , 61 , 62 , 63 ].…”

“…We have previously provided conclusive but indirect evidence that epithelial cells differentiate into chondrocytes during salivary gland PA tumorigenesis [ 61 ]. Our study found that epithelial cells express Sox9 and Sox6 and produce aggrecan and type II collagen, which are substances in the extracellular matrix peculiar to cartilage.…”