Background: Mammalian Ste20-like kinase 4  (MST4 ), also known as serine/threonine kinase 26 (STK26 ), promotes development of several cancers and is found to be highly expressed in the placenta. However, in choriocarcinoma that originated from the placenta, the expression of MST4  was undetermined and its mechanism was unknown. In this study, the expression of MST4  in choriocarcinoma as well as the underlying mechanism was explored.
Purpose: To detect the expression of MST4  in patient samples and mechanism of mediating EMT by MST4  in choriocarcinoma.
Patients and Methods: The metastatic lesions of choriocarcinoma (n=17) and volunteer villus (n=17) were collected to determine MST4  expression using immunohistochemistry and H&E staining. We use siRNA and lentiviral vector to knockdown MST4  and use plasmid to overexpress MST4  in choriocarcinoma. Then, we apply real-time polymerase chain reaction (RT-PCR), Western blot assay and immunofluorescence assay to detect target protein expressions. Cell invasion and migration and cell proliferation were detected by transwell assay and wound healing assay and CCK-8 and cell colony formation.
Results: MST4  is lowly expressed in the metastatic lesions of choriocarcinoma patients when compared with normal villus. Knockdown of MST4  activated epithelial–mesenchymal transition (EMT) process, significantly increasing the ability of invasion and migration in choriocarcinoma cell lines (JAR and JEG-3). In contrast, the EMT process was restrained in choriocarcinoma cell lines with overexpressed MST4 . Meanwhile, genome-wide gene expression array, Western blot and ELISA revealed that tumor growth factor-beta 1 (TGF-β 1) has significantly increased. The EMT process and metastatic prompting biofunction were reversed after using TGF-β 1 inhibitor (LY364947) in the choriocarcinoma cell lines with MST4  knockdown.
Conclusion: Our studies demonstrated that MST4  was lowly expressed in patient samples. Additionally, JAR and JEG-3 increase cell invasion and migration ability while there is no influence on cell proliferation with MST4  knockdown. Conversely, the metastatic ability of JAR and JEG-3 was decreased with overexpressed MST4 . Moreover, TGF-β 1 was a key factor after MST4  knockdown. In conclusion, MST4  affects choriocarcinoma EMT by mediating TGF-β 1 expression.
Keywords: choriocarcinoma, TGF-β 1, EMT, MST4