Stem cell protein Piwil1 endowed endometrial cancer cells with stem-like properties via inducing epithelial-mesenchymal transition

Background: Stem cell protein Piwil1 functions as an oncogene in various tumor types. However, the exact function and mechanism of Piwil1 in endometrial cancer remains unclear. Methods: The expression of Piwil1 and its relationships with clinicopathological factors were investigated using immunohistochemistry. Up-or down-regulation of Piwil1 were achieved by stable or transient transfection with plasmids or short hairpin RNA (shRNA). Effects of Piwil1 on cancer cells viability, invasion and migration were evaluated by MTT, plate colony formation, transwell assay and nude mouse tumor xenograft assay. The stem-like properties of endometrial cancer cells was detected by spheroid formation assay. Effects of Piwil1 on expression levels of target genes were detected by qRT-PCR, western blotting and Immunofluorescence. Results: Compared with atypical hyperplasia and normal tissues, Piwil1 was much higher in endometrial carcinoma tissues. We found that Piwil1 expression was significantly correlated with FIGO stage, lymphovascular space involvement, lymph node metastasis and level of myometrial invasion. Overexpression of Piwil1 functioned to maintain stem-like characteristics, including enhancing tumor cell viability, migration, invasion and sphere-forming activity. Conversely, Piwil1 knockdown inhibited cell viability, migration, invasion, sphere-forming activity in vitro and tumor formation in xenograft model in vivo. Furthermore, study of the expression of epithelial and mesenchymal markers showed that Piwil1 was responsible for an EMT-like phenotype associated with an increase in mesenchymal markers and suppression of E-cadherin. Moreover, Piwil1 augmented expression levels of CD44 and ALDH1 expression, two known endometrial CSC markers, as well as other stemness-associated genes. Conclusions: Our results suggested that stem cell protein Piwil1 play important roles in regulating EMT and the acquisition of stem-like properties of endometrial cancer cells. Therefore, it indicated that Piwil1 may represent a promising target for developing a novel treatment strategy for endometrial cancer.