MELK promotes Endometrial carcinoma progression via activating mTOR signaling pathway.

Endometrial carcinoma (EC) is one of the most common gynecological malignancies among women. Maternal embryonic leucine Zipper Kinase (MELK) is upregulated in a variety of human tumors, where it contributes to malignant phenotype and correlates with a poor prognosis. However, the biological function of MELK in EC progression remains largely unknown. We explored the MELK expression in EC using TCGA and GEO databases and verified it using clinical samples by IHC methods. CCK-8 assay, colony formation assay, cell cycle assay, wound healing assay and subcutaneous xenograft mouse model were generated to estimate the functions of MELK and its inhibitor OTSSP167. qRT-PCR, western blotting, co-immunoprecipitation, chromatin immunoprecipitation and luciferase reporter assay were performed to uncover the underlying mechanism concerning MELK during the progression of EC. MELK was significantly elevated in patients with EC, and high expression of MELK was associated with serous EC, high histological grade, advanced clinical stage and reduced overall survival and disease-free survival. MELK knockdown decreased the ability of cell proliferation and migration in vitro and subcutaneous tumorigenesis in vivo. In addition, high expression of MELK could be regulated by transcription factor E2F1. Moreover, we found that MELK had a direct interaction with MLST8 and then activated mTORC1 and mTORC2 signaling pathway for EC progression. Furthermore, OTSSP167, an effective inhibitor, could inhibit cell proliferation driven by MELK in vivo and vitro assays. We have explored the crucial role of the E2F1/MELK/mTORC1/2 axis in the progression of EC, which could be served as potential therapeutic targets for treatment of EC. This research was supported by National Natural Science Foundation of China (No:81672565), the Natural Science Foundation of Shanghai (Grant NO:17ZR1421400 to Dr. Zhihong Ai) and the fundamental research funds for central universities (No: 22120180595).