Simple Summary Endometrial cancer (EC) is the second most common female malignancy worldwide, but the pathogenesis is not fully understood. Tribbles pseudokinase 3 (TRIB3) is a kind of scaffold protein that may regulate multiple cellular processes by organizing binding partner proteins involving signaling transduction pathways. The goal of this study is to investigate if TRIB3 is involved in the malignant features of EC. Our data demonstrate that TRIB3 positively regulates the cancer stem-cell activity and in vivo tumorigenicity of EC cells by modulating beta-catenin signaling through directly interacting with the ELF4 transcription factor. Our results could lead to new insight for developing a novel therapeutic strategy for EC by targeting TRIB3. Endometrial cancer (EC) is the second most common gynecological malignancy worldwide. Tribbles pseudokinase 3 (TRIB3) is a scaffolding protein that regulates intracellular signal transduction, and its role in tumor development is controversial. Here, we investigated the biological function of TRIB3 in EC. We found that the messenger RNA (mRNA) expression level of TRIB3 was significantly and positively correlated with shorter overall survival of EC patients in The Cancer Genome Atlas database. The protein expression of TRIB3 was found to be significantly increased in EC cancer stem cells (CSCs) enriched by tumorsphere cultivation. Knockdown of TRIB3 in EC cells suppressed tumorsphere formation, the expression of cancer stemness genes, and the in vivo tumorigenesis. The expression of beta-catenin at both the protein and the mRNA levels was downregulated upon TRIB3 silencing. TRIB3 was found to interact with E74 Like ETS transcription factor 4 (ELF4) in the nucleus and bound to ELF4 consensus sites within the catenin beta 1 (CTNNB1) promoter in EC cell lines. These data indicated that TRIB3 may regulate CTNNB1 transcription by enhancing the recruitment of ELF4 to the CTNNB1 promoter. In conclusion, our results suggest that TRIB3 plays an oncogenic role in EC and positively regulates the self-renewal and tumorigenicity of EC-CSCs. Targeting TRIB3 is considered as a potential therapeutic strategy in future EC therapy.
