Background and Purpose In non‐small‐cell lung carcinoma (NSCLC) patients, the L858R/T790M mutation of the epithelial growth factor receptor (EGFR) is a major cause of acquired resistance to EGFR‐TKIs treatment that limits their therapeutic efficacy. Identification of drugs that can preferentially kill the NSCLC harbouring L858R/T790M mutation is therefore critical. Here, we have evaluated the effects of ursolic acid, an active component isolated from herbal sources, on erlotinib‐resistant H1975 cells that harbour the L858R/T790M mutation. Experimental Approach Gene expression omnibus (GEO) profiles analyses was applied to detect differentially expressed genes in NSCLC cells harbouring EGFR mutation. AnnexinV‐FITC/PI, TUNEL staining, MTT, wound healing, RT‐PCR, qRT‐PCR, western blots, immunostaining, dual‐luciferase reporters and ChIP‐PCR were utilized to investigate the effects of ursolic acid in vitro and in vivo. Key Results The cancer/testis antigen family 45 member A2 (CT45A2) was highly expressed in H1975 cells. Ectopic expression of CT45A2 in H1975 cells increased cell proliferation and motility in vitro. Silencing the CT45A2 expression strongly attenuated H1975 cells motility and growth. The anti‐cancer effect of ursolic acid was critically dependent on CT45A2 expression in H1975 cells. Ursolic acid suppressed CT45A2 gene transcription mediated by transcriptional factor TCF4 and β‐catenin signalling. Conclusions and Implications CT45A2 is a novel oncogene for NSCLC with an EGFR T790 mutation. Ursolic acid induced apoptosis and inhibited proliferation of H1975 cells by negatively regulating the β‐catenin/TCF4/CT45A2 signalling pathway. Therefore, ursolic acid may be a potential candidate treatment for NSCLC harbouring the EGFR‐L858R/T790M mutation.

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Cancer stem-like cells (CSCs) have been reported to play major roles in tumorigenesis, tumor relapse, and metastasis after therapy against colorectal carcinoma (CRC). Therefore, identification of colorectal CSC regulators could provide promising targets for CRC. Ligand-of-Numb protein X1 (LNX1) is one E3 ubiquitin ligase which mediates the ubiquitination and degradation of Numb. Although several studies indicate LNX1 could be a potential suppressor of cancer diseases, the functions of LNX1 in mediating cancer stemness remain poorly understood. In this study, LNX1 was identified as a negative regulator of cancer stemness in CRC, which was downregulated in colonospheres or side population (SP) cells. Furthermore, the coxsackievirus and adenovirus receptor (CXADR) was found to be one critical downstream mediator of cancer stemness regulated by LNX1. Interestingly, the anti-breast cancer drug tamoxifen was found to be an agonist of LNX1 and suppress cancer stemness in CRC. In sum, this study provided the evidences that LNX1 signaling plays important roles in regulating the stemness of colon cancer cells.

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