SummaryWnt signalling through b-catenin and the lymphoid-enhancing factor 1/T-cell factor (LEF1/TCF) family of transcription factors maintains stem cell properties in both normal and malignant tissues; however, the underlying molecular pathway involved in this process has not been completely defined. Using a microRNA microarray screening assay, we identified let-7 miRNAs as downstream targets of the Wnt-b-catenin pathway. Expression studies indicated that the Wnt-b-catenin pathway suppresses mature let-7 miRNAs but not the primary transcripts, which suggests a post-transcriptional regulation of repression. Furthermore, we identified Lin28, a negative let-7 biogenesis regulator, as a novel direct downstream target of the Wnt-b-catenin pathway. Loss of function of Lin28 impairs Wnt-bcatenin-pathway-mediated let-7 inhibition and breast cancer stem cell expansion; enforced expression of let-7 blocks the Wnt-b-catenin pathway-stimulated breast cancer stem cell phenotype. Finally, we demonstrated that the Wnt-b-catenin pathway induces Lin28 upregulation and let-7 downregulation in both cancer samples and mouse tumour models. Moreover, the delivery of a modified lin28 siRNA or a let-7a agomir into the premalignant mammary tissues of MMTV-wnt-1 mice resulted in a complete rescue of the stem cell phenotype driven by the Wnt-b-catenin pathway. These findings highlight a pivotal role for Lin28/let-7 in Wnt-b-catenin-pathwaymediated cellular phenotypes. Thus, the Wnt-b-catenin pathway, Lin28 and let-7 miRNAs, three of the most crucial stem cell regulators, connect in one signal cascade.

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SummaryWnt-b-catenin signaling participates in the epithelial-mesenchymal transition (EMT) in a variety of cancers; however, its involvement in hepatocellular carcinoma (HCC) and downstream molecular events is largely undefined. HNF4a is the most prominent and specific factor maintaining the differentiation of hepatic lineage cells and a potential EMT regulator in HCC cells. However, the molecular mechanisms by which HNF4a maintains the differentiated liver epithelium and inhibits EMT have not been completely defined. In this study, we systematically explored the relationship between Wnt-b-catenin signaling and HNF4a in the EMT process of HCC cells. Our results indicated that HNF4a expression was negatively regulated during Wnt-b-catenin signaling-induced EMT through Snail and Slug in HCC cells. In contrast, HNF4a was found to directly associate with TCF4 to compete with b-catenin but facilitate transcription corepressor activities, thus inhibiting expression of EMT-related Wnt-b-catenin targets. Moreover, HNF4a may control the switch between the transcriptional and adhesion functions of b-catenin. Overexpression of HNF4a was found to completely compromise the Wnt-b-catenin-signaling-induced EMT phenotype. Finally, we determined the regulation pattern between Wnt-b-catenin signaling and HNF4a in rat tumor models. Our studies have identified a double-negative feedback mechanism controlling Wnt-b-catenin signaling and HNF4a expression in vitro and in vivo, which sheds new light on the regulation of EMT in HCC. The modulation of these molecular processes may be a method of inhibiting HCC invasion by blocking Wnt-b-catenin signaling or restoring HNF4a expression to prevent EMT.

There is a double-negative feedback mechanism that controls TEAD-YAP and HNF4α expression in vitro and in vivo, thereby regulating cellular proliferation and differentiation. Given that YAP acts as a dominant oncogene in HCC and plays a crucial role in stem cell homeostasis and tissue regeneration, manipulating the interaction between YAP, TEADs, and HNF4α may provide a new approach for HCC treatment and regenerative medicine. (Hepatology 2017;65:1206-1221).

Our analysis identified several clinicopathologic factors associated with CLNM. These findings may guide the necessity and extent of prophylactic CLND and ultimately improve the outcomes of patients with PTC.