SCF E3 ubiquitin ligase targets the tumor suppressor ZNRF3 for ubiquitination and degradation

Wnt signaling has emerged as a major regulator of tissue development by governing the self-renewal and maintenance of stem cells in most tissue types. As a key upstream regulator of the Wnt pathway, the transmembrane E3 ligase ZNRF3 has recently been established to play a role in negative regulation of Wnt signaling by targeting Frizzled (FZD) receptor for ubiquitination and degradation. However, the upstream regulation of ZNRF3, in particular the turnover of ZNRF3, is still unclear. Here we report that ZNRF3 is accumulated in the presence of proteasome inhibitor treatment independent of its E3-ubiquitin ligase activity. Furthermore, the Cullin 1-specific SCF complex containing β-TRCP has been identified to directly interact with and ubiquitinate ZNRF3 thereby regulating its protein stability. Similar with the degradation of β-catenin by β-TRCP, ZNRF3 is ubiquitinated by β-TRCP in both CKI-phosphorylation- and degron-dependent manners. Thus, our findings not only identify a novel substrate for β-TRCP oncogenic regulation, but also highlight the dual regulation of Wnt signaling by β-TRCP in a context-dependent manner where β-TRCP negatively regulates Wnt signaling by targeting β-catenin, and positively regulates Wnt signaling by targeting ZNRF3.

miR-let-7d regulates lung cancer cell proliferation and invasion abilities through nuclear receptor PPARγ / 中国病理生理杂志

AIM: To investigate the phenomenon that miR-let-7d regulates the proliferation and invasion abilities of the lung cancer cells through nuclear receptor peroxisome proliferator-activated receptors γ (PPARγ).METHODS: The relation between PPARγ and microRNA was analyzed by bioinformatics.The plasmid reporter assay was used to verify that PPARγ was the target of miR-let-7d.The lung cancer cell line with low expression of PPARγ was selected from different lung cancer cell lines by Western blot.The regulatory role of miR-let-7d in the lung cancer cells was determined by dual luciferase labeling and Western blot.The effect of miR-let-7d on the proliferation ability of lung cancer cells was detected by colony formation assay, the effect of miR-let-7d on the invasive ability of lung cancer cells was detected by Transwell invasion assay.RESULTS: The results of bioinformatic analysis showed that miR-let-7d regulated the expression of PPARγ, and the 3'UTR of PPARγ contained 2 functional miR-let-7d binding sites, indicating that PPARγ is a direct target of miR-let-7d.miR-let-7d was able to directly regulate the expression of PPARγ at mRNA and protein levels.Transfection of miR-let-7d inhibitor promoted the proliferation and invasion abilities of lung cancer cells by increasing the expression of PPARγ.CONCLUSION: miR-let-7d increases the expression of tumor suppressor PPARγ to inhibit the proliferation and invasive abilities of lung cancer cells.