Ehrlichia chaffeensis TRP120 ubiquitinates tumor suppressor APC to modulate Hippo and Wnt signaling.

Ehrlichia chaffeensis: TRP120 is a multifunctional effector that acts as a ligand mimic to activate evolutionary conserved eukaryotic signaling pathways Notch, Wnt, Hedgehog and Hippo. In addition, TRP120 is also a HECT E3 ubiquitin ligase known to ubiquitinate several host cell regulatory proteins (FBW7, PCGF5 and ENO-1) for degradation. We previously determined that TRP120 ubiquitinates the Notch negative regulator, FBW7, to maintain Notch signaling and promote infection. In this study, we investigated a potential mechanism used by Ehrlichia chaffeensis to maintain Hippo and Wnt signaling by ubiquitinating the tumor suppressor, adenomatous polyposis coli (APC), a negative regulator of Wnt and Hippo signaling. We determined that APC was rapidly degraded during E. chaffeensis infection despite increased APC transcription. Moreover, RNAi knockdown of APC significantly increased E. chaffeensis infection and coincided with increased active Yap and ß-catenin in the nucleus. We observed strong nuclear colocalization between TRP120 and APC in E. chaffeensis-infected THP-1 cells and after ectopic expression of TRP120 in HeLa cells. Additionally, TRP120 interacted with both APC full length and truncated isoforms via co-immunoprecipitation. Further, TRP120 ubiquitination of APC was demonstrated in vitro and confirmed by ectopic expression of a TRP120 HECT Ub ligase catalytic site mutant. This study identifies APC as a TRP120 HECT E3 Ub ligase substrate and demonstrates that TRP120 ligase activity promotes ehrlichial infection by degrading tumor suppressor APC to positively regulate Hippo and Wnt signaling.

Enhanced ApcMin/+ adenoma formation after epithelial CUL4B deletion by recruitment of myeloid-derived suppressor cells.

Colorectal cancer (CRC) stands as a prevalent malignancy globally. A pivotal event in CRC pathogenesis involves the loss-of-function mutation in the APC gene, leading to the formation of benign polyps. Despite the well-established role of APC, the contribution of CUL4B to CRC initiation in the pre-tumorous stage remains poorly understood. In this investigation, we generated a murine model by crossing ApcMin/+ mice with Cul4bΔIEC mice to achieve specific deletion of Cul4b in the gut epithelium against an ApcMin/+ background. By employing histological methods, RNA-sequencing (RNA-seq), and flow cytometry, we assessed alterations and characterized the immune microenvironment. Our results unveiled that CUL4B deficiency in gut epithelium expedited ApcMin/+ adenoma formation. Notably, CUL4B in adenomas restrained the accumulation of tumor-infiltrating myeloid-derived suppressor cells (MDSCs). In vivo inhibition of MDSCs significantly delayed the growth of CUL4B deleted ApcMin/+ adenomas. Furthermore, the addition of MDSCs to in vitro cultured ApcMin/+; Cul4bΔIEC adenoma organoids mitigated their alterations. Mechanistically, CUL4B directly interacted with the promoter of Csf3, the gene encoding granulocyte-colony stimulating factor (G-CSF) by coordinating with PRC2. Inhibiting CUL4B epigenetically activated the expression of G-CSF, promoting the recruitment of MDSCs. These findings offer novel insights into the tumor suppressor-like roles of CUL4B in regulating ApcMin/+ adenomas, suggesting a potential therapeutic strategy for CRC initiation and progression in the context of activated Wnt signaling.

Design, synthesis and structure-activity relationship study of APC/Asef inhibitors / 上海交通大学学报（医学版）

Objective: To design and synthesize APC/Asef peptide inhibitors and investigate the structure-activity relationship between peptides inhibitors and APC protein for exploring better inhibitors. Methods: Based on the best-class inhibitor we had found before-MAI-400, eleven peptide inhibitors were designed, which included the changes of N-terminal capping group, the first amino acid Ala, the fifth amino acid Leu and the last amino acid Glu. According to the results of fluorescence polarization activity detection system and molecular docking, the structure-activity relationship of peptide inhibitors was investigated. Results: Among the eleven peptides, MPI-11 had the highest affinity, whose half maximal inhibitory concentration (IC50) was 0.973 1 mmol/L. The capping group of peptide N-terminal with tert-butoxycarbonyl group reduced the activity slightly. The substitution of the Ala caused different results, changing into Trp, His and Thr definitely reduced the activity but the substitution by Tyr or Phe did not influence the activity too much. And introducing benzene ring into the side chain of Leu had few effects on activity improving. The substitution of side chain carboxyl for amide at the C-terminal glutamate had little effect on the activity. Conclusion: Among the eleven peptides, the capping group of peptide N-terminal cannot be substituted into small groups and Ala cannot be substituted into other amino acids.

Expression of beta-catenin and Adenomatous Polyposis Coli(APC) Protein in Squamous Cell Carcinoma of the Laryngeal Cancers / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: beta-catenin has an essential role in intercellular adhesion and signal transduction. The Adenomatous poliposis coli (APC) protein interacts with beta-catenin in a multi-protein complex to regulate the level of expression of beta-catenin. Mutations in beta-catenin or APC gene can lead to the accumulation of beta-catenin in the cytosol and the nucleus. This study was designed to investigate the expression of APC and beta-catenin in laryngeal cancer. SUBJECTS AND METHOD: Immunohistochemical methods were used to determine the beta-catenin and APC protein expression in 15 laryngeal cancers. Results were correlated with clinicopathological parameters. RESULTS: beta-catenin expression to the plasma membrane was reduced or absent in 11 of 15 cases (73%) of the laryngeal cancers. Cytoplasmic expression of the beta-catenin was seen in 6 out of 15 cases (40%). APC immunoactivity was negative in 5 of 15 (33%) of the laryngeal cancers. One of the six cytoplasmic expressions of the beta-catenin was negative for APC immunoactivity, and one of the five negative for APC immunoactivity was cytoplasmic expression of the beta-catenin. CONCLUSION: There was no correlation between beta-catenin and APC protein in the analysis. This finding suggests that cytoplasmic expression of the beta-catenin resulted not from the APC mutation but from the beta-catenin mutation and abnormal Wnt signal. Only the expression of the beta-catenin in cytoplasm was associated with lymph node metastasis.