The canonical Wnt/β-Catenin signaling pathway is widely involved in regulating diverse biological processes. Dysregulation of the pathway results in severe consequences, such as developmental defects and malignant cancers. Here, we identified Ube2s as a novel activator of the Wnt/β-Catenin signaling pathway. It modified β-Catenin at K19 via K11-linked polyubiquitin chain. This modification resulted in an antagonistic effect against the destruction complex/β-TrCP cascade-orchestrated β-Catenin degradation. As a result, the stability of β-Catenin was enhanced, thus promoting its cellular accumulation. Importantly, Ube2s-promoted β-Catenin accumulation partially released the dependence on exogenous molecules for the process of embryonic stem (ES) cell differentiation into mesoendoderm lineages. Moreover, we demonstrated that UBE2S plays a critical role in determining the malignancy properties of human colorectal cancer (CRC) cells in vitro and in vivo. The findings in this study extend our mechanistic understanding of the mesoendodermal cell fate commitment, and provide UBE2S as a putative target for human CRC therapy.

Introduction: UEV1A encodes a ubiquitin-conjugating enzyme variant (Ubc13), which is required for Ubc13-catalyzed Lys63-linked polyubiquitination of target proteins and nuclear factor κB (NF-кB) activation. Previous reports have correlated the level of UEV1A expression with tumorigenesis; however, the detailed molecular events leading to tumors particularly breast cancer and metastasis are unclear. This study is to investigate roles of different UEV1 splicing variants, and its close homolog MMS2, in promoting tumorigenesis and metastasis in breast cancer cells. Methods: We experimentally manipulated the UEV1 and MMS2 levels in MDA-MB-231 breast cancer cells and monitored their effects on cell invasion and migration, as well as tumor formation and metastasis in xenograft mice. The underlying molecular mechanisms leading to metastasis were also examined. Results: It was found that overexpression of UEV1A alone, but not UEV1C or MMS2, is sufficient to induce cell invasion in vitro and metastasis in vivo. This process is mediated by NF-κB activation and requires functional Ubc13. Our experimental data establish that among NF-κB target genes, UEV1A-regulated matrix metalloproteinase-1 (MMP1) expression plays a critical role in cell invasion and metastasis. Interestingly, experimental depletion of UEV1 in MDA-MB-231 cells reduces MMP1 expression and prevents tumor formation and metastasis in a xenograft mouse model, while overexpression of MMP1 overrides the metastasis effects in UEV1-depleted cells. Conclusions: These results identify UEV1A as a potential therapeutic target in the treatment of metastasic breast cancers.

Sox2 has a critical role in embryonic stem (ES) cell maintenance and differentiation. Interestingly, its activity is highly dosage-dependent. Although transcriptional regulation of Sox2 has been extensively studied, the mechanisms orchestrating its degradation remain unclear. In this study, we identified ubiquitin-conjugating enzyme E2S (Ube2s) as a novel effector for Sox2 protein degradation. Ube2s mediates K11-linked polyubiquitin chain formation at the Sox2-K123 residue, thus marking it for proteasome-mediated degradation. Besides its role in fine-tuning the precise level of Sox2, Ube2s reinforces the self-renewing and pluripotent state of ES cells. Importantly, it also represses Sox2-mediated ES cell differentiation toward the neural ectodermal lineage.

Ubiquitination regulates nearly every aspect of cellular events in eukaryotes. It modifies intracellular proteins with 76-amino acid polypeptide ubiquitin (Ub) and destines them for proteolysis or activity alteration. Ubiquitination is generally achieved by a tri-enzyme machinery involving ubiquitin activating enzymes (E1), ubiquitin conjugating enzymes (E2) and ubiquitin ligases (E3). E1 activates Ub and transfers it to the active cysteine site of E2 via a transesterification reaction. E3 coordinates with E2 to mediate isopeptide bond formation between Ub and substrate protein. The E1-E2-E3 cascade can create diverse types of Ub modifications, hence effecting distinct outcomes on the substrate proteins. Dysregulation of ubiquitination results in severe consequences and human diseases. There include cancers, developmental defects and immune disorders. In this review, we provide an overview of the ubiquitination machinery and discuss the recent progresses in the ubiquitination-mediated regulation of embryonic stem cell maintenance and cancer biology.

Immune therapy based on programmed death-ligand 1 (PD-L1) is widely used to treat human tumors. The current strategies to improve immune checkpoint blockade therapy fail in rescuing increased expression of PD-L1 in tumor issues. Here, we for the first time synthesized the metal—organic framework (MOF) nanocrystals of rare-earth element dysprosium (Dy) coordinated with tetrakis(4-carboxyphenyl) porphyrin (TCPP), which show well-defined two-dimensional morphologies. The MOF nanocrystals of Dy-TCPP could apparently reduce PD-L1 expression in tumor cells both in vitro and in vivo, and therefore display effective tumor treatment through immune therapy without any immune checkpoint inhibitor drugs. Considering the sensitivity of TCPP ligand toward ultrasound, the prepared Dy-TCPP can also realize sonodynamic therapy (SDT) besides immune therapy. In addition, the Dy-TCPP nanocrystals can efficiently obtain T₂-weight magnetic resonance imaging (MRI) of tumor sites. Our study provides the Dy-TCPP nanocrystals as promising diagnostic MRI-guided platforms for the combined treatment on tumors with SDT and immune therapy. Moreover, this strategy succeeds in reducing the elevated expression of PD-L1 in tumor cells, which might serve as a novel avenue for tumor immunotherapy in future.

Hypoxia in the tumor microenvironment (TME) greatly limits the tumor-killing therapeutic efficacy of sonodynamic therapy (SDT); this phenomenon is further exacerbated by increased glutathione (GSH) levels in cancer cells. Simultaneously, cancer starvation therapy is increasingly recognized nowadays as a promising clinical translation, but the efficacy of glucose oxidase (GOx)-based starvation therapy is also limited by the lack of oxygen in the tumor. Glycer-aldehyde-3-phosphate dehydrogenase (GAPDH) is a key glycolytic enzyme and can therefore be a target for starvation therapy in the absence of oxygen engagement. Here, we proposed thiol-ene click reactions based on a two-dimensional metal-organic framework (MOF) modification for tumor treatments to enable the combination of SDT and starvation therapy. Experimental studies demonstrated that the prepared material could consume GSH and GAPDH free from oxygen in TME, which benefited from the thiol-ene click reactions between the MOFs and thiol substances in cancer cells. Further experiments in vitro and in vivo indicated the prepared MOF materials could kill cancer cells efficiently. This study is expected to create a promising avenue for thiol-ene click reactions in SDT and starvation therapy for cancer.