A Novel Role of Dickkopf-Related Protein 3 in Macropinocytosis in Human Bladder Cancer T24 Cells

A Comprehensive Identification of Chicken Egg White Phosphoproteomics Based on a Novel Digestion Approach

There are plenty of phosphoproteins in chicken egg white (CEW), which are of great significance for the biological activity and function of CEW. In this study, phosphorylated proteins in CEW were identified and analyzed based on two digestion strategies (trypsin and trypsin/glutamyl endoproteinase). Besides, the enrichment strategy of immobilized metal affinity chromatography was used, and phosphopeptides were identified by nano liquid chromatography/tandem mass spectrometry. A total of 189 phosphosites mapped onto 166 phosphopeptides corresponding to 96 phosphoproteins were identified. Gene ontology analysis suggested that these phosphoproteins of CEW mainly participated in biological processes such as "cell process", "biological regulation", and "response to stimulus". Moreover, the phosphoproteins of CEW were involved in molecular functions, primarily including "binding" and "catalytic activity". On the basis of the available literature, the research was the first comprehensive identification of chicken egg white phosphoproteins. This study further enriched the identification of phosphoproteins in CEW and laid a foundation for the subsequent study of phosphoproteins.

MiR-425 Promotes Migration and Invasion in Bladder Cancer by Targeting Dickkopf 3

Background: Bladder cancer (BC) is a common malignancy with high morbidity and mortality. MicroRNAs (miRNAs) are critical post-transcriptional regulators in various cancers. This study aimed to investigate the effect of miR-425 on the migration and invasion of BC.

Methods: The expression of miR-425 and Dickkopf 3 (DKK3) was examined in clinical BC specimens. T24 and 5637 BC cell lines were employed and transfected with miR-425 inhibitors. The correlation between miR-425 and DKK3 was determined by a luciferase reporter assay. Cell migration and invasion capacity were measured by wound healing and Transwell assays. The expression levels of DKK3, E-cadherin, N-cadherin and vimentin were analysed by Western blotting and qRT-PCR.

Results: miR-425 was negatively correlated with the expression of DKK3 in clinical BC specimens. Further studies identified DKK-3 as a direct target of miR-425. Moreover, knockdown of miR-425 promoted the expression of DKK3 and suppressed cell migration and invasion capacity. miR-425 silencing increased E-cadherin levels but decreased vimentin and N-cadherin protein levels in T24 and 5637 cells.

Conclusion: Our study indicated that miR-425 promoted the migration and invasion of BC via targeting DKK3.

Meridianin C inhibits the growth of YD-10B human tongue cancer cells through macropinocytosis and the down-regulation of Dickkopf-related protein-3

Meridianin C is a marine natural product known for its anti-cancer activity. At present, the anti-tumour effects of meridianin C on oral squamous cell carcinoma are unknown. Here, we investigated the effect of meridianin C on the proliferation of four different human tongue cancer cells, YD-8, YD-10B, YD-38 and HSC-3. Among the cells tested, meridianin C most strongly reduced the growth of YD-10B cells; the most aggressive and tumorigenic of the cell lines tested. Strikingly, meridianin C induced a significant accumulation of macropinosomes in the YD-10B cells; confirmed by the microscopic and TEM analysis as well as the entry of FITC-dextran, which was sensitive to the macropinocytosis inhibitor amiloride. SEM data also revealed abundant long and thin membrane extensions that resemble lamellipodia on the surface of YD-10B cells treated with meridianin C, pointing out that meridianin C-induced macropinosomes was the result of macropinocytosis. In addition, meridianin C reduced cellular levels of Dickkopf-related protein-3 (DKK-3), a known negative regulator of macropinocytosis. A role for DKK-3 in regulating macropinocytosis in the YD-10B cells was confirmed by siRNA knockdown of endogenous DKK-3, which led to a partial accumulation of vacuoles and a reduction in cell proliferation, and by exogenous DKK-3 overexpression, which resulted in a considerable inhibition of the meridianin C-induced vacuole formation and decrease in cell survival. In summary, this is the first study reporting meridianin C has novel anti-proliferative effects via macropinocytosis in the highly tumorigenic YD-10B cell line and the effects are mediated in part through down-regulation of DKK-3.

The Canonical Wnt Pathway Drives Macropinocytosis in Cancer

Macropinocytosis has emerged as an important pathway of protein acquisition in cancer cells, particularly in tumors with activated Ras such as pancreatic and colon cancer. Macropinocytosis is also the route of entry of Bacillus Calmette-Guerin (BCG) and other microbial therapies of cancer. Despite this important role in tumor biology and therapy, the full mechanisms by which cancer cells can activate macropinocytosis remain incompletely defined. Using BCG uptake to assay macropinocytosis, we executed a genome-wide shRNA screen for macropinocytosis activators and identified Wnt pathway activation as a strong driver of macropinocytosis. Wnt-driven macropinocytosis was downstream of the β-catenin-dependent canonical Wnt pathway, was PAK1 dependent, and supported albumin-dependent growth in Ras-WT cells. In cells with activated Ras-dependent macropinocytosis, pharmacologic or genetic inhibition of Wnt signaling suppressed macropinocytosis. In a mouse model of Wnt-driven colonic hyperplasia via APC silencing, Wnt-activated macropinocytosis stimulated uptake of luminal microbiota, a process reversed by topical pharmacologic inhibition of macropinocytosis. Our findings indicate that Wnt pathway activation drives macropinocytosis in cancer, and its inhibition could provide a therapeutic vulnerability in Wnt-driven intestinal polyposis and cancers with Wnt activation.Significance: The Wnt pathway drives macropinocytosis in cancer cells, thereby contributing to cancer growth in nutrient-deficient conditions and, in the context of colon cancer, to the early phases of oncogenesis. Cancer Res; 78(16); 4658-70. ©2018 AACR.

Dickkopf homolog 3 (DKK3): A candidate for detection and treatment of cancers?

Wnt signaling is an evolutionary highly conserved pathway that is modulated by several inhibitors and activators, and plays a key role in numerous physiological processes. One of the extracellular Wnt inhibitors is the DKK (Dickkopf Homolog) family which has four members (Dkk1-4) and a unique Dkk3-related gene, Dkkl1 (soggy). DKK3 is a divergent member of the DKK protein family. Evidence suggests that DKK3 may serve as a potential therapeutic target in several types of human cancers. We review here the biological role of DKK3 as a tumor suppressor gene (TSG) or oncogene, and its correlation with various miRNAs. In addition, we discuss the role of polymorphisms and promoter methylation of the DKK3 gene, and of its expression in regulating cancer cell proliferation. Finally, we propose that DKK3 may be considered as both a biomarker and a therapeutic target in different cancers.