Discovery of a small molecule that inhibits Bcl-3-mediated cyclin D1 expression in melanoma cells.

Molecular targeted therapy using a drug that suppresses the growth and spread of cancer cells via inhibition of a specific protein is a foundation of precision medicine and treatment. High expression of the proto-oncogene Bcl-3 promotes the proliferation and metastasis of cancer cells originating from tissues such as the colon, prostate, breast, and skin. The development of novel drugs targeting Bcl-3 alone or in combination with other therapies can cure these patients or prolong their survival. As a proof of concept, in the present study, we focused on metastatic melanoma as a model system. High-throughput screening and in vitro experiments identified BCL3ANT as a lead molecule that could interfere with Bcl-3-mediated cyclin D1 expression and cell proliferation and migration in melanoma. In experimental animal models of melanoma, it was demonstrated that the use of a Bcl-3 inhibitor can influence the survival of melanoma cells. Since there are no other inhibitors against Bcl-3 in the clinical pipeline for cancer treatment, this presents a unique opportunity to develop a highly specific drug against malignant melanoma to meet an urgent clinical need.

Nemo-like kinase regulates the expression of vascular endothelial growth factor (VEGF) in alveolar epithelial cells.

The canonical Wnt signaling can be silenced either through ß-catenin-mediated ubiquitination and degradation or through phosphorylation of Tcf and Lef by nemo-like kinase (NLK). In the present study, we generated NLK deficient animals and found that these mice become cyanotic shortly before death because of lung maturation defects. NLK-/- lungs exhibited smaller and compressed alveoli and the mesenchyme remained thick and hyperplastic. This phenotype was caused by epithelial activation of vascular endothelial growth factor (VEGF) via recruitment of Lef1 to the promoter of VEGF. Elevated expression of VEGF and activation of the VEGF receptor through phosphorylation promoted an increase in the proliferation rate of epithelial and endothelial cells. In summary, our study identifies NLK as a novel signaling molecule for proper lung development through the interconnection between epithelial and endothelial cells during lung morphogenesis.

CYLD controls c-MYC expression through the JNK-dependent signaling pathway in hepatocellular carcinoma.

Posttranslational modification of different proteins via direct ubiquitin attachment is vital for mediating various cellular processes. Cylindromatosis (CYLD), a deubiquitination enzyme, is able to cleave the polyubiquitin chains from the substrate and to regulate different signaling pathways. Loss, or reduced expression, of CYLD is observed in different types of human cancer, such as hepatocellular carcinoma (HCC). However, the molecular mechanism by which CYLD affects cancerogenesis has to date not been unveiled. The aim of the present study was to examine how CYLD regulates cellular functions and signaling pathways during hepatocancerogenesis. We found that mice lacking CYLD were highly susceptible to chemically induced liver cancer. The mechanism behind proved to be an elevated proliferation rate of hepatocytes, owing to sustained c-Jun N-terminal kinase 1 (JNK1)-mediated signaling via ubiquitination of TNF receptor-associated factor 2 and expression of c-MYC. Overexpression of wild-type CYLD in HCC cell lines prevented cell proliferation, without affecting apoptosis, adhesion and migration. A combined immunohistochemical and tissue microarray analysis of 81 human HCC tissues revealed that CYLD expression is negatively correlated with expression of proliferation markers Ki-67 and c-MYC. To conclude, we found that downregulation of CYLD induces tumor cell proliferation, consequently contributing to the aggressive growth of HCC. Our findings suggest that CYLD holds potential to serve as a marker for HCC progression, and its link to c-MYC via JNK1 may provide the foundation for new therapeutic strategies for HCC patients.

Serum response factor controls CYLD expression via MAPK signaling pathway.

Tumor suppressor gene CYLD is a deubiquitinating enzyme which negatively regulates various signaling pathways by removing the lysine 63-linked polyubiquitin chains from several specific substrates. Loss of CYLD in different types of tumors leads to either cell survival or proliferation. In this study we demonstrate that lack of CYLD expression in CYLD-/- MEFs increases proliferation rate of these cells compared to CYLD+/+ in a serum concentration dependent manner without affecting cell survival. The reduced proliferation rate in CYLD+/+ in the presence of serum was due to the binding of serum response factor (SRF) to the serum response element identified in the CYLD promoter for the up-regulation of CYLD levels. The serum regulated recruitment of SRF to the CYLD promoter was dependent on p38 mitogen-activated protein kinase (MAPK) activity. Elimination of SRF by siRNA or inhibition of p38 MAPK reduced the expression level of CYLD and increased cell proliferation. These results show that SRF acts as a positive regulator of CYLD expression, which in turn reduces the mitogenic activation of serum for aberrant proliferation of MEF cells.