CYLD inhibits tumorigenesis and metastasis by blocking JNK/AP1 signaling at multiple levels.

CYLD has been recognized as a tumor suppressor due to its dominant genetic linkage to multiple types of epidermal tumors and a range of other cancers. The molecular mechanisms governing CYLD control of skin cancer are still unclear. Here, we showed that K14-driven epidermal expression of a patient-relevant and catalytically deficient CYLD truncated mutant (CYLD(m)) sensitized mice to skin tumor development in response to 7,12-dimethylbenz[α]anthracene (DMBA)/(12-O-tetradecanoylphorbol-13-acetate) TPA challenge. Tumors developed on transgenic mice were prone to malignant progression and lymph node metastasis and displayed increased activation of c-Jun-NH2-kinase (JNK) and the downstream c-Jun and c-Fos proteins. Most importantly, topical application of a pharmacologic JNK inhibitor significantly reduced tumor development and abolished metastasis in the transgenic mice. Further in line with these animal data, exogenous expression of CYLD(m) in A431, a human squamous cell carcinoma (SCC) cell line, markedly enhanced cell growth, migration, and subcutaneous tumor growth in an AP1-depdendent manner. In contrast, expression of the wild-type CYLD inhibited SCC tumorigenesis and AP1 function. Most importantly, CYLD(m) not only increased JNK activation but also induced an upregulation of K63 ubiquitination on both c-Jun and c-Fos, leading to sustained AP1 activation. Our findings uncovered c-Jun and c-Fos as novel CYLD targets and underscore that CYLD controls epidermal tumorigenesis through blocking the JNK/AP1 signaling pathway at multiple levels.

The c-Jun NH2-terminal kinase 2 plays a dominant role in human epidermal neoplasia.

The c-Jun NH(2)-terminal kinase (JNK) signaling cascade has been implicated in a wide range of diseases, including cancer. It is unclear how different JNK proteins contribute to human cancer. Here, we report that JNK2 is activated in more than 70% of human squamous cell carcinoma (SCC) samples and that inhibition of JNK2 pharmacologically or genetically impairs tumorigenesis of human SCC cells. Most importantly, JNK2, but not JNK1, is sufficient to couple with oncogenic Ras to transform primary human epidermal cells into malignancy with features of SCC. JNK2 prevents Ras-induced cell senescence and growth arrest by reducing the expression levels of the cell cycle inhibitor p16 and the activation of NF-kappaB. On the other hand, JNK, along with phosphoinositide 3-kinase, is essential for Ras-induced glycolysis, an energy-producing process known to benefit cancer growth. These data indicate that JNK2 collaborates with other oncogenes, such as Ras, at multiple molecular levels to promote tumorigenesis and hence represents a promising therapeutic target for cancer.