The impact of CYLD on chromatin structure and histone methylation in malignant melanoma

The crucial role of the tumor suppressor CYLD is known in melanoma. However, the precise mechanisms of CYLD`s tumor suppressive function have still to be clarified. For this reason, a new melanoma mouse model was generated revealing accelerate tumor growth in Cyld-knockout (Cyld-/-) compared to Cyld-wild type (Cyld+/+) mice. To unravel the underlying molecular mechanism, mutation analysis of primary tumor-derived cell lines from Cyld+/+ and Cyld-/- mice was performed on RNA-Seq data. Variant calling revealed no common mutations in the Cyld-/- cells compared to the Cyld+/+ cells. Thus, we further focused on epigenetic processes influencing development and progression of melanoma. Initial analyses showed no pivotal role of CYLD on DNA methylation. Chromatin accessibility and a histone 3 modification assay uncovered a role of CYLD in the formation of chromatin structure. Subsequent inhibitor studies confirmed the impact of CYLD especially on dimethylation of H3K9, which is associated with heterochromatin. Furthermore, the enhanced H3K9 dimethylation in Cyld-/- melanoma cells apparently correlates with an upregulation of the methyltransferase EHMT2. Moreover, the specific inhibitor of EHMT2, CM272, initiates decreased proliferation and relaxation of the compact chromatin in Cyld-deficiency. These results reveal a new role of CYLD in the field of histone methylation and chromatin packaging.