Epiproteomic Landscape and Histone Code of Cutaneous T-Cell Lymphoma/Sézary Syndrome

Background: The genetic basis and the genome-wide abnormalities underlying most forms of cancer are being comprehensively annotated in many human malignancies. However, the contribution of epigenetic aberrations, particularly the post-translational modifications (PTM) of histone tails has not been investigated. This is largely due to lack of approaches to comprehensively interrogate the status of the numerous PTMs that define histone marks which control gene expression and complex biologic processes such as cancer. Sézary Syndrome (SS) is an aggressive form of cutaneous T-cell lymphoma (CTCL) characterized by poor outcomes and complex genetic alterations frequently targeting epigenetic regulators and chromatin remodelers. CTCLs represent the first FDA-approved disease for treatment using histone deacetylase inhibitors (HDACi) such as romidepsin, but the direct consequences of this treatment on histone PTMs remain unknown. Here we define the histone PTM signatures of CTCL/SS by using a novel unbiased strategy leveraging tandem mass spectrometry (MS/MS)-based quantitative proteomics to study the comprehensive combinatorial histone PTM code in a cohort of primary SS samples, and 4 CTCL/SS cell lines in comparison with normal reactive CD4+ T-lymphocytes from healthy individuals.