Abstract: Accurate classification of melanocytic tumors is important for prognostic evaluation, treatment and follow‐up protocols of patients. The majority of melanocytic proliferations can be classified solely based on clinical and pathological criteria, however in select cases a definitive diagnostic assessment remains challenging and additional diagnostic biomarkers would be advantageous. We analyzed melanomas, nevi, Spitz nevi and atypical spitzoid tumors using parallel sequencing (exons of 611 genes and 507 gene translocation analysis) and methylation arrays (850k Illumina EPIC). By combining detailed genetic and epigenetic analysis with reference‐based and reference‐free DNA methylome deconvolution we compared Spitz nevi to nevi and melanoma and assessed the potential for these methods in classifying challenging spitzoid tumors. Results were correlated with clinical and histologic features. Spitz nevi were found to cluster independently of nevi and melanoma and demonstrated a different mutation profile. Multiple copy number alterations and TERT promoter mutations were identified only in melanomas. Genome‐wide methylation in Spitz nevi was comparable to benign nevi while the Leukocytes UnMethylation for Purity (LUMP) algorithm in Spitz nevi was comparable to melanoma. Histologically difficult to classify Spitz tumor cases were assessed which, based on methylation arrays, clustered between Spitz nevi and melanoma and in terms of genetic profile or copy number variations demonstrated worrisome features suggesting a malignant neoplasm. Comprehensive sequencing and methylation analysis verify Spitz nevi as an independent melanocytic entity distinct from both nevi and melanoma. Combined genetic and methylation assays can offer additional insights in diagnosing difficult to classify Spitzoid tumors.

Abstract: One of the key risk factors for developing acute myeloid leukemia (AML) is advanced age. With a median age of approximately 68 years at diagnosis, AML predominantly affects an elderly population with poor prognosis. Understanding age-related mechanisms preceding AML might foster the development of new therapeutic approaches targeting more specifically pre-malignant genetic or epigenetic changes. Age-related clonal hematopoiesis (ARCH or CHIP) increases the risk of developing leukemia and predominantly affects genes encoding epigenetic modifiers such as DNMT3A or TET2. Changes in the DNA methylome are a characteristic feature of AML and epigenetic therapies with hypomethylating agents are approved for therapy. As demonstrated in murine models, DNA methylation can shape hematopoietic stem cell (HSC) differentiation and aging phenotypes. Here, we aimed to examine genome-wide changes in the DNA methylome and transcriptome of aging human HSCs. Previous studies of aging-related changes in HSC methylomes used murine HSCs, covered only a fraction of the human methylome or were biased towards promoters and CpG islands. Here, we took advantage of tagmentation-based whole-genome bisulfite sequencing (TWGBS) to cover all CpG sites genome-wide using small amounts of input DNA (Wang et al., Nature protocols 2013). We purified HSCs from cord blood (n=3) and bone marrow of young (n=5, defined as age 23-27) and old donors (n=4, defined as age 63-72) using fluorescence-activated cell sorting (FACS) with an 8-color HSC/LSC-panel (Zeijlemaker et al., Leukemia 2016). None of the samples carried CHIP mutations. With low-input RNA-Seq and TWGBS we successfully obtained an integrative data set of the methylome and transcriptome of human HSCs from newborn, young and old individuals. We found that human HSCs show age-specific DNA methylation patterns that progressively change during aging and predominantly clusters with progressive and age-dependent degradation of methylation marks. In addition, we observed an increase in epigenetic heterogeneity in aged HSCs, extending into methylation-based proliferative clocks. We further revealed that wide-spread and progressive degradation of DNA methylation marks during HSC aging largely affected gene regulatory regions such as promoters, enhancers and transcription factor (TF) binding sites. These differentially methylated regions were highly enriched for genes playing a role in T-cell activation, cell adhesion and hematopoietic differentiation. Binding sites for transcription factors associated with AML, as for example the RUNX and GATA family of TFs were highly affected by age-dependent loss of DNA methylation. We further identified regulatory networks with target genes of transcriptional master regulators such as LYL1, regulating HSC pluripotency in combination with GATA2 and RUNX1, or ZNF639, upregulated in leukemic stem cells (LSC), or senescence and cell cycle genes to be upregulated upon aging. Besides known hallmark genes of HSC aging, such as CLU and SELP, we identified candidate genes to be differentially methylated such as HOX genes and other AML-associated genes. We observed deregulated gene expression in aged HSCs affecting HOXA cluster genes, as well as aging and longevity-associated pathways and G2M-checkpoint genes, relevant to DNA damage response. Correlation of epigenome and transcriptome identified a promising set of novel HSC aging-related candidate genes, putatively controlled by DNA methylation and functionally associated with apoptosis and cell adhesion. Furthermore, we discovered age-related epigenetic remodelling of the mTORC1 pathway, a central regulator of aging and cellular senescence. Pharmacological inhibition of mTORC1 using rapamycin was shown to increase lifespan in several model organisms. In summary, we unravel a comprehensive roadmap of the changing epigenome and transcriptome of human HSCs throughout human lifespan. This enables us to precisely pinpoint DNA methylation marks that progressively degrade during aging. Restoring these DNA methylation marks in aged HSCs could potentially ameliorate age-related decline in HSC function and might protect against leukemic transformation. Disclosures Heuser: Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer Pharma AG: Research Funding; Karyopharm: Research Funding; Astellas: Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Honoraria; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Tolremo: Membership on an entity's Board of Directors or advisory committees; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; BergenBio: Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding. Buske: Pfizer: Honoraria, Speakers Bureau; Celltrion: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; MSD: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bayer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Research Funding.

Abstract: Cancer cells recruit and rewire normal fibroblasts in their microenvironment to become protumorigenic cancer-associated fibroblasts (CAF). These CAFs are genomically stable, yet their transcriptional programs are distinct from those of their normal counterparts. Transcriptional regulation plays a major role in this reprogramming, but the extent to which epigenetic modifications of DNA also contribute to the rewiring of CAF transcription is not clear. Here we address this question by dissecting the epigenetic landscape of breast CAFs. Applying tagmentation-based whole-genome bisulfite sequencing in a mouse model of breast cancer, we found that fibroblasts undergo massive DNA methylation changes as they transition into CAFs. Transcriptional and epigenetic analyses revealed RUNX1 as a potential mediator of this process and identified a RUNX1-dependent stromal gene signature. Coculture and mouse models showed that both RUNX1 and its stromal signature are induced as normal fibroblasts transition into CAFs. In breast cancer patients, RUNX1 was upregulated in CAFs, and expression of the RUNX1 signature was associated with poor disease outcome, highlighting the relevance of these findings to human disease. This work presents a comprehensive genome-wide map of DNA methylation in CAFs and reveals a previously unknown facet of the dynamic plasticity of the stroma. Significance: The first genome-wide map of DNA methylation in breast cancer–associated fibroblasts unravels a previously unknown facet of the dynamic plasticity of the stroma, with far-reaching therapeutic implications.

Abstract: Large-scale genome sequencing efforts of human tumours identified epigenetic modifiers as one of the most frequently mutated gene class in human cancer. However, how these mutations drive tumour development and tumour progression are largely unknown. Here, we investigated the function of the histone demethylase KDM6A in gastrointestinal cancers, such as liver cancer and pancreatic cancer. Design Genetic alterations as well as expression analyses of KDM6A were performed in patients with liver cancer. Genetic mouse models of liver and pancreatic cancer coupled with Kdm6a-deficiency were investigated, transcriptomic and epigenetic profiling was performed, and in vivo and in vitro drug treatments were conducted. Results KDM6A expression was lost in 30% of patients with liver cancer. Kdm6a deletion significantly accelerated tumour development in murine liver and pancreatic cancer models. Kdm6a-deficient tumours showed hyperactivation of mTORC1 signalling, whereas endogenous Kdm6a re-expression by inducible RNA-interference in established Kdm6a-deficient tumours diminished mTORC1 activity resulting in attenuated tumour progression. Genome-wide transcriptional and epigenetic profiling revealed direct binding of Kdm6a to crucial negative regulators of mTORC1, such as Deptor, and subsequent transcriptional activation by epigenetic remodelling. Moreover, in vitro and in vivo genetic epistasis experiments illustrated a crucial function of Deptor and mTORC1 in Kdm6a-dependent tumour suppression. Importantly, KDM6A expression in human tumours correlates with mTORC1 activity and KDM6A-deficient tumours exhibit increased sensitivity to mTORC1 inhibition. Conclusion KDM6A is an important tumour suppressor in gastrointestinal cancers and acts as an epigenetic toggle for mTORC1 signalling. Patients with KDM6A-deficient tumours could benefit of targeted therapy focusing on mTORC1 inhibition.