Targeting epigenetic abnormalities to inhibit cutaneous squamous cell carcinoma

点击翻译按钮获取中文摘要

Project Summary/Abstract Chronic ultraviolet (UV) radiation induces not only genetic mutations but also aberrant epigenetic modifications that affect the expression of transcription factors, oncogenes, and tumor suppressors, leading to the development of cutaneous squamous cell carcinoma (cSCC), the second most common cancer in the United States. A better understanding of the mechanisms underlying UV-associated epigenetic abnormalities will provide novel approaches to inhibit skin malignancies. Strikingly, chronic UV exposure induces DNA hypermethylation at the promoter of CDKN2A gene, which encodes tumor suppressors p16INK4A and p14ARF. This epigenetic alteration silences CDKN2A, promoting tumor growth and metastasis. However, it remains unclear whether the reversal of this epigenetic aberration can reactivate CDKN2A and inhibit malignant phenotypes of cSCC. In Aim 1, we will use our CRISPR-Cas9-based epigenome editing tools to specifically demethylate the CDKN2A promoter and investigate the effect of targeted DNA demethylation on cancer phenotypes. UV radiation increases the expression of Myc, which is an oncogenic transcription factor. Myc activation is a cancer hallmark, and the Myc oncogene family is deregulated in many human cancers. When overexpressed, Myc binds to noncanonical (low-affinity) motifs, invading enhancers, and potentially activates super-enhancers (noncoding genomic regions defined by unusually high levels of H3K27 acetylation). Cancer-specific super- enhancers strongly upregulate oncogenes, driving malignancies. However, it remains elusive how aberrant super-enhancers are formed in cSCC. We hypothesize that overexpressed Myc binds to low-affinity Myc binding sites, recruits histone acetyltransferase p300, and generates aberrant super-enhancers that drive malignancy. In Aim 2, we will determine the role of overexpressed Myc in super-enhancer formation in cSCC. A subset of cSCC displays poor differentiation, which correlates with poor patient survival. However, it remains unclear what confers the aggressiveness of poorly differentiated cSCC. We hypothesize that small-molecule inhibitors of DNA methylation and/or Myc suppress poorly differentiated cSCC in vivo by reactivating CDKN2A and/or inhibiting Myc-associated super-enhancers. In Aim 3, we will use poorly differentiated cSCC patient- derived xenografts as preclinical models to assess the effects of these inhibitors on tumor growth and metastasis. Innovative technologies will be used for epigenetic analyses: “PIXUL-ChIP” (high-throughput chromatin shearing for robust ChIP signals) and “EVA” (epigenetic visualization assay that detects specific DNA methylation at the single-cell level). With our epigenome editing tools, the proposed study will elucidate the contribution of epigenetic abnormalities to cSCC aggressiveness and reveal therapeutic potential of modulating epigenetic marks to suppress cSCC.